Protonation equilibria of cardiotonic polyaza heterocycles
- 1 January 1988
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 10,p. 1839-1846
- https://doi.org/10.1039/p29880001839
Abstract
The pKa values of fifteen sulmazole analogues have been measured spectrophotometrically. The major protonation sites for most of these heterocycles were determined by 1H and 13C n.m.r. methods. Sulmazole (1), isomazole (7), 1H-imidazo[4,5-d] pyridazine (14), 1H-pyrrolo[2,3-c]pyridine (17), and 1H-pyrrolo[3,2-c]pyridine (18) underwent protonation at the pyridyl nitrogen. The purine (11) and 7H-imidazo[4,5-e]-1,2,4-triazine (16) were protonated mainly at N-1, and 1H-imidazo[4,5-c]pyridazine (13) at N-2. The benzimidazole (4) and 1H-imidazo[4,5-b]pyrazine (15) were protonated at the imidazole nitrogens. In some cases the various 1H- and 3H-tautomers were identified; their relative proportions were found to vary with the ring system.Keywords
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