2-THIOALKYL PENEMS - AN EFFICIENT SYNTHESIS OF SULOPENEM, A (5R,6S)-6-(1(R)-HYDROXYETHYL)-2-[(CIS-1-OXO-3-THIOLANYL)THIO]-2-PENEM ANTIBACTERIAL

A practical synthesis of potent penem antibacterials, CP-70,429 (1) (sulopenem) and CP-81,054 (2), is described. (L)-Aspartic acid was utilized to generate both the (3S)- and (3R)-thiolanylthio side chains of (5R,6S)-6-(1-(R)-hydroxyethyl)-2-[(cis-1-oxo-3-thiolanyl)thio]-2-penem-3-carboxylic acids 1 and 2. This synthetic pathway provided in high yield enantiopure thioacetate intermediates 15 and 19. To accommodate the fragile side chain sulfoxide moiety of the targeted beta-lactams, standard penem synthetic methodology was modified to facilitate the conversion of 15 and 19 to 1 and 2. The reactive chloroazetidinone 4b was utilized to generate key azetidinone trithiocarbonate intermediate 22 which contains the requisite penem side chain. A chemoselective oxalofluoride-based azetidinone N-acylation procedure, which avoids sulfoxide O-acylation, was required for the conversion of 22 to the penem framework.