Chem. Pharm. Bull. 53(8) 984—988 (2005)

oxidation of xanthine and hypoxanthine into uric acid, and plays a vital role in producing hyperuricemia and gout. Allopurinol is a clinically used XO inhibitor in the treatment of gout, which blocks the terminal step in uric acid biosynthesis can lower the plasma uric acid concentration. However, due to unwanted side effects of allopurinol, such as hepatitis, nephropathy, and allergic reactions, new alternatives with increased therapeutic activity and less side effects are desired. Moreover, superoxide anion radicals generated by XO are involved in various pathological states such as hepatitis, inflammation, aging, carcinogenesis, and ischemia-reperfusion. Thus, the search for novel XO inhibitors would be beneficial not only to treat gout but also to combat various other diseases. The heartwood of Caesalpinia sappan L. (Caesalpiniaceae) has been used in Vietnamese traditional medicine for the treatment of rheumatism and inflammatory diseases and as an emmenagogue and homeostatic agent. Our preliminary screening study revealed that the methanolic extract of the heartwood of C. sappan exhibited significant XO inhibitory activity with an IC50 value of 14.2 mg/ml. Therefore, we carried out fractionation of the MeOH extract and isolated a dibenzoxocin possessing a novel carbon skeleton named neosappanone A (4), which was reported in our preliminary communication. Further investigation on this active MeOH extract led to the isolation of 16 additional phenolic compounds including a new benzindenopyran, neoprotosappanin (1) having a novel carbon framework, protosappanin E-2 (2), and protosappanin A dimethyl acetal (3). In this paper, we report the isolation and structure elucidation of these compounds by spectroscopic techniques, together with the XO inhibitory activity of the isolated compounds.