Vitamin K-dependent carboxylation. Mechanistic studies with 3-fluoroglutamate-containing substrates

The tripeptides t-butyloxycarbonyl-Xaa-Glu-[3H]Val, where Xaa is either (2R,3S)- or (2R,3R)-3-fluoroglutamate (respectively the erythro and the threo isomer), were synthesized and their behaviour during vitamin K-dependent carboxylation was studied. Neither peptide was carboxylated. The erythro compound gave rise to an HF-elimination product representing 1% of the starting material. This HF elimination did not occur during incubation of the threo compound. The formation of the dehydropeptide, probably by elimination of an F- anion from an intermediate carbanion, favours the ionic pathway for vitamin K-dependent carboxylation.