Premium
Sites of protonation in cardiotonic polyazaindolizines by NMR spectroscopy
Author(s) -
Barraclough Paul,
Firmin David,
Lindon John C.,
Nobbs Malcolm S.,
Sanderson Paul N.,
Smith Steven,
Gillam Janet M.
Publication year - 1991
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260290511
Subject(s) - chemistry , pyrazine , protonation , pyridazine , pyrimidine , nitrogen , aryl , nuclear magnetic resonance spectroscopy , medicinal chemistry , triazine , stereochemistry , organic chemistry , ion , alkyl
The p K a , values of six sulmazole analogues were measured spectrophotometrically. The major protonation sites for most of these bridgehead nitrogen heterocycles were determined by 1 H and 13 C NMR methods. The aryl‐substituted imidazo[1,2‐ a ]pyrimidine (4), 8‐methoxyimidazo[1,2‐ a ]pyrazine (6), imidazo[1,2‐ b ]pyridazine (9) and imidazo[1,2‐ b ][1,2,4]triazine (11) undergo protonation at the imidazo nitrogen. The imidazo[1,2‐ a ]pyrazine (5) protonates mainly at N‐7. In some cases differences in basicity properties between these aryl analogues and the bridgehead heterocycles have been observed.