A Bisbenzamidine Phosphonate as a Janus-faced Inhibitor for Trypsin-like Serine Proteases

A hybrid approach was applied for the design of an inhibitor of trypsin-like serine proteases. Compound 16 [(R,R)- and (R,S)-diphenyl (4-(1-(4-amidinobenzylamino)-1-oxo-3-phenylpropan-2-ylcarbamoyl)phenylamino)(4-amidinophenyl)methylphosphonate hydrochloride], prepared in a convergent synthetic procedure, possesses a phosphonate warhead prone to react with the active site serine residue in a covalent, irreversible manner. Each of the two benzamidine moieties of 16 can potentially be accommodated in the S1 pocket of the target enzyme, but only the benzamidine close to the phosphonate group would then promote an irreversible interaction. The Janus-faced inhibitor 16 was evaluated against several serine proteases and caused a pronounced inactivation of human thrombin with a second-order rate constant (k(inac)/K-i) of 59500M(-1)s(-1). With human matriptase, 16 showed preference for a reversible mode of inhibition (IC50=2.6M) as indicated by linear progress curves and enzyme reactivation.