Abstract
Condensation of 2-amino-6-chloropyridine (1) with diethyl ethoxymethylenemalonate gave the aminomethylenemalonate 2, which upon thermal cyclization (Gould-Jacobs reaction) afforded ethyl 7-chloro-1, 4-dihydro-4-oxo-1, 8-naphthyridine-3-carboxylate (3). Alkylation of 3 produced the 1-alkyl derivative 4. Substitution of 4 with a cyclic amine gave ethyl 7-substituted 1-alkyl-1, 4-dihydro-4-oxo-1, 8-naphthyridine-3-carboxylate (5). The ester 5 was hydrolyzed to the corresponding carboxylic acid 6. 7-Substituted 1-alkyl-1, 4-dihydro-4-oxo-1, 6-naphthyridine-3-carboxylic acids (20) were also synthesized from 4-amino-2-chloropyridine (13) in a similar manner. The in vitro antibacterial activity was enhanced by the presence of a cyclic amine at position 7 on 6 and 20. In general, the 1, 8-naphthyridine 6 was more active than the 1, 6-naphthyrdine counterpart 20. 1-Ethyl-1, 4-dihydro-4-oxo-7-(1-piperazinyl)-1, 8-naphthyridine-3-carboxylic acid (6e) (an analog of both pipemidic acid and nalidixic acid) was comparable to pipemidic acid but superior to nalidixic acid in terms of activity in vitro against Pseudomonas aeruginosa.
