Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
- ~ 3~
RAN 4039/34
The present invention relates to novel citric acid
derivatives of the formula
H ~ ~ CO2H
~CI la
~ OH
H02C/ ~cH2co2H
and corresponding threo-~-lactones of the formula
HO2C ` H
< Cl lb
~
H02C
as well as pharmaceutically acceptable salts of these
compounds.
The chlorocitric acids of formula Ia and certain star-
ting materials and intermediates in the preparation there-
of, bear two asymmetric centers and thus exist in two
relative stereochemical forms: a threo form and an erythro
25 form. The chlorocitric acid-~-lactones of formula Ib have
the threo form. Each form, i.e. the threo form and erythro
form, can exist as a racemate and two optical antipodes,
the (+)-optical antipode and the (-)-optical antipode.
In conjunction therewith, the threo-erythro nomenclature
30 as defined in J. Amer. Chem. Soc., 74, 5828 (1952) and
Experientia, 12, 81 (1956) has been adopted.
Mé/5.11.1979
~"3!~47~
As used throughout the specification and appended
claims, the term "alkali metal" and "alkaline earth me-
tal" refer to lithium, sodium and potassium, and calcium,
respectively. The term "alkanol" refers to the compound
5 derived by replacement of a proton of a straight or branched
chain alkane having 1 to 20 carbon atoms by a hydroxyl
moiety. Examples of alkanols include methanol, ethanol
and 2-propanol.
The compounds of ~ormulae Ia and Ib and the salts
thereof exhibit anorectic activity and are thus useful
as anorectic agents for the treatment of obesity in mam-
mals. The invention relates to the compounds of formulae
Ia and Ib and the pharmaceutically acceptable salts there-
15 Of as pharmaceutical, particularly anorectic, agents,as well as to pharmaceutical compositions, particularly
anorectic compositions, comprising a compound of formula
Ia or Ib or a pharmaceutically acceptable salt thereof,
and to a process for the manufacture of such compositions.
The invention also relates to a process for the manu-
facture of the compounds of formulae Ia and Ib and of
the pharmaceutically acceptable salts thereof, which pro-
cess comprises
a) for the preparation of a (+)-threo-lactone of formula
Ib contacting an aqueous solution of a tri-alkali metal
salt or tri-alkaline earth metal salt of cis- or
trans-aconitic acid with chlorine or hypochlorous acid
30 and contacting the obtained salt of (~)-threo-chlorocitric
acid-R-lactone of the formula
~ -
" ' ' . ' ' . , ' '
1~.3B470
-- 3 -
MO2C H
\<CI I b 1
M02C <~co
wherein M is an alkali or alkaline earth metal,
with an acid,
b) for the preparation of (+)-threo-chlorocitric acid
of the formula
HO2C H
~ OCH lla 1
H 02C H2C 02H
20 hydrolyzing a compound of formula Ib or Ib1,
c) for the preparation of a compound of formula Ia clea-
ving epoxyaconitic acid with an alkali metal chloride
or alkaline earth metal chloride in an aqueous solvent
25 in the presence of an acid,
d) for the preparation of (+)-erythro-chlorocitric acid
of the formula
H CO2H
~ ~Cl la2
~OH
H 02C/ \CH2C 2 H
35 cleaving an epoxide of the formula
1~3~4';'~
-- 4
M~02C H
11
M02C CH2C02R
wherein M' is an alkali metal and R is hydrogen or
M',
10 with in alkali metal chloride in an aqueous solvent in
the presence of an acid,
e) if desired, resolving an obtained (+)-threorcitric acid derivative
of formula Ia or Ib or (+)-erythro-citric acid derivative
15 of formula Ia into its optically active antipodes and
isolating a desired antipode,
f) if desiredlisolating an obtained compound of formula
Ia or Ib in form of a pharmaceutically àcceptable salt
20 thereof.
The aqueous solution of process step a), which can
be obtained by dissolving aconitic acid in an aqueous
solution of an alkali or alkaline earth metal hydroxide,
25 preferably sodium or potassium hydroxide, is conveniently
cooled to about 0 to 30C, preferably 5C, and treated
with excess chlorine or hypochlorous acid, preferably
chlorine.
Suitable aqueous solvents include water and mixtures
of water and a lower alkanol, water and an ether, such
as dimethoxyethane, tetrahydrofuran or dioxane, and water
- and a polar aprotic solvent, such as dimethylacetamide,
dimethylformamide, dimethylsul~oxide or hexamethylphos-
35 phoramide.
Among acids suitable for the conversion of the salt
,. ..
~8~
Ib1 to the corresponding free acid Ib may be mentioned
mineral acids, e.g. hydrochloric, sulfuric, nitric or
phosphoric acid, sulfonic acids, such as methanesulfonic,
phenylsulfonic or p-toluenesulfonic acid, and strong orga-
nic carboxylic ~cids, such as trifluoro- or trichloroace-
tic acid.
The hydrolysis of the ~-lactone function of the di-
acid of formula Ib or the disalt thereof of formula Ib1
10 according to process step b), can be accomplished by sus-
pending or dissolving the diacid or the disalt in an aqueous
solvent containing an acid, such as those employed for
the acidification of the disalt Ib1 to the diacid Ib,
ard heating the resulting reaction system, conveniently
15 at a-temperature of about 30 to 80C to complete the
hydrolysis. A temperature of about 50 to 70C, particu-
larly of about 70C, is preferred.
While the chlorohydrination of step a) and the hy-
20 drolysis of step b) may be performed stepwise, it is moreconvenient and efficient to acidify the disalt Ib1 and
heat the resulting reaction mixture to complete the hy-
drolysis of the diacid Ib to afford (+)-threo-chlorocitric
acid. Thus, upon completion of the chlorohydrination,
25 the reaction mixture is acidified, preferably with a mineral
acid, most preferably hydrochloric acid, and heated from
about 30 to 100C, preferably from about 50 to 90C, most
preferably at about 70C, to complete the conversion of
the B-lactone Ib to the acid Ia1.
The cleavage of step c) is carried out with an al-
kali or alkaline earth metal chloride in an aqueous sol-
vent in the presence of an acid.
Thus (+)-threo-epoxyaconitic acid may be cleaved by
an alkali metal chloride dissolved in an aqueous solvent
in the presence of an acid, preferably by excess sodium
~3~
-- 6
chloride dissolved in water in the presence of one molar
equivalent of hydrochloric acid at a temperature within
the range of about 50 to 80C, most preferably at about
70C
Likewise, (+)-threo-epoxyaconitic acid is cleaved
to (-)-threo-chlorocitric acid, (-)-threo-epoxyaconitic
acid is cleaved to (+)-threo-chlorocitric acid, (-)-ery-
thro-epoxyaconitic acid is cleaved to (+)-erythro-chloro-
10 citric acid and (+)-erythro-epoxyaconitic acid is cleaved
to (-)-erythro-chlorocitric acid by an alkali metal chlo-
ride dissolved in an aqueous solvent in the presence of
an acid, preferably by excess sodium chloride dissolved
in water in the presence of one molar equivalent of hydro-
5 chloric acid at a temperature within the range of about
50 to 80C, most preferably at about 70C.
(+)-Erythro-chlorocitric acid can be prepared in a
high yield process involving the cleavage of the epoxide
20 ring of (+)-erythro-epoxyaconitic acid which can be
generated in situ by the epoxidation of cis-aconitic acid
or of the corresponding anhydride. The epoxidation is
readily performed utilizing hydrogen peroxide in conjunction
with an epoxidation catalyst, e.g. tungstic acid or a
25 salt thereof, preferably an alkali metal salt, most
preferably the sodium salt. While the epoxidation is
preferably carried out in water, containing about 0 molar
equivalents to about 2.9 molar equivalents of an alkali
metal hydroxide, preferably about 2.5 molar equivalents
30 of sodium hydroxide, an organic solvent such as lower
alkanol or a water soluble ether, such as dimethoxyethane,
tetrahydrofuran or dioxane, may be employed as a diluent.
The epoxidation is conveniently performed at a temperature
of about 0 to 100C, preferably of about 20 to 50C. Without
35 isolation, the resulting (+)-erythro-epoxyaconitic acid
or the salt thereof of the formula II can be acidified
and then cleaved by treatment with an alkali metal chloride,
, .
t~
preferably sodium chloride. Suitable acids include mineral
acids, e.g. hydrochloric, sulfuric or phosphoric acid,
sulfonic acids, such as methanesulfonic, phenysulfonic
or p-toluenesulfonic acid, and strong organic acids, such
as trifluoroacetic or trichloroacetic acid. Hydrochloric
acid is preferred.
To avoid possible side reactions involving the so-
formed (+)-erythro-chlorocitric acid, it is desirable
10 to perform the cleavage in the presence of about one to
10 molar equivalents of the abovementioned acids. Thus,
when the epoxidation is carried out in the absence of
an alkali metal hydroxide, it i5 desirable to employ about
one to about 10 molar equivalents of acid, and when the
15 epoxidation is accomplished in the presence of about 2.5
molar equivalents of alkali metal hydroxide, it is desi-
rable to utilize about 3.5 to 12.5 molar equivalents of
acid.
- 20 While not narrowly critical, the cleavage reaction
temperature is normally maintained within the range of
about 50 to 80C, preferably at about 70C.
.. . .
While the afore described process for the preparation
25 of (+)-erythro-chlorocitric acid Ia2 i9 efficiently
performed by cleaving the (+)-erythro-epoxyaconitic acid
generated in situ, this acid, prepared and isolated by
the method disclosed in the U.S. Patent 3,969,772, may
also be cleaved to the erythro-chloroacid as hereinbefore
30 described for the cleavage of (+)-threo-epoxyaconitic
acid.
While the optically active citric acid derivatives
of formulae Ia and Ib are more readily prepared by chlo-
~84
-- 8
rinolysis of the oxirane ring of optically active epoxy-
aconitic acid, as hereinbefore described, these compounds
may also be prepared from racemic threo- and erythro-ci-
tric acid derivatives by resolution methods known in the
art.
For example, by employing (+)-p-nitro-a-methylbenzyl-
amine and (-)-p-nitro-x-methylbenzylamine sequentially
as the resolving agents, (+)-erythro-chlorocitric acid
10 may be resolved into its optical antipodes, (+)-
erythro-chlorocitric acid and (-)-erythro-chlorocitric
acid, by separation of the diastereoisomeric salts
so formed, according to the procedure outlined in U.S.
Patent 3,901,915.
Further, (+)-threo-chlorocitric acid-R-lactone of
formulaIbcan beresolved into its optically active anti-
podes by conventional resolving techniques such as set
forth in the preceding paragraph. More particularly, (+)-
20 threo-chlorocitric acid-~-lactone can be treated with
~; (+)-p-nitro-~-methylbenzylamine in a lower alkanol, such
as methanol, to ~orm the diastereomeric salts of threo-
chlorocitric acid-R-lactone. The salts then are separated
by known techniques, such as crystallization.
In an additional and highly efficient synthesis of
(+)-threo-chlorocitric acid (Ia1), trans-aconitic acid
is converted to a readily isolable and highly crystalline
mono-alkali metal salt of (+)-threo-epoxyaconitic acid
30 which is cleaved by the hereinbefore described methods,
e.g. with sodium chloride in the presence of hydrochloric
acid.
The conversion of trans-aconitic acid to a mono-al-
35 kali metal salt of (+)-threo-epoxyaconitic acid may be
accomplished by one of several processes.
., ~
113~
In the first, trans-aconitic acid is transformed into
a di-alkali metal salt of (+)-threo-chlorocitric acid-
~-lactone as herein described. Instead of hydrolyzing
the R-lactone directly to the chloroacid Ia1 under aci-
dic conditions as herein disclosed, it has been foundefficacious to first hydrolyze t`ne ~-lactone function
and concomitantly displace the chloro function to a tri-
alkali metal of (+)-threo-epoxyaconitic acid under alkaline
conditions, then partially neutralize the tri-
10 salt to the desired mono-salt.
The alkali induced hydrolysis - displacement of the
dialkali metal salt of (+)-threo-chlorocitric acid-
~-lactone is performed with an alkali metal hydroxide,
15 preferably potassium hydroxide, while maintaining the
reaction temperature between about 0 to 40C, more pre-
ferably at about 0 to 25C.
The partial neutralization of the tri-salt of (+)-
20 threo-epoxyaconitic acid is accomplished by adjusting
the pH of the hydrolysis - displacement reaction mixture
to a value within the range of about 7.0 to 7.5, preferably
to a value of about 7.2, cooling the resulting reaction
mixture to a temperature of about -20 to 20C, preferably
- 25 to about 0 to 5C, adding about two molar-equivalents
of acid, collecting the precipitate and purifying it by
recrystallization from water or water-alkanol mixtures,
water being preferred.
In the second process, trans-aconitic acid is chloro-
hydrinated to a tri-alkali metal salt of (+)-threo-
chlorocitric acid which is cyclized under alkaline condi-
tions and partially neutralized under acidic conditions
to the tri-alkali metal salt of (+)-threo-epoxyaconitic
35 acid.
The chlorohydrination is carried out by treating trans-
~3~47'(~
- 10 -
aconitic acid with an alkali metal hypochlorite, prefer-
ably potassium hypochlorite, preformed by the dissolution
of chlorine in an alkali metal hydroxide solution, prefera-
bly aqueous potassium hydroxide. While the chlorohydrina-
tion temperature is not narrowly critical, ik is preferredto perform the reaction at a temperature within the range
of about -20 to 25C, more preferably of about -5 to 5C,
most preferably of about 0C. About two molar-equivalents
of alkali metal hydroxide are initially employed to form
10 a di-alkali metal salt of trans-aconitic acid and two
additional molar-equivalents of alkali metal hydroxide
are subsequently employed to form sufficient alkali metal
hypochlorite for the hypochlorination of the di-salt.
The cyclization of the tri-alkali metal salt of (+)-
threo-chlorocitric acid to the tri-alkali metal salt of
(+)-threo-epoxyaconitic acid is accomplished by treating
the chlorohydrination reaction mixture or the tri-
alkali metal salt of (+)-threo-chlorocitric acid, dissolved
20 in a suitable solvent, with an alkali metal hydroxide,
preferably potassium hydroxide. The cyclization temperature
is not narrowly critical. Nevertheless it is preferred
to carry out the reaction at a temperature of about 15
to 60C, more preferably at about 25C. Suitable cyclization
25 solvents include water and mixtures of water and lower
alkanols. Water is preferred.
The partial neutralization of the tri-alkali metal
salt of (+)-threo-epoxyaconitic acid is effected by treating
30 it, or the reaction mixture in which it is derived, with
a mineral or organic acid according to the hereinbefore
described procedure for the related conversion of the
di-alkali metal salt of (+)-threo-chlorocitric
acid-~-lactone.
In the third process, a variant of the second method,
about two-thirds of a molar-equivalent of trans-aconitic
:1~, 3~t~
-- 1 1 --
acid is treated with about two molar-equivalents of an
alkali metal hydroxide, preferably potassium hydroxide,
in an appropriate solvent, followed by about one molar-
equivalents of preformed alkali metal hypochlorite, pre-
ferably potassium hypochlorite, and about one-third mo-
lar-equivalents of trans-aconitic acid to form a tri-al-
kali metal salt of (+)-threo-chlorocitric acid.
As appropriate solvent there may be mentioned water
10 and mixtures of water and lower alkanols. Water is pre-
ferred. While the hypochlorination temperature is not
narrowly critical, it is preferable to perform the reac-
tion at a temperature from about -20 to 10C, more pre-
ferably from about -10 to -5C.
The so obtained tri-salt is transformed to the mono-
alkali metal salt of (+)-threo-epoxyaconitic acid by the
methods hereinbefore described in the description of the
first process.
In the fourth process, (+)-threo-epoxyaconitic acid
is converted to its mono-alkali metal salt, preferably
the mono-potassium salt, by treatment of the acid with
about one equivalent of an alkali metal hydroxide,
25 preferably potassium hydroxide, in a suitable solvent,
such as water and mixtures of water and lower alkanols.
It is preferred to carry out the reaction at about 5C,
although the temperature is not critical. The mono-salt
so obtained, is isolated and purified as hereinbefore
30 disclosed for the product of the other variants.
The mono-alkali metal salts of (+)-threo-epoxyaconitic
acid are generally isolated as the monohydrates.
(-)-Threo-chlorocitric acid may also be prepared by
neutralizing a mono-alkali metal salt of (+)-threo-
epoxyaconitic acid to (+)-threo-epoxyaconitic acid, which
~!.3~
- 12 -
'';
is then resolved into (+)-threo-epoxyaconitic acid via
its bis (+)-p-nitro-a-methylbenzylamine salt and clea-
ved int~ (-)-threo-chlorocitric acid as described herein-
before.
The neutralization is conveniently performed by trea-
ting the mono-alkali metal salt, preferably the potassium
salt, with a strong acid in an appropriate solvent. Among
strong acids there may be mentioned mineral acids, such
10 as hydrochloric, hydrobromic, nitric, perchloric and sul-
furic acid, and organic acids, such as methanesulfonic,
benzenesulfonic, p-toluenesulfonic, trifluoroacetic and
trichloroacetic acid. Among appropriate solvents there
may be mentioned water, lower alkanols, mixtures of water
15 and lower alkanols and ketones, such as acetone, methyl-
ethyl ketone and diethylketone. Mineral acids and keto-
nes, particularly sulfuric acid and acetone, are preferred.
~` Of particular interest as anorectic agents are the
20 compounds of formula Ia and the pharmaceutically accep-
table salts thereof, more particularly (-)-threo-chloro-
citric acid and pharmaceutically acceptable salts thereof,
which are significantly more active in reducing food con-
- sumption than hydroxycitric acid or citric acid, as can
25 be seen from the following test reports.
~. .
Female rats weighing 150 to 175 g,were housed in indi-
vidual cages, fasted 48 hr, then fed a 70 o/o glucose
diet from 8 to 11 a.m. Following 5 to 13 days alimenta-
30 tion, rats were dosed with the appropriate compounds orallyby intubation 1~2 hr before the 3 hr meal. Food cups were
weighed immediately after the meal. The control group
consists of 31 rats while each drug treated group corsists
of 5 to 12 rats. The results are given in Table I.
g,
- ~.3~'70
-- 1 3 --
~ ~o' o o~ ~ o ~
L O O 1~ ~ ~ _ O
r
o
O
~l ~ ~
E ~ 0 o ~o r~ ~>
O _ o O
O ~0 ,q~ +, +, +1 +, +1 .
E .. - 0~ cr~ o Lo c
C ~0 . ~
O ~I' O et oo L~
H~0 u O o ~) c~ )
R ~ o c
: s E
O ~ ~ * * * * ~ .
~ In ~ o ~
, R O O o O o O O ~U
+l t~l +l +l +l +l +l +l +l ~
~ ca et ~ ~
_~ _ ~
o ._ ~ s
~ ~ . ~ :~
+ ~ ~ 3
~_) ~1 ~0 ~ _ o o o' o ~ ~O
1~3134~
- 14 -
Female rats weighing 130 to 150 g, were housed in
individual cages, fasted 48 hr, then ~ed a 70 o/o glu-
cose diet from 8 to 11 a.m. Following 5 to 12 days ali-
mentation, rats were dosed with the appropriate compounds
orally by intubation 1/2 hr before the 3 hr meal. Food
cups were weighed immediately after the meal. The con-
trol group consisted of 5 to 10 rats, while the experi-
mental group consisted of 4 to 6 rats. The results are
given in Table II.
.: .
- 25
~ .
.. .
113134~7V
-- 1 5 _
+, ~ o I ~ a~ u~ a~
,~o~ o
O r v) C`l O 1~ a- CD
E O c~ ~0 00 O.
O
O O _ _ O _ O
. ~ ~ +~ +1 +1 ~1 +1 +1
~ Ir) I~ _ C~l N ~n
C~.l ~ O
~ ~ LLI
+E ~ U ~
~0 ~ s
1~l384~7~)
The citric acid derivatives of the present invention
can be made up in the form of conventional pharmaceuti-
cal preparations containing, in addition to the active
ingredients, carrier material, such as conventional orga-
nic or inorganic inert pharmaceutical adjuvants, addi-
tives and excipients suitable for parenteral or enteral
administration, e.g. water, gelatin, lactose, starch,
magnesium stearate, talc, vegetable oil or gums. They
can be administered in conventional pharmaceutical forms,
10 e.g. solid forms, for example tablets, dragees, capsules
or suppositories; or in liquid forms, for example sus-
pensions or emulsions. Moreover, the pharmaceutical com-
po~sitions can be subjected to conventional pharmaceuti-
cal expedients, such as sterilization, and can contain
15 conventional pharmaceutical excipients such as preserva-
tives, stabilizing or emulsifying agents, salts for the
adjustment of osmotic pressure or buffers. The composi-
tion can also contain other therapeutically active mate-
rials.
` 20
A suitable pharmaceutical dosage unit can contain
from about 10 to 1000 mg of (-)-threo-chlorocitric acid
or its isomers. Suitable parenteral and oral dosage regi-
mens in mammals comprise from about 1 to 150 mg/kg per
day.
The citric acid derivatives of the present invention
can also be compounded with a feed additive, premix or
concentrate for administration to an animal. -
A feed premix or complete feed can e.g. contain suffi-
cient active ingredient to provide from about 0.0025 to
1.00 o/o, preferably, about 0.0625 to 0.40 o/o, most pre-
ferably about 0.125 o/o, by weight of the daily feed con-
sumption.
3?3'~70
- 17 -
Example l
Preparation of the starting material.
174 g of trans-aconitic acid was added portionwise
to a stirred solution of 120 g of sodium hydroxide in
400 ml of water. The temperature was maintained at 25.
When the acid had completely dissolved, the solution was
at pH 7.5.
The process.
The solution was cooled to 5 and purged with argon.
Chlorine gas was then added to the stirred mixture as
fast as it could be consumed. The temperature was main-
tained at 10-15. When no more gas was absorbed, the
15 addition o~ chlorine was stopped and the mixture was stirred
at iO for 10 minutes. Excess chlorine gas was purged
by bubbing argon gas through the mixture.
.
The reaction was acidified using 175 ml conc. hydro-
20 chloric acid and then heate`d at 70 for 1 hour to hydrolyze
the ~-lactone. The solution was concentrated to dryness
and the residue was triturated with ethyl acetate. The
combined extracts were filtered to remove residual sodium
chloride and then dried. Evaporation of the solvent gave
25 a solid which was redissolved in ethyl acetate. The solution
was diluted with carbon tetrachloride. After stirring,
the solid which had ~ormed was recovered by filtration
to give 102.0 g of (+)-threo-chlorocitric acid, mp 96-101.
The mother liquors were concentrated to dryness and
then crystallized as above to give an addition 60.7 g
of pure (+)-threo-chlorocitric acid.
Example 2
To a solution of 123 g o~ mono-potassium (+)-
- threo-epoxyaconitic acid monohydrate and 28 g o~ potassium
..
- 18 -
chloride in 120 ml of water, was added 88 ml of conc.
hydrochloric acid. The reaction mixture was heated at
70 for 15 nours, allowed to cool to room temperature
and concentrated. Ethyl acetate (250 ml) was added and
the mixture was agitated at 40. The precipitated potas-
sium chloride was collected and washed with 350 ml of
ethyl acetate. The filtrate was evaporated to dryness.
The residue was dissolved in ethyl acetate, treated with
anhydrous magnesium sulfate and filtered. The filter cake
was washed with ethyl acetate. Carbon tetrachloride was
added to the filtrate. The mixture was seeded with crys-
talline (+)-threo-chlorocitric acid monohydrate, stir-
red for 2 hours and allowed to stand for 16 hours in a
refrigerator. The precipitate was collected, washed with
carbon tetrachloride-ethyl acetate (3:1) and dried to
afford 70.9 g of (+)-threo-chlorocitric acid monohydrate,
m.p. 74-76.
The mother liquors were evaporated to dryness. The
residue was dissolved in 125 ml of ethyl acetate and trea-
ted with carbon tetrachloride to give 20.7 g of product.
; A 91.0 g-portion of the combined first and second
crops was dissolved in 250 ml of ethyl acetate and trea-
ted with 500 ml of carbon tetrachloride. The solution
was seeded with crystalline (+)-threo-chlorocitric acid
monohydrate and stored in a refrigerator overnight. The
precipitate was collected, washed with carbon tetrachloride
and ethyl acetate and dried to yield 84.3 g of purified
30 product, m.p. 74_76 .
Example 3
74.0 g of cis-aconitic anhydride was dissolved in
200 ml of water containing 100 g ice. A solution of 46.25 g
of sodium hydroxide in 100 ml of water was added slowly
with stirring. The temperature was held below 20. Then
1~3~}4~
~ g
15.25 g sodium tungstate dihydrate, followed by 55.5 ml
of 30 o/o hydrogen peroxide was added to the mixture.
The stirred solution was warmed to 23. The external heat
source was then removed whereupon the heat of reaction
caused the mixture temperature to slowly climb to 51.5
over 25 minutes after which it started to decline. After
stirring 30-40 minutes, the mixture was treated with 150
ml conc. hydrochloric acid and 150 g sodium chloride and
heated at 75 for 15 minutes. In this way the intermediate
(+)-erythro-epoxyaconitic acid was converted to (+)-ery-
thro-chlorocitric acid. After the reaction mixture was
cooled to room temperature, 2.3 g sodium bisulfite was
added to destroy residual hydrogen peroxide. The solution
was then continuously extracted using ether.
The first extract collected after 21 hours was dried
and concentrated to give 73.0 g of crude chlorocitric
acid. Crystallization of this material twice from ethyl
acetate-carbon tetrachloride furnished essentially pure
(+)-erythro-chlorocitric acid, mp 162-164.
A second extract gave an additional 18.5 g of the
acid, mp 163-165.
Example 4
A solution of trisodium trans-aconitate prepared from
58.0 g trans-aconitic acid and 40 g sodium hydroxide in
300 ml of water was cooled to 5 and chlorinated as in
30 Example 1. The resulting solution of disodium chlorocitric
acid-R-lactone was purged free of excess chlorine gas
and then treated with 60 ml 12N hydrochloric acid. The
mixture was extracted with ethyl acetate and the extracts
were combined and dried. The ethyl acetate solution was
35 concentrated and then diluted with carbon tetrachloride.
The resulting crystalline material was collected by
filtration to give 41.5 g of pure (+)-threo-
1~3~7(~
- 2~) -
chlorocitric acid-~-lactone, mp 162-164.
Example ~
30 g of (+)-erythro-chlorocitric acid was dissolved
in 175 ml of a methanol-water mixture (49:1). The solution
was cooled to 15 and 39.5 g (-)-p-nitro-a-methylbenzyl-
amine in 75 ml of the same methanol-water mixture was
added. The mixture was stirred at room temperatur for
18 hours. The solids were collected by filtration and
then washed with ethanol and ether to give 24.0 g of
partially resolved (+)-erythro-chlorocitric
acid-bis(-)-p-nitro-a-methylbenzylamine salt.
The impure salt was then split in the following manner:
hydrogen chloride gas was bubbled through a stirred sus-
pension of finely divided salt (27.1 g) in ether for 30
minutes. The resulting solid (-)-p-nitro-a-methylbenzyl-
amine hydrochloride (19.9 g, mp 247-249) was removed
20 by filtration and the filtrate was concentrated to give
10.9 g of partially resolved (+)-erythro-chlorocitric
acid a~ an oil (65 o/o optical purity).
The (-)-p-nitro-a-methylbenzylamine hydrochloride
25 was partitioned between dichloromethane and 1N sodium
hydroxide. The amine recovered from this process (1~.6 g)
in 40 ml methanol-water (49:1) was added to a solution
of the crude (+)-erythro-chlorocitric acid in 40 ml metha-
nol-water (49:1) and the mixture, after stirring, deposi-
30 ted 18.1 g of enriched bis-amine chlorocitrate.
The salt was again split using ethereal hydrogen chlo-
ride and was then reformed in the manner described above.
This gave 14.4 g of the bis-amine chlorocitrate. The (+)-
35 erythro-chlorocitric acid recovered from the latest salt
was recrystallized from ethyl acetate-carbon tetrachloride
to give 4.3 g of material (29 o/o chemical yield) which
1~38~7()
- 21 -
was 85 o/o optically pure.
The mother liquors of the solution of the partially
resolved (+)-erythro-chlorocitric acid-bis(-)-p-nitro-a-
methylbenzylamine salt were treated with 13 ml of conc.hydrochloric acid and evaported. 1,2-Dimethoxyethane was
added and the ~olution was evaporated to dryness. Ether
was added to the residue, the mixture was stirred and
the precipitate was collected to afford 29.2 g of (-)-p-
10 nitro-a-methylbenzylamine hydrochloride.
The filtrate was concentrated to dryness and the resi-
due, rich in (-)-erythro-chlorocitric acid, was dissolved
in 90 ml of methanol-water (49:1). A solution of 25.3 g
15 of (+)-p-nitro-a-methylbenzylamine and 50 ml of methanol-
water (49:1) was added. The resulting mixture was stirred
for 20 hours and the precipitate was collected to afford
15.0 g of bis-(+)-p-nitro-a-methylbenzylamine salt en-
riched in (-)-erythro-chlorocitric acid. The salt was
20 suspended in 185 ml of ether and hydrogen chloride was
added to the suspension. The precipitated (+)-p-nitro-a-
methylbenzylamine hydrochloride (10.7 g) was collected
on a filter. The filtrate was concentrated to dryness
and the residue was dissolved in 40 ml of methanol-water
(49:1). To the methanol-water solution was added a solu-
tion of 8.9 g of (+)-p-nitro-a-methylbenzylamine and 15 ml
of methanol-water (49:1) and the solution was stirred
for 2.5 hours. The precipitate (11.75 g) enriched in (-)-
erythro-chlorocitric acid-bis-(+)-p-nitro-a-methylbenzyl-
30 amine salt, was suspended in ether and the resulting sus-
pension was saturated with hydrogen chloride. The preci-
pitated (+)-p-nitro-a-methylbenzylamine hydrochloride
(8.o9 g) was collected and the filtrate was concentrated.
Recrystallization of the residue from ethyl acetate-car-
35 bon tetrachloride gave 3.9 g of (-)-erythro-chlorocitric
acid (85 o/o optical purity).
.
' ~
'.
~3~4~0
- 22 -
Example 6
10S g (+)-threo-epoxyaconitic acid monohydrate was
dissolved in 150 ml of water containing 43 ml conc. hy-
drochloric acid. Sodium chloride (50 g) was added to the
~; stirred solution and the mixture was heated at 70 for
12 hours. The solution wa3 evaporated to dryness and the
residue was triturated with 400 ml ethyl acetate. The
mixture was filtered and the filtrate was decolorized,
dried and concentrated. The residue was dissolved in 250 mlethyl acetate and the solution was treated with carbon
tetrachloride. The mixture was stirred several hours and
then chilled. The solids were removed by filtration to
give 68.5 g of (-)-threo-chlorocitric acid, mp 138-140,
ra]D5 -6.60 (c, 2.0, H20). An additional 20.2 g of material
were recovered from the mother liquors.
Example ?
(-)-Threo-epoxyaconitic acid monohydrate ( 105 g) was
dissolved in 150 ml of water containing 43.0 ml conc.
hydrochloric acid. To the stirred solution 50 g of sodium
chloride was added and the mixture was heated at 70 for
12 hours. The reaction was worked up as in example 6 to
25 give (+)-threo-chlorocitric acid in two crops:
crop 1: mp 138-140; ~a]~5 +6.65 (c, 2.0, H20); 55.2 g
crop 2: mp 138-140; ~a]D5 +6.55 (c, 2.0, H20); 23.0 g.
Recrystallization of the solid from ethyl acetete-car-
30 bon tetrachloride gave the analytically pure material,
~ mp 140.5-142; ~a]D5 +6.9 (c, 2.0, H20).
Example 8
A solution of 8.1 g (+)-erythro-epoxyaconitic acid
35 in 43 ml 1N hydrochloric acid containing 15 g sodium chlo-
ride was heated at 78 for 25 minutes and an additional
20 minutes at 80. Evaporation of the solvent left a residue
3~14
- 23 -
consisting of crude (-)-erythro-chlorocitric acid and
sodium chloride. The organic material was dissolved in
glyme and the resulting solution was filtered to remove
sodium chloride, dried and concentrated. Crystallization
of the product from ethyl acetate-carbon tetrachloride
afforded 7.4 g of essentially pure (-)-erythro-chloro-
citric acid. Recrystallization furnished 5.4 g of pure
acid, mp 133.5-135; [a~D5 -2.2 (c, 2.0, H20).
Exam_le 9
(-)-Erythro-epoxyaconitic acid (9.~ g) was converted
into 7.6 g of (+)-erythro-chlorocitric acid (mp 132-134)
by a procedure essentially identical to that described
in example 8. Recrystallization of the chlorocitric acid
thus obtained afforded 5.3 g of analytically pure mate-
rial, mp 133.5-135; [~]D- +2.2 (c, 2.0, H20).
Example 10
Trans-aconitic acid (87.0 g) was added portionwise
to a solution of 60.0 g of sodium hydroxide in 200 ml
of water. The mixture was cooled and chlorinated as in
Example 1. The resulting solution of (+)-threo-chloro-
25 citric acid-B-lactone disodium salt (purged free of excess
chlorine gas) was cooled to -10 and treated with 40.0 g
sodium hydroxide. The solution was stirred and the reac-
tion temperature was moderated by cooling so that it did
not exceed 20. The mixture was stirred at 20 for 20
30 minutes and then 42 ml of conc. sulfuric acid was added
dropwise with cooling. The solution was extracted with
diethyl ether. The ether extract was dried and concentra-
ted. The resulting solid was crystallized from ethyl ace-
tate-carbon tetrachloride to give 67.8 g of (+)-threo-
35 epoxyaconitic acid, mp 169-172. A second crop (8.85 g;
mp 167-170) was collected from the mother liquors.
:,
,
.
--- 113F~470
- 24 _
Example 11
Tablets with the following composition were prepared:
Amount (mg/tablet)
~ threo-chlorocitric acid 50
polyvinylpyrrolidone 2
microcrystalline cellulose 10
silicone dioxide
10 magnesium stearate
'
