Secondary metabolites of endophytic fungi from santol (Sandoricum koetjape) leaves

Abstract

The endophytic fungi, 213 isolates were isolated from Sandoricum koetjape leaves collected in 10 provinces. Based on fungal morphology, those fungi were identified as Alternaria sp. (2 isolates), Aspergillus sp. (3 isolates), Cladosporium sp. (5 isolates), Colletotrichum sp. (6 isolates), Fusarium sp. (8 isolates), Pestalotia sp. (4 isolates), Phomopsis sp. (13 isolates), Xylariaceae (18 isolates), and Mycelia sterilia (155 isolates). Among these fungi, there are 54 isolates exhibited antimicrobial activity (at least against two microorganisms) with the inhibition zone of 1-12 mm and the endophytic fungi exhibited antimicrobial activity against gram-positive bacteria, Bacillus subtilis and Staphylococcus aureus, were more than against gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa. The endophytes, PB-30 and MK-22, were selected for further studies. On the basis of fungal morphology and analysis of the DNA sequence of the ITS region, the fungi PB-30 and MK-22 were identified to Xylaria sp. Chemical investigation of the metabolites produced by the endophytic fungus PB-30 was carried out to afford 6 compounds including D-mannitol 1, mellein 2, 4-hydroxymellein 3, 2-chloro-5-methoxy-3-methylcyclohexa-2,5-diene-1,4-dione 4, 7-hydroxy-8-methoxy-3,6-dimethyl-dibenzofuran-1,4-dione 5 and 2-hydroxy-5-methoxy-3-methylcyclohexa-2,5-diene-1,4-dione 6. Isolation of metabolite from mycelia MeOH extract of the endophytic fungus MK-22 gave integric acid 7. Compounds 2-6 were examined antiplasmodial activity against Plasmodium falciparum (K1 strain). Compounds 4 and 5 exhibited antiplasmodial activity with the IC50 values of 1.83 and 6.69 microM, respectively while compounds 2, 3 and 6 were inactive. Cytotoxic activity of compound 2-7 were examined against 5 human cancer cell lines including, BT474 (breast), CHAGO (lung), HEP-G2 (hepatoma), KATO-3 (gastric) and SW620 (colon). Compound 2 and 3 were inactive while compound 4-7 exhibited cytotoxic activity against all cell lines. Moreover, compounds 4 and 5 exhibited cytotoxic activity against Vero cells (African green monkey kidney fibroblasts) with the IC50 values of 1.34 and >181 microM, respectively.