8-Methyl-7-substituted-1,6-naphthyridine-3-carboxylic Acids as New 6-Desfluoroquinolone Antibacterials

1,6-Naphthyridine-8-methyl-7-substituted-3-carboxylic acids were synthesized as new 6-desfluoro-quinolone antibacterials in which the usual fluorine atom at C-6 position was replaced by an endocyclic nitrogen atom. Comparing the antibacterial activity of these 6-azaquinolones with our previous 6-amino and 6-hydrogen counterparts, they resulted always less active. However, the presence of methyl group at C-8 position ensure good Gram- positive antibacterial activity, with minimum inhibitory concentrations values on the same order of ciprofloxacin for piperidinyl derivative 3d and tetrahydroisoquinolinyl derivative 3c.