STUDIES ON CONDENSED-HETEROCYCLIC AZOLIUM CEPHALOSPORINS .2. SYNTHESIS AND ANTIBACTERIAL ACTIVITY OF 7-BETA-[2-(2-AMINOTHIAZOL-4-YL)-2(Z)-ALKOXYIMINOACETAMIDO]-3-(CONDENSED-HETEROCYCLIC AZOLIUM)METHYL-3-CEPHEM-4-CARBOXYLATES

From our series of studies on cephalosporins bearing condensed-heterocyclic azolium methyl groups at the 3 position in the cephalosporin nucleus, we describe here the synthesis and antibacterial activity of 7-beta-[2-(2-aminothiazol-4-yl)-2(Z)-alkoxyiminoacetamido]cephalosporins containing imidazo[1,5-a]pyridinium, imidazo[1,2-b]pyridazinium, imidazo[1,2-a]pyrimidinium, imidazo[1,2-c]pyrimidinium, and pyrazolo[1,5-a]pyridinium methyl groups at the 3 position. Among the cephalosporins tested, 7-beta-[2-(2-aminothiazol-4-yl)-2(Z)-methoxyiminoacetamido]-3(imidazo[1,5-a]pyridinium-2-yl) (1), (imidazo[1,2-b]pyridazinium-1-yl) (2), and (pyrazolo[1,5-a]-pyridinium-1-yl) (3)methyl-3-cephem-4-carboxylates showed potent antibacterial activity and broad antibacterial spectrum. The antibacterial activity of these cephalosporins (1 approximately 3) was superior to that of ceftazidime (CAZ). These results imply that the delocalization of the positive charge of the imidazo[1,5-a]pyridinium, pyrazolo[1,5-a]pyridinium and imidazo[1,2-b]pyridazinium groups leads to an expanded antibacterial spectrum and increased activity and that these condensed-heterocyclic compounds as well as imidazo[1,2-a]pyridine are effective moieties for improving antibacterial activity and spectrum.