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

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.