Two cytotoxic triterpenes from cultures of a Kenyan Laetiporus sp (Basidiomycota)

HPLC profiling of the mycelial culture of a poroid basidomycete collected in Mount Elgon, Kenya, which probably represents a new species of the genus Laetiporus, led to isolation of two previously undescribed lanostane type triterpenes. We propose the trivial names laetiporins A (1) and B (2). In addition, five known ones: dehydrosulphurenic acid (3), sulphurenic acid (4), eburicoic acid (5), 15 alpha-hydroxytrametenolic acid (6) and trametenolic acid (7) were also isolated. The laetiporins (1-2) exhibited significant cytotoxic effects against various human cancer cells. The known compounds (3-5) and (7) also showed moderate cytotoxic activity, but none of the compounds showed any significant antimicrobial activity.