Synthesis and antibacterial activities of 2-oxaisocephems

A series of 2-oxaisocephems with a thio-substituted methyl group at the 3-position and a 2-aminothiazol-4-yl moiety at the 7-position was synthesized via benzyl 3-acetyloxymethyl-7-azido-8- oxo-1-aza-4-oxabicyclo[4.2.0]oct-2-ene-2-carboxylate (2), derived from benzyl acetoacetate (1). The new 2-oxaisocephems were tested for antibacterial activities. Among them, the derivatives having a [2-(2-aminothiazol-4-yl)-2- (Z)-cyclopentyloxyimino]acetamido group at the 7-position characteristically showed potent activities against gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis as compared with cefuzonam and cefmenoxime, which are third-generation cephalosporins.