Sites of protonation in cardiotonic polyazaindolizines by NMR spectroscopy

✍ Scribed by Paul Barraclough; David Firmin; John C. Lindon; Malcolm S. Nobbs; Paul N. Sanderson; Steven Smith; Janet M. Gillam

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 661 KB
• Volume: 29
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260290511

✦ Synopsis

Abstract

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.