Retention of stereochemistry in the ring-opening of penicillin V sulphone p-nitrobenzyl ester

Abstract

By careful control of the basic catalyst, the solvent, and the temperature, p-nitrobenzyl phenoxymethylpenicillinate 1,1-dioxide (penicillin V sulphone p-nitrobenzyl ester)(1d) can be converted into (2R,3R)-1-[2-methyl-(p-nitrobenzyloxycarbonyl)prop-1-enyl]-4-oxo-3-phenoxyacetamidoazetidine-2-sulphinic acid (3) with almost complete retention of stereochemistry at C-5 and C-6 of the starting ester (1d). The sulphinic acid (3) is unstable, but its sodium salt is readily methylated by iodomethane to afford the stable crystalline sulphone (6).