DETERMINATION OF CONFIGURATION OF 4 D-BENZYLPENICILLOATES

The configuration of the 4 dimethyl D-benzylpenicilloates was determined and their stereochemical relationship to the dimethyl phthalimidopenicilloates, prepared according to Sheehan et al., was established, using a series of transformations and physicochemical techniques. The compounds designated as .beta. and .gamma. isomers in the Sheehan nomenclature corresponded to the .gamma. and .delta. isomers of "Chemistry of Penicillin" and had the 5R,6S and the 5S,6S configuration, respectively. In the course of this study, 5-epi-6-epibenzylpenicillin methyl ester having the 5S,6S configuration was prepared for the 1st time. The isomer with the 5S,6R configuration, which was consequently denoted as .delta. isomer, was prepared from 5-epibenzylpenicillin methyl ester and was identical with the .beta. isomer of "Chemistry of Penicillin". Sodium benzylpenicilloate .alpha. isomer, having the 5R,6R configuration of the natural penicillins, isomerized in aqueous solution to a mixture, containing mainly the .delta. isomer (5S,6R).