Inhibition of serine proteases by benzoxazinones: effects of electron withdrawal and 5-substitution.

A series of substituted 4H-3,1-benzoxazin-4-ones have been made and assayed as inhibitors of human leukocyte elastase (HLE) and other serine proteases. The benzoxazinones are kinetically competitive, alternate substrate inhibitors that inhibit by acylation and slow deacylation. Two structure-activity relationships have been found which are consistent with this mechanism. First, electron withdrawal at position 2 gives better inhibition (lower Ki values) because acylation rates are increased while deacylation is relatively unaffected. Second, benzoxazinones with methyl or ethyl substitution at position 5 are better inhibitors of HLE because the acyl enzymes formed from these compounds are 2,6-disubstituted benzoic acid esters and their deacylation is sterically hindered.