NEW MATERIAL:A compound shown by the formula I (R1 is lower alkyl; R2 is H, or lower alkyl; Y is 5- - 6-membered heterocyclic ring; n is 0-2) and its salt. EXAMPLE:7beta-[2-( 2-Aminothiazol-4-yl )-2-methoxyiminoacetamido]-3-[4-(imidazol-1- yl)pyridinio]methyl-3-cephem-4-carboxylate.trihydrochloride(syn-isomer). USE:An antibacterial agent against Gram-positive and Gram-negative bacteria including Peudomonas aeruginosa. PREPARATION:A compound shown by the formula II (R3 is lower alkyl) or its salt is reacted with a compound shown by the formula III in the presence of an inorganic salt such as sodium iodide, etc. or an organic salt such as sodium p- toluenesulfonate, etc. in the minimum amount of water or water-containing solvent under heating, so that the acyloxyl group at the 3-position of cephem ring of the compound shown by the formula II is converted to a substituted pyridino group.
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