Chapter 60 - The biosynthesis of plant alkaloids and nitrogenous microbial metabolites

Abstract

This chapter discusses the biosynthesis of plant alkaloids and nitrogenous microbial metabolites. The majority of pyrrolidine and piperidine alkaloids are biosynthesized along routes that occupy the amino-acids ornithine and lysine as starting points. The key idea is that those alkaloids, which are formed with symmetrization of a lysine label are biosynthesized by way of free cadaverine. Two enzymes are isolated from Conium maculatum, which mediate the transamination. One enzyme occurs in chloroplasts the other in mitochondria; the former is normally responsible for alkaloid biosynthesis. The latter could involve a reordering of the skeleton associated with the formation of C-2 as the spiro centre. The pyrrolidine ring of nicotine is biosynthesized from ornithine along a pathway involving the symmetrical diamine, putrescine. The tiglic acid moieties, found in some tropane alkaloids, arise from isoleucine via 2-methylbutanoic acid. The mechanism of the rearrangement that occurs during the biosynthesis of tropic acid residues found in some tropane alkaloids is a highly intriguing mystery. It is known that during the rearrangement the carboxyl group of phenylalanine undergoes an intramolecular 1,2-shift.