Lanostane-type triterpenoids from Abies faxoniana and their DNA topoisomerase inhibitory activities

Nine lanostane-type triterpenoids were isolated from branches and leaves of Abies faxoniana, along with 10 known compounds. Two were isolated as inseparable mixtures of epimers at C-23 of the γ-lactone ring that had a lactol structure. The structures of the nine compounds were established by spectroscopic analysis and circular dichroism (CD) data. The absolute configurations at the stereogenic centres of two of the known compounds were confirmed by X-ray crystallography. One compound showed cytotoxic activities against HCT-116, MCF-7, and A549 cells with IC50 values of 8.9, 7.6, and 4.2μM, respectively. The isolated compounds were tested for their effects on human DNA topoisomerases I and II. One was found to be a selective inhibitor of human topo II activity with an IC50 value of 53.5μM, which was comparable to that of the topo II inhibitor etoposide (IC50=49.6μM).