Inhibitors of Plasmin that Extend into Both the S and S‘ Binding Sites:  Cooperative Interactions between S1 and S2

A new procedure for the synthesis of cyclohexanone-based inhibitors of serine proteases is reported. In this procedure the reactive ketone functionality is carried through the synthesis in masked form as a TBDMS-protected alcohol. Deprotection followed by oxidation of the alcohol generates the final form of the inhibitor. Two new inhibitors, which interact with the S1−S3 and S2‘ subsites of plasmin, are synthesized using this procedure. Inhibitors 1 and 2 have IC₅₀ values against plasmin of 20 and 24 μM, respectively. The inhibition studies show that cooperative binding of inhibitors in the S1 and S2 subsites of plasmin is important for determining inhibitor selectivity.