Studies of enzyme-mediated reactions. Part I. Syntheses of deuterium- or tritium-labelled (3S)- and (3R)-phenylalanines: stereochemical course of the elimination catalysed by L-phenylalanine ammonia-lyase

Abstract

Two rational syntheses of L-phenylalanine [(2S)-isomer] have been devised which allow labelling with isotopic hydrogen at C-3 in configurations established by chemical correlation with [2-²H₁]succinic acid. The labelled samples have been used to prove that L-phenylalanine ammonia-lyase eliminates the 3-pro-S hydrogen atom of L-phenylalanine together with ammonia to give trans-cinnamic acid (a) with the isolated enzyme from potatoes and (b) during the biosynthesis of colchicine in intact Colchicum autumnale plants.

The biochemical formation of the C₆–C₁ unit required for the construction of haemanthamine (30) in Amaryllidaceae plants involves loss of the hydrogen atom from C-3 of cinnamic acid.