New bioactive triterpenoids from Melia volkensii.

Bioactivity-directed fractionation of the root bark of Melia volkensii resulted in the isolation of two new natural products, meliavolkinin (1) and melianin C (3), together with two known compounds, 1,3-diacetylvilasinin (2) and melianin B (4). Jones oxidation of 4 gave compounds 3, 23,24-diketomelianin B (5), and 16,23,24-triketomelianin B (6). The structures of the new compounds were elucidated by spectral and chemical data. Compounds 1-6 all showed marginal cytotoxicities against certain human tumor cell lines, while 5 showed selective cytotoxicities for the human prostate (PC-3) and pancreatic (PACA-2) cell lines with potencies comparable to those of adriamycin.