Isoleucine biosynthesis and metabolism: stereochemistry of the formation of L-isoleucine and of its conversion into senecic and isatinecic acids in Senecio species

Incorporation experiments with isoleucine (1) stereospecifically labelled at C-4, and 2-aminobutanoic acid (10) stereospecifically labelled at C-3, in Senecio species have shown that the ethyl migration step during the biosynthesis of L-isoleucine (1) takes place with retention of configuration at the migrating centre, and that during conversion into necic acids of the senecic acid (4) type, both C5 units are formed with loss of the C-4pro-S hydrogen atom of L-isoleucine (1) and retention of the C-4 pro-R hydrogen atom.