Design and synthesis of conformationally restricted eight-Membered ring diketones as potential serine protease inhibitors

The design of conformationally restricted eight-membered ring diketones as transition state mimics of the mechanism of action of cyclotheonamides on serine proteases is described. Two target compounds are prepared from mutilin, derived from the natural product pleuromutilin. Compound 3 shows significant inhibition of plasmin and urokinase in enzyme rate assays, but an analogue 4 in which the amide moiety has been omitted does not. An X-ray crystal structure of the diketone 3 confirms the conformational predictions made by molecular modelling. Potential serine protease inhibitors 3 and 4 were prepared from mutilin and evaluated. X-ray crystallography confirmed structure of the acetamide 4, which inhibited plasmin and urokinase in vitro.