Enzymatic kinetic resolution of desmethylphosphinothricin indicates that phosphinic group is a bioisostere of carboxyl group

Escherichia coli glutamate decarboxylase (EcGadB), a pyridoxal 5'-phosphate (PLP)-dependent enzyme, is highly specific for L-glutamate and was demonstrated to be effectively immobilized for the production of γ-aminobutyric acid (GABA), its decarboxylation product. Herein we show that EcGadB quantitatively decarboxylates the L-isomer of D,L-2-amino-4-(hydroxyphosphinyl)butyric acid (D,L-Glu-γ-PH), a phosphinic analogue of glutamate containing C-P-H bonds. This yields 3-aminopropylphosphinic acid (GABA-PH), a known GABAB receptor agonist and provides previously unknown D-Glu-γ-PH, allowing us to demonstrate that L-Glu-γ-PH, but not D-Glu-γ-PH, is responsible for D,L-Glu-γ-PH antibacterial activity. Furthermore, using GABase, a preparation of GABA-transaminase and succinic semialdehyde dehydrogenase, we show that GABA-PH is converted to 3-(hydroxyphosphinyl)propionic acid (Succinate-PH). Hence, PLP-dependent and NADP+-dependent enzymes are herein shown to recognise and metabolise phosphinic compounds, leaving unaffected the P-H bond. We therefore suggest that the phosphinic group is a bioisostere of the carboxyl group and the metabolic transformations of phosphinic compounds may offer a ground for prodrug design.