Note: Descriptions are shown in the official language in which they were submitted.
CA 02285175 1999-09-27
WO 98144329 PCT/US98/05860
RINK-CHLORIDE LINKER FOR SOLID PHASE ORGANIC
SYNTHESIS OF ORGANIC MOLECULES
FIELD OF THE INVENTION
This invention relates to a novel linker for use in solid phase chemistry, its
preparation and methods of use of the linker.
BACKGROUND OF THE INVENTION
In the continuing search for new chemical moieties that can effectively
modulate a variety of biological processes, the standard method for conducting
a
search is to screen a variety of pre-existing chemical moieties, for example,
naturally
occurring compounds or compounds which exist in synthetic libraries or
databanks.
The biological activity of the pre-existing chemical moieties is determined by
applying the moieties to an assay which has been designed to test a particular
property of the chemical moiety being screened, for example, a receptor
binding
assay which tests the ability of the moiety to bind to a particular receptor
site.
In an effort to reduce the time and expense involved in screening a large
number of randomly chosen compounds for biological activity, several
developments have been made to provide libraries of compounds for the
discovery
of lead compounds. The chemical generation of molecular diversity has become a
major tool in the search for novel lead structures. Currently, the known
methods for
chemically generating large numbers of molecularly diverse compounds generally
involve the use of solid phase synthesis, in particular to synthesize and
identify
peptides and peptide libraries. See, for example. Lebl et al., Int. J. Pept.
Prot. Res.,
?5 41, p. 201 ( 1993) which discloses methodologies providing selectively
cleavable
linkers between peptide and resin such that a certain amount of peptide can be
liberated from the resin and assayed in soluble form while some of the peptide
still
remains attached to the resin, where it can be sequenced: Lam et al., Nature,
354, p.
82 ( 1991 ) and (WO 92/00091 ) which disclose a method of synthesis of linear
peptides on a solid support such as polystyrene or polyacrylamide resin;
Geysen et
al., J. Lremunol. Meth., 102, p. 259 ( 1987) which discloses the synthesis of
peptides
on derivatized polystyrene pins which are arranged on a block in such a way
that
they correspond to the arrangement of wells in a 96-well microtiter plate: and
Houghten et al., Nature, 354, p. 84 ( 1991 ) and WO 92/09300 which disclose an
approach to de novo determination of antibody or receptor binding sequences
involving soluble peptide pools.
The major drawback, aside from technical considerations, with all of these
methods for lead generation is the quality of the lead. Linear peptides
historically
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have represented relatively poor leads for pharmaceutical design. In
particular, there
is no rational strategy for conversion of a linear peptide into a non-peptide
lead. As
noted above. one must resort to screening large databanks of compounds, with
each
compound being tested individually, in order to determine non-peptide leads
for
peptide receptors.
In this respect, there has been increasing interest in the application of
solid
phase synthesis to the preparation of organic compounds, especially in the
context of
combinatorial chemistry and multiple simultaneous synthesis, or parallel
synthesis.
One of the limitations in the solid phase approach in general, involves the
linker by
IO which the organic molecule is attached to the solid support. The Rink
linker (Rink,
H., Tetrahedron Lea., 1987,28, 3787-3790) has been effectively applied to the
synthesis of some chemical libraries (Gordeev, M. F.; Patel, D. V.; Gordon, E.
M. J.
Org. Chem. 1996, 61, 924-928; Norman, T. C.; Gray, N. S.; Koh. J. T.: Schultz,
P.
G. J. Am. Chem. Soc. 1996, p. 118, 7430-7431; Ward, Y. D.; Farina, V.
Tetrahedron
Lett., 1996, 37, 6993-6996), because of the ease of use and mild conditions
for
release of the library component. However the Rink linker is currently limited
to
use in the preparation of amides and carboxylic acids. Therefore, a need
exists for a
Rink linker useful for a broader range of solid phase chemistry. Herein, we
describe
the preparation of a Rink-chloride linker, which allows a very general and
practical
method for the attachment of, inter alia, amines, alcohols and thiols to a
solid
support.
SUMMARY OF THE INVENTION
This invention relates to a novel solid phase Rink linker of formula (I),
?5 hereinafter referred to as a resin-bound Rink-chloride linker or a Rink-
chloride
linker. This represents a significant improvement over the current use of the
Rink-
acid linker. At present the use of the known Rink-acid linker is limited to
preparing
amides and carboxylic acids. The use of the instant improved Rink-chloride
linker
of formula (I) makes Rink technology available to a broad number of functional
group attachments. The use of the Rink-chloride linker allows a very general
and
practical method for the attachment of amines, alcohols and thiols, including
phenols
and thiophenols to a solid support. Therefore, another aspect of the instant
invention
is in a method for making compounds by resin-bound synthesis using the Rink-
chloride linker in solid phase synthesis. This method is applicable to mailing
combinatorial libraries of compounds designed around a core molecular
structure
using known methods of solid phase combinatorial chemistry or multiple
simultaneous synthesis ("parallel synthesis"). The compounds or libraries of
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compounds made using this linker may be tested in biologically assays designed
to
test for a particular physical characteristic potentially useful in drug
therapy.
DETAILED DESCRIPTION OF THE INVENTION
The terms "resin." "solid support." "inert resin." polymeric resin" or
"polymeric resin support" are used herein at all occurrences to mean a bead or
other
solid support such as beads, pellets, disks, capillaries, hollow fibers,
needles, solid
fibers, cellulose beads, pore-glass beads, silica gels, grafted co-poly beads,
poiy-
acrylamide beads, latex beads, dimethylacrylamide beads optionally cross-
linked
with N,N =bis-acryloyl ethylene diamine, glass particles coated with a
hydrophobic
polymer, etc., i.e., a material having a rigid or semi-rigid surface. The
solid support
is suitably made of, for example, cross linked polystyrene resin, polyethylene
glycol-
polystyrene resin, and any other substance which may be used as such and which
would be known or obvious to one of ordinary skill in the art.
I S The term "substituted resin-bound Rink-chloride intermediate" is used
herein
at all occurrences to mean the intermediate produced by coupling a resin-bound
Rink-chloride linker with a suitable nucleophile (with displacement of the
chloride
of the Rink linker) such that to the nucleophile is linked to the resin
through the
Rink linker.
The term "additional synthetic chemistry" is used herein at all occurrences to
mean chemical reactions which are performed on the substituted resin-bound
Rink-
chloride intermediate prior to cleavage of the nucleophile from the polymeric
resin,
wherein said chemical reactions are compatible with and non-reactive with the
Rink-
chloride linker and may be used to prepare derivatives of the nucleophile. It
will be
?5 understood by the skilled artisan that the additional synthetic chemistry
performed
on the substituted resin-bound Rink-chloride intermediate, is done so prior to
cleavage of the derivatized nucleophile. Chemical reactions which are
incompatible
with the nucleophile/Rink-chloride linkage, i.e., they cause cleavage of the
nucleophile from the Rink-chloride linker, are not among the additional
synthetic
chemistry that may be used in the methods of this invention.
The terms "resin-bound synthesis" and "solid phase synthesis" are used
herein interchangeably to mean a series of chemical reactions used to prepare
either
a single molecule/compound or a library of molecularly diverse compounds,
wherein
the chemical reactions are performed on a compound which is bound to a polymer
resin through a linkage, in particular, a Rink-chloride linkage.
Chemical synthesis on solid supports has become a cornerstone in the
generation
of small organic molecule combinatorial libraries. Paramount to the success of
any solid-
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phase synthetic strategy is a reliable and general method for coupling the
initial starting
materials onto the solid support, namely through linker technology. Such
linker
technology should also be amenable to ready cleavage of the reaction products
under
relatively mild conditions, and without compromising the structure of the
reaction
products. The Rink linker has been effectively applied to the synthesis of
some chemical
libraries because of its ease of use and the mild conditions for release of
library
components from the solid support. However the Rink technology is currently
limited to
the preparation of amides and carboxylic acids. Herein, we describe the
preparation and-
utility of a Rink-chloride linker, which allows a very general and practical
method for the
attachment of amines, alcohols and thiols to a solid support, derivatization
of these resin
bound compounds, and their eventual release from the resin with
trifluoroacetic acid.
The resin-bound Rink-acid linker 1-Scheme 1 can be converted to the resin-
bound
Rink-chloride resin of this invention, 2-Scheme 1, by treatment of the resin-
bound Rink-
acid linker with triphenyl phosphine and hexachloroethane. 2-Scheme 1 so
obtained is
1 S stable at room temperature for several days and can be used without any
loss of activity.
Scheme 1
2-Scheme 1 can be reacted cleanly with a variety of nucleophiles ("Nu") under
mild reaction conditions (see, Scheme 2 and Table I below). The nucleophiles
depicted
herein are either commercially available or can be made using known
procedures.
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Scheme 2
Nucleophiie
y Hunig-s base --' ~O Nu
/ \ dichloroethane / \
- resin resin
/ ~ \ /
2-Scheme 1 j 2.Scheme 2
Table I
Nucleo hile Yield Puritv Nucleo hile Yield Puritv
;N / \ 0 95 93 °.H 90 - 95
° H 94 90 ° ° 85 80
"H ~ ~H
H 95 96 ~ 96 91
i ". o
0
\ / v
0
90 94 / S ~ ~ 84 90
H," ~ ~ ~
F
H CH2Ph g
'n, / \ 0 95 95 i I vH 92 95
H
°'H 85 95 ° 96 95
°~H
H~"'FMOC
Rink-chloride efficiently reacts with primary and secondary amines, anilines,
alcohols, phenols, thiols, thiophenols, and carboxylic acids. The coupling is
usually
carried out in dichloroethane in the presence of Hiinig's base, under inert
atmosphere for
18-26 hours at room temperature. The extent of coupling efficiency is
monitored by
MASNMR and then by cleaving the product from the resin with about 3-5% TFA in
s
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CH~CI~. Release of the ligands from the resin is complete within 30 minutes as
evidenced by MASNMR of the residual resin. As is apparent from Table I, the
coupling is
general and highly efficient. While cleavage from the resin is facile, it is
sufficiently
stable enough to carry out a wide range of chemistry commonly used in small
molecule
~ library construction. Some illustrative examples are shown in Scheme 3.
Scheme 3
1. FMOC-glyine / \
p-naphthyl acid chloride/ / \ 5%TFA ~N /
a~ ~ / \ Hunig's base.._> ~ _in CH2C1
Cl / 2.20%piperidine N / v
R«in~bound ~ in DMF O
Rink-chloride 75%
Linker H O
H~N~H
H~N~H
maieic O
furfuryl O ~ PhH/RT a 05%TFq Product
alcohol ------> ~ in CH2CI decomposed
_ ._ 2> upon
CI p O ~ O cleavage.
Resio-bound
Rink~Chloride
Linker
3-bromo
benzyi Br
amine ~N ~ _... i
I _ > N / .. _...
CI H ~ Pd(O) I ~ 5%TFA
R«in-donna 4-formylboronic acid H ~ in CH2CI2
Rink-Chloride aq. K2CO3
Linker
EtOH/xylene
NH
60%
It will be understood that after making the substituted resin-bound Rink-
chloride intermediate, and prior to cleavage with TFA. additional syntheic
chemistry
may be performed on the intermediate in order to derivatize the nucleophile
core.
Therefore, another aspect of the invention is in a method for synthesizing a
1 S compound by resin-bound synthesis comprising the steps of: (a) converting
a resin
bound Rink-acid linker into a resin-bound Rink-chloride linker of formula (I)
6
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\ / O / \ CI
resin
O \ /
/
O
/
(b) coupling the resin-bound Rink-chloride linker with a suitable nucleophile
under
appropriate conditions to provide a substituted resin-bound Rink-chloride
intermediate;
and (c) performing additional synthetic chemistry on the substituted resin-
bound Rink-
chloride intermediate to provide a resin-bound derivatized nucleophile. The
resin-bound
derivatized nucleophile can remain bound to the resin for storage and/or
further
derivatization, or it may be cleaved from the resin with between about 3 and
S% TFA.
In yet another aspect, this invention is in a method for synthesizing a
library
of molecularly diverse compounds by resin-bound synthesis, comprising the
steps
of: (a) convening a resin-bound Rink-acid linker into a resin-bound Rink-
chloride
linker of formula (I)
\ / o / \ cl
resin
O \ /
/
O
/
(b) coupling the resin-bound Rink-chloride linker with a suitable nucleophile
under
appropriate conditions to provide a substituted resin-bound Rink-chloride
intermediate: (c)
optionally dividing said substituted resin-bound Rink-chloride intermediate
into a plurality
of portions; (d) performing additional synthetic chemistry on the substituted
resin-bound
Rink-chloride intermediate to provide a resin-bound derivatized nucleophile;
and (e)
optionally recombining the portions.
Based upo the disclosure herein, it will be clear to one of ordinary skill in
the art that there are many possible synthetic approaches to creating the
libraries of
this invention. For example the libraries may be prepared using the split and
mix
technique or parallel synthesis techniques. The libraries generated from
either of the
the synthetic methods are molecularly diverse and are prepared simultaneously.
The
libraries are prepared on the polymer resins using the Rink-chloride linker
described
herein. For example, the compound to be derivatized (suitable nucleophile), is
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attached to the polymer resin through the Rink-chloride linker to give a
substituted
resin-bound Rink-chloride intermediate. In one embodiment, the substituent(s)
are
modified by reacting the resin-bound Rink-chloride intermediate, with a
mixture of
reagents. In an alternative embodiment, aliquots of the resin-bound Rink-
chloride
intermediate are reacted with individual reagents each one of which will
modify a
position on the core of the resin-bound nucleophile, and then the resultant
products
are mixed together to form the library of derivatized resin-bound
intermediates. This
library may then be further derivatized by repeating the process of dividing
and
recombining the intermediates formed by the additional synthetic chemistry. It
will
be clear to one of ordinary skill in the art that when the libraries of the
invention are
prepared according to the instant disclosure, each polymer support bears a
single
species created by the additional synthetic chemistry performed on the
substituted
resin-bound Rink-chloride intermediate.
It will be obvious to one of skill in the art that the steps of optionally
dividing and recombining the resin-bound aryl silane intermediate into
portions are
for purposes of varying the derivatization on the resin-bound nucleophiles
which are
generated by the combinatorial synthesis. Of course, it will be obvious to the
skilled
artisan that the resin-bound nucleophile intermediates may be divided into
portions
at any point during the synthetic sequence. The portions may be recombined at
any
point during the sequence or, further iterations may be applied if more
derivatization
is required. Therefore, it will be obvious to the skilled artisan that the
steps of
dividing the portions, performing additional synthetic chemistry and
recombining
the portions, may each be carried out more than once, depending upon the type
of
diversity required for the library of end-product compounds being prepared.
According to this invention, after the additional synthetic chemistry has been
performed on the resin-bound aryl silane intermediate so that a library of
molecularly diverse compounds has been prepared, the compounds can be
separated
and characterized by conventional analytical techniques known to the skilled
artisan,
for example infrared spectrometry or mass spectrometry. The compounds may be
characterized while remaining resin-bound or they can be cleaved from the
resin
using the conditions described above, and then analyzed. In addition, a
partial array
of compound members of the library may be cleaved from the resin,
characterized
and analyzed, while leaving a partial array of the compound members of the
library
bound to the resin.
s
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EXAMPLES
Preparation of Rink-chloride (2-Scheme 1)
To a suspension of resin-bound Rink-acid, 1-Scheme 1, ( I .Og, l.6mmol.) in
- THF (25mL) was added triphenylphosphine (2.328, 8.8mmol.) and
hexachloroethane (2.13g, 8.8mmol.). The reaction mixture was agitated with a
constant flow of argon for 6h. The resin-bound Rink-chloride, 2-Scheme 1, was
filtered and washed with THF and acetone. Completion of the reaction was
affirmed
by chlorine analysis and MASNMR (the signal for CH(OH)at 8 5.85 disappears
completly). Chlorine analysis indicated a stoichometric amount of chlorine.
Reaction of rink-chloride with various nucleophiles
To a suspension of 2-Scheme 1 (0.96g, l.6mMol.) in dichloroethane (25mL)
was added Hiinig's base ( 1mL) and the requisite nucleophile ( lOmMol.). The
reaction mixture was agitated with a constant flow of argon for 6-12h. The
resin
was filtered and washed with dichloromethane, MeOH, H20, EtOH, CH2Cl2 and
MeOH.
Completion of the reaction was confirmed by MASNMR, IR or elemental
analysis. Elemental analysis indicates no chlorine and a stoichometric amount
of
nitrogen or sulfur for the appropriate compounds.
Cleavage from Rink-linked lisands
3% TFA/CH2Cl2 was added to the substituted resin-bound Rink chloride
moieties, either as individual beads or in bulk quantity. The cleavage was
carried
out for 30 min., and the product was isolated by extraction with 1:1/
MeOH:MeCN.
All the cleaved products from Table I were identified by comparing them with
an
authentic sample of the starting material (nucleophile).
The above description fully discloses the invention including preferred
embodiments thereof. Modifications and improvements of the embodiments
specifically disclosed herein are within the scope of the following claims.
Without
further elaboration, it is believed that one skilled in the art can, using the
preceding
description, utilize the present invention to its fullest extent. Therefore
any
examples are to be construed as merely illustrative and not a limitation on
the scope
of the present invention in any way. The embodiments of the invention in which
an
exclusive property or privilege is claimed, are defined as follows.
9
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