Investigation of the applicability of cis-urocanic acid as a model for the catalytic Asp-His dyad in the active site of serine proteases based on H-1 NMR hydrogen bonding studies and spectroscopic pK(a) measurements

摘要

The intramolecular hydrogen bond of cis-urocanic acid, (Z)-3-(1H-imidazol-4-yl)prop-2-enoic acid (cis-UCA) in DMSO has been evaluated by the H-1 NMR chemical shift approach to. assess the suitability of cis-UCA as a model for the Asp-His dyad in the active site of serine proteases, Both the acidic OH proton and the C2 proton of the imidazole ring of cis-UCA resonate at exceptionally low field, at ca. 17.4 and 8.2 ppm, respectively, indicating a strong N-H-O type intramolecular hydrogen bond, The nucleophilic reactivity of cis-UCA toward the acyl carbon of 4-nitrophenyl chloroacetate has been compared with that of the trans-isomer and other imidazole derivatives with the aid of kinetic studies. The non-linear kinetic behaviour observed for the reaction of cis-UCA is attributed to complex formation with the reacting acyl derivative and cis-UCA, pK(a) determinations of imidazole derivatives in DMSO have also been performed and a value of 3.2 has been observed for cis-UCA. [References: 70]