Ent-pimarane and ent-trachylobane diterpenoids from Mitrephora alba and their cytotoxicity against three human cancer cell lines.

Bioassay-guided fractionation of the hexane extract of the branches of Mitrephora alba led to the isolation of five diterpenoids: ent-8β-hydroxypimar-15-en-18-oic acid, ent-15,16-dihydroxypimar-8(14)-en-18-oic acid, ent-3β-hydroxytrachyloban-18-oic acid, ent-3β-hydroxytrachyloban-18-al and methyl ent-3β-hydroxytrachyloban-18-oate, together with five related known diterpenoids. The structures were elucidated by spectroscopic analysis and comparison with literature data. All isolated compounds were evaluated for their cytotoxic activities against three human cancer cell lines. The results showed that three ent-trachylobane diterpenes had moderate cytotoxicity against NCI-H187 cancer cells.