ent-Beyerane diterpenoids from the heartwood of Excoecaria parvifolia

The heartwood of Excoecaria parvifolia afforded 12 beyerane diterpenes (1-12), four of which (5-7 and 12) have unusual structures: ent-3-oxa-beyer-15-en-2-one, (5); ent-15,16-epoxy-2-hydroxy-19-norbeyer-1,4-dien-3-one (6); methyl ent-2,4-seco-15,16-epoxy-4-oxo-3,19-dinorbeyer-15-en-2-oate (7); and ent-2,17-dihydroxy-19-norbeyer-1,4,15-trien-3-one (12). The isolated diterpenes were tested for their cytotoxic activity against leukemia cells (L1210), but only compounds 2 and 5 exhibited potent activity.