A CONVENIENT SYNTHESIS OF OPTICALLY PURE (2R,3R)-2,3-EPOXYSUCCINYL-DIPEPTIDES

(2R,3R)-trans-Epoxysuccinyl-dipeptides (7a-7d) were synthesized by acy lation of dipeptides with the N-hydroxysuccinimide or pentafluoropheny l ester of monoethyl (2R,3R)-trans-epoxysuccinate (6a,6b). A nucleophi lic oxirane ring opening by N-hydroxysuccinimide and pentafluorophenol during the preparation of the active esters could not be observed. Su bsequent saponification of the monoethyl ester 7a-7d with KOH in ethan olic solution allowed to produce the dipeptide derivatives as potassiu m salts (8a,8d) which were found to be stable on storage in the cold. The attempts to convert (2R,3R)-trans-epoxysuccinyl-glycyl-proline (7a ) into the corresponding (2S,3S)-trans-epithiosuccinyl derivative via an oxygen sulfur exchange reaction with 3-methylbenzothiazole-2-thione failed completely as among the various products of unknown nature for med only the desulfurated fumaryl derivative could be isolated and cha racterized.