The pyrrolizidine alkaloids of Amsinckia menziesii

Abstract

Methanolic extracts of fresh Arnsinckia menziesii (Lehm.) Nels, and Macbr. (Boraginaceae) yielded three known pyrrolizidine alkaloids, intermedinet (I), lycopsaminet (2) and 7-acetyllycopsaminet (3). In addition, two new alkaloids were isolated and shown to be 9-[(2'S,3'S)-3'-acetoxy-2'-hydroxy- 2'-isopropylbutanoyl]retronecine,t (3'-acetyllycopsamine) (4) and 7-acetoxy-9-[(2'S,3'S)-3'-acetoxy- 2'-hydroxy-2'-isopropylbutanoyl]retronecine, (3',7-diacetyllycopsamine) (5). Structures of all of the alkaloids were determined by means of mass spectrometry and ¹³C and ¹H n.m.r. spectroscopy. The structures of the new alkaloids were confirmed by acetylation of lycopsamine (2) to give 3'-acetyl- lycopsamine (4) and 3',7-diacetyllycopsamine (5).