Synthesis of antimicrobial agents. IV. Synthesis and antimicrobial activities of imidazo[4,5-b][1,8]naphthyridine derivafives.

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Abstract
As part of a search for new antimicrobial agents, some 3,5-disubstituted 5,8-dihydro-8-oxoimidazo and triazolo[4,5-b][1,8]naphthyridine-7-carboxylic acids and related compounds which contain a new ring system were prepared. The reactions of 6-amino-7-alkylamino-1-ethyl-1,4-dihydro-4-oxo-1,8-naphthyridine derivatives with acid, acetic anhydride, ethyl orthoformate and ethylxanthate afforded several imidazo[4,5-b][1,8]naphthyridine derivatives. Treatment of the diamines with sodium nitrite gave the triazolo[4,5-b][1,8]naphthyridine derivatives. Reaction of the 7-acetylamino-4-hydroxy-1,8-naphthyridine-3-carboxylate with 1,2-bromochloroethane gave different products, depending upon the reaction conditions. 3-Methyl-5-vinyl-5,8-dihydro-8-oxoimidazo[4,5-b][1,8]naphthyridine-7-carboxylic acid was prepared by successive chloroethylation, nitration, chlorination, substitution with methylamine, reduction of the nitro group, imidazole cyclization and elimination of HCl with simultaneous hydrolysis of the ester group. Some compounds obtained in this work showed activity nearly equal to that of pipemidic acid but were slightly less active against Pseudomonas aeruginosa.