Inhibition of human folylpolyglutamate synthetase by diastereomeric phosphinic acid mimics of the tetrahedral intermediate

Abstract

Phosphorus-containing pseudopeptides, racemic at the C-terminal α-carbon, are potent mechanism-based inhibitors of folylpolyglutamate synthetase (FPGS). They are mimics of the tetrahedral intermediate postulated to form during FPGS-catalyzed biosynthesis of poly(γ- l-glutamates). In the present paper, the FPGS inhibitory activity of each diastereomer coupled to three heterocycles is reported. The high R f pseudopeptide containing the 5,10-dideazatetrahydropteroyl (DDAH 4Pte) heterocycle is most potent ( K is = 1.7 nM). While the heterocyclic portion affects absolute FPGS inhibitory potency, the high R f species is more potent in each pair containing the same heterocycle. This species presumably has the same stereochemistry as the natural folate polyglutamate, i.e., ( l-Glu-γ- l-Glu). Unexpectedly, the low R f (presumed l-Glu-γ- d-Glu) species are only slightly less potent (<30-fold) than their diastereomers. Further study of this phenomenon comparing l-Glu-γ- l-Glu and l-Glu-γ- d-Glu dipeptide-containing FPGS substrates shows that <1% contamination of commercial d-Glu precursors by l-Glu may give misleading information if l-Glu-γ- l-Glu substrates have low K m values.