Abstract: The p-amidinophenyl ester of@ hydroxy-a-methylcinnamic acid has been synthesized and characterized. This compound irreversibly inhibits thrombin, Factor Xa, and trypsin. Inhibition by this derivative is, however, reversible (80-100%) upon irradiation of the enzyme in the presence of excess compound. Photolysis of the inactive 1: l acylenzyme complexes of all three enzymes (purified to homogeneity) also regenerated full enzymatic ...