Biosynthesis of the necic acids of the pyrrolizidine alkaloids. Further investigations of the formation of senecic and isatinecic acids in Senecio species

Abstract

Five-carbon intermediates of the pathway of isoleucine metabolism, 2-methylbutanoic acid, angelic acid (5), and 2-methyl-3-oxobutanoic acid, were not specifically incorporated into senecic acid (1), the necic acid component of senecionine (2) in Senecio magnificus. The mechanism of the coupling of isoleucine-derived units during necic acid biosynthesis was investigated through incorporation experiments with [6-³H]- and [4-³H₂]-isoleucine (3) in S. magnificus and S. isatideus. 2-Amino-3-[³H₂]methylenepentanoic acid (β-[³H₂]methylenenorvaline)(13) was incorporated specifically into senecic acid (1).