The new isoflavone glucoside vavain 3'-O-beta-d-glucoside (1) and its aglycon, vavain (2), were isolated from the bark of Ceiba pentandra, together with the known flavan-3-ol, (+)-catechin, These novel structures were elucidated by one- and two-dimensional NMR experiments and by MS, IR, and UV spectroscopy as 5-hydroxy-7,4',5'-trimethoxyisoflavone 3'-O-beta-D-glucoside (1) and 5,3'-dihydroxy-7,4',5'-trimethoxyisoflavone (2), respectively. The compounds were isolated following bioactivity-directed fractionation, using a cyclooxygenase-1-catalyzed prostaglandin biosynthesis assay in vitro, in which compounds 1 and 2 and (+)-catechin exhibited IC50 values of 381, 97, and 80 microM, respectively (standard: indomethacin, IC50 1,1 microM). When further tested for their inhibitory effects on cyclooxygenase-2-catalyzed prostaglandin biosynthesis, 1 and 2 were found to be inactive (IC50 > 1200 and > 900 microM, respectively).