HYBRID MAGNETIC RESONANCE CONTRAST AGENTS

AGENTS DE CONTRASTE HYBRIDES POUR LA RESONANCE MAGNETIQUE NUCLEAIRE

English Abstract

Novel MRI contrast agents that comprise one or more metal-ion chelates in
juxtaposition with one or more free-radical nitroxide compounds in a polymeric
or oligomeric molecule. Both the chelate units and the free radical units may,
independently, be inside the main chain of the polymer or in a side chain of
the linkage portion of the polymer. The number of combined units of chelates
and free radicals in the polymer or oligomer is at least two.

French Abstract

L'invention concerne de nouveaux agents de contraste pour l'imagerie par résonance magnétique nucléaire, comprenant un ou plusieurs chélates ion-métal juxtaposés avec un ou plusieurs radicaux libres dérivés de composés de nitroxyde, dans une molécule polymère ou oligomère. Les unités de chélate et les unités de radicaux libres peuvent être, d'une manière indépendante, à l'intérieur de la chaîne principale du polymère ou dans une chaîne latérale de la portion de liaison du polymère. Le nombre combiné d'unités de chélate et d'unités de radicaux libres dans le polymère ou l'oligomère est d'au moins deux.

Claims

46
I claim:
1. A hybrid, copolymeric magnetic-resonance-imaging contrast
agent comprising:
at least one chelating unit monomer;
at least one free radical monomer linked to said at
least one chelating unit monomer; and
at least one paramagnetic ion combined with at least one
of said at least one chelating unit monomer;
wherein said chelating unit monomer is a polynitrilo
chelating agent and said free radical monomer is a nitroxide.
2. The contrast agent of Claim 1, having the following
structure:
<IMG>
wherein Ch is a polynitrilo chelating unit monomer, L is a
linker monomer, FR is a nitroxide free radical monomer, and M
is a paramagnetic ion;
wherein q = 1 to 10,000;
wherein, within each of the q polymeric groups
<IMG>
independently, p = 0 to 10,000 and p' = 0 to 10,000;

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wherein, within each of the p oligomeric groups
<IMG>
independently, n = 0 to 10,000 and j - 0 to 10,000;
for each group of paramagnetic ions (M)k chelated by
each
of the n chelating unit monomers --Ch-- in the p
oligomeric
groups, independently, k = 0 to 2; and
for each group of free radical monomers (FR)m linked to
each
of the j linker monomers --L-- in the p oligomeric
groups,
independently, m = 0 to 2; and
wherein, within each of the p' oligomeric groups
<IMG>
independently, n = 0 to 10,000 and m - 0 to 10,000; and
for each group of paramagnetic ions (M)k chelated by
each
of the n chelating unit monomers --Ch-- in the p'
oligomeric
groups, independently, k = 0 to 2.
3. The contrast agent of Claim 1, wherein each polynitrilo
chelating agent comprises at least one COOH, COOR1, or COZ
group; each R1 being, independently, a C1-C20 substituted or
unsubstituted, saturated or unsaturated, alkyl or cycloalkyl

48
group or an anhydride; and each Z being, independently, Cl,
Br, or I.
4. The contrast agent of Claim 3, wherein at least one of
said C1-C20 alkyl or cycloalkyl group is substituted with at
least one moiety selected from the group of OH, NH2, SH,
COOH, and PO4, or mixtures thereof.
5. The contrast agent of Claim 3, wherein each R1 is,
independently, a polyhydroxy-substituted alkyl or cycloalkyl
group.
6. The contrast agent of Claim 5, wherein said
polyhydroxy-substituted alkyl or cycloalkyl group is selected
from the group consisting of sugar alcohols, monosaccharides,
polysaccharides, and synthetic polymers, or mixtures thereof.
7. The contrast agent of Claim 1, wherein each polynitrilo
chelating unit monomer consists, independently, of a
chelating agent selected from the group consisting of
ethylenediamine tetraacetic acid; diethylenetriamine
pentaacetic acid; 1,5-di-.beta.-methoxyethylene-iminocarbonyl-
methylene-1,3,5-tricarboxymethylene-1,3,5,-triazapentane;
1,5-di-.alpha.,.beta.-dihydroxypropeneimino-carbonyl-methylene-1,3,5-
tricarboxymethylene-1,3,5-triazapentane; 1,4,7,10-
tetraazacyclododecane-1,4,7,10-tetraacetic acid; 1,4,7,10-
tetraazacyclododecane-N,N',N"-triacetic acid; 3,6,9-triaza-
12-oxa-3,6,9-tricarboxymethylene-10-carboxy-13-phenyl-

49
tridecanoic acid; hydroxybenzyl-ethylenediamine diacetic
acid; N,N'-bis(pyridoxyl-5-phosphate)ethylenediamine-N,N'-
diacetic acid; 1,4,7-triazacyclononane-N,N',N"-triacetic
acid; 1-oxa-4,7,10-triazacyclododecane-triacetic acid;
1,4,8,11-tetraazacyclotetradecane-N,N',N",N'"-tetraacetic
acid; triethylenetetraamine hexaacetic acid; 1,2-
diaminocyclohexane-N,N,N',N'-tetraacetic acid; and anhydrides
thereof.
8. The contrast agent of Claim 1, wherein each free radical
monomer is selected from the group consisting of heterocyclic
nitroxide monomers and non-heterocyclic nitroxide monomers.
9. The contrast agent of Claim 8, wherein said heterocyclic
nitroxide monomers have the following general structure:
<IMG>
wherein
a five member ring is pyrrolidine, oxazolidine,
imidazolidine, or thiazolidine;
a six member ring is piperidine; and
each of Ra, Rb, Rc and Rd is, independently, a C1-C20

alkyl or cycloalkyl group, said alkyl or cycloalkyl group
being interrupted or terminated with OH, SH, NH2, NHR1, COOH,
COOR1, NCS, COCHCH2, or COZ, each R1 being, independently, a
C1-C20 substituted or unsubstituted alkyl or cycloalkyl group
or an anhydride, and each Z being, independently, Cl, Br, or I.
10. The contrast agent of Claim 8, wherein said non-heterocyclic
nitroxide monomers are selected from the group
consisting of diphenylnitroxide and di-tert-butyl nitroxide.
11. The contrast agent of Claim 1, wherein each nitroxide
free radical monomer is selected from the group consisting of
2,2,6,6-tetramethylpiperidine-1-oxyl; 2,2,4,4-tetramethyl-
pyrrolidine-1-oxyl; 2,2,4,4-tetramethyl-imidazolidine-3-oxyl;
2,2,4,4-tetramethyl-1,3-thiazolidine-3-oxyl; 2,2,4,4-
tetramethyl-1,3-oxazolidine-3-oxyl; 2,2,6,6-
tetramethylpyrimidine-1-oxyl; diphenyl-nitroxide; and
di-tert-butylnitroxide; and wherein each nitroxide may have one
or more OH, SH, NH2, NHR1, COOH, COOR1, NCS, COCHCH2, or COZ,
each R1 being, independently, a C1-C20 substituted or
unsubstituted alkyl or cycloalkyl group or an anhydride, and
each Z being, independently, Cl, Br, or I.

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12. The contrast agent of Claim 1, wherein each nitroxide
free radical monomer is a monofunctionalized compound
selected from the group consisting of 1-oxyl-2,2,6,6-
tetramethyl-4-piperidinyl acrylate;
4-(iodomethylenecarbonylimino)-2,2,6,6-tetramethyl-piperdinyl-
1-oxy; 4-(bromomethylenecarbonylimino)-2,2,6,6-tetramethyl-
piperidinyl-1-oxy; 3-carboxy-2,2,5,5-tetramethylpyrrolidinyl-
1-oxy;
3-chlorocarbonyl-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-aminomethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-hydroxymethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-hydroxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 3-
chloroformyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 4-amino-
2,2,6,6-tetramethylpiperidine-1-oxyl; 4-hydroxy-2,2,6,6-
tetramethylpiperidine-1-oxyl; and 3-thiocabamoylmethylene-
2,2,5,5-tetramethylpyrrolidinyl-1-oxy.
13. The contrast agent of Claim 1, wherein each nitroxide
free radical monomer is a difunctionalized compound selected
from the group consisting of cis-1-oxyl-2,2,5,5-
tetramethylpyrrolidine; trans-1-oxyl-2,2,5,5-
tetramethylpyrrolidine; 3-amino-4-aminomethylene-2,2,5,5-
tetramethylpyrrolidine; cis-2,5-dimethyl-2(aminomethyl)-5-(2-
carboxyethyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2-
(hydroxymethyl)-5-(methoxycarbonylmethyl)-tetrahydropyrrole-
1-oxyl; cis-2,5-dimethyl-2-(hydroxymethyl)-5-(2-
hydroxyhexyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2,5-
bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-dimethyl-

52
2,5-bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-
dimethyl-2,5-bis(2-carboxyethyl)-pyrrolidinyl-1-oxy; cis-2,5-
dimethyl-2,5-bis(2-hydroxy-5-methylphenyl)-
tetrahydroxypyrrol-1-oxy; 3-amino-4-carboxy-2,2,5,5-
tetramethylpyrrolidinyl-1-oxy; 2,5-di-tert-butyl-3,4-
diethyloxycarbonyl-pyrrol-1-oxyl; and 1,4-bis(4-hydroxy-
2,2,6,6-tetramethyl-1-oxyl-4-piperidyl)-butane.
14. The contrast agent of Claim 1, wherein each paramagnetic
ion is selected from the group consisting of transition and
lanthanide elements.
15. The contrast agent of Claim 1, wherein each paramagnetic
ion is selected from the group consisting of Gd(III), Mn(II),
Cu(II), Cr(III), Fe(II), Fe(III), Co(II), Er(II), Ni(II),
Eu(III), Dy(III), Yb(III), and Ho(III).
16. The contrast agent of Claim 1, wherein each paramagnetic
ion is selected from the group consisting of Gd(III), Mn(II)
and Fe(III).
17. The contrast agent of Claim 2, wherein each linker
monomer has the following general structure:
X1 [ ( CHR2 ) n-CHR2-Y]n-Gq-(CHR2)m'-CHR2-X2
wherein
each R2 is, independently, a C1-C20 substituted or

53
unsubstituted, saturated or unsaturated, alkyl or cycloalkyl
group;
X1 and X2 are, independently, OH, NH2, NHR1, COOH, COOR1,
SH, Z or NCS;
Y is O, NH, NR1, S or CO;
each R1 is, independently, a C1-C20 substituted or
unsubstituted alkyl or cycloalkyl group or an anhydride;
each Z is, independently, Cl, Br, or I;
G is a C1-C20 substituted or unsubstituted alkyl or
cycloalkyl group, a saccharide, a peptide or a polysulfide;
and
m, m', n, and q are, independently, 0 to 10,000.
18. The contrast agent of Claim 17, wherein each linker
monomer is, independently, a polyamino linker monomer
selected from the group consisting of 1,2-diaminoethane,
13-diaminopropane, 1,4-diaminobutane, 1,5-diamino-3-(2-
aminoethyl)-pentane, N,N'-dimethyl-1,2-diaminoethane, N,N'-
dimethyl-1,3-diaminopropane, 2-hydroxy-1,3-diaminopropane, 2-
amino-1,3-diaminopropane, 2,3-diamino-1,4-butanediol, 1,4-
diamino-2,3-butane diol, 1,4-diaminocyclohexane, 1,4-
phenylenediamine, 1,1,1-tris-(aminomethyl)ethane, 2,2',2"-
tris-aminoethylamine, tris-(aminomethylene)methane,
diethylenetriamine, triethylenetetraamine, 1,3,5-
triaminocyclohexane, and 1,3,5-triaminobenzene.
19. The contrast agent of Claim 17, wherein each linker
monomer is a polyhydroxy linker monomer selected from the

54
group consisting of 2,2-dimethyl-1,3-propanediol, tris-(2-
hydroxyethyl)amine, 1,1,1-tris-(hyroxymethylene)ethane,
glycerine, erythritol, sugar alcohols, polyethyleneglycol,
w-amino-polyethyleneglycol, N-substituted-w-
aminopolyethyleneglycol, w-thiol-polyethyleneglycol,
polysulfide-blocked polyethyleneglycol, and polyethylene-
imine.
20. The contrast agent of Claim 17, wherein each linker
monomer is selected from the group consisting of
ethylenedioxydiethylamine, N,N'-bis-dihydroxypropyl-
ethylenedioxydiethylamine, and
ethylenedioxydiethylmercaptane.
21. The contrast agent of Claim 2, wherein each polynitrilo
chelating unit monomer comprises at least one COOH, COOR1, or
COZ group; each R1 being, independently, a C1-C20 substituted
or unsubstituted, saturated or unsaturated, alkyl or
cycloalkyl group or an anhydride; and each Z being,
independently, Cl, Br, or I.
22. The contrast agent of Claim 21, wherein at least one of
said C1-C20 alkyl or cycloalkyl group is substituted with at
least one moiety selected from the group of OH, NH2, SH,
COOH, and PO4, or mixtures thereof.
23. The contrast agent of Claim 21, wherein each R1 is,
independently, a polyhydroxy-substituted alkyl or cycloalkyl

group.
24. The contrast agent of Claim 23, wherein said
polyhydroxy-substituted alkyl or cycloalkyl group is selected
from the group consisting of sugar alcohols, monosaccharides,
polysaccharides, and synthetic polymers.
25. The contrast agent of Claim 2, wherein each polynitrilo
chelating unit monomer consists, independently, of a
chelating agent selected from the group consisting of
ethylenediamine tetraacetic acid; diethylenetriamine
pentaacetic acid; 1,5-di-.beta.-methoxyethylene-iminocarbonyl-
methylene-1,3,5-tricarboxymethylene-1,3,5,-triazapentane;
1,5-di-.alpha.,.beta.-dihydroxypropeneimino-carbonyl-methylene-1,3,5-
tricarboxymethylene-1,3,5-triazapentane; 1,4,7,10-
tetraazacyclododecane-1,4,7,10-tetraacetic acid; 1,4,7,10-
tetraazacyclododecane-N,N',N"-triacetic acid; 3,6,9-triaza-
12-oxa-3,6,9-tricarboxymethylene-10-carboxy-13-phenyl-
tridecanoic acid; hydroxybenzyl-ethylenediamine diacetic
acid; N,N'-bis(pyridoxyl-5-phosphate)ethylenediamine-N,N'-
diacetic acid; 1,4,7-triazacyclononane-N,N',N"-triacetic
acid; 1-oxa-4,7,10-triazacyclododecane-triacetic acid;
1,4,8,11-tetraazacyclotetradecane-N,N',N",N'"-tetraacetic
acid; triethylenetetraamine hexaacetic acid; 1,2-
diaminocyclohexane-N,N,N',N'-tetraacetic acid; and anhydrides
thereof.
26. The contrast agent of Claim 2, wherein each free radical

56
monomer, independently, is selected from the group consisting
of heterocyclic nitroxide monomers and non-heterocyclic
nitroxide monomers.
27. The contrast agent of Claim 26, wherein said
heterocyclic nitroxide monomers have the following general
structure:
<IMG>
wherein
a five member ring is pyrrolidine, oxazolidine,
imidazolidine, or thiazolidine;
a six member ring is piperidine; and
each of Ra, Rb, Rc and Rd is, independently, a C1-C20
alkyl or cycloalkyl group, said alkyl or cycloalkyl group
being interrupted or terminated with OH, SH, NH2, NHR1, COOH,
COOR1, NCS, COCHCH2, or COZ, each R1 being, independently, a
C1-C20 substituted or unsubstituted alkyl or cycloalkyl group
or an anhydride, and each Z being, independently, Cl, Br, or
I.
28. The contrast agent of Claim 26, wherein said non-heterocyclic

57
nitroxide monomers are selected from the group
consisting of diphenylnitroxide and di-tert-butyl nitroxide.
29. The contrast agent of Claim 2, wherein each nitroxide
free radical monomer is, independently, selected from the
group consisting of 2,2,6,6-tetramethylpiperidine-1-oxyl;
2,2,4,4-tetramethyl-pyrrolidine-1-oxyl; 2,2,4,4-tetramethyl-
imidazolidine-3-oxyl; 2,2,4,4-tetramethyl-1,3-thiazolidine-3-
oxyl; 2,2,4,4-tetramethyl-1,3-oxazolidine-3-oxyl; 2,2,6,6-
tetramethylpyrimidine-1-oxyl; diphenyl-nitroxide; and di-
tert-butylnitroxide; and wherein each nitroxide may have one
or more OH, SH, NH2, NHR1, COOH, COOR1, NCS, COCHCH2, or COZ,
each R1 being, independently, a C1-C20 substituted or
unsubstituted alkyl or cycloalkyl group or an anhydride, and
each Z being, independently, Cl, Br, or I.
30. The contrast agent of Claim 2, wherein each nitroxide
free radical monomer is, independently, a monofunctionalized
compound selected from the group consisting of 1-oxyl-
2,2,6,6-tetramethyl-4-piperidinyl acrylate; 4-
(iodomethylenecarbonylimino)-2,2,6,6-tetramethyl-piperdinyl-
1-oxy; 4-(bromomethylenecarbonylimino)-2,2,6,6-tetramethyl-
piperidinyl-1-oxy; 3-carboxy-2,2,5,5-tetramethylpyrrolidinyl-
1-oxy;
3-chlorocarbonyl-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-aminomethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-hydroxymethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxyl;
3-hydroxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 3-

58
chloroformyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 4-amino-
2,2,6,6-tetramethylpiperidine-1-oxyl; 4-hydroxy-2,2,6,6-
tetramethylpiperidine-1-oxyl; and 3-thiocabamoylmethylene-
2,2,5,5-tetramethylpyrrolidinyl-1-oxy.
31. The contrast agent of Claim 2, wherein each nitroxide
free radical monomer is, independently, a difunctionalized
compound selected from the group consisting of cis-1-oxyl-
2,2,5,5-tetramethylpyrrolidine; trans-1-oxyl-2,2,5,5-
tetramethylpyrrolidine; 3-amino-4-aminomethylene-2,2,5,5-
tetramethylpyrrolidine; cis-2,5-dimethyl-2(aminomethyl)-5-(2-
carboxyethyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2-
(hydroxymethyl)-5-(methoxycarbonylmethyl)-tetrahydropyrrole-
1-oxyl; cis-2,5-dimethyl-2-(hydroxymethyl)-5-(2-
hydroxyhexyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2,5-
bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-dimethyl-
2,5-bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-
dimethyl-2,5-bis(2-carboxyethyl)-pyrrolidinyl-1-oxy; cis-2,5-
dimethyl-2,5-bis(2-hydroxy-5-methylphenyl)-
tetrahydroxypyrrol-1-oxy; 3-amino-4-carboxy-2,2,5,5-
tetramethylpyrrolidinyl-1-oxy; 2,5-di-tert-butyl-3,4-
diethyloxycarbonyl-pyrrol-1-oxyl; and 1,4-bis(4-hydroxy-
2,2,6,6-tetramethyl-1-oxyl-4-piperidyl)-butane.
32. The contrast agent of Claim 2, wherein each paramagnetic
ion is selected from the group consisting of transition and
lanthanide elements.

59
33. The contrast agent of Claim 2, wherein each paramagnetic
ion is selected from the group consisting of Gd(III), Mn(II),
Cu(II), Cr(III), Fe(II), Fe(III), Co(II), Er(II), Ni(II),
Eu(III), Dy(III), Yb(III), and Ho(III).
34. The contrast agent of Claim 2, wherein each paramagnetic
ion is selected from the group consisting of Gd(III), Mn(II)
and Fe(III).
35. The contrast agent of Claim 1, having the following
structure:
<IMG>
wherein Ch is a polynitrilo chelating unit monomer, L is a
linker monomer, FR is a nitroxide free radical monomer,
and M is a paramagnetic ion;
wherein, independently, p = 1 to 10,000 and p' = 1 to 10,000;
wherein, within each of the p oligomeric groups
<IMG>
independently, n = 0 to 10,000 and j = 0 to 10,000;
for each group of paramagnetic ions <IMG> chelated by
each
of the n chelating unit monomers --Ch-- in each of the p
oligomeric groups, independently, k = 0 to 2: and
for each group of free radical monomers <IMG> linked to

each of the j linker monomers --L-- in each of the
oligomeric groups, independently, m = 0 to 2; and
wherein, within each of the p' oligomeric groups
<IMG> ,
independently, n = 0 to 10,000 and m = 0 to 10,000; and
for each group of paramagnetic ions <IMG> chelated by
each
of the n chelating unit monomers --Ch-- in each of the
p'
oligomeric groups, independently, k = 0 to 2.
36. The contrast agent of Claim 35, wherein each linker
monomer has the following general structure:
X1[(CHR2)m-CHR2-Y]n-Gq-(CHR2)m'-CHR2-X2
wherein
each R2 is, independently, a C1-C20 substituted or
unsubstituted, saturated or unsaturated, alkyl or cycloalkyl
group;
X1 and X2 are, independently, OH, NH2, NHR1, COOH, COOR1,
SH, Z or NCS;
Y is O, NH, NR1, S or CO;
each R1 is, independently, a C1-C20 substituted or
unsubstituted alkyl or cycloalkyl group or an anhydride;
each Z is, independently, Cl, Br, or I;

61
G is a C1-C20 substituted or unsubstituted alkyl or
cycloalkyl group, a saccharide, a peptide or a polysulfide;
and
m, m', n, and q are, independently, 0 to 10,000.
37. The contrast agent of Claim 36, wherein each linker
monomer is, independently, a polyamino linker monomer
selected from the group consisting of 1,2-diaminoethane, 13-
diaminopropane, 1,4-diaminobutane, 1,5-diamino-3-(2-
aminoethyl)-pentane, N,N'-dimethyl-1,2-diaminoethane, N,N'-
dimethyl-1,3-diaminopropane, 2-hydroxy-1,3-diaminopropane, 2-
amino-1,3-diaminopropane, 2,3-diamino-1,4-butanediol, 1,4-
diamino-2,3-butane diol, 1,4-diaminocyclohexane, 1,4-
phenylenediamine, 1,1,1-tris-(aminomethyl)ethane, 2,2',2"-
tris-aminoethylamine, tris-(aminomethylene)methane,
diethylenetriamine, triethylenetetraamine, 1,3,5-
triaminocyclohexane, and 1,3,5-triaminobenzene.
38. The contrast agent of Claim 36, wherein each linker
monomer is a polyhydroxy linker monomer selected from the
group consisting of 2,2-dimethyl-1,3-propanediol, tris-(2-
hydroxyethyl)amine, 1,1,1-tris-(hyroxymethylene)ethane,
glycerine, erythritol, sugar alcohols, polyethyleneglycol,
w-amino-polyethyleneglycol, N-substituted-w-
aminopolyethyleneglycol, w-thiol-polyethyleneglycol,
polysulfide-blocked polyethyleneglycol, and polyethylene-
imine.

62
39. The contrast agent of Claim 36, wherein each linker
monomer is selected from the group consisting of
ethylenedioxydiethylamine, N,N'-bis-dihydroxypropyl-
ethylenedioxydiethylamine, and
ethylenedioxydiethylmercaptane.
40. The contrast agent of Claim 35, wherein each polynitrilo
chelating unit monomer comprises at least one COOH, COOR1, or
COZ group; each R1 being, independently, a C1-C20 substituted
or unsubstituted, saturated or unsaturated, alkyl or
cycloalkyl group or an anhydride; and each Z being,
independently, Cl, Br, or I.
41. The contrast agent of Claim 40, wherein at least one of
said C1-C20 alkyl or cycloalkyl group is substituted with at
least one moiety selected from the group of OH, NH2, SH,
COOH, and PO4, or mixtures thereof.
42. The contrast agent of Claim 40, wherein each R1 is,
independently, a polyhydroxy-substituted alkyl or cycloalkyl
group.
43. The contrast agent of Claim 42, wherein said
polyhydroxy-substituted alkyl or cycloalkyl group is selected
from the group consisting of sugar alcohols, monosaccharides,
polysaccharides, and synthetic polymers.
44. The contrast agent of Claim 35, wherein each polynitrilo

63
chelating unit monomer consists, independently, of a
chelating agent selected from the group consisting of
ethylenediamine tetraacetic acid; diethylenetriamine
pentaacetic acid; 1,5-di-.beta.-methoxyethylene-iminocarbonyl-
methylene-1,3,5-tricarboxymethylene-1,3,5,-triazapentane;
1,5-di-.alpha.,.beta.-dihydroxypropeneimino-carbonyl-methylene-1,3,5-
tricarboxymethylene-1,3,5-triazapentane; 1,4,7,10-
tetraazacyclododecane-1,4,7,10-tetraacetic acid; 1,4,7,10-
tetraazacyclododecane-N,N',N"-triacetic acid; 3,6,9-triaza-
12-oxa-3,6,9-tricarboxymethylene-10-carboxy-13-phenyl-
tridecanoic acid; hydroxybenzyl-ethylenediamine diacetic
acid; N,N'-bis(pyridoxyl-5-phosphate)ethylenediamine-N,N'-
diacetic acid; 1,4,7-triazacyclononane-N,N',N"-triacetic
acid; 1-oxa-4,7,10-triazacyclododecane-triacetic acid;
1,4,8,11-tetraazacyclotetradecane-N,N',N",N'"-tetraacetic
acid; triethylenetetraamine hexaacetic acid; 1,2-
diaminocyclohexane-N,N,N',N'-tetraacetic acid; and anhydrides
thereof.
45. The contrast agent of Claim 35, wherein each free
radical monomer, independently, is selected from the group
consisting of heterocyclic nitroxide monomers and non-
heterocyclic nitroxide monomers.
46. The contrast agent of Claim 45, wherein said
heterocyclic nitroxide monomers have the following general
structure:

64
<IMG>
wherein
a five member ring is pyrrolidine, oxazolidine,
imidazolidine, or thiazolidine;
a six member ring is piperidine; and
each of Ra, Rb, Rc and Rd is, independently, a C1-C20
alkyl or cycloalkyl group, said alkyl or cycloalkyl group
being interrupted or terminated with OH, SH, NH2, NHR1, COOH,
COOR1, NCS, COCHCH2, or COZ, each R1 being, independently, a
C1-C20 substituted or unsubstituted alkyl or cycloalkyl group
or an anhydride, and each Z being, independently, Cl, Br, or
I.
47. The contrast agent of Claim 45, wherein said non-heterocyclic
nitroxide monomers are selected from the group
consisting of diphenylnitroxide and di-tert-butyl nitroxide.
48. The contrast agent of Claim 35, wherein each nitroxide
free radical monomer is, independently, selected from the
group consisting of 2,2,6,6-tetramethylpiperidine-1-oxyl;
2,2,4,4-tetramethyl-pyrrolidine-1-oxyl; 2,2,4,4-tetramethyl-
imidazolidine-3-oxyl; 2,2,4,4-tetramethyl-1,3-thiazolidine-3-
oxyl; 2,2,4,4-tetramethyl-1,3-oxazolidine-3-oxyl; 2,2,6,6-

tetramethylpyrimidine-1-oxyl; diphenyl-nitroxide; and di-
tert-butylnitroxide; and wherein each nitroxide may have one
or more OH, SH, NH2, NHR1, COOH, COOR1, NCS, COCHCH2, or COZ,
each R1 being, independently, a C1-C20 substituted or
unsubstituted alkyl or cycloalkyl group or an anhydride, and
each Z being, independently, Cl, Br, or I.
49. The contrast agent of Claim 35, wherein each nitroxide
free radical monomer is, independently, a monofunctionalized
compound selected from the group consisting of 1-oxyl-
2,2,6,6-tetramethyl-4-piperidinyl acrylate; 4-
(iodomethylenecarbonylimino)-2,2,6,6-tetramethyl-piperdinyl-
1-oxy; 4-(bromomethylenecarbonylimino)-2,2,6,6-tetramethyl-
piperidinyl-1-oxy; 3-carboxy-2,2,5,5-tetramethylpyrrolidinyl-
1-oxy;
3-chlorocarbonyl-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-aminomethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-hydroxymethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxyl;
3-hydroxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 3-
chloroformyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 4-amino-
2,2,6,6-tetramethylpiperidine-1-oxyl; 4-hydroxy-2,2,6,6-
tetramethylpiperidine-1-oxyl; and 3-thiocabamoylmethylene-
2,2,5,5-tetramethylpyrrolidinyl-1-oxy.
50. The contrast agent of Claim 35, wherein each nitroxide
free radical monomer is, independently, a difunctionalized
compound selected from the group consisting of cis-1-oxyl-
2,2,5,5-tetramethylpyrrolidine; trans-1-oxyl-2,2,5,5-

66
tetramethylpyrrolidine; 3-amino-4-aminomethylene-2,2,5,5-
tetramethylpyrrolidine; cis-2,5-dimethyl-2(aminomethyl)-5-(2-
carboxyethyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2-
(hydroxymethyl)-5-(methoxycarbonylmethyl)-tetrahydropyrrole-
1-oxyl; cis-2,5-dimethyl-2-(hydroxymethyl)-5-(2-
hydroxyhexyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2,5-
bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-dimethyl-
2,5-bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-
dimethyl-2,5-bis(2-carboxyethyl)-pyrrolidinyl-1-oxy; cis-2,5-
dimethyl-2,5-bis(2-hydroxy-5-methylphenyl)-
tetrahydroxypyrrol-1-oxy; 3-amino-4-carboxy-2,2,5,5-
tetramethylpyrrolidinyl-1-oxy; 2,5-di-tert-butyl-3,4-
diethyloxycarbonyl-pyrrol-1-oxyl; and 1,4-bis(4-hydroxy-
2,2,6,6-tetramethyl-1-oxyl-4-piperidyl)-butane.
51. The contrast agent of Claim 35, wherein each
paramagnetic ion is selected from the group consisting of
transition and lanthanide elements.
52. The contrast agent of Claim 35, wherein each
paramagnetic ion is selected from the group consisting of
Gd(III), Mn(II), Cu(II), Cr(III), Fe(II), Fe(III), Co(II),
Er(II), Ni(II), Eu(III), Dy(III), Yb(III), and Ho(III).
53. The contrast agent of Claim 35, wherein each
paramagnetic ion is selected from the group consisting of
Gd(III), Mn(II) and Fe(III).

67
54. The contrast agent of Claim 1, having the following
structure:
<IMG>
wherein Ch is a polynitrilo chelating unit monomer, L is a
linker monomer, FR is a nitroxide free radical monomer,
and M is a paramagnetic ion;
wherein p = 1 to 10,000; and
wherein, within each of the p oligomeric groups
<IMG>
independently, n = 0 to 10,000 and j = 0 to 10,000;
for each group of paramagnetic ions <IMG> chelated by
each
of the n chelating unit monomers --Ch-- in each of the p
oligomeric groups, independently, k = 0 to 2; and
for each group of free radical monomers <IMG> linked to
each of the j linker monomers --L-- in each of the
oligomeric groups, independently, m = 0 to 2.
55. The contrast agent of Claim 54, wherein each linker
monomer has the following general structure:
X1[(CHR2)m-CHR2-Y]n-Gq-(CHR2)m'-CHR2-X2
wherein
each R2 is, independently, a C1-C20 substituted or

68
unsubstituted, saturated or unsaturated, alkyl or cycloalkyl
group;
X1 and X2 are, independently, OH, NH2, NHR1, COOH, COOR1,
SH, Z or NCS;
Y is 0, NH, NR1, S or CO;
each R1 is, independently, a C1-C20 substituted or
unsubstituted alkyl or cycloalkyl group or an anhydride;
each Z is, independently, Cl, Br, or I;
G is a C1-C20 substituted or unsubstituted alkyl or
cycloalkyl group, a saccharide, a peptide or a polysulfide;
and
m, m', n, and q are, independently, 0 to 10,000.
56. The contrast agent of Claim 55, wherein each linker
monomer is, independently, a polyamino linker monomer
selected from the group consisting of 1,2-diaminoethane,
13-diaminopropane, 1,4-diaminobutane, 1,5-diamino-3-(2-
aminoethyl)-pentane, N,N'-dimethyl-1,2-diaminoethane, N,N'-
dimethyl-1,3-diaminopropane, 2-hydroxy-1,3-diaminopropane,
2-amino-1,3-diaminopropane, 2,3-diamino-1,4-butanediol, 1,4-
diamino-2,3-butane diol, 1,4-diaminocyclohexane, 1,4-
phenylenediamine, 1,1,1-tris-(aminomethyl)ethane, 2,2',2"-
tris-aminoethylamine, tris-(aminomethylene)methane,
diethylenetriamine, triethylenetetraamine, 1,3,5-
triaminocyclohexane, and 1,3,5-triaminobenzene.
57. The contrast agent of Claim 55, wherein each linker
monomer is a polyhydroxy linker monomer selected from the

69
group consisting of 2,2-dimethyl-1,3-propanediol, tris-(2-
hydroxyethyl)amine, 1,1,1-tris-(hyroxymethylene)ethane,
glycerine, erythritol, sugar alcohols, polyethyleneglycol,
w-amino-polyethyleneglycol, N-substituted-w-
aminopolyethyleneglycol, w-thiol-polyethyleneglycol,
polysulfide-blocked polyethyleneglycol, and polyethylene-
imine.
58. The contrast agent of Claim 55, wherein each linker
monomer is selected from the group consisting of
ethylenedioxydiethylamine, N,N'-bis-dihydroxypropyl-
ethylenedioxydiethylamine, and
ethylenedioxydiethylmercaptane.
59. The contrast agent of Claim 54, wherein each polynitrilo
chelating unit monomer comprises at least one COOH, COOR1, or
COZ group; each R1 being, independently, a C1-C20 substituted
or unsubstituted, saturated or unsaturated, alkyl or
cycloalkyl group or an anhydride; and each Z being,
independently, Cl, Br, or I.
60. The contrast agent of Claim 59, wherein at least one of
said C1-C20 alkyl or cycloalkyl group is substituted with at
least one moiety selected from the group of OH, NH2, SH,
COOH, and P04, or mixtures thereof.
61. The contrast agent of Claim 59, wherein each R1 is,
independently, a polyhydroxy-substituted alkyl or cycloalkyl

group.
62. The contrast agent of Claim 61, wherein said
polyhydroxy-substituted alkyl or cycloalkyl group is selected
from the group consisting of sugar alcohols, monosaccharides,
polysaccharides, and synthetic polymers.
63. The contrast agent of Claim 54, wherein each polynitrilo
chelating unit monomer consists, independently, of a
chelating agent selected from the group consisting of
ethylenediamine tetraacetic acid; diethylenetriamine
pentaacetic acid; 1,5-di-.beta.-methoxyethylene-iminocarbonyl-
methylene-1,3,5-tricarboxymethylene-1,3,5,-triazapentane;
1,5-di-.alpha.,.beta.-dihydroxypropeneimino-carbonyl-methylene-1,3,5-
tricarboxymethylene-1,3,5-triazapentane; 1,4,7,10-
tetraazacyclododecane-1,4,7,10-tetraacetic acid; 1,4,7,10-
tetraazacyclododecane-N,N',N"-triacetic acid; 3,6,9-triaza-
12-oxa-3,6,9-tricarboxymethylene-10-carboxy-13-phenyl-
tridecanoic acid; hydroxybenzyl-ethylenediamine diacetic
acid; N,N'-bis(pyridoxyl-5-phosphate)ethylenediamine-N,N'-
diacetic acid; 1,4,7-triazacyclononane-N,N',N"-triacetic
acid; 1-oxa-4,7,10-triazacyclododecane-triacetic acid;
1,4,8,11-tetraazacyclotetradecane-N,N',N",N'"-tetraacetic
acid; triethylenetetraamine hexaacetic acid; 1,2-
diaminocyclohexane-N,N,N',N'-tetraacetic acid; and anhydrides
thereof.
64. The contrast agent of Claim 54, wherein each free

71
radical monomer, independently, is selected from the group
consisting of heterocyclic nitroxide monomers and
non-heterocyclic nitroxide monomers.
65. The contrast agent of Claim 64, wherein said
heterocyclic nitroxide monomers have the following general
structure:
<IMG>
wherein
a five member ring is pyrrolidine, oxazolidine,
imidazolidine, or thiazolidine;
a six member ring is piperidine; and
each of Ra, Rb, Rc and Rd is, independently, a C1-C20
alkyl or cycloalkyl group, said alkyl or cycloalkyl group
being interrupted or terminated with OH, SH, NH2, NHR1, COOH,
COOR1, NCS, COCHCH2, or COZ, each R1 being, independently, a
C1-C20 substituted or unsubstituted alkyl or cycloalkyl group
or an anhydride, and each Z being, independently, Cl, Br, or
I.
66. The contrast agent of Claim 64, wherein said non-heterocyclic
nitroxide monomers are selected from the group
consisting of diphenylnitroxide and di-tert-butyl nitroxide.
67. The contrast agent of Claim 54, wherein each nitroxide

72
free radical monomer is, independently, selected from the
group consisting of 2,2,6,6-tetramethylpiperidine-1-oxyl;
2,2,4,4-tetramethyl-pyrrolidine-1-oxyl; 2,2,4,4-tetramethyl-
imidazolidine-3-oxyl; 2,2,4,4-tetramethyl-1,3-thiazolidine-3-
oxyl; 2,2,4,4-tetramethyl-1,3-oxazolidine-3-oxyl; 2,2,6,6-
tetramethylpyrimidine-1-oxyl; diphenyl-nitroxide; and di-
tert-butylnitroxide; and wherein each nitroxide may have one
or more OH, SH, NH2, NHR1, COOH, COOR1, NCS, COCHCH2, or COZ,
each R1 being, independently, a C1-C20 substituted or
unsubstituted alkyl or cycloalkyl group or an anhydride, and
each Z being, independently, Cl, Br, or I.
68. The contrast agent of Claim 54, wherein each nitroxide
free radical monomer is, independently, a monofunctionalized
compound selected from the group consisting of 1-oxyl-
2,2,6,6-tetramethyl-4-piperidinyl acrylate; 4-
(iodomethylenecarbonylimino)-2,2,6,6-tetramethyl-piperdinyl-
1-oxy; 4-(bromomethylenecarbonylimino)-2,2,6,6-tetramethyl-
piperidinyl-1-oxy; 3-carboxy-2,2,5,5-tetramethylpyrrolidinyl-
1-oxy;
3-chlorocarbonyl-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-aminomethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-hydroxymethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxyl;
3-hydroxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 3-
chloroformyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 4-amino-
2,2,6,6-tetramethylpiperidine-1-oxyl; 4-hydroxy-2,2,6,6-
tetramethylpiperidine-1-oxyl; and 3-thiocabamoylmethylene-
2,2,5,5-tetramethylpyrrolidinyl-1-oxy.

73
69. The contrast agent of Claim 54, wherein each nitroxide
free radical monomer is, independently, a difunctionalized
compound selected from the group consisting of cis-1-oxyl-
2,2,5,5-tetramethylpyrrolidine; trans-1-oxyl-2,2,5,5-
tetramethylpyrrolidine; 3-amino-4-aminomethylene-2,2,5,5-
tetramethylpyrrolidine; cis-2,5-dimethyl-2(aminomethyl)-5-(2-
carboxyethyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2-
(hydroxymethyl)-5-(methoxycarbonylmethyl)-tetrahydropyrrole-
1-oxyl; cis-2,5-dimethyl-2-(hydroxymethyl)-5-(2-
hydroxyhexyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2,5-
bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-dimethyl-
2,5-bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-
dimethyl-2,5-bis(2-carboxyethyl)-pyrrolidinyl-1-oxy; cis-2,5-
dimethyl-2,5-bis(2-hydroxy-5-methylphenyl)-
tetrahydroxypyrrol-1-oxy; 3-amino-4-carboxy-2,2,5,5-
tetramethylpyrrolidinyl-1-oxy; 2,5-di-tert-butyl-3,4-
diethyloxycarbonyl-pyrrol-1-oxyl; and 1,4-bis(4-hydroxy-
2,2,6,6-tetramethyl-1-oxyl-4-piperidyl)-butane.
70. The contrast agent of Claim 54, wherein each
paramagnetic ion is selected from the group consisting of
transition and lanthanide elements.
71. The contrast agent of Claim 54, wherein each
paramagnetic ion is selected from the group consisting of
Gd(III), Mn(II), Cu(II), Cr(III), Fe(II), Fe(III), Co(II),
Er(II), Ni(II), Eu(III), Dy(III), Yb(III), and Ho(III).

74
72. The contrast agent of Claim 54, wherein each
paramagnetic ion is selected from the group consisting of
Gd(III), Mn(II) and Fe(III).
73. The contrast agent of Claim 1, having the following
structure:
<IMG>
wherein Ch is a polynitrilo chelating unit monomer, FR is a
nitroxide free radical monomer, and M is a paramagnetic
ion; wherein p' = 1 to 10,000; and
wherein, within each of the p' oligomeric groups
<IMG> ,
independently, n = 0 to 10,000 and m = 0 to 10,000; and
for each group of paramagnetic ions <IMG> chelated by
each
of the n chelating unit monomers --Ch-- in each of the
p' oligomeric groups, independently, k = 0 to 2.
74. The contrast agent of Claim 73, wherein each polynitrilo
chelating unit monomer comprises at least one COOH, COOR1, or
COZ group; each R1 being, independently, a C1-C20 substituted
or unsubstituted, saturated or unsaturated, alkyl or
cycloalkyl group or an anhydride; and each Z being,
independently, Cl, Br, or I.

75. The contrast agent of Claim 74, wherein at least one of
said C1-C20 alkyl or cycloalkyl group is substituted with at
least one moiety selected from the group of OH, NH2, SH,
COOH, and PO4, or mixtures thereof.
76. The contrast agent of Claim 74, wherein each R1 is,
independently, a polyhydroxy-substituted alkyl or cycloalkyl
group.
77. The contrast agent of Claim 76, wherein said
polyhydroxy-substituted alkyl or cycloalkyl group is selected
from the group consisting of sugar alcohols, monosaccharides,
polysaccharides, and synthetic polymers.
78. The contrast agent of Claim 73, wherein each polynitrilo
chelating unit monomer consists, independently, of a
chelating agent selected from the group consisting of
ethylenediamine tetraacetic acid; diethylenetriamine
pentaacetic acid; 1,5-di-.beta.-methoxyethylene-iminocarbonyl-
methylene-1,3,5-tricarboxymethylene-1,3,5,-triazapentane;
1,5-di-.alpha.,.beta.-dihydroxypropeneimino-carbonyl-methylene-1,3,5-
tricarboxymethylene-1,3,5-triazapentane; 1,4,7,10-
tetraazacyclododecane-1,4,7,10-tetraacetic acid; 1,4,7,10-
tetraazacyclododecane-N,N',N"-triacetic acid; 3,6,9-triaza-
12-oxa-3,6,9-tricarboxymethylene-10-carboxy-13-phenyl-
tridecanoic acid; hydroxybenzyl-ethylenediamine diacetic
acid; N,N'-bis(pyridoxyl-5-phosphate)ethylenediamine-N,N'-
diacetic acid; 1,4,7-triazacyclononane-N,N',N"-triacetic

76
acid; 1-oxa-4,7,10-triazacyclododecane-triacetic acid;
1,4,8,11-tetraazacyclotetradecane-N,N',N",N'"-tetraacetic
acid; triethylenetetraamine hexaacetic acid; 1,2-
diaminocyclohexane-N,N,N',N'-tetraacetic acid; and anhydrides
thereof.
79. The contrast agent of Claim 73, wherein each free
radical monomer, independently, is selected from the group
consisting of heterocyclic nitroxide monomers and
non-heterocyclic nitroxide monomers.
80. The contrast agent of Claim 79, wherein said
heterocyclic nitroxide monomers have the following general
structure:
<IMG>
wherein
a five member ring is pyrrolidine, oxazolidine,
imidazolidine, or thiazolidine;
a six member ring is piperidine; and
each of Ra, Rb, Rc and Rd is, independently, a C1-C20
alkyl or cycloalkyl group, said alkyl or cycloalkyl group

77
being interrupted or terminated with OH, SH, NH2, NHR1, COOH,
COOR1, NCS, COCHCH2, or COZ, each R1 being, independently, a
C1-C20 substituted or unsubstituted alkyl or cycloalkyl group
or an anhydride, and each Z being, independently, Cl, Br, or
I.
81. The contrast agent of Claim 79, wherein said non-heterocyclic
nitroxide monomers are selected from the group
consisting of diphenylnitroxide and di-tert-butyl nitroxide.
82. The contrast agent of Claim 73, wherein each nitroxide
free radical monomer is, independently, selected from the
group consisting of 2,2,6,6-tetramethylpiperidine-1-oxyl;
2,2,4,4-tetramethyl-pyrrolidine-1-oxyl; 2,2,4,4-tetramethyl-
imidazolidine-3-oxyl; 2,2,4,4-tetramethyl-1,3-thiazolidine-3-
oxyl; 2,2,4,4-tetramethyl-1,3-oxazolidine-3-oxyl; 2,2,6,6-
tetramethylpyrimidine-1-oxyl; diphenyl-nitroxide; and di-
tert-butylnitroxide; and wherein each nitroxide may have one
or more OH, SH, NH2, NHR1, COOH, COOR1, NCS, COCHCH2, or COZ,
each R1 being, independently, a C1-C20 substituted or
unsubstituted alkyl or cycloalkyl group or an anhydride, and
each Z being, independently, Cl, Br, or I.
83. The contrast agent of Claim 73, wherein each nitroxide
free radical monomer is, independently, a monofunctionalized
compound selected from the group consisting of 1-oxyl-
2,2,6,6-tetramethyl-4-piperidinyl acrylate; 4-
(iodomethylenecarbonylimino)-2,2,6,6-tetramethyl-piperdinyl-

78
1-oxy; 4-(bromomethylenecarbonylimino)-2,2,6,6-tetramethyl-
piperidinyl-1-oxy; 3-carboxy-2,2,5,5-tetramethylpyrrolidinyl-
1-oxy;
3-chlorocarbonyl-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-aminomethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-hydroxymethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxyl;
3-hydroxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 3-
chloroformyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 4-amino-
2,2,6,6-tetramethylpiperidine-1-oxyl; 4-hydroxy-2,2,6,6-
tetramethylpiperidine-1-oxyl; and 3-thiocabamoylmethylene-
2,2,5,5-tetramethylpyrrolidinyl-1-oxy.
84. The contrast agent of Claim 73, wherein each nitroxide
free radical monomer is, independently, a difunctionalized
compound selected from the group consisting of cis-1-oxyl-
2,2,5,5-tetramethylpyrrolidine; trans-1-oxyl-2,2,5,5-
tetramethylpyrrolidine; 3-amino-4-aminomethylene-2,2,5,5-
tetramethylpyrrolidine; cis-2,5-dimethyl-2(aminomethyl)-5-(2-
carboxyethyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2-
(hydroxymethyl)-5-(methoxycarbonylmethyl)-tetrahydropyrrole-
1-oxyl; cis-2,5-dimethyl-2-(hydroxymethyl)-5-(2-
hydroxyhexyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2,5-
bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-dimethyl-
2,5-bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-
dimethyl-2,5-bis(2-carboxyethyl)-pyrrolidinyl-1-oxy; cis-2,5-
dimethyl-2,5-bis(2-hydroxy-5-methylphenyl)-
tetrahydroxypyrrol-1-oxy; 3-amino-4-carboxy-2,2,5,5-
tetramethylpyrrolidinyl-1-oxy; 2,5-di-tert-butyl-3,4-

79
diethyloxycarbonyl-pyrrol-1-oxyl; and 1,4-bis(4-hydroxy-
2,2,6,6-tetramethyl-1-oxyl-4-piperidyl)-butane.
85. The contrast agent of Claim 73, wherein each
paramagnetic ion is selected from the group consisting of
transition and lanthanide elements.
86. The contrast agent of Claim 73, wherein each
paramagnetic ion is selected from the group consisting of
Gd(III), Mn(II), Cu(II), Cr(III), Fe(II), Fe(III), Co(II),
Er(II), Ni(II), Eu(III), Dy(III), Yb(III), and Ho(III).
87. The contrast agent of Claim 73, wherein each
paramagnetic ion is selected from the group consisting of
Gd(III), Mn(II) and Fe(III).

Description

CA 02217718 1997-10-08
W 096/32967 PCTrUS95/04697
HYBRID MAGNETIC RESONANCE CONTRAST AGENTS
RELATED APPLICATIONS
5 This application is a continuation-in-part of U.S.
Application Ser. No. 07/949,691, filed September 22, 1992,
currently copending. The joint inventors of the present
application are the same joint inventors of the parent
application. Both applications have been assigned to the
10 same assignee.
BACKGROUND OF THE INVENTION
15 Field of the Invention
This invention pertains to the general field of magnetic
resonance contrast agents used for medical diagnostic and
therapeutic applications. In particular, the invention
relates to the utilization of synthetic copolymeric compounds
20 in novel hybrid configurations comprising metal ions in
conjunction with nitroxide compounds.
Background of the Invention
Nuclear magnetic resonance imaging (generally referred to as
25 NMR or MRI) is based, among other factors, on the detection
of spatial variations in the Tl and T2 relaxation times in
the tissues under observation. Therefore, contrast agents
have been developed for imaging purposes to increase the
natural relaxivity of tissues (i.e, to decrease Tl and T2) at
30 the sites of interest.
High relaxivity is desirable for several reasons. Because
the contrast effectiveness of contrast agents is proportional
in large part to relaxivity, an agent with much greater
relaxivity can be administered in much lower dosages, thus
35 reducing the overall toxicity to which a patient is exposed
during MRI. Furthermore, extremely high relaxivity agents

CA 02217718 1997-10-08
W 096/32967 PCTrUS95/04697
make it possible to design targeted agents (such as
antibodies) labeled with ultra-high relaxivity contrast
agents.
5 The prior art describes many compounds cont~; n; ng
paramagnetic metal ions (such as gadolinium and manganese,
for example) utilized as contrast agents in various chemical
formulations. Such agents' relaxivity has been found to be
proportional to the unpaired electrons in the metal ions, as
10 well as being affected by water exchange and electron and
rotational correlation times. Because these metal ions tend
to be toxic, they need to be chelated with a ligand in order
to reduce the body tissue's ability to absorb them. Contrast
agents are thus created, for example, by combining
15 diethylenetriamine pentaacetic acid (DTPA) with gadolinium
and ethylenediamine tetraacetic acid (EDTA) with manganese.
Unfortunately, though, as a result of the metal ion's
combination with a ligand, the relaxivity of the metal ion is
decreased significantly, thus also reducing its effectiveness
20 as a contrast agent. As shown in the examples of Table 1, at
least one of the relaxation parameters of metal ions
generally decreases substantially when the ions are chelated.
Table 1
Relaxivitv of Metal Ions v~L ~ Chelat
Contrast Agent R1 R2
FeCl3 0.94+0.06 1.14+0.12
Fe-DTPA 0.7 - 0-7
30 MnCl2 8.73+0.52 39.45+0.52
Mn-DPDP Z.8 3.7
Mn-EDTA-MEA 3.29+0.14 5.76+0.13
GdC13 8.1 - 8.1
Gd-DTPA 4.33+0.15 5.19+0.10
35 ~ R2 is always greater than or equal to Rl
(Measurements were taken using 0.5 Tesla and 20 MHz.)

CA 02217718 1997-10-08
W 096/32967 PCTrUS9~/04697
It is known that the relaxivity of metal-ion chelates may be
increased by attaching the chelates to macromolecules such as
~ albumin or dextran, as shown by Gibby in U.S. Patent No.
4,822,594 (1989). In theory, the polymeric macromolecules
5 should increase the correlation time of the molecule
resulting in a decrease of T1 and, possibly, of T2, which
would enhance NMR imaging. In practice, though, such
improvements in relaxivity are relatively modest.
10 Another class of well-known contrast agents consists of
compounds that comprise nitroxide free radicals as the
paramagnetic material used to improve the relaxivity for MRI
purposes. Tn~! ~ch as nitroxide free radicals are
metabolically reduced and converted to diamagnetic material
15 in the body, their concentration rapidly decreases below
useful levels for relaxation enhancement. Thus, in order to
produce the desired image enhancement, nitroxide-based agents
have to be used at high concentrations that may be
unacceptably toxic. Therefore, nitroxides are often combined
20 with other functional molecules in an attempt to extend their
effectiveness at concentrations that are tolerable for
diagnostic and therapeutic applications.
For example, U.S. Patent No. 4,863,717 to Keana (1989)
25 describes a long--lasting nitroxide-bearing contrast agent
that comprises a large molecule having surfaces covered with
nitroxide free radicals and a liposome molecule that
encapsulates an oxidant used to reoxidize the reduced

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nitroxide group back to its paramagnetic form. In U.S.
Patent No. 5,135,737 (1992), Keana also discloses the use of
branched organic structures terminating with amine groups to
which pharmacologically active groups, such as nitroxides and
5 metal ions, can be chemically attached. These amplifier
molecules are utilized to provide a stable contrast agent by
combining a plurality of contrast-enhancing groups (such as
nitroxides or paramagnetic metal ions) in the various
branches of the molecule with a reactive moiety for attaching
10 the molecule to target-specific biomolecules at the site of
interest.
In U.S. Patents No. 4,834,964 (1989) and No. 5,104,641
(1992), Rosen describes MRI image-enhancing agents based on
15 charged, stable, organic nitroxides. Specific classes of
nitroxide compounds are disclosed for scanning the spinal
cord and organs associated with the cardiovascular system of
a patient.
20 In our copending applications we disclose the use of
copolymers containing paramagnetic metal ions dispersed along
the copolymer chain, which, because of the size and spatial
distribution of the resulting molecule, tends to increase the
relaxivity and stability of the contrast agent. In a
25 continuing effort to refine the use of oligomers and polymers
as base molecules for introducing paramagnetic material in
the human body, the present invention is related to a
discovery that enables the design and synthesis of contrast

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agents with a yet much higher relaxivity than previously
reported.

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SU~ RY OF THE INVENTION
An object of the present invention is to provide a contrast
5 agent with sufficiently high relaxivity to permit a
significant reduction of the dosages of agent used during
MRI, thus reducing the patient's exposure to toxic material.
Another object of the invention is to provide a contrast
10 agent that combines cumulatively the image enhancing
properties of metal ions and of nitroxides in the same
molecule.
A further goal is to provide a general structural framework
15 within which specific contrast agents can be designed for
synthetic derivation directed at particular diagnostic or
therapeutic objectives.
According to these and other objectives, the present
20 invention consists of novel MRI contrast agents comprising
one or more metal-ion chelates in juxtaposition with one or
more free-radical nitroxide compounds in a polymeric or
oligomeric molecule. Both the chelate units and the free
radical units may, independently, be inside the main chain of
25 the polymer or in a side chain of the linkage portion of the
polymer. The number of combined units of chelates and free
radicals in the polymer or oligomer is at least two.

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These and other objects, features and advantages of the
present invention, as well as details of the preferred
_ embodiments thereof, will be more fully understood from the
following detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The heart of this invention lies in the discovery that metal
ion chelates, when juxtaposed to free-radical nitroxides in
oligomeric and polymeric molecules, produce a marked
15 increases in relaxivity, greater than either can produce
alone. As illustrated by the examples shown in Table 2,
relatively low molecular weight oligomeric compounds composed
of paramagnetic chelates and nitroxide subunits show a
substantial increase in relaxivity when compared to compounds
20 with the same paramagnetic metal ions but without the
combination with nitroxides.

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Table 2
Relaxivity of Hybrid Complexes vs. Similar Non-Hybrid Complexes
Agent Rl R2
Mn-EDTA-EOEA-DP 6.48+0.103 13.29+0.40
Mn-Poly(A)-ATMPO 35.55+1.59 57.21+2.09
Mn-Poly-EED-EEA(l) 38.31+1.03 46.31+0.41
10 Mn-Poly-EED-EEA(2) 46.55+0.42 78.01+1.65
(Measurements were taken using 0.5 Tesla and 20 MHz.)
Without limiting the scope of this invention to a specific
15 mechanism of action causing this increase in relaxivity, the
inventors hypothesize that the nitroxide radical relaxes
other nuclei because of the much larger angular momentum of
the unpaired electron spin. In tandem, the paramagnetic
center has the same effect, thus producing an additive
20 result. Thus, the resulting extremely high relaxivity of
these hybrid contrast agents has applicability for the
development of general-purpose vascular imaging and
gastrointestinal MRI contrast agents.
25 In accordance with one preferred generic characterization of
the embodiments of this invention, the general structure of a
hybrid-polymer contrast agent according to the invention is
represented by the following general formula:

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__----(Ch)n------(L)~ (Ch)n------(FR),,,----------
~ 5 (M)k (FR)n (M)k
_p _ _ p~
_ q
wherein Ch is a polynitrilo chelating unit monomer, L is a
10 linker monomer, FR is a nitroxide free radical monomer, and M
is a paramagnetic ion;
wherein q = 1 to 10,000;
wherein, w thin each of the q polymeric groups
----(Ch)n---(L)~ (ch)n---(FR)
(M)k (FR)~ (M)k
_ p _ _p~
independently, p = 0 to 10,000 and p' = 0 to 10,000;
20 wherein, within each of the p oligomeric groups
~----(Ch)n------(L~
(M)k (FR)~
independently, n = 0 to 10,000 and j - 0 to 10,000;
for each group of paramagnetic ions (M)k chelated by
25 each
of the n chelating unit monomers --Ch-- in the p
oligomeric
groups, independently, k = 0 to 2; and
for each group of free radical monomers (FR)~ linked to
30 each
of the j linker monomers --L-- in the p oligomeric
groups,
independently, m = 0 to 2; and
wherein, within each of the p' oligomeric groups

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~~~(ch)n - - - (FR)n
(M)k
independently, n = 0 to 10,000 and m - 0 to 10,000; and
for each group of paramagnetic ions (M)~ chelated by
each
of the n chelating unit monomers --Ch-- in the p'
oligomeric
groups, independently, k = 0 to 2.
According to a more special characterization of this
invention, a class of hybrid-polymer contrast agents may be
represented by the following formula:
---(Ch)n---(L)~ (Ch)n---(FR)~--- (2)
~ I I ~
(M)k (FR)~ (M)k
_ p _ _ p,
wherein Ch, L, FR and M are as described above;
wherein, independently, p = 1 to 10,000 and p' = 1 to 10,000;
wherein, within each of the p oligomeric groups
---(Ch) ---(L)~---,
(M)~ (FR)~
independently, n = 0 to 10,000 and j - f 0 to 10,000;
for each group of paramagnetic ions (M)k chelated by
each
of the n chelating unit monomers --Ch-- in each of the p
oligomeric groups, independently, k = 0 t7 2; and
for each group of free radical monomers (FR)~ linked to
each of the j linker monomers --L-- in each of the

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11
oligomeric groups, independently, m = 0 to 2; and
wherein, within each of the p' oligomeric groups
_ ---(Ch)"---(FR)~--- ,
(M)k
independently, n = 0 to 10,000 and m - 0 to 10,000; and
for each group of paramagnetic ions (M)k chelated by
each
of the n chelating unit monomers --Ch-- in each of the
P'
oligomeric groups, independently, k = 0 to 2.
Note that Formula 2 is a special case of Formula 1 where q =
15 1.
According to another special characterization of the
embodiments of the invention, another class of hybrid-polymer
contrast agents may be represented by the following formula:
---(Clh)~---(L)~ (3)
(M)k (FR)~
~ _ P
wherein Ch, L, FR and M are as described above;
wherein p = 1 to 10,000; and
wherein, within each of the p oligomeric groups
---(C~h)~---(L~)~---,
(M)k (FR)~
independently, n = 0 to 10,000 and j = 0 to 10,000;

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12
for each group of paramagnetic ions (M)k chelated by
each
of the n chelating unit monomers --Ch-- in each of the p
oligomeric groups, independently, k = 0 to 2; and
for each group of free radical monomers (FR)m linked to
each of the j linker monomers --L-- in each of the
oligomeric groups, independently, m = 0 to 2.
Note that Formula 3 is a special case of Formula 1 where q =
10 l and p' = 0.
Finally, according to yet another special characterization of
the contrast agents of the invention, another class of hybrid
polymers may be represented by the following formula:
- _
---(Ch)n---(FR)~--- (4)
(M)k
~_
wherein Ch, FR and M are as described above;
wherein p' = 1 to 10,000; and
wherein, within each of the p' oligomeric groups
---(Ch) ---(FR) ---
(M)k
independently, n = 0 to 10,000 and m T ~ to 10,000; and
for each group of paramagnetic ions (M) k chelated by
each
of the n chelating unit monomers --Ch-- in each of the
p' oligomeric groups, independently, k = 0 to 2.

-
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13
Note that Formula 4 is a special case of Formula l where q =
1 and p = O.
The chelating unit monomer Ch in Formulae (1)-(4) is a
5 polynitrilo chelating agent having at least one COOH, COORl,
or COZ group, wherein each R1 is, independently, a Cl-C20
substituted or unsubstituted and saturated or unsaturated
alkyl or cycloalkyl group or an anhydride, and each Z is,
independently, Cl, Br, or I. The COOH groups may, if
10 desired, be in the form of an acid anhydride, as those
skilled in the art will recognize, and such variations are
intended to be literally encompassed within the term COOH, as
employed in connection with the polynitrilo chelating agents
of this invention. By substituted, with regard to Cl-C20, it
15 is meant substituted with such moieties as OH, NH2, SH, COOH,
P04~ and the like. Preferably, Rl is a polyhydroxy-
substituted alkyl or cycloalkyl group. By polyhydroxy-
substituted alkyl or cycloalkyl group, it is meant that the
alkyl or cycloalkyl group is substituted with at least two
20 hydroxyl groups. Suitable substituted and unsubstituted
alkyl or cycloalkyl groups, including polyhydroxy-substituted
alkyl or cycloalkyl groups, will be readily apparent to those
skilled in the art. Preferred polyhydroxy-substituted alkyl
or cycloalkyl groups, for example, include sugar alcohols
25 (such as glycidol, inositol, mannitol, sorbitol,
pentaerythritol, galacitol, adonitol, xylitol, and alabitol),
monosaccharides (such as sucrose, maltose, cellobiose, and
lactose), polysaccharides (such as starch), and synthetic

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14
polymeric alcohols (such as polyvinylalcohol).
As those skilled in the art understand, a chelating agent is
an organic compound capable of combining with a metal (and,
5 particularly for the purposes of this invention, with a
paramagnetic ion). Also, by polynitrilo it is meant a
compound containing at least two nitrogen groups. Such
polynitrilo chelating agents may include either open chain or
cyclic structures, as desired. Polynitrilo chelating agents
10 are well known in the art; accordingly, suitable chelating
agents for the purposes of this disclosure will be readily
apparent to those skilled in the art. Examples of suitable
chelating agents include such compounds as ethylenediamine
tetraacetic acid (EDTA); diethylenetriamine pentaacetic acid
15 (DTPA); 1,5-di-B-methoxyethylene-iminocarbonyl-methylene-
1,3,5-tricarboxymethylene-1,3,5,-triazapentane; 1,5-di-~,~-
dihydroxypropeneimino-carbonyl-methylene-1,3,5-
tricarboxymethylene-1,3,5-triazapentane; 1,4,7,10-
te~raazacyclododecane-1,4,7,10-tetraacetic acid (DOTA);
20 1,4,7,10-tetraazacyclododecane-N,N',N"-triacetic acid (DO3A);
3,6,9-triaza-12-oxa-3,6,9-tricarboxymethylene-10-carboxy-13-
phenyl-tridecanoic acid (B-19036); hydroxybenzyl-
ethylenediamine diacetic acid (HBED); N,N'-bis(pyridoxyl-5-
phosphate)ethylenediamine-N,N'-diacetic acid (DPDP); 1,4,7-
25 triazacyclononane-N,N',N"-triacetic acid (NOTA); l-oxa-
4,7,10-triazacyclododecane-triacetic acid (OTTA); 1,4,8,11-
tetraazacyclotetradecane-N,N',N",N'"-tetraacetic acid (TETA);
triethylenetetraamine hexaacetic acid (TTHA); 1,2-

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diaminocyclohexane-N,N,N',N'-tetraacetic acid; as well as
anhydrides of the foregoing compounds, such as, for example,
ethylenediamine dianhydride (EDTA-dianhydride) and
diehtylenetriamine pentaacetic acid dianhydride (DTPA-
5 dianhydride). Preferably, the complexing agents are DTPA,EDTA and DOTA, most preferably DTPA and EDTA. Examples of
these and other chelating agents are described in U.S. Patent
No. 4,933,441 to Gibby, the disclosure of which is hereby
incorporated by reference in its entirety.
Many of the foregoing chelating agents are available
commercially, such as, for example, ethylenediamine
tetraacetic acid (and its anhydride) and diethylenetriamine
pentaacetic acid (and its anyhydride), which may be purchased
15 from the Aldrich Chemical Co. of Milwaukee, Wisconsin, or
from the Sigma Chemical Co. of St. Louis, Missouri. Such
chelating agents may also be prepared by conventional
techniques, as would be readily apparent to those skilled in
the art.
The free radical monomer Fr in Formulae (1)-(4) above
consists of heterocyclic or non-heterocyclic nitroxide
monomers. The heterocyclic nitroxides have the following
general structure:

-
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16
R- ~ ~
10 wherein a five member ring is pyrrolidine, oxazolidine,
imidazolidine, or thiazolidine; a six member ring is
piperidine; and each of the four substitute radicals Ra, Rb,
Rc, Rd is, independently, a C1-C20 (substituted or
unsubstituted and saturated or unsaturated) alkyl or
15 cycloalkyl group, interrupted or terminated with OH, SH, NH2,
NHRl, COOH, COOR1, NCS, COCHCH2, or COZ, where Z and R1 are as
descri~ed above. Non-heterocyclic nitroxides comprise
diphenylnitroxide and di-tert-butyl nitroxide.
20 Preferred for this invention are the following nitroxide
stable free radicals: 2,2,6,6-tetramethylpiperidine-1-oxyl;
2,2,4,4-tetramethyl-pyrrolidine-1-oxyl; 2,2,4,4-tetramethyl-
imidazolidine-3-oxyl; 2,2,4,4-tetramethyl-1,3-thiazolidine-3-
oxyl; 2,2,4,4-tetramethyl-1,3-oxazolidine-3-oxyl; 2,2,6,6-
25 tetramethylpyrimidine-1-oxyl; diphenyl-nitroxide; and di-
tert-butylnitroxide; wherein each nitroxide may have one or
more OH, SH, NH2, NHR1, COOH, COOR1, NCS, COCHCH2, or COZ, Z
and R1 being as described above.

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17
These nitroxide monomers may be combined with one or two
functional groups. Monofunctionalized nitroxide monomers
O comprise l-oxyl-2,2,6,6-tetramethyl-4-piperidinyl acrylate;
4-(iodomethylenecarbonylimino)-2,2,6,6-tetramethyl-
5 piperdinyl-1-oxy; 4-(bromomethylenecarbonylimino)-2,2,6,6-
tetramethyl-piperidinyl-1-oxy; 3-carboxy-2,2,5,5-
tetramethylpyrrolidinyl-1-oxy; 3-chlorocarbonyl-2,2,5,5-
tetramethylpyrrolidinyl-1-oxy;
3-aminomethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
10 3-hydroxymethylene-2,2,5,5-tetramethylpyrrolidinyl-1-oxy;
3-hydroxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 3-
chloroformyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl; 4-amino-
2,2,6,6-tetramethylpiperidine-1-oxyl; 4-hydroxy-2,2,6,6-
tetramethylpiperidine-1-oxy; and 3-thiocabamoylmethylene-
15 2,2,5,5-tetramethylpyrrolidinyl-1-oxy.
Difunctionalized nitroxide monomers comprise cis-1-oxyl-
2,2,5,5-tetramethylpyrrolidine; trans-1-oxyl-2,2,5,5-
tetramethylpyrrolidine; 3-amino-4-aminomethylene-2,2,5,5-
20 tetramethylpyrrolidine; cis-2,5-dimethyl-2(aminomethyl)-5-(2-
carboxyethyl)-tetrahydropyrrole-1-o~yl; cis-2,5-dimethyl-2-
(hydroxymethyl)-5-(methoxycarbonylmethyl)-tetrahydropyrrole-
1-oxyl; cis-2,5-dimethyl-2-(hydroxymethyl)-5-(2-
hydroxyhexyl)-tetrahydropyrrole-1-oxyl; cis-2,5-dimethyl-2,5-
25 bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-dimethyl-
2,5-bis(3-hydroxypropyl)-pyrrolidinyl-1-oxy; trans-2,5-
dimethyl-2,5-bis(2-carboxyethyl)-pyrrolidinyl-1-oxy; cis-2,5-
dimethyl-2,5-bis(2-hydroxy-5-methylphenyl)-

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18
tetrahydroxypyrrol-1-oxy; 3-amino-4-carboxy-2,2,5,5-
tetramethylpyrrolidinyl-l-oxy; 2,5-di-tert-butyl-3,4-
diethyloxycarbonyl-pyrrol-l-oxyl; and 1,4-bis(4-hydroxy-
2,2,6,6-tetramethyl-1-oxyl-4-piperidyl)-butane.
In Formulae (1), (2) and (3), L is linker monomer having the
following general structure:
,Xl[(CHR2)~--CHR2--Y]n~Gq~(CHR2)~,,--CHR2--X2
wherein Xl and X2 are, independently, OH, NH2, NHRl, COOH,
COORl, SH, Z or NCS; Y is O, NH, NRl, S or CO; each Z and
each Rl are, independently, as described above; R2 is a C1-
C20 substituted or unsubstituted, saturated or unsaturated,
15 alkyl or cycloalkyl group; G is a.C1-C20 substituted or
unsubstituted alkyl or cycloalkyl group, a saccharide, a
peptide or a polysulfide; and m, m', n, and q are,
independently, 0 to 10,000. With regard to the C1-C20
groups, by substituted it is meant the same substituting
20 moieties as described above for Rl in the formulation of
polynitrilo chelating agents.
Suitable polyamino linker monomers comprise compounds such as
1,2-diaminoethane; 1,3-diaminopropane; 1,4-diaminobutane;
25 1,5-diamino-3-(2-aminoethyl)-pentane; N,N'-dimethyl-1,2-
diaminoethane; N,N'-dimethyl-1,3-diaminopropane; 2-hydroxy-
1,3-diaminopropane; 2-amino-1,3-diaminopropane; 2,3-diamino-
1,4-butanediol; 1,4-diamino-2,3-butane diol; 1,4-

-
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19
diaminocyclohexane; 1,4-phenylenediamine; 1,1,1-tris-
(aminomethyl)ethane; 2,2',2"-tris-aminoethylamine; tris-
(aminomethylene)methane; diethylenetriamine;
triethylenetetraamine; 1,3,5-triaminocyclohexane; and 1,3,5-
5 triaminobenzene.
Suitable polyhydroxy linker monomers comprise compounds such
as 2,2-dimethyl-1,3-propanediol; tris-(2-hydroxyethyl)amine;
1,1,1-tris-(hyroxymethylene)ethane; glycerine; erythritol;
10 sugar alcohols; polyethyleneglycol; w,w'-diamino-
polyethyleneglycol; N-substituted-w-aminopolyethyleneglycol;
w,w'-dithiol-polyethyleneglycol; polysulfide-blocked
polyethyleneglycol; and polyethylene-imine.
15 Most preferred linker monomers are ethylenedioxydiethylamine;
N,N'-bis-dihydroxypropyl-ethylenedioxydiethylamine; and
ethylenedioxydiethylmercaptane.
The molecular weight of a copolymer having a structure
20 according to one of the disclosed formulae can vary as widely
as desired. Preferably, however, the molecular weight of
such copolymer is between l,000 and 500,000 (weight-average
molecular weight), and most preferably between 3,000 to
30,000.
The copolymer may be prepared by using polycondensation
polymerization techniques. Such polymerization techniques
include those described in McCrum et al., Principles of

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Polymer Engineering, Oxford University Press (NY 1988), which
is hereby incorporated herein by reference in its entirety.
The monomers bind to one another to form a copolymer through
an ester, amide, or carboxylic thioester linkage of at least
5 one of the reactive functional groups OH, NH2, NHRl, COOH,
COZ, COOR1, SH, NCS, COCHCH2, or Z groups in each monomer.
If desired, one may employ any one of a number of
condensation reagents such as dicyclohexylcarbodiimide (DCC),
to facilitate the polymerization reaction. Also, if desired,
10 polynitrilo chelating agents may be employed in the form of
acid anhydrides to facilitate the polymerization reaction.
As those skilled in the art will recognize, the copolymer may
take any one of a variety of forms such as linear, branched,
15 cyclic and/or cross linked, depending upon the particular
monomers employed, the number of reactive sites that the
monomers possess, the particular reaction conditions, etc.,
as would be apparent to those skilled in the art. The
copolymer may consist of more than one type of chelating unit
20 monomer, more than one type of nitroxide free radical
monomer, and more than one type of linker monomer.
In accordance with the main aspect of the invention, the
copolymer further comprises paramagnetic ions chelated into
25 the polynitrilo chelating unit Ch, which renders the
invention particularly suited for magnetic resonance imaging.
Exemplary paramagnetic ions suitable for use in the present
invention comprise the transition elements and lanthanides.

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21
Preferred elements include Gd(III), Mn(II), Cu(II), Cr(III),
Fe(II), Fe(III), Co(II), Er(II), Ni(II), Eu(III), Dy(III),
Yb(III), and Ho(III). The most preferred elements are
Gd(III), Mn(II) and Fe(III). If desired, different
5 paramagnetic ions may be employed in combination with one
another and may be chelated to a combination of different
chelating units within the polymer chain.
The following examples are provided to illustrate the
10 invention.
Example 1
Synthesis of Manganese Poly-EDTA-(2,2'-
ethylenedioxydiethylamine)-(2,2,6,6-tetramethyl-1-oxyl-
piperidin-4-yl acrylate)
[Mn-Poly(A)-ATMPO]
Poly-EDTA-2,2'-(ethylenedioxy)-diethylamine (EOEA) was first
synthesized by dissolving 3.16 g (0.021 M) of 2,2'-
(ethylenedioxy)-diethylamine in 75 ml of dry methanol; by
20 suspending 4.60 g (0.018 M) of ethylenediamine tetracetic
dianhydride in 75 ml of dry methanol; and by adding the
suspension dropwise to the first solution over the course of
about 1.5 hours while continuously stirring. Stirring was
further continued for another 5 hours at room temperature.

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22
O~. "0
H2N O~ O~ N~2 + o~ N~ N O >
1 0 9
ol 1~l 2 1~
HO-C ~ ~C-OH HO-C~ ~C-OH
H2N~ O~ O~ H-,C, C NH~ O~ O~ NH ,C, o ~--J
Poly(A)
10 At the end of this time, it was no longer possible to see the
suspended EDTA-dianhydride. The admixture was kept
overnight. The solution was then heated and kept at about
40-45 C for 8 hours in order to ensure the completion of the
polymerization reaction. The unreacted dianhydride was
15 filtered out and the solvent was evaporated off the solution,
yielding 7.49 g (96.S% yield) of Poly(A), a white foamy
solid.
2, 2,6,6--tetramethyl--1--oxyl--piperidin--4--ylacrylate (ATMPO)
20 was then synthesized by dissolving 10 g of 4-OH-2,2,6,6-TMP-
1-oxyl and 10. 53 g of triethylamine (TEA) in 100 ml of CH2Cl2
and cooling the solution to about 0 to 4 C; further by
dissolving 4.74 g of acryloyl chloride in 20 ml of CH2Cl2 and
adding this solution dropwise into the first solution while
25 stirring at about 0-4 C.

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N--o ~ H2C=CHCCI TEA ~' HzC=CHC--~CHz
(ATMP0)
Stirring continued for another hour, when a precipitate was
observed in the reaction solution. The temperature of the
10 solution was then raised to room temperature and left
overnight. The precipitate was filtered and washed with
water. The organic layer was separated and dried over
anhydrous sodium sulfate. The CH2Cl2 was evaporated leaving
a red solid (ATMP0) which was recrystallized with hexane.
15 The melting point was determined to be 99 C.
Poly(A) and ATMP0 were then combined to synthesize Poly(A)-
ATMP0 as follows:
~BS~iTUTE SHEE~ (RULE 26)

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24
H>~CH3
Poly(A) + H2~:CHCOO ~ CH
o- ~ OOCCH2c~2 R fH2C~lCO ~ N-O-
HO-c-~ ~-C-OH
~o ~ ~-- ~ ~ Y( )\--~--&
~C~ OOCCH2CH~ _ _ CH2CH2COO\ ~
10 '~'~>~< ~ ~-
1.43 g of Poly(A) was dissolved in 40 ml of water and 50 ml
of CH3CN. 0.37 g of ATMP0 was dissolved in 25 ml of CH3CN.
15 These solutions were then mixed, heated and kept at about
80 C for 3 hours and left at room temperature overnight.
This mixture was then refluxed at about 90-9S C for 5 hours.
The solvents were evaporated off and 1.8 g of red orange
solid Poly(A.)-ATMP0 resulted, with a 100% yield.
Finally, the polymer was chelated to yield the Mn-Poly(A)-
ATMP0 as follows:
SUBST~TIJTE SH~FT ~P.llLE 26)

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.O-N~kOoccH2cH2 R ?~-~
~~--C~ ,0, ''H2CH2Co
O~NH~ Poly(A) ~ ~ NH~o/~r
~.O-N~xooccH2cH2 - _ CH2CH2C~
+ MnC03
-O~
1 0 OOCCH2CH2
HO C~ rC~O~O-C~ R CH2cH2
~ \~ ~H ,f~fi~ o
~o- ~ - - 8 ~H2cH2c
1.67 g of Poly(A)-ATMPO, 0.60 g of MnCO3 and 100 ml of water
were heated and maintained at about 40 C for 5 hours. The
20 temperature was then raised to about 70 C and kept there for
2 hours. Unreacted MnCO3 was filtered out and the water
evaporated. 1.43 g of orange solid resulted [yield of 76%
Mn-Poly(A)-ATMPO].
Example 2
Synthesis of Mn-Poly-EED-EEA (First Method)
EOEA ( 2,2'-ethylenedioxydiethylamine) was first reacted with
SU~STlTU~E Sl ZEET (R~LE 26)

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26
2,2,6,6-tetramethyl-1-oxyl-piperidinyl-4-yl acrylate (ATMPO)
to produce EOEA-ATMPO (Component 1), as follows:
H2N~ 0 ~ NH2 CH2=CHCOO ~ C~,CN
.O-N ~ ooccH2c~H2 N,CH~CH~Coo ~ N-O
H H ~ H H ~
0.56 g (0.0025 M) of ATMPO (prepared as illustrated in
15 Example 1) and 0.25 g (0.0017 M) of EOEA were dissoved in 50
ml CH3CN and stirred at room temperature for about 3 hours
and refluxed for about 8 hours. The CH3CN was evaporated and
a viscous EOEA-ATMPO li~uid resulted (100% yield).
20 N,N'-(2,3-dihydroxypropyl)-2,2'-(ethylenedioxy)-diethylamine
(EOEA-DP) was then synthesized as follows:
~ ~ ~ H2 .~. 2 CH~ CH-CH20H
C~ H~ j H--CH~NH~ O~ O )Y C~l CH

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8.88 g (0.06 M) of 2,2~-(ethylenedioxy)-diethylamine (EOEA)
was dissolved in 50 ml of dry methanol and heated to about
5 60 C. 8.88 g of glycidol (0.12 M) was added dropwise under
stirrlng over the course of approximately 2 hours in a water
bath at about 70~ C. Stirring was continued for about an
additional hour at which time the methanol was evaporated
off. A viscous liquid EOEA-DP (Component 2) resulted (100%
10 yield).
Poly-EED-EEA was then synthesized as follows:
-O--N~ H ~--~'
CH2 ~CH -CH2NH~ O~ O ~ HCH2- ,CH - CH2
O N N O
,CJ \-J--C~
OH o,~ ,OH HO~,oHO O~ ,OH HO~C,,
N N ~ ~~ ~N ~ O IH2CH2C
o - C-N o q ~ N~C ~ ~ - C-N O O
H> ~ N--O-
_. -~ ~ m

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28
0.81 g (0.00135 M) of EOEA-ATMPO (Component 1) was dissolved
in 10 ml of dry methanol. 1.91 g (O. 0065 M) of EOEA-DP
(Component 2) was dissolved in 20 ml of dry methanol. These
10 two solutions were mixed together. 1. 9968 g (0.0078 M) of
EDTA-dianhydride (Component 3) was suspended in 20 ml dry
methanol. This suspension was added to the solution
cont~;n;ng Components 1 and 2 and stirred at about 50 C for
approximately 2 hours. The methanol was evaporated off and
15 4.99 g of Poly--EED-EEA were obtained (approximately 100%
yield).
Finally, the Poly-EED-EEA was chelated as follows:
_, MnCO3 +
<OH o~, ,OH HO, "o HO ~ C~ ~C~~ ~-~'
<~--OH ~ ~ HO--~R N N R CIH2CH2c 7<
N--C~ C--N OQ ~--C-- \_/ --C--N O O
~I 11 // \1\ \/ \ \ \
~ ~ CH2CH2COO ~
~N - O-
_ _ m

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29
0~ 0 ~ n ~ ,O HO~ ~ ~ ~~-
N N ~, N N O C~2CH2
N-C - \___/ - fi-N O O N-C - ' - C-NI O O
H >~<N.--O-
_m
4.94 g (0.00141 M) of Poly-EED-EEA was reacted with 0.17 g
10 (0.00147 M) of MnCO3 in water at about 40 C for about 2
hours; then the temperature was raised to about 70 C for
approximately 2 additional hours. The product was then
filtered and the unreacted nitroxide was extracted with 30 ml
of ethylacetate. The organic layer was separated off. The
15 water was evaporated and the residue dried in a vacuum oven.
This yielded 4.49 g (89.8% yield) of orange solid Mn-Poly-
EED-EEA. The molecular weight of the polymer was 3559. The
percentage of manganese was found to be 1.46% by structure
and 1.45% by.analysis.
Example 3
Synthesis of Mn-Poly-EED-EEA (Second Method)
25 EOEA was first reacted with 2,2, 6,6-tetramethyl-1-oxyl--
piperidinyl-4-yl acrylate (ATMPO) to produce EOEA-ATMPO
(Component 1), as shown in Example 1 above.

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Similarly, N,N'-(2,3-dihydroxypropyl)-2,2'-(ethylenedioxy)-
diethylamine (EOEA-DP) was synthesized to produce Component 2
as shown in Example 2.
5 Poly-EED-EEA was also synthesized as shown in Example 2 by
combining EOEA-ATMPO (Component 1) with EOEA-DP (Component 2)
and then by mixing the resulting solution with EDTA-
dianhydride (Component 3).
10 Finally, the Poly-EED-EEA was chelated according to the
following second method:
MnCO~ ~
C~ ~C ~ O~ C,CH }~ ~ "o ~N-O-
N--C-- /N O N\ N ~
CH2CH2COO /~
H>~N~~-
- m

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31
~''C'~ ~'C~O ~-~~
N 'N R N ~ o CIH2c~2c
N-C ~ C-.N ~ CH2CH2cOo ~
_ H ~ N-O.
- m
1.24 g (O.3537 mM) of Poly-EED-EEA was reacted with 0.194 g
20 (1.6876 mM) of MnCO3 in water at about 40 C for about 8
hours; then the temperature was raised to about 70 C for
approximately 1 additional hour. The water was then
evaporated off and a 100% yield of solid Mn-Poly-EED-EEA was
provided. The molecular weight of the polymer was 3760. The
- 25 percentage of manganese was found to be 7.01~ by structure
and 6.6% by analysis.

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Example 4
Synthesis of Gd-Poly-DTPA-DiaminoPROXYL
Poly-DTPA-diaminoPROXYL is first synthesized according to the
5 following reaction shown by H. R. Wenzel et al. in Chemische
Berichte 111, 2453 (1978):
0~ ~COO~f ~O O .
O~N~ N N ~
H2N ' CH2NH2
HOOC--~ ~ ~COOH HOOO~ ~COOH COOH
--HN--C~ ~C--~,H2NH--C-- ~ C--~--
o
3.57 g of DTPA-dianhydride and 1.86 g of 2,2,5,5-tetramethyl-
3-amino-4-aminomethylene-pyrrolidine-1-oxyl are mixed in
20 anhydrous methanol, stirred at room temperature overnight,
and evaporated to dryness. This process produced 5 g of
poly-DTPA-PROXYL copolymer.
The chelate was then prepared by dissolving 5.43 g poly-DTPA-
25 PROXYL in 100 ml of water, suspending 2 g of gadolinium oxidein the solution, stirring at about 45 C for approximately 10
hours, and filtering the excess gadolinium oxide out. The
solution was then evaporated until dry. 6.5 g of Gd-poly-

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33
DTPA-PROXYL was thus obtained having the following structure:
HOOC-~ ~cooH COOH H~~q (COOH COOH
o --~ ~C--t~ ,H2NH--C-- --/ ~-- ~C--NH-- f Gd203
O.
COO~C~~ OOC
~N' ' 'N~ ~'NJ HOOC~ ~C0 ~--COOH
~ >~k 2 , " ~-- ~C--NH--

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Exam~le 5
Synthesis of Gadolinium-DO~A-Poly-ethylenedioxydiethylamine-
PROXYL
5 Poly-ethylenedioxydiethylamine-PROXYL (poly-DOEA-PROXYL) is
first synthesized as follows, as shown by Keanna, J.F.W. et
al, Can. J. Chem., 60, 1439 (1982):
10HOOC>~,OOH SOCIC10C~;;~,OCI
O~ O
CIOC COCI H2N O O Hl'C Cl~ ~ ~ NH2
>t;~S< I H2N 0~--0~--NH2 ~ ~
O O _ p
6.13 g of cis-1-oxyl-2,2,5,5-tetramethyl-3,4-
20 dicarboxypyrrolidine and 5.3 g of dried triethylamine were
dissolved in 50 ml of chloroform. 6.3 g of freshly distilled
sulfonyl chloride was added at about 0 to 5 C, drop by drop,
while stirring, and then stirred for approximately 2
additional hours. The reaction mixture was evaporated to
25 remove the chloroform and traces of unreacted sulfonyl
chloride and triethylamine. The residue was redissolved into
50 ml of chloroform, yielding a 3,4-dichlorocarbonyl-2,2,5,5-
tetramethylpyrrolidine-1-oxyl (di-Cl-PROXYL) product.
SUBSTITUTE SHEET (RULE 26)

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The solution of di-Cl-PROXYL thus obtained was added to 4.44
g of ethylenedioxydiethylamine dissolved 100 ml of
chloroform, drop by drop at about 0 to 5 C; the resulting
mixture was stirred for about 5 hours, and then evaporated to
5 dryness. The process yielded the amino-terminated copolymer
shown above, having a molecular weight of about 3,000.
The copolymer was then combined with 1,4,7,10-
tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)
10 according to the following reaction:
r~~o A o A 11 " ~-~ ~
~C + DOTA
~' ~
O _ p
HOOC A /--COOH HOOC--\ ~_~ /--COOH
HOOC ~ ~ \--C-~N o~ o A HNC CNH O ~ ~ NH - C ~ COOH
O i ~
O- _ p
25 0.81 g of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic
acid was dissolved in 30 ml of chloroform; a solution of 0.51
g of dicyclohexylcarbodiimide (DCC) in 20 ml of chloroform
was then added and stirred for about 4 hours. A solution of

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36
3.2 g of the amino--terminated copolymer prepared according to
the step above in 50 ml of chloroform was added to the
mixture, at about 0 to 5 C, and then stirred for
approximately 6 hours. The reaction mixture was evaporated
5 to dryness and then redissolved in 30 ml of water. The
precipitate dicyclohexylurea was filtered out, and the
solution was reacted with acetone to produce a viscous solid
precipitate consisting of DOTA-poly-EOEA-PROXYL. The product
was washed several times with acetone and dried under
10 vacuum.
Finally, Gd-DOTA-poly-ethylenedioxydiethylamine-PROXYL (Gd-
DOTA-poly-EOEA-PROXYL) was obtained by chelating the polymer
with gadolinium oxide. 4 g of DOTA-poly-EOEA--PROXYL were
15 dissolved in 100 ml of water, and 0.5 g of a gadolinium oxide
suspension were stirred into this solution at about 40 C for
approximately 24 hours. The excess gadolinium oxide was
filtered out and the solution was evaporated dry, thus
producing a ohelated Gd-DOTA-poly-EOEA-PROXYL copolymer of
20 the following structure:
~ HNC ~ O o ~ -c ~
~ ~NS< o
O~ P

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37
As demonstrated by these examples and as one skilled in the
art would recognize, the invention has a wide range of
applications for creating contrast agents with great
improvements in relaxivity. The exact formulation of a
5 specific contrast agent will vary depending upon the intended
use and will include small molecular-weight chelates such as
a single monomeric chelate unit with one or more R groups
bearing one or more nitroxide units, an oligomer with several
chelates and several nitroxide units, a polymer comprising
10 many chelate and nitroxide units, branching or star shaped
compounds with many chelates and nitroxide units (e.g.
branching polymers), and particles, either gel-like or solid,
cont~in;ng many nitroxides and metal ions or metal oxides.
The key is that the metal ions and nitroxides are in
15 juxtaposition or close approximation to one another to
achieve the increase in relaxivity of this invention.
As indicated above, the extremely high relaxivity of these
contrast agents has applicability particularly for the
20 development of general purpose vascular imaging and
gastrointestinal MRI contrast agents. Low molecular weight
contrast agents, e.g. under 10,000 molecular weight, are
preferred as general purpose agents for the central nervous
system, particularly as markers of cerebral perfusion and
25 blood brain barrier breakdown. Additionally, these smaller
compounds may be used as targeted agents attached to
peptides, antibodies, glycoproteins, liposomes and
carbohydrate moieties. Higher molecular weight compounds,

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38
e.g. over 10,000 MW, may be designed as blood pool contrast
agents and likewise used for in vivo targeting. Compounds
over 30, OOO MW generally have a longer intravascular half-
life and compounds over 60,000 MW will generally not be
5 excreted by the kidneys until broken down into smaller
subunits.
These hybrid contrast agents may also be formulated as
nanoparticles wherein one or more paramagnetic ions is held
10 together with one or more nitroxides, so as to create
particles with extremely high relaxivity and longer
intravascular half-life. These particles may be designed to
be either paramagnetic or superparamagnetic.
15 Polymers useful in the present invention can be of natural or
synthetic or semisynthetic origin. The term semisynthetic
polymer, as employed herein, denotes a natural polymer that
has been chemically modified in some fashion. Preferably,
the polymer is natural or semisynthetic, most preferably
20 natural. Further, as used herein, the term polymer denotes a
compound comprised of two or more repeating monomeric units,
preferably three or more repeating monomeric units, more
preferably five or more repeating units, and most preferably
ten or more repeating units.
Exemplary natural polymers suitable for use in the present
invention may include naturally occurring polysaccharides
such as, for example, arabinans, fructans, fucans, galactans,

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39
galacturonans, glucans, mannans, xylans (e.g., inulin),
levan, fuciodan, carrageenan, galactocarolose, pectins
including high methoxy pectin and low methoxy pectin; low
methoxy pectin denoting pectin in which less than 40% of the
5 carboxylic acid groups are esterified and or amidated, and
high methoxy pectin denoting pectin in which 40% or more of
the carboxylic acid groups are esterified and/or amidated),
pectic acids, amylose, pullulan, glycogen, amylopectin,
cellulose, dextran, pustulan, chitin, agarose, keratin,
10 chondroitin, dermatan, hyaluronic acid, alginic acid, xanthan
gum, starch, and various other natural homopolymers or
heteropolymers such as those containing one or more of the
following aldoses, ketoses, acids or amines: erythrose,
threose, ribose, arabinose, xylose, lyxose, allose, altrose,
15 glucose, mannose, gulose, idose, galactose, talose,
erythrulose, ribulose, xylulose, psicose, fructose, sorbose,
tagatose, glucuronic acid, gluconic acid, glucaric acid,
galacturonic acid, mannuronic acid, glucosamine,
galactosamine and neuraminic acid; as well as naturally
20 occurring derivatives thereof such as polygalacturonic acid
(and other polyuronic acids, such as polyglucuronic acid,
polymannuronic acid, polyguluronic acid, hyaluronic acid,
etc.) and cellulose. Exemplary natural polymers may also
include, for example, polypeptides and polyalcohols, as will
25 be readily apparent to those skilled in the art.
Exemplary semisynthetic polymers include such modified
natural polymers as carboxymethylcellulose,

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hydroxymethylcellulose, hydroxypropylmethylcellulose,
methylcellulose and methoxycellulose.
Exemplary synthetic polymers suitable for use in the present
5 invention include polyethylenes (such as, for example,
polyethylene glycol, polyoxyethylene, polyoxyethylene glycol,
and polyethylene terephthlate), polypropylenes (such as, for
example, polypropylene glycol), polyurethanes (such as, for
example, polyurethane ureas), pluronic acids and alcohols,
10 polyvinyls (such as, for example polyvinyl alcohol,
polyvinylchloride and polyvinylpirrolidone), nylon,
polystyrene, polyactic acids, fluorinated hydrocarbons,
fluorinated carbons (such as, for example,
polytetrafluoroethylene), polyacrylates (such as, for
15 example, polymethylmethacrylate), polyacrylic acids (such as,
for example, polymethacrylic acid) and polyacrylamides, as
well as derivatives thereof.
Preferred polymers include polygalacturonic acid and pectins.
20 As those skilled in the art are aware, pectins are generally
methyl esters of polygalacturonic acid. The polymers may be
cross-linked, if desired. Preferably, however, the polymers
are not cross-linked. It is also recognized that some
polymers may be prepared by chemically modifying naturally
25 occurring polymers. Such chemically modified natural
polymers are to be considered within the scope of the phrase
natural polymer, as used herein.

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41
The polymers of the present invention may be employed in
various shapes and forms, such as fibers, beads, and
particles. The polymers may also be of varying molecular
weight, including high molecular weight polymers (that is,
5 equal to or greater than 30,000 weight-average molecular
weight). For reasons of diagnostic efficacy, preferably the
polymers are low molecular weight polymers, more preferably
having a molecular weight (weight average) of about 25,000 or
less, still more preferably less than about 20,000, even more
10 preferably less than about 15,000, and most preferably less
than about 10,000. One highly preferable weight average
molecular weight range is between about 1,500 and about
25,000.
15 Polyethylene glycol (PEG), a synthetic polymer that exhibits
a high water binding capacity, is particularly preferred for
use in the subject invention. Due to their high water
binding capacity and the accompanying decrease in the amount
of free water in solution, PEG and similar polymers serve to
20 alter the proton density in solution. Furthermore, PEG is
used for the fractional precipitation of proteins from
solution, which is believed to be due in part to the excluded
volume effects caused by this polymer, whereby the protein is
excluded from regions of the solution occupied by the polymer
25 and is concentrated in the water spaces, that is, the
extrapolymer spaces between the individual molecules of the
polymer. For these and other reasons, PEG and related
polymers are particularly preferred polymers for the subject

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42
invention. PEG, as well as other synthetic polymers, may be
prepared, in varying molecular weights, using conventional
methodology.
5 If desired, the contrast medium may further comprise a
physiologically compatible suspending or viscosity-increasing
agent, referred to herein collectively as a suspending agent.
The phrase suspending agent is intended to denote a compound
that assists in providing relative uniformity or homogeneity
lO to the contrast medium. A number of such agents are
available, including xanthan gum, acacia, agar, alginic acid,
aluminum monostearate, bassorin, karaya, gum arabic,
unpurified bentonite, purified bentonite, bentonite magma,
carbomer 934P, calcium carboxymethylcellulose, sodium
15 carboxymethylcellulose, carboyymethylcellulose sodium 12,
carrageenan, cellulose (microcrystalline), dextran, gelatin,
guar gum, hydroxyethylcellulose, hydroxypropylcellulose,
hydroxypropylmethylcellulose, magnesium aluminum silicate,
methylcellulose, pectin, casein, polyethylene oxide,
20 polyvinyl alcohol, povidone, propylene glycol, alginate,
silicon dioxide, silicon dioxide colloidal, sodium alginate
and other alginates, and tragacanth. As those skilled in the
art would recognize, wide ranges of suspending agents can be
employed in the contrast medium of the invention, as needed
25 or desired. Preferably, however, the suspending agent is
present in an amount of at least about 0.05% by weight, more
preferably at least about 0.1% by weight, and generally less
than about 1% by weight, more preferably less than about 0.5%

W 096/32967 PCTrUS95/04697
43
by weight.
In addition, in order to cause gelation with polymers and
metals that do not gel spontaneously, or to enhance gelation,
5 gelling agents such as polyvalent metal cations, sugars and
polyalcohols may be employed. Exemplary polyvalent metal
cations useful as gelling agents include calcium, zinc,
manganese, iron and magnesium. Useful sugars include
monosaccharides such as glucose, galactose, fructose,
10 arabinose, allose and altrose; disaccharides such as maltose,
sucrose, cellobiose and lactose; and polysaccharides such as
starch. Preferably, the sugar is a single sugar, that is, a
monosaccharide or a disaccharide. Polyalcohol gelling agents
useful in the present invention include, for example,
15 glycidol, inositol, mannitol, sorbitol, pentaerythritol,
galacitol and polyvinylalcohol. Most preferably, the gelling
agent employed in the present invention is sucrose and/or
calcium. The particular gelling agents which may be employed
in the various formulations of the present invention will be
20 readily apparent to one skilled in the art in view of the
present disclosure.
Since the compositions of the invention are used as
intravascular agents, osmolarity is important to prevent
25 blood cell damage. It should be approximately the same value
as that of human blood. As those skilled in the art will
recognize, the osmolarity of a solution may be controlled by
regulating the use of osmotically active materials in the

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44
contrast medium formulation. Osmotically active materials
include such physiologically compatible compounds as
monosaccharide sugars or sugar alcohols, disaccharide sugars,
amino acids and various synthetic compounds. Suitable
5 monosaccharide sugars or sugar alcohols include, for example,
erythrose, threose, ribose, arabinose, xylose, lyxose,
allose, altrose, glucose, mannose, idose, galactose, talose,
ribulose, fructose, sorbitol, mannitol and sedoheptulose,
with preferable monosaccharides being fructose, mannose,
10 xylose, arabinose, mannitol and sorbitol. Suitable
disaccharide sugars include, for example, lactose, sucrose,
maltose, and cellobiose. Suitable amino acids include, for
example, glycine, serine, threonine, cysteine, tyrosine,
asparagine, glutamine, aspartic acid, glutamic acid, lysine,
15 arginine and histidine. Synthetic compounds include, for
example, propylene glycol, polypropylene glycol, ethylene
glycol, polyethylene glycol and polyvinylpyrrolidone.
Various other suitable osmotically active materials are well
known to those skilled in the art, and are intended to be
20 within the scope of the term osmotically active agent, as
used herein.
Typically, to achieve the preferred ranges of osmolarity in
the contrast medium of the invention, less than about 25 g/l,
25 more preferably less than about 20 g/l, even more preferably
less than about 15 g/l, and most preferably less than about
10 g/l of the osmotically active materials are employed, and
in some instances no osmotically active material is used. A

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most preferred range of osmotically active material is
between about 1 and 10 g/l.
Although the most desirable pH for the contrast medium of the
5 present invention may vary, as those skilled in the art will
recognize, the preferred pH range for most diagnostic uses is
generally between about 3 and about 10 pH units, more
preferably between about 5 and 8 pH units. The desired pH
can be achieved and maintained through the use of
10 physiologically compatible pH regulating additives such as
suitable bases, buffers and the like, as one skilled in the
art will recognize. Particularly preferred buffers include
sodium acetate and glacial acetic acid buffer.
15 Many of the compounds used for the synthesis of the contrast
agents of this invention are available commercially. The
compounds may also be prepared by conventional techniques
such as the polymerization techniques described in McCrum et
al., referenced above.
Thus, while the invention has been particularly shown and
described with reference to preferred embodiments thereof, it
will be understood by those skilled in the art that changes
in form and detail may be made therein without departing from
25 the spirit and scope of the invention.