Stereochemical course of the elimination catalysed by L-phenylalanine ammonia-lyase and the configuration of 2-benzamidocinnamic azlactone

Abstract

Two rational syntheses of L-phenylalanine are described which allow stereospecific labelling with isotopic hydrogen at C-3; the labelled materials are used to establish that L-phenylalanine ammonia-lyase eliminates the pro-S proton from C-3 of L-phenylalanine together with ammonia to generate trans-cinnamate (antiperiplanar elimination).