Secondary metabolites of oil palm isolates of Ganoderma zonatum Murill. from Cameroon and their cytotoxicity against five human tumour cell lines
Three lanostane-type triterpenoids [lanosta-7,9(11),24-trien-3-one 15,26-dihydroxy, lanosta-7,9(11),24- trien-26-oic,3-hydroxy and ganoderic acid y], four steroids[ (22E,24R)-ergosta-7,22-dien-3β,5α.6β-triol, 5α,8α-epidiory (22E,24R-ergosta-6,22-dien-3β-ol, ergosta-5,7,22-trien-3β-ol,7 (ergosterol) and ergosta- 7,22-dien-3β-ol,6] and a benzene derivative (dimethyl phthalate) were isolated from ethyl acetate crude extract of Ganoderma zonatum Murill. of oil palm from Cameroon. Their structures were elucidated by nuclear magnetic resonance (NMR), electron impact ionization mass spectrum experiments (EI-MS) and by comparing with the data reported in literature. The highly oxygenated lanostane triterpenoid - ganoderic acid y- showed moderate cytotoxicity against two human tumour cell lines, SMMC-7721 (liver cancer) and A549 (lung cancer) with IC50 values of 33.5 and 29.9 μM, respectively and no activity on HL-60, MCF-7 and SW480, while lanosta-7,9(11),24-trien-3-one,15;26-dihydroxy and lanosta- 7,9(11),24-trien-26-oic,3-hydroxy, showed no activity. The three lanostane triterpeniods had the same molecular formula, molecular weight, behaviour on the TLC plates, with the same retention factor value of 3 (when petroleum ether-acetone was used in the ratio of 3:1), but with slightly different structures. These compounds have not been reported occurring together from any other species of Ganoderma. Their simultaneous occurrence might thus, serve as a diagnostic chemotaxonomic character for G. zonatum, The 1H NMR data is provided for the first time for lanosta-7,9(11),24-trien-26-oic,3-hydroxy.
Key words: Secondary metabolites, Ganoderma zonatum, chemotaxonomic character, cytotoxicity.