NEW MECHANISM-BASED INACTIVATORS OF TRYPSIN-LIKE PROTEINASES - SELECTIVE INACTIVATION OF UROKINASE BY FUNCTIONALIZED CYCLOPEPTIDES INCORPORATING A SULFONIOMETHYL-SUBSTITUTED M-AMINOBENZOIC ACID RESIDUE

In order to obtain selective suicide substrates of trypsin-like protea ses including plasminogen activators, plasmin, and thrombin, a series of cyclopeptides cyclo[Arg or Lys-aB(CH2X)-Gly4], in which a substitut ed o- or m-aminobenzoyl group constitutes a latent electrophile, have been prepared. Treatment of the corresponding phenyl ethers cyclo[P1-a B(CH2OC6H5)-GlY4] with HBr/HOAc or R1R2S/TFA gives the bromides (X = B r) or the sulfonium salts (X = +SR1R2 with R1 = R2 = Me or R1 = Me and R2 = C6H5), respectively. These water-soluble cyclopeptides behave as time-dependent inhibitors of bovine trypsin and human urokinase (u-PA ) but have no effect on tissue plasminogen activator (t-PA) and no or poor effect on plasmin and thrombin. The compounds containing a m-amin obenzoic acid residue are more efficient inactivators than their anthr anilic analogues. The kinetic criteria expected for a suicide inhibiti on are met. A mechanism of inhibition involving the formation of a qui nonimmonium methide intermediate is proposed. The activity of the inhi bitors is very sensitive to the nature of the X benzylic substituent. An increased efficiency for the inactivation of human urokinase is obs erved with the sulfonium salts. The selectivity of the inactivation of u-PA compared to t-PA could be of therapeutical significance in contr olling cell proliferation and invasion.