Novel Biologically Active Bibenzyls from Bauhinia saccocalyx P ierre

Four new bibenzyls, bauhinols A–D ( 1 – 4 ), together with the two known bibenzyls 5 and 6 , were isolated from the roots of Bauhinia saccocalyx , and their structures were elucidated by analyses of spectroscopic data. Bauhinol A ( 1 ) exhibits significant cytotoxicity towards NCI‐H187 (small‐cell lung cancer), BC (breast cancer), and KB (oral‐cavity cancer) cell lines, with IC 50 values of 2.7–4.5 μg/ml. Bauhinol B ( 2 ) is cytotoxic against NCI‐H187 ( IC 50 =1.1 μg/ml) and BC ( IC 50 =9.7 μg/ml) cell lines, but inactive toward the KB cell line (at 20 μg/ml). Compound 2 also is mildly antifungal towards Candia albicans ( IC 50 =28.9 μg/ml). Bibenzyl 6 is active against NCI‐H187 ( IC 50 =14.1 μg/ml) and BC ( IC 50 =4.0 μg/ml) cells, but inactive (at 20 μg/ml) toward the KB cell line. Compounds 1, 2 , and 6 show mild antimycobacterial activities, with MIC values of 25–50 μg/ml, but are inactive at 20 μg/ml against the K1 malarial parasite strain ( Plasmodium falciparum ). While bauhinol A ( 1 ) is inactive against cyclooxygenase 1 (COX‐1) and cyclooxygenase 2 (COX‐2), compounds 2 and 6 inhibit both COX‐1 and COX‐2, with IC 50 values comparable to those of the standard drug, aspirin ( Table 3 ).