Novel N-oxide derivatives of benzyltetrahydroisoquinoline alkaloid from the tubers of Stephania viridiflavens H.S. Lo et M. Yang

Abstract

An investigation on the phytochemistry of the medicinal plant Stephania viridiflavens H.S. Lo et M. Yang led to isolate two new naturally occurring benzyltetrahydroisoquinoline alkaloids, (+)-1S, 2R-laudanidine-Nβ-oxide 2 and (+)-1S, 2S-laudanidine-Nα-oxide 3, along with four known benzyltetrahydroisoquinoline alkaloids: (+)-laudanidine 1, (+)-reticuline 4, (+)-1S, 2R-reticuline-Nβ-oxide 5 and (+)-1S, 2S-reticuline-Nα-oxide 6. The structure and the stereochemistry of these compounds were determined on the basis of spectroscopic methods and also confirmed by partial synthesis. To examine putative acetycholinesterase (AChE) inhibitory or cytotoxic activities, various bioassays were performed, the N-oxide derivatives (5 and 6) demonstrated more potent cytotoxicity than the corresponding free base.