Cytotoxic clerodane diterpenoids from the leaves of Polyalthia longifolia.

The ethanolic extract of Polyalthia longifolia var. pendula was fractionated to get a hexane-soluble residue, which led to the isolation of four clerodane diterpenes: (-)-3α,16α-dihydroxycleroda-4(18),13(14)Z-dien-15,16-olide (1), (-)-3β,16α-dihydroxycleroda-4(18), 13(14)Z-dien-15,16-olide (2), (-)-16α-hydroxycleroda-3,13(14)Z-dien-15,16-olide (3) and (-)-16-oxocleroda-3,13(14)E-dien-15-oic acid (4). Diterpene 1 is a new compound, while 2 is reported for first time from this plant. Both 1 and 2 were tested for their growth inhibitory activity on four cancer cell lines in vitro. IC(50) values suggest that they are effective as cytotoxic agents.