Exploration of a fundamental substituent effect of alpha-ketoheterocycle enzyme inhibitors: Potent and selective inhibitors of fatty acid amide hydrolase.

A series of C4 substituted alpha-ketooxazoles were examined as inhibitors of the serine hydrolase fatty acid amide hydrolase in efforts that further define and generalize a fundamental substituent effect on enzyme inhibitory potency. Thus, a plot of the Hammett sigma(m) versus -logK(i) provided a linear correlation (R(2)=0.90) with a slope of 3.37 (rho=3.37), that is of a magnitude that indicates that of the electron-withdrawing character of the substituent dominates its effects (a one unit change in sigma(m) provides a >1000-fold change in K(i)).