Chapter 5 The Biotransformation of Protoberberine Alkaloids by Plant Tissue Cultures

Abstract

This chapter describes three pathways; first, second, and third pathway for the biotransformation of protoberberine alkaloids by plant tissue cultures. The chapter emphasizes on biosynthetic studies using plant tissue cultures on nonphenolic protoberberines and 13-methyl- and 13-hydroxyprotoberberines possessing substituents at C-2 and C-3, and either at C-9 and C-10 or at C-10 and C-11. The biosynthetic conversion of the protoberberine system into other alkaloidal types, such as protopines, benzophenanthridines, rhoeadines, benzindanoazepines, and spirobenzylisoquinolines are also discussed. The α-N-metho salts of the trans- and cis-13-methyltetrahydroprotoberberines are bioconverted into (13S)- and (13R)-13-methylprotopines, respectively. The α-N-metho salts of the trans-13-methyltetrahydroprotoberberines with the methoxyl groups on ring A are poor substrates in comparison with alkaloids having a methylenedioxy bridge on ring A. Therefore, the biochemical processes in the conversion of the protoberberines into the benzophenanthridines occur similarly in intact plants and callus tissues. Benzophenanthridine alkaloids are biosynthesized from protoberberine alkaloids via oxidation at C-14 and then again at C-6 to furnish an intermediate 6,14-dihydroxyprotoberberine.