The decomposition compound formed by xenon irradiation of nafamstat mesilate in aqueous solution and its kinetics were studied and the following findings were obtained. Nafamstat mesilate was decomposed by xenon irradiation to form 4-guanidinobenzoic acid (PGBA), 6-amino-2-naphthol (AN) and compound II having yellow color. The structure of the compound II was studied in comparison with nafamstat mesilate by chemical and physical methods and shown to be an amide type compound of PGBA and AN. Photodemposition reaction of nafamstat mesilate was found to follow the pseudo-second order reaction.
