Résumé
(R)‐ and (S)‐2‐amino[2‐D1]ethylphosphonic acids ([2‐D1]AEP) were synthesised to investigate the stereochemistry of the reaction catalysed by 2‐aminoethylphosphonate aminotransferase from Pseudomonas aeruginosa. This enzyme catalyses the transfer of the amino group of AEP to pyruvate to produce 2‐phosphonoacetaldehyde and alanine. The enzymic reaction proceeding through the ion of a proton from the Schiff‐base complex formed between the enzyme‐bound pyridoxal 5′‐phosphate, and the substrate, was carried out in an aqueous buffer at pH 8.5; it was followed by high‐field 1H‐NMR measurements (500 MHz, H2O) on an AMX 500 Bruker spectrometer. The spectra, recorded with chiral (R)‐ or (S)‐[2‐D1]AEP, both showed the methylenic signal (3.0 ppm), whereas (S)‐[2‐D1]AEP gave the additional aldehydic signal (CHO, 9.6 ppm). These data clearly show that AEP‐aminotransferase catalyses the ion of the pro‐S hydrogen atom at the prochiral C2 carbon of AEP. Furthermore, careful timing of NMR measurements over a 2‐hour period allows us to show the occurrence of an isotopic effect.