Biosynthesis. Part 23. Degradative studies on the alkaloids hasubanonine and protostephanine from Stephania japonica

Abstract

Degradative schemes are reported for the alkaloids hasubanonine (1) and protostephanine (2) of Stephania japonica to allow labelling patterns to be determined. Acetolysis of (1) leads eventually to a phenanthrene (5c) by removal of the ethanamine bridge. N-Methylation and Hofmann elimination of (2) gives one major olefinic product, assigned structure (6a) from ¹H n.m.r. data and confirmed by synthesis of specifically ¹³C-labelled material.