NO784398L - PROCEDURE FOR THE PREPARATION OF TIOALKANOYL ALCANIC ACID COMPOUNDS - Google Patents

Description

"Procedure for the manufacture of

thioalkanoylalkanoic acid compounds"

This invention relates to the preparation of new thioalkanoyl-alkanoic acid compounds with the formula:

(IN)

where

R 1 , R 2 /R 3 and each are hydrogen or lower alkyl; R,, is hydrogen, lower alkanoyl, benzoyl or

A and B are each hydrogen or are bonded together to complete a cycloalkyl ring; and

m is 0 or 1;

and basic salts thereof.

The invention relates in particular to the preparation of the compounds of formula I and salts thereof where A and B together complete a cycloalkyl group, i.e. compounds of the formula

(II)

where R 1 , R 2 , R 5 and m have the meanings given above (especially when m is 1), and n is 2, 3 or 4, resulting in a cyclobutane, cyclopentane or cyclohexane ring, respectively.

Compounds with less activity and interest are the compounds of formula I and their salts where A and B are both hydrogen, i.e. the 3-oxohexanoic acid or 3-oxopentanoic acid derivatives of formula

(III)

where the symbols have the meanings indicated above.

The new intermediates which are useful for the preparation of compounds of formula II, especially when m is 1, are compounds of the formula

(IV)

where R 2 , R 3 , R 3 and h have the meanings given above, and R is hydrogen, phenyl-lower alkyl or diphenyl-lower alkyl, preferably benzyl or diphenylmethyl.

Particularly preferred modifications are compounds of formula I where R 1 , R 2 , R 2 and R 4 are hydrogen or lower alkyl, especially hydrogen or methyl and especially hydrogen; and R 1 is hydrogen or lower alkanoyl, especially hydrogen or acetyl. These preferred meanings of the symbols apply to both the compounds of formula II and formula III, but as indicated above, the compounds of formula II are preferred over those of formula III.

The lower alkyl groups denoted by the symbols are linear or branched hydrocarbon radicals containing up to 7 carbon atoms, such as methyl, ethyl, propyl, . isopropyl, butyl, isobutyl and the like. In general, the C^-C-^ groups are preferred.

The lower alkanoyl groups are the acyl radicals of the lower (up to 7 carbon atoms) fatty acids, e.g. acetyl, propionyl, butyryl, isobutyryl and the like. In general, the aforementioned groups are preferred, and particularly acetyl.

The new compounds are produced according to the invention by several methods. According to one method, especially when m is 1, an acid is reacted with the formula

(IVa)

with the thiol R^-SH, where R5<1>is lower alkanoyl or benzoyl, to form a product of the formula

(V)

This reaction can be carried out by dissolving or suspending the compound of formula IVa in an inert, organic solvent such as chloroform, dichloromethane, tetrahydrofuran, dioxane or the like, and slowly adding the thiol, preferably at a reduced temperature in the range from approx. 0 to 25°C. The product of formula V where R, - is lower alkanoyl or benzoyl, can then be converted into the corresponding product where R, - is hydrogen, by treatment with aqueous ammonia or sodium hydroxide solution.

According to a variation of this procedure, the compound of formula IVa can be treated with a thiol as above, followed directly by treatment with concentrated ammonium hydroxide solution to directly form the product where R 1 - is hydrogen.

An alternative method comprises that an ester of a compound of formula IVa above, e.g. a phenyl 1-lower alkyl ester or di phenyl 1-lower alkyl ester, preferably the diphenyl methyl ester, is reacted with the thiol as above, the protecting ester group is removed, e.g. with trifluoroacetic acid and anisole when the ester is a diphenylmethyl ester, and then treated with aqueous ammonia to remove the R 1 group, resulting in a product where R 1 - is hydrogen.

Another method, particularly when m is 0, involves using an ester with the formula

(WE)

which is converted with a halogenating agent such as oxalyl chloride to the acyl halide of the formula

(VIII)

Treatment of this intermediate with a diazoalkane gives a diazoalkyl ketone of the formula

(VIII)

The compound of formula VIII can then be reacted with the thiol R, -' -SH as described above, to obtain a product of formula I where R is lower alkanoyl or benzoyl. Treatment of the latter product with ammonia or sodium hydroxide, likewise as described above, gives a product where R^ is hydrogen.

The esters where R^ is lower alkyl can be prepared by usual esterification methods or by using an ester as starting material. They can correspondingly be converted into the free acid by usual methods such as hydrolysis etc.

The disulfides or bis compounds where R■ Dc in formula I is

is prepared from a compound of formula I where R,, is hydrogen, by direct oxidation, e.g. with an alcoholic iodine solution. The acid with formula IVa is produced by reacting an anhydride with formula (IX).

with ethylene in the presence of a Friedel-Crafts catalyst such as aluminum chloride, in a solvent, preferably 1,2-dichloroethane, or by reacting a starting material of the formula

(X)

with a Grignard reagent of the formula

(XI)

hydrolysis of this reaction product with an aqueous base such as sodium hydroxide to form the hydroxy acid, conversion of this to the diphenylmethyl ester with diphenyldiazomethane, and oxidation of the alcohol group to a keto group with chromium trioxide or manganese dioxide.

The aldehyde esters of formula X can be prepared by

an anhydride of formula IX is treated with methanol, the acid obtained is reduced to an alcohol with diborane, and the alcohol is oxidized with chromium trioxide. Alternatively, a halogenated compound of the formula

(XII)

is converted to the compound of formula X with aqueous silver nitrate.

The compounds of formula I form basic salts with various inorganic or organic bases. These salts can also be prepared according to the invention. Such salts include alkali metal salts, in particular the sodium and potassium salts, alkaline earth metal salts, in particular calcium and magnesium salts, aluminium, dicyclohexylamine salt, benzathine salt, N-methylglucamine salt, hydrabamine salt, salts with naturally occurring amino acids such as arginine, lysine etc., lower alkylamine salts such as methylamine, ethylamine, dimethylamine, triethylamine salts, etc. The non-toxic, physiologically acceptable salts are preferred, although other salts are also useful, e.g. by isolating or purifying the products as illustrated in the following examples. The salts are formed in the usual way by reacting the free acid form of the product with one or more equivalents of the appropriate base which provides the desired salt ion in a solvent or medium in which the salt is insoluble, or in water after which the water is removed by freeze-drying. By neutralizing the salt by usual methods, the free acid form can be obtained, and possibly another salt can be formed.

Further experimental details are given in the examples which represent preferred embodiments and also serve as a model for the preparation of other compounds in the relevant group.

The compounds produced according to the invention have one or more centers of asymmetry. The compounds thus exist in stereoisomeric forms or in racemic mixtures thereof. All of these can be produced according to the invention.

The compounds produced according to the invention inhibit the conversion of the decapeptide angiotensin I to angiotensin II by means of angiotensin-converting enzyme, and are therefore useful as hypotensive agents, particularly for reducing or alleviating hypertension. By administering a preparation containing a compound or a combination of compounds of formula I or physiologically acceptable salts thereof, angiotensin-dependent hypertension is alleviated in mammals, e.g. rats, cats, dogs, etc., which have such disorder. A single dose, or preferably 2-4 separate daily doses, administered on the basis of approx. 0.1 to 100 mg per

kg per day, preferably approx. 1 to 50 mg per kg per day, is appropriate for reducing blood pressure as indicated in the animal model experiments described by S. L. Engel, T. R. Schaeffer, M.H. Waugh and B. Rubin,

Pro. Soc. Exp. Biol. With. 143, 483 (1973). The active compound is preferably administered orally, but parenteral forms of administration such as subcutaneous, intramuscular, intravenous or intraperitoneal

can also be used.

The compounds produced according to the invention can be used to achieve a reduction of blood pressure by preparing suitable preparations such as tablets, capsules or elixirs for oral administration or in sterile solutions or suspensions for parenteral administration. About. 10 to 500 mg of a compound or a mixture of compounds of formula I or physiologically acceptable salts thereof are mixed with a physiologically acceptable carrier, excipient, binder, preservative, stabilizer, flavoring agent, etc. in a unit dosage form depending on what is desired according to accepted pharmaceutical practice. The amount of active substance in these preparations is such that a suitable dose is achieved in the specified range.

Sterile preparations for injection may be prepared according to ordinary pharmaceutical practice by dissolving or suspending the active substance in a vehicle such as water for injection, a naturally occurring vegetable oil such as sesame oil, coconut oil, peanut oil, cottonseed oil, etc., or a synthetic fatty acid such as ethyl oleate or the like. Buffers, preservatives, antioxidants etc. can be incorporated as desired.

The following examples shall serve to illustrate the invention and represent particularly preferred embodiments within the framework described above. All temperatures are in °C.

Example 1

ci s- 1, 2- cyclopentanedicarboxylic acid anhydride

Method A: [cf. S.F. Birch et al., J. Org. Chem. , 20 1178 (1955)]. A mixture of 5.ag (31.6 mmol) of trans-1,2-cyclopentanedicarboxylic acid and 30 ml of acetic anhydride is refluxed under nitrogen for 18 hours. The acetic anhydride is removed in vacuo and the residue distilled to give 2.75 g of cis-1,2-cyclopentane-dicarboxylic anhydride, b.p. 110-120°/0.3 mm, which hardens on standing. Direct recrystallization of this material from isopropyl ether/ether yields 1.8 g of crystalline material, m.p. 50-60°. Another recrystallization from ether gives 1.4 g of analytically pure anhydride, m.p. 69-72°.

Method B: [cf. Chem. Pharm. Bull., 6^, 446 (1961)].

a) 1-cyclopentene-1,2-dicarboxylic acid

A mixture of 200 g (1.28 mol) ethyl1-2-oxo-cyclopentane-

carboxylate, 400 g (430 ml, 4.50 mol) acetone-cyanohydrin,

5 g anhydrous potassium carbonate and 20 drops of 10% aqueous potassium cyanide solution are stirred at room temperature overnight under extraction. The mixture is then filtered, the filtrate is carefully acidified with 10% sulfuric acid to pH 3, and insoluble material is removed by filtration. Methanol is removed from the filtrate by distillation at atmospheric pressure. Distillation of the residue gives 128.3 g (55%) of the desired cyanohydrin, b.p. 150-157°/8 mm,

which is used immediately.

The distilled cyanohydrin (128.3 g, 0.7 mol) is cooled

in an ice bath and dilute with 250 ml of pyridine. To this cold, stirred solution, 68 ml of phosphorus oxychloride are added dropwise over the course of 45 minutes, and the resulting mixture is allowed to stand at 0-5° for 18 hours. The reaction mixture is heated on a steam bath for 1 hour, cooled and added to excess of diluted hydrochloric acid ice. This mixture is carefully extracted with ether, and the combined extracts are dried and concentrated in vacuo. Distillation of the residue gives 91.4 g (79%), b.p. 118-120°/3 mm.

A mixture of the above liquid (91.4 g, 0.55 mol)

and 200 ml of concentrated hydrochloric acid are refluxed for 6 hours, cooled, and the resulting precipitate f raf is evaporated. Direct recrystallization from water (200 ml) [charcoal decolorization], followed by drying in vacuo over phosphorus pentoxide at 60°, gives 59.3 g (69%) of 1-cyclopentene-1,2-d,icarboxylic acid, m.p. 177-179°.

b) cis-1,2-cyclopentanedicarboxylic acid

1-Cyclopentene-1,2-dicarboxylic acid (10.0 g, 0.064 mol)

in 200 ml of absolute ethanol is hydrogenated (Paar shaker) in the presence of Raney nickel at 2.8-3.5 kg/cm.^ at 60°. After absorption of one equivalent of hydrogen (24 hours), the mixture is cooled, filtered through a "Celite" (diatomaceous earth) pad, and the filtrate is concentrated in vacuo to a solid. Direct recrystallization from water (30 ml) followed by drying in vacuo over phosphorus pentoxide gives 6 g

(60%) cis-1,2-cyclopentanecarboxylic acid, m.p. 132-135°. The mother liquor from the recrystallization can be lyophilized to a solid that is sufficiently pure for use in the next step.

c) c is- 1, 2- cyclopentanedicarb oxic anhydride A mixture of 4 3.15 g (0.273 mol) of the above

diacid and 350 ml of acetyl chloride are refluxed for 2 hours and then brought to dryness in vacuo. Distillation of the residue

gives 34.6 g (91%) of cis-1,2-cyclopentanedicarboxylic anhydride,

k.p. 100-110/0.5 mm, which crystallizes on standing.

Example 2

cis- 2-( 3- methyl- 1- oxo- 2- butenyl) cyclopentanecarboxylic acid

To a stirred suspension of 4.38 g (32.86 mmol) anhydrous. aluminum chloride in 100 ml of 1,2-dichloroethane at room temperature, 2.30 g (16.43 mmol) of cis-1,2-cyclopentanedicarboxylic acid anhydride are added. The ethylene is then bubbled through the clear solution with stirring for 4 hours.

The solution is poured into 150 ml of 5% aqueous hydrochloric acid, and the layers are separated. The aqueous layer is extracted with ether, the ether extracts are mixed with the dichloroethane solution, dried and concentrated in vacuo. The remaining oil is heated for 15 minutes on a steam bath with 25 ml of 10% aqueous potassium carbonate, cooled and extracted with ether. The aqueous layer is acidified with cold, concentrated hydrochloric acid, and the resulting solution is carefully extracted with ether. The combined extracts are dried and concentrated in vacuo to give 1.9 g of oil.

The oil is taken up in chloroform, applied to a silica gel column (60 g) and eluted with chloroform (100 ml fractions are collected). Fractions 10-15 are combined, concentrated in vacuo and triturated with petroleum ether to give 0.460 g (14.3%) of cis-2-(3-methyl-1-oxo-2-butenyl)cyclopentanecarboxylic acid, which is recrystallized from hexane, m.p. p. 85-88°.

Example 3

trans- 2-[ 3-( acetylthio)- 1- oxopropyl] cyclohexane- carboxylic acid

a) . trans-3-[l-oxo-2-propenyl] cyclohexane-carboxylic acid A mixture of aluminum chloride (66.7 g, 0.5 mol), trans-1,2-cyclohexanedicarboxylic acid anhydride (38.5 g, 0.25 mol) and 1,2-dichloroethane (1 liter) in a 2 liter 3-necked flask equipped with gas inlet tube, mechanical stirrer and drying tube, stir rapidly, and ethylene is bubbled in for 4.5 hours. This mixture is poured into 900 ml of 5% hydrochloric acid and ice. The layers are separated, and the organic layer is washed with water and brought to dryness in vacuo. The aqueous layer is extracted with ether (300 ml). This extract is washed with water and mixed with material from the original organic layer and brought to • dryness. The residue is heated with 300 ml of 10% potassium carbonate on a

steam bath for 15 minutes. After cooling, the mixture is extracted three times with ether. The aqueous layer is acidified, and the product trans-2-[1-oxo-2-propenyl]cyclohexanecarboxylic acid (31.6 g) is extracted into ether, dried and concentrated in vacuo. The crude, crystalline trans-2-(1-oxo-2-propenyl)cyclohexanecarboxylic acid is crystallized from ether-hexane, m.p. 101-102°.

b) trans- 2-[ 3-( acetylthio)- 1- oxopropyl] cyclohexanecarboxylic acid

The crude olefinic acid obtained above (22 g) is dissolved

in 100 ml of chloroform, and while gently cooling and stirring, 15 ml (0.21M) thiolacetic acid is added dropwise over a period of 10 minutes. After stirring for 1 hour at room temperature, the mixture is brought to dryness in vacuo to give a yellow gummy material. This is dissolved in chloroform and chromatographed on silica gel (450 g) with chloroform as eluent, to give 17 g of oil which crystallizes on trituration with hexane. A 3.0 g sample is recrystallized from isopropyl ether to give 1.7 g of trans-2-[3-(acetylthio)-1-oxopropyl]-cyclohexanecarboxylic acid, m.p. 65-68°.

Example 4

trans-2-(3-mercapto-1-oxopropyl)cyclohexanecarboxylic acid

trans-2-[3-(acetylthio)-1-oxopropyl]cyclohexanecarboxylic acid (3.0 g, 11.6 mmol) is added to a cold mixture of 5 mL of concentrated ammonium hydroxide and 5 mL of water under argon. The mixture is stirred at room temperature for 30 minutes. While cooling to 0°, the solution is acidified with concentrated hydrochloric acid. The mixture is extracted 4 times with ethyl acetate. The extracts are dried, and the solvent is removed in vacuo. The oily product is chromatographed on 90 g of silica gel with ethyl acetate as eluent. You get a total of 2.2 g (88%) of material that is contaminated with somewhat more polar material. Chromatography of 1.9 g of this material on 60 g of silica gel by elution with chloroform and 2% methanol in chloroform gives 1.4 g of trans-2-(3-mercapto-1-oxopropyl)cyclohexanecarboxylic acid, recrystallized from isopropyl ether-hexane, 1.0 g, (46%), m.p. 71-74°.

Example 5

cis- 2-[ 3-( acetylthio)- 1- oxopropylj cyclohexane- carboxylic acid

a) cis-2-[l-oxo-2-propenyl]cyclohexane-carboxylic acid A mixture of 66.7 g (0.5 mol) anhydrous aluminum chloride and 38.5 g (0.25 mol) freshly distilled cis-1,2 -cyclohexanedicarboxylic acid anhydride in 1 liter of 1,2-dichloroethane is stirred vigorously while ethylene is bubbled in for 4.5 hours. The mixture is then poured into 900 ml of 5% aqueous hydrochloric acid and ice. The layers are separated, and the organic layer is washed with water and brought to dryness in vacuo. The aqueous layer is extracted with 300 ml of ether, the extract is washed with water and then mixed with material from the original organic layer and brought to dryness in vacuo.

The residue is heated with 150 ml of 10% aqueous potassium carbonate solution on a steam bath for 15 minutes. After cooling, the mixture is extracted with ether. The aqueous layer is acidified and the product, cis-2-[l-oxo-2-propeny1]cyclohexane-carboxylic acid is extracted into ether.

The first ether extracts are extracted with 150 ml of 10% aqueous potassium carbonate. This aqueous layer is then acidified with dilute aqueous hydrochloric acid, and the product is extracted into ether. Post-drying and concentration in vacuum gives 23.4 g of viscous foam which is used without further purification.

b) cis-2-[,3-(acetylthio)-1-oxopropyl]cyclohexane-carboxylic acid-dicyclohexy1-amine salt

To a stirred solution of 22 g of the above-mentioned crude foam in 100 ml of chloroform at 0-5° is added dropwise 15 ml of thiolacetic acid. After the addition is complete, the solution is allowed to stand at 0-5° for 1 hour and is then brought to dryness in a vacuum.

The residue is taken up in chloroform and applied to a silica gel column (450 g) and eluted as follows:

Fractions 30-32 are combined, treated with hot isopropyl ether, filtered to remove polymeric material, and the filtrate concentrated in vacuo. The resulting oil is taken up in ether (total volume = 200 ml) and treated with 10 ml of dicyclohexylamine. The resulting crystalline solid dicyclohexylamine salt is filtered off, washed with ether and dried in vacuo to

yield 9.45 g, m.p. 134-138°.

c) cis- 2-[ 3-( acetylthio)- 1- oxopropyl] cyclohexanecarboxylic acid

A suspension of 2.0 g (4.5 mmol) of the dicyclohexylamine salt from part b in ethyl acetate is treated with an excess of 10% aqueous potassium bisulphate, and the layers are separated. The aqueous layer is extracted with ethyl acetate, and the combined organic layers are dried and concentrated in vacuo to give 1.35 g of oil. Trituration of 1.2 g of this oil with petroleum ether gives 0.80 g (69%) of cis-2-[3-(acetylthio)-1-oxopropyl]cyclohexanecarboxylic acid which is recrystallized from isopropyl ether, m.p. 79-81°.

Example 6

L-cis-2-(3-mercaptol-l-oxopropyl)cyclohexanecarboxylic acid

A solution of 2.5 g (9.68 mmol) of cis-2-[3-(acetylthio)-1-oxopropyl]cyclohexanecarboxylic acid in 5 ml of concentrated ammonium hydroxide and 5 ml of water is kept at 0-5° for 1 hour. The cold reaction mixture is then acidified with cold concentrated hydrochloric acid and carefully extracted with ethyl acetate. The combined extracts are dried and concentrated in vacuo to 2.3 g of oil. This oil is taken up in chloroform and applied to a silica gel column (60 g) and eluted as follows:

Fractions 6-13 give a solid when triturated with hexane. Solids are collected (total 1.5 g = 72%) and recrystallized from isopropyl ether/hexane to give L-cis-2-(3-mercapto-1-oxopropyl)cyclohexanecarboxylic acid (1.1 g), m.p. . 82.5-84.5°.

Example 7

trans-2-[3-(acetylthio)-2-methyl-1-oxopropyl]cyclohexanecarboxylic acid (isomer A)

a) trans-1, 2-cyclohexanedicarboxylic acid monomethyl ester

A mixture of 53.3 g (0.346 mol) of trans-1,2-cyclohexanedicarboxylic anhydride and 75 ml of methanol is heated under reflux for 2 hours. After cooling, the methanol is removed in a vacuum. The residue is treated with hexane, and crystalline material is precipitated. This is collected and washed with more hexane to give 58.2 g (90%) of trans-1,2-cyclohexane-dicarboxylic acid monomethyl ester, m.p. 93-97° [cf. J. Amer. Chem. Soc. 72, 4406 (1950)].

b) trans-2-(hydroxymethyl)cyclohexanecarboxylic acid methyl ester

A solution of 18.6 g (0.1 mol) of the acid ester from part a in 50 ml of dry tetrahydrofuran under nitrogen is treated dropwise over a period of 1 hour with 100 ml of 1M borane solution (in tetrahydrofuran) while maintaining the temperature at 20-30° with occasional cooling. After the addition is complete, the mixture is stirred at room temperature for 1 hour. Water is added drop by drop to break down any excess borane. The solvent is removed in vacuo. Water is added to the residue and the product, trans-2-(hydroxymethyl)-cyclohexanecarboxylic acid methyl ester, is extracted into ether.

After drying and removal of solvent, it remains

16.8 g (98%) product as an oil.

c) trans-2-formylcyclohexanecarboxylic acid methyl ester

Chromium trioxide (60 g, 0.6 mol) is added to a mech

stirred, cooled solution of 95 g (1.2 mol) pyridine in 1.5 liters of methylene chloride. The mixture is stirred at room temperature for 2Q minutes. A solution of 16.8 g (0.098 mol) of the product from part b in 100 ml of methylene chloride is added. The mixture is stirred at room temperature for 20 minutes. The solution is decanted from the dark, rubbery material on the side of the flask. A small amount of methylene chloride is used for washing. The solvent is removed from the decanted solution in vacuo. Ether is added to the residue. Chromium salts are removed by filtration through diatomaceous earth. The solvent is removed in vacuo to give 15.2 g (91%) of trans-2-formylcyclohexanecarboxylic acid methyl ester as a reddish oil.

d) trans-2-(1-hydroxy-2-methyl-2-propeny1)cyclohexan-carboxylic acid

The Grignard reagent of 2-bromopropene is prepared in tetrahydrofuran using 2.19 g (0.09 mol) of magnesium and 12.1 g (0.1 mol) of 2-bromopropene. This is added drop by drop over the course of 35 minutes to a cooled. (0-5°) stirred solution of 15.2 g

(0.09 mole) of the crude aldehyde from part c in 12 5 ml of tetrahydrofuran. Stirring and cooling are continued for 15 minutes after the addition is complete. Saturated, aqueous ammonium chloride solution 100 ml) is then added dropwise. The layers are separated, and the aqueous part is extracted again with ether. The combined organic layers are washed with saturated saline twice, dried and the solvent removed in vacuo to leave 12.8 g (79%) oil which is chromatographed on 450 g silica gel eluting with benzene and 20% chloroform in benzene. Fractions appearing pure by thin layer chromatography are pooled to give 7.2 g of oily addition product.

The above oil (5.2 g, 29 mmol) and 29 mL of 1N sodium hydroxide are heated under reflux under nitrogen for 90 minutes. After cooling, the solution is extracted twice with ethyl acetate to remove any neutral material. The aqueous layer is acidified with cold 10% potassium bisulphate solution while under a layer of ethyl acetate. The layers are separated, and the aqueous part is extracted twice more with ethyl acetate.

The combined organic layers are dried, filtered and freed of solvent in vacuo to leave 5.5 g (96%) of the essentially crystalline product trans-2-(1-hydroxy-2-methyl-2-propenyl)cyclohexane -carboxylic acid. The material is used immediately.

e) trans-2-(1-hydroxy-2-methyl-2- propenyl)cyclohexane-carboxylic acid dipheny Ime ty lester

The olefinic hydroxy acid from part d (5.5 g, 27.7 mmol) is partially dissolved in 100 mL of ethyl acetate. While stirring under nitrogen, diphenyl-diazomethane (5.4 g, 27.7 mmol) is added portionwise over a period of 30 minutes. The mixture is stirred overnight at room temperature. The solution is washed twice with saturated sodium bicarbonate solution, dried and desolvated in vacuo to give the crude ester, trans-2-(1-hydroxy-2-methyl-2-propenyl)cyclohexanecarboxylic acid diphenyl methyl ester, as a reddish oil, 9.8 g (97%).

f) trans-2-(2-methyl-1-oxo-2-propenyl)cyclohexane-carboxylic acid diphenylmethyl ester

Chromium trioxide (24 g, 240 mmol) is added to a cooled, stirred solution of 38 g (480 mmol) of pyridine in 600 ml of methylene chloride. The mixture is stirred at room temperature for 20 minutes. A solution of 9.8 g (27 mmol) of the ester from part e in a small amount of methylene chloride is added and stirring is continued for 20 minutes. The solution is then decanted from the dark, gummy residue. A small amount of methylene chloride is used to wash the residue and mixed with the original, decanted solution. This is brought to dryness in a vacuum. Ether is added, and filtration is carried out through diatomaceous earth to remove chromium salts. The solvent is removed in vacuo to leave 8.4 g of partially crystalline product, trans-2-(1-oxo-2-methyl-2-propenyl)-cyclohexanecarboxylic acid diphenyl methyl ester, which is recrystallized from hexane (150 mL) to give 4, 5 g (46%), m.p. 90-95°.

Some of this (0.5 g) is recrystallized from hexane to

give an analytical sample (450 mg), m.p. 92-94°.

g) trans- 2-[ 3-( acetylthio)- 2- methyl- l- oxopropyl] cyclohexane-carboxylic acid di- phenyl Ime ty ester

The crystalline material from part f (4.0 g, 11 mmol) is dissolved in 40 mL of methylene chloride. Thiolacetic acid (4.5 ml) is added, and the solution is stirred at room temperature for 2 hours. The solvent is removed in vacuo to leave an oil. This is dissolved in benzene and chromatographed on 250 g of silica gel. After elution of trace amounts of impurities with benzene and benzene-chloroform (1:1), the product, trans-2-[3-(acetylthio.)-2-methyl-1-oxopropyl] cyclohexanecarboxylic acid ddphenylmethyl ester, 4.7 g ( 97%) as an oil.

h) trans-2-[3-(acetylthio)-2-methyl-1-oxopropyl]-cyclohexanecarboxylic acid (isomer A)

The chromatographed compound from part g (4.7 g, 10.7 mmol) and anisole (21.6 g, 200 mmol) are cooled to 0° under nitrogen. Trifluoroacetic acid (60 ml) is added dropwise over a period of 60 minutes while stirring and cooling. After cooling for a further 60 minutes, the trifluoroacetic acid is removed in vacuo.

Ether is added and the product is extracted 3 times into a saturated sodium bicarbonate solution. The combined aqueous layer is washed twice with ether and then acidified with hydrochloric acid. The product is extracted into ether, dried and brought to dryness in vacuo to leave 3.0 g of oil. NMR of this material shows two sharp peaks for S-acetylmethyl groups, indicating a mixture of isomers. This is crystallized from isopropyl ether/hexane to give 1.3 g of material enriched in trans-2-[3-(acetylthio)-2-methyl-1-oxopropyl]cyclohexanecarboxylic acid, isomer A.. The mother liquor is brought to dryness to give 1.1 g of oil which is highly enriched in isomer B and is used in Example 9. The crystalline material is recrystallized from isopropyl ether-hexane to give 700 mg (24%) of trans-2-[3-(acetylthio)-2-methyl- 1-oxopropyl]-cyclohexanecarboxylic acid, whose NMR indicates that it is a single isomer (A), m.p. 103-108°.

Example 8

trans- 2-( 3- mercapto- 2- methyl1- 1- oxopropyl1) cyclohexanecarboxylic acid (isomer A)

The crystalline trans-2-[3-(acetylthio)-2-methyl-1-oxopropyl]cyclohexanecarboxylic acid, isomer A from part h, Example 7

(680 mg, 2.5 mmol) is added to a cold mixture of 1.5 ml conc. ammonium hydroxide and 1.5 ml of water under argon. The mixture is stirred at room temperature for 30 minutes, then cooled and acidified with hydrochloric acid. The product is extracted into ethyl acetate, dried and freed from solvent in vacuo to leave a yellow oil which crystallizes on standing. This material is dissolved in chloroform and chromatographed on 15 g of silica gel. The product is eluted with 2% methanol in chloroform. Fractions which give a strong sulfhydryl positive test with sodium nitroprusside spray and appear pure by thin layer chromatography (silica gel, developed with ethyl acetate) are collected and freed of solvent in vacuo to give 500 mg of crystalline trans-2-(3-mercapto- 2-Methyl-1-oxopropyl)cyclohexanecarboxylic acid which is recrystallized from isopropyl ether (^3 mL)

to give 230 mg (40%) of very dense, white, crystalline material, m.p. 87-90°.

Example 9

trans- 2-( 3- mercapto- 2- methyl- l- oxopropyl) cyclohexanecarboxylic acid

(isomer B)

The mother liquor from the first crystallization of trans-2-[3-(acetylthio)-2-methyl-1-oxopropyl]cyclohexanecarboxylic acid in Example 7 is brought to dryness and found by NMR to be almost pure isomer B. This oil (900 mg, 3f3 mmol) is treated with a cold mixture of 2 ml of concentrated ammonium hydroxide and 2 ml of water in an argon atmosphere. After stirring for 30 minutes at room temperature, the mixture is washed once with ether. The aqueous layer is cooled and acidified with hydrochloric acid. The product is extracted into ethyl acetate, dried and freed from solvent in vacuo to leave 0.65 g of material which is mainly crystalline. This is dissolved in chloroform and chromatographed on 20 g of silica gel. The product is eluted with 2% methanol in chloroform. Fractions appearing pure by TLC (silica gel, EtOAc or 10% MeOH in CHClg, detected by sodium nitroprusside spray) are collected to give 550 mg (^72%) of crystalline material. Recrystallization from ^2 ml of isopropyl ether gives 165 ml (22%) of fluffy, white, crystalline trans-2-(3-mercapto-2-methyl-1-oxopropyl)cyclohexanecarboxylic acid, m.p. 91-93°.

Example 10

cis- 2-( 3- mercapto- 3- methyl1- 1- oxobuty1) cyclopentane- carboxylic acid

A solution of 600 mg (3.06 mmol) of crude cis-2-(3-methyl-1-oxo-2-propeny1)cyclopentanecarboxylic acid in 5 ml of chloroform is treated with 1 ml of thiolacetic acid and allowed to stand at room temperature for 64 hours. The solution is concentrated in vacuo to an oil which is taken up in chloroform, applied to a silica gel column and eluted with chloroform (50 ml fractions are collected). Fractions 8 and 9 yield 437 mg (50%) of cis-2-(3-acetylthio-3-methyl-1-oxobutyl)cyclopentanecarboxylic acid as an oil.

The oil is stirred for 30 minutes at room temperature in a mixture of 1 ml each of water and concentrated ammonium hydroxide. The solution is cooled, acidified with dilute hydrochloric acid and carefully extracted with ethyl acetate. The combined extracts are dried and concentrated in vacuo to 277 mg (74%) oil. The oil is taken up in chloroform and applied to a preparative TLC plate (silica gel, 20 x 20 cm, 2 mm, 5% MeOH/CHClg). The major band (Rf = 0.4) is extracted with hot ethyl acetate to give 140 mg of oil. The oil is taken up in 5 ml of ether and treated with 0.2 ml of dicyclohexylamine to give 73 mg of dicyclohexylamine salt, m.p. 127-130°.

The dicyclohexylamine salt is converted to the free acid by treatment with 10% aqueous potassium bisulfate and extracted with ethyl acetate to give 31 mg of low-melting, solid cis-2-(3-mercapto-,3-methyl-1-oxobutyl)cyclopentanecarboxylic acid.

The potassium salt is obtained by treating the oil with potassium hydroxide solution and lyophilization.

Example 11

trans- 2-[ 3-( acetylthio)- 1- oxopropyl 3 cyclopentan- carboxylic acid

a) trans-2-formylcyclopentanecarboxylic acid methyl ester A solution of 25 g (83.3 mmol) trans-2-dibromomethyl-1-cyclopentanecarboxylic acid methyl ester [prepared as described in Chem. Pray. 110, 1823 (1977), from the cyclopentene and the dibromoketene] i

140 ml of tetrahydrofuran are heated under reflux in a nitrogen atmosphere. While stirring, a solution of 33.0 g (19 4 mmol) of silver nitrate in 55 ml of water is added over a period of 10 minutes. After a further 30 minutes of heating and stirring, the mixture is cooled, and saturated aqueous sodium chloride solution is added. The mixture is then neutralized with saturated aqueous sodium carbonate solution and the insoluble salts are removed by filtration through a "Celite" (diatomaceous earth) pad. The pad is washed with ether, and some solid sodium chloride is added to the filtrate. The layers are separated, and the aqueous part is extracted again twice with ether. The combined organic layers are dried over magnesium sulfate, filtered and brought to dryness in vacuo to leave 7.5 g of amber oil. This is distilled under reduced pressure to give 4.1 g (32%) of product, trans-2-formyl cyclopentanecarboxylic acid methyl ester, boiling at 60-85°/0.4 mm; b) trans- 2-( l- hydroxy- 2- propeny1) cyclopene tankcarboxylic acid •

The Grignard reagent of vinyl bromide is prepared in tetrahydrofuran using 0.39 g (16 mmol) of magnesium and 2.5 g of vinyl bromide. This is added dropwise over 30 minutes to a cooled (0-5°), stirred solution of 2.5 g (16 mmol) of distilled aldehyde from part a in 20 ml of tetrahydrofuran. Stirring and cooling are continued for 15 minutes after the addition is complete. Saturated aqueous ammonium chloride solution (20 mL) is then added dropwise. The layers are separated, and the aqueous layer is extracted again with ether.

The combined organic layers are washed twice with saturated sodium chloride solution, dried, and the solvent removed in vacuo to leave 2.3 g of trans-2-(1-hydroxy-2-propenyl)cyclopentanecarboxylic acid as a yellow oil.

The oil containing a small amount of the corresponding lactone is added to 18 ml of 1N sodium hydroxide and heated under reflux in a. nitrogen atmosphere for 1.5 hours. After cooling, the solution is extracted twice with ethyl acetate to remove any neutral material. The aqueous layer is acidified with cold 10% potassium bisulphate solution. The product is extracted in ethyl acetate, dried and freed from solvent to leave 2.0 g (73%) of product.

c) trans-2-(1-hydroxy-2-propenyl) cyclopentane-carboxylic acid redi f en y Ime ty le ter

The material obtained in part b (2.0 g, 11.7 mmol) is dissolved

in 50 ml of ethyl acetate. While stirring under nitrogen, diphenyldiazomethane (2.2 g, °» 11.5 mmol) is added in several portions over a period of 30 minutes. The mixture is stirred overnight at room temperature. The solution is washed twice with saturated sodium bicarbonate solution, dried and desolvated in vacuo to leave 3.65 g of a reddish viscous oil. The oil is dissolved in chloroform and chromatographed on a 100 g silica gel column using chloroform as eluent. Fractions appearing pure by TLC are collected and brought to dryness in vacuo to leave 1.35 g (35%) of trans-2-(1-hydroxy-2-propenyl)cyclopentanecarboxylic acid diphenylmethyl ester as an oil.

d) trans-2-(1-oxo-2-propenyl) cyclopentanecarboxylic acid diphenyl methyl ester

The oil obtained in part d (1.35 g, 4.0 mmol) is dissolved in 60 ml of methylene chloride, and 13 g of activated manganese dioxide is added, and the mixture is stirred overnight under argon. The manganese dioxide is removed by filtration. The filtrate is brought to dryness and gives 1.0 g of yellow oil. This is chromatographed on 25 g of silica gel using benzene as eluent. Fractions which appear almost pure by TLC are combined and brought to dryness in vacuo to give 0.7 g (52%) of trans-2-(1-oxo-2-propenyl)cyclopentanecarboxylic acid diphenyl methyl ester as a yellow oil .

e) trans- 2-[ 3-( acetylthio)- 1- oxopropyl] cyclopentanecarboxylic acid diphenyl methyl ester

The oil obtained in part d (0.7 g, 2.1 mmol) is dissolved in 10 ml of chloroform, and 0.7 ml of thiolacetic acid is added. After stirring for 1 hour at room temperature, the mixture is brought to dryness in vacuo to give 0.8 g of pale yellow oil. This is chromatographed on 25 g of silica gel using benzene as eluent. Fractions that appear to be pure. by TLC, collected and brought to dryness in vacuo to give 625 mg (72%) of trans-2-[3-(acetylthio)-1-oxopropyl] cyclopentane carboxylic acid diphenyl methyl ester as an oil.

f) trans- 2-[ 3-( acetylthio)- 1- oxopropyl] cyclopentanecarboxylic acid

The oil obtained in part e (625 mg, 1.5 mmol) in 3.25 g

(30 mmol) of anisole is stirred and cooled (0-5°) in a nitrogen atmosphere, and 10 ml of trifluoroacetic acid is added dropwise over a period of 40 minutes. After the addition is complete, the mixture is stirred under cooling for a further 60 minutes. The trifluoroacetic acid is removed in vacuo. The residue is dissolved in ether and extracted three times with saturated sodium bicarbonate solution. The combined aqueous layers are washed twice with ether to remove any neutral material. The aqueous portion is then acidified with hydrochloric acid and extracted three times with ether. These ether extracts are dried (MgSO4), filtered, and the solvent is removed in vacuo to

give 400 mg (quantitative) of trans-2-[3-(acetylthio)-1-oxopropyl]-cyclopentanecarboxylic acid as a yellow oil. TLC (silica gel,

10% MeOK in CHClg, I2) shows a main spot at Rf = 0.55.

Example 12

trans-2-(3-mercaptol-ol-oxopropyl)cyclopentane-carboxylic acid

A cold, argon-saturated mixture of 1 ml of concentrated ammonium hydroxide and 1 ml of water is added to trans-2-[3-(acetylthio)-1-oxopropyl]cyclopentanecarboxylic acid (1.5 mmol) which is stirred at room temperature for 30 minutes, cooled and then acidified with concentrated hydrochloric acid. The mixture is extracted three times with ethyl acetate. The combined ethyl acetate extracts are dried, filtered,

0<3 the solvent is removed in vacuo to give 350 mg which is dissolved in chloroform and spread as spots on a 20 x 20 cm preparative silica gel plate. The plate is developed in 10% methanol in chloroform.

When detecting with UV, the band corresponding to a spot that gives a positive SH test on an analytical plate is removed and eluted with hot ethyl acetate. The ethyl acetate solution is washed twice with water, dried and brought to dryness in vacuo to give 135.7 mg (45%) of trans-2-(3-mercapto-1-oxopropyl)cyclopentanecarboxylic acid as a yellow oil.

This oil (0.67 mmol) is dissolved in a small amount of isopropyl ether and converted to the dicyclohexylamine salt by adding a small excess of dicyclohexylamine. Crystalline material (202 mg) is collected and recrystallized from isopropyl ether to give trans-2-

(3-Mercapto-1-oxopropyl)cyclopentanecarboxylic acid-dicyclohexy1-amine salt (171 mg, 67%), m.p. 126-128°.

The main amount of the salt (150 mg, 0.39 mmol) is converted back to the free acid with 10% potassium bisulphate solution. The acid is extracted into ethyl acetate, dried and freed from solvent in vacuo to give 74.4 mg of the acid (94%) as an oil.

TLC (silica gel, 10% MeOH in CHClg, detected with SH spray and I2),

large main spot (SH positive) R f = 0.41.

Example 13

Cis- 2-[ 3-( acetylthio)- 1- oxopropyl] cyclobutane- carboxylic acid

a) cis-2-[l-oxo-2-propenyl] cyclobutane-carboxylic acid

A mixture of aluminum chloride (66.7 g, 0.5 M),

1,2-Cyclobutanedicarboxylic anhydride (31.5 g, 0.24M) and 1,2-dichloroethane (1 L) in a 2 L three-necked flask equipped with a gas inlet tube, mechanical stirrer, and drying tube are stirred rapidly, and ethylene is bubbled into 4.5 hours. This mixture is poured into 900 ml of 5% hydrochloric acid and ice. The layers are separated, and the organic layer is washed with water and brought to dryness in vacuo. The aqueous layer is extracted with ether (300 ml). The extract is washed with water and mixed with material from the original organic layer and brought to dryness. The residue is heated with 150 ml of 10% potassium carbonate on a steam bath for 15 minutes. After cooling, the mixture is extracted three times with ether. The aqueous portion is acidified, and the product (1.5 g) is extracted into ether. The original ether extracts are collected and extracted with 150 ml of 10% potassium carbonate solution. This aqueous layer is then acidified with hydrochloric acid and the product, cis-2-[1-oxo-2-propenyl] cyclobutancarboxylic acid (24.3 g) is extracted into ether. Both samples (25.8 g, 67%) crystallize on standing.

b) cis-2-[3-(acetylthio)-1-oxopropyl] cyclobutane carboxylic acid

The raw. acid obtained in part a (24.3 g, 0.16 M) is dissolved in

100 ml of chloroform. The solution is cooled in an ice bath, and 15 ml of 0.21 M) thiolacetic acid is added dropwise over a period of 20 minutes. After stirring for 1 hour at room temperature, the mixture is brought to dryness in vacuo to give a viscous oil (36 g). This is dissolved in chloroform and chromatographed on 450 g of silica gel

to give a material which crystallizes on trituration with hexane.

The crystalline material (10.6 g, 29%) is recrystallized from isopropyl ether to give cis-2-[3-(acetylthio)-1-oxopropyl]cyclobutanecarboxylic acid, 6.6 g, m.p. 50-54°.

Example 14

cis-2-(3-mercaptol-1-oxopropyl)cyclobutanecarboxylic acid

cis-2-[3-(acetylthio)-1-oxopropyl]cyclobutanecarboxylic acid (2.5 g, 10.9 mmol) is added to a cold mixture of 5 ml of concentrated ammonium hydroxide and 5 ml of water in an argon atmosphere. The solution is stirred at room temperature for 30 minutes. On cooling, the mixture is acidified with hydrochloric acid, and the product is extracted into ethyl acetate, dried and freed from solvent in vacuo to give 2.1 g of oil. This is chromatographed on 50 g of silica gel eluting with chloroform and 2% methanol in chloroform. The oil obtained (pure by TLC, silica gel, 10% methanol in chloroform - Rf = 0.43) (1.35 g, 66%) is dissolved in ether and converted into cis-2-(3-mercapto-1-oxopropyl) -cyclobutanecarboxylic acid-dicyclohexylamine salt, by adding a small excess of dicyclohexylamine. The white solid is recrystallized from ethyl acetate to give 2.0 g, m.p. 129-132°.

The salt is converted to the free acid with 10% potassium bisulphate solution and extracted into ethyl acetate to give 0.95 g of cis-2-(3-mercapto-1-oxopropyl)cyclobutanecarboxylic acid as an oil.

Example 15

trans-2-(3-mercaptol-ol-oxopropyl)cyclobutane-carboxylic acid

A solution of 460 mg (2 mmol) of cis-2-[3-(acetylthio)-1-oxopropyl]cyclobutanecarboxylic acid in 10 ml of methanol is cooled to 0° in an argon atmosphere, and 324 mg (6 mmol) of sodium methoxide is added. The mixture is stirred at 0° for 2 hours and then acidified with 2N hydrochloric acid. The methanol is removed in vacuo. Water is added,

and the product is extracted into ethyl acetate to give 320 mg of an oil. This is purified on a preparative TLC plate (silica gel, developed with 10% MeOH in CHClg). The band containing the product is scraped off and eluted with ethyl acetate to give 150 mg of oil (40%). This oil is dissolved in ether and converted to the dicyclohexylamine salt by adding a small excess of dicyclohexylamine. The white solid is recrystallized from ethyl acetate to give 250 mg of trans-2-(3-mercapto-1-oxopropyl)cyclobutanecarboxylic acid-dicyclohexylamine salt, m.p. 140-144°.

The salt is converted to the free acid with a 10% potassium bisulphate solution. The acid is extracted into ethyl acetate, dried and freed from solvent to give trans-2-(3-mercapto-1-oxopropyl)cyclobutanecarboxylic acid as an oil (120 mg) which is dissolved in water containing a few drops of ethanol and lyophilized.

The sodium salt is obtained from the oil by adding an equivalent amount of sodium hydroxide solution, and then lyophilization.

Example 16

6-(acetylthio)-4-oxohexanoic acid

a) ' 4-oxo-5-hexenoic acid

[cf. J. Chem. Soc, 3922 (1958)]. A mixture of

aluminum chloride (66.7 g, 0.5 M), succinic anhydride (25 g, 0.25 M)

And 1,2-dichloroethane (1 liter) in a 2 liter three-necked flask equipped with gas inlet tube, mechanical stirrer and drying tube, stirred rapidly,

and ethylene is bubbled in for 4.5 hours. The mixture is poured into 900 ml

5% hydrochloric acid and ice. The layers are separated, and the organic layer

washed with water and brought to dryness in vacuo. The aqueous layer is extracted with ether (300 ml). This extract is washed with water and mixed with material from the original organic layer. After removing the solvent, 150 ml of 10% potassium carbonate solution is added, and the mixture is heated on a steam cone in

15 minutes. After cooling, the product, 4-oxo-5-hexenoic acid, is extracted into ether, dried and freed from solvent in vacuo to give 10.9 g (34%) of a brownish liquid which solidifies on standing. This is distilled to give 7.1 g (22%) colorless liquid

which hardens on standing, b.p.^J_20-130°/0.5 mm.

b) 6-(acetylthio)-4-oxohexanoic acid

The distilled 4-oxo-5-hexenoic acid (6.8 g, 58 mmol) is dissolved in 30 ml of methylene chloride. Thiolacetic acid (4.0 g, 65 mmol) is added dropwise. After stirring at room temperature for 45 minutes, a very small amount of insoluble material is removed by filtration. The solvent is removed in vacuo to give 9.9 g (84%) of an off-white solid. Petroleum ether is added, and crystalline material is collected by filtration. This is recrystallized from benzene to give 6-(acetylthio)-4-oxohexanoic acid, 6.2 g (52%), m.p. 72-74°.

Example 17

6- mercapto- 4- ox or hex an acid

6-(acetylthio)-4-oxohexanoic acid (3.5 g, 17 mmol) is added to a cold solution of 5 ml of concentrated ammonium hydroxide and 5 ml of water under argon. The solution is stirred at room temperature for 30 minutes. While cooling in an ice bath, the mixture is acidified with concentrated hydrochloric acid. The mixture is continuously extracted with ethyl acetate for 24 hours to give a total of 3.6 g of extracted material, mainly oil but containing some crystalline material. Trituration with ether gives 240 mg of solid material.

The ether-soluble part of the ethyl acetate extract is brought to dryness and chromatographed on 90 g of silica gel using chloroform as eluent. The resulting crystalline material (1.6 g, 58%) is recrystallized from ether-hexane to give 6-mercapto-4-oxohexanoic acid, 850 g (31%), m.p. 40-42°.

The sodium salt is formed as in example 15.

Example 18

trans- 2-(mercaptoacety1)cyclohexanecarboxylic acid

a) trans-1,2-cyclohexanedicarboxylic acid monomethyl ester is prepared as described in example 7a. It is converted to the acid chloride by dissolving 7.4 g (40 mmol) in 100 ml of ether and treating with 4 ml of oxalyl chloride and a few drops of dimethylformamide. The solution is stirred for 90 minutes at room temperature, and the solvent is removed in vacuo without heating. The acid chloride is dissolved in 200 ml of ether, cooled in an ice bath and treated with an ether solution of diazomethane (prepared from 20 g of N-methyl-N<1->nitro-N-nitrosoguanidine). The solution is stirred with cooling for 2 hours, and 1 hour and 15 minutes at room temperature. A very small amount of insoluble material is removed by filtration. The filtrate is washed once with saturated sodium bicarbonate solution and once with saturated sodium chloride solution, dried and freed of solvent in vacuo to give 7.4 g (88%) of material which solidifies on standing. b) The diazomethyl ketone obtained in part a (7.4 g, 35.2 mmol) is dissolved in 70 ml of chloroform and 10.5 ml of thiolacetic acid. After standing for 4 days at room temperature, the solvent is removed in vacuo to give 9.1 g of yellow oil. The material is dissolved in benzene and chromatographed on 200 g of silica gel. After removing the impurities with benzene and mixtures of benzene and chloroform, the desired 2-(acetylthio)cyclohexanecarboxylic acid is eluted with chloroform. Fractions that appear pure by TLC are pooled for

to give 2.15 g (24%) of material as an oil. Another mixture of fractions (2.5 g) contaminated with a significant amount of a slower moving material is set aside.

c) Chromatographed S-acetyl compound from part b (2.6 g,

10 mmol) is treated with 50 ml IN sodium hydroxide which is saturated with

argon, and the mixture is stirred overnight under argon. After extracting twice with ether to remove any non-acidic material, the aqueous solution is cooled and acidified with hydrochloric acid. The product is extracted into ethyl acetate, dried and freed from solvent in vacuo to give 2.1 g of yellow oil. The oil is dissolved in chloroform and chromatographed on 60 g of silica gel eluting with chloroform. Fractions that give a strong positive reaction with SH spray are examined by TLC, and those fractions that appear pure are pooled and brought to dryness to give 900 mg (44%) of crystalline material. This is recrystallized from isopropyl ether with charcoal decolorization to give trans-2-(mercaptoacetyl)cyclohexanecarboxylic acid, 618 mg (30%), shrink at 102°, m.p. 112-117°.

Example 19

( trans)- 2, 2'--[ dithiobis( l- oxo- 3, 1- propanediy1)] bis- cyclohexanecarboxylic acid

3.0 g (13.89 mmol) of trans-2-(3-mercapto-1-oxopropyl)-cyclohexanecarboxylic acid is partially dissolved in a mixture of 15 ml of 1N sodium hydroxide and 100 ml of water. 0.5 µM iodine in absolute ethanol is added dropwise to this quickly stirred mixture (almost all solids in solution). During the addition, the pH of the reaction mixture is kept at 5.5-6.5 by dropwise addition of 1N sodium hydroxide. The solution is stirred for 15 minutes at room temperature, traces of excess iodine are removed with aqueous sodium thiosulphate, the mixture is acidified with concentrated hydrochloric acid and extracted carefully with ethyl acetate. The combined extracts are dried and concentrated in vacuo to give 2.1 g (70%) of crude (trans)-2,21-[dithiobis-(1-oxo-3,1-propanediy1)]biscyclohexanecarboxylic acid. The oil is taken up in 25 ml of ether, treated with 3 ml of dicyclohexylamine and allowed to stand overnight at low temperature to give 3.3 g (85% conversion) of

bisdicyclohexylaminesa.lt. Recrystallization from ethyl acetate/methanol gives the analytical sample (2.9 g), m.p. 167-170°.

The dicyclohexylamine salt is converted to (trans)-2,2<1->

[dithiobis(1-oxo-3,1-propanediy1)]bis-cyclohexanecarboxylic acid by treatment with 10% aqueous potassium bisulphate and extraction with ether.

Example 20

( trans)- 2, 2'-[ dithiobis( 1- oxoethyl)] biscyclohexane- carboxylic acid

By using trans-2-(mercaptoacetyl)cyclohexanecarboxylic acid instead of trans-2-(3-mercapto-1-oxopropyl)cyclohexanecarboxylic acid in the method according to example 19, (trans)-2,2'-[dithiobis(1- oxoethyl)]bis-cyclohexanecarboxylic acid.

Claims (3)

1. Procedure for preparing a compound of the formula: where R 1 , R 2 , R 8 and R 1 are each hydrogen or lower alkyl; Rj. is hydrogen, lower alkanoyl, benzoyl or A and B are each hydrogen or are bonded together to complete a cycloalkyl ring; and m is 0 or 1; and salts thereof, characterized by (a) when m is 1, a compound reacts with the formula or (b) when m is 0, a compound of the formula is reacted with a thiol of the formula R' SH where Rn<1> is lower alkanoyl or benzoyl, to form a product where R,- is lower alkanoyl or benzoyl, and optionally treating the product formed with ammonia or sodium hydroxide to form a product where R^ is hydrogen, and optionally this product is treated with an alcoholic solution of iodine to form a product where R, is 2. Method as stated in claim la), characterized in that a starting material is used in which each of R^ , R2 , Rg and R^ is hydrogen, A and B are bonded together to complete a cyclohexane ring, and R. is converted to 3. Method as stated in claim 1b), characterized in that a starting material is used where R 1 and R 2 are hydrogen, A and B are bound together to complete a cyclohexane ring, and R 2 is converted to hydrogen.