New tirucallane-type triterpenes from Dysoxylum variabile

Eight new tirucallane-type triterpenes, dyvariabilins A-H (1-8), three know n tirucallanes, niloticin (9), dihydroniloticin (10), and tirucalla-7,24-di ene-3 beta ,23-diol (11), and two known sesquiterpenes, 1-(1-hydroxy-2-meth ylpropyl)-3a-methyl-7-methyleneoetahydroinden-4-ol and (+)-aphanamol I, wer e isolated from the stem bark of Dysoxylum variabile. Tirucallanes 1 and 11 with an allylic hydroxy group in the side chain and dyvariabilin C (3) wit h an alpha -epoxy group at positions 7 and 8 showed high instabilty in acid ic medium and formed five hitherto unknown semisynthetic tirucallanes. Dyva riabilins B (2) and C (3) as well as the mixtures of dyvariabilins E and F (5 and (6) and dyvariabilins G and H (7 and 8) showed weak cytotoxicity aga inst KB cells.