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New 2-methyl-1-oxacephem compounds having 2-(2-aminothiazol-4-yl)-2-(alkoxyimino)acetamido substituents at C-7 and various C-3 side chains were synthesized starting from (3R,4S)-phenyloxazolinoazetidinone (8). Introduction of the 2 beta-methyl group into the 1-oxacephem nucleus increased the stability to beta-lactamases. OCP-9-176 (7b) having the (1-methylpyridinium-4-yl)thiomethyl group at C-3 showed potent antibacterial activity and a broad spectrum.

The labile tert-butyldimethylsilyl esters of the azetidinones 6-8b served as the crucial synthons in the preparation of the potentially useful ylide pyridyl thio esters 18-20. These intermediates were utilized to synthesize a host of title carbapenems 25-30d, 32, and 49-53. The antimicrobial properties and DHP-I susceptibility of these carbapenems were studied with reference to thienamycin.