The stereochemical course of the water elimination from (2R)-phenyllactate in the amino acid fermentation of Clostridium sporogenes.

(2R,3R)-[3-3H]- and (2R,3S)-[3-3H]- phenyllactate were synthesized from phenylpyruvate with the help of phenylpyruvate tautomerase and an NADH-dependent 2-oxo-acid reductase from Clostridium sporogenes. With whole cells of C. sporogenes both (2R)-phenyllactates are mainly transformed to phenylpropionate and, to a minor extent to phenylalanine. According to recently published results, the former transformation leads from phenyllactate, or an activated derivative of it, to (E)-cinnamate which is reduced to phenylpropionate in a fast consecutive reaction. The 3H/14C-ratio of phenylpropionate deriving from (2R,3R)-[3-3H,U-14C]phenyllactate was about 85% of that of the phenyllactate and the corresponding ratio for phenylpropionate deriving from the (2R,3S)-[3-3H,U-14C]phenyllactate about 7%, respectively. Assuming that the E-configuration of cinnamate is formed directly from (2R)-phenyllactate, the water elimination occurs in a syn fashion.