Synthesis and spectroscopic properties of novel polyfunctionally substituted 2,6- and 2,7-naphthyridines

Series of 5,6-dihydro-8-hydroxy-5-oxo-2,6-naphthyridine-7-carboxylic acid derivatives (2,4) and the isomeric 7,8-dihydro-5-hydroxy-8-oxo-2,7-naphthyridine-6-carboxylic acid derivatives (3,5) having potential pharmacological activity were synthesized from 3,4-pyridinedicarboxylic acid derivatives. Spectroscopic data (IR, 1H- and 13C-NMR, MS) are analyzed and support the enol–lactam structure of compounds 2–5 in solution, solid state and gas phase. Results in the different series (2,6- vs 2,7- naphthyridines and N-unsubstituted lactam vs N-methyl derivatives) are compared, and common and differential features amongst them are indicated.