Pyrrolizidine alkaloids from Lithospermum canescens Lehm.

Abstract

Seven pyrrolizidine alkaloids (PAs) have been isolated from Lithospermum canescens and their structures determined by spectroscopical methods. Besides the known lycopsamine, O7-acetyl-lycopsamine and O7-acetylintermedine four new PAs were found. Their structures are O7-(3-hydroxy-3-methyl-butanoyl)-O9-(+)- trachelanthoyl-heliotridine (= O7-(3-hydroxy-3-methyl-butanoyl)-rinderine = canescine), O7-(3-hydroxy-3-methyl-butanoyl)-O9-(-)-viridifloryl- heliotridine (= O7-(3-hydroxy-3-methyl-butanoyl)-echinatine = canescenine) and their O13-acetyl-derivatives (= acetylcanescine; acetylcanescenine).