Alpinigenine from Papaver bracteatum Lindl. Restricted rotation in an unusual oxidation product

Abstract

Alpinigenine (1) was isolated in relatively large amount from a type of Papaver bracteatum Lindl. from Iran. Oxidation of this alkaloid with Jones reagent produced a lactone function and, unexpectedly, converted the NMe into an NCHO, present as a mixture of rotamers. Crystallization afforded one pure component, which equilibrated in solution within 2 h. ¹³C N.m.r. spectroscopy was used to confirm these results and enabled an insight into the conformation in solution of the seven-membered rings in alpinigenine and its oxidation product. X-Ray analysis determined unambiguously the absolute configuration of alpinigenine.