Xanthones from roots of Calophyllum thwaitesii and their bioactivity

Abstract

Extracts from several endemic Calophyllum species were tested for antifungal, antibacterial and antioxidant activities. The crude extracts of these plants were subjected to preliminary screening for antibacterial activity against human pathogenic bacteria, Enterococci faecalis, Escherichia coli, Klebsiella, Pseudomonas aeruginosa and Staphylococcus aureus and 17 methicillin resistant Staphylococcus aureus (MRSA) strains isolated from hospitals. Antifungal activity was investigated against plant pathogenic fungi, Aspergillus and Cladosporium. Disk diffusion method was used to determine the antimicrobial activities against bacteria and the fungus Aspergillus, while TLC bioautography was used to detect the antifungal activity against Cladosporium. The results of the preliminary screening suggested that only the root methanol extract of Calophyllum thwaitesii possesed both antibacterial and antifungal activities and activity guided fractionation of this extract yielded seven xanthones. Four xanthones showed antifungal properties and were identified as l,6-dihydroxy-5-methoxyxanthone, 1-hydroxy-5,6- dimethoxyxanthone, 1 -hydroxy-5-methoxyxanthone and l-methoxy-5-hydroxyxanthone using spectroscopic methods and comparison with literature data. Inactive compounds were identified as 1-hydroxy-7-methoxyxanthone, l,5-dihydroxy-6-methoxyxanthone and 1,7dihydroxyxanthone. This is the first report of above xanthones except the latter, from Calophyllum thwaitesii. Further five of the above xanthones showed free radical scavenging properties, when tested with DPPH. None of the xanthones showed prominent antibacterial activities even the crude extract did. This could possibly be due to the presence of other active minor constituents in the plant extract or some synergistic effect of combination of compounds present in the plant extract. Further, isolation of methylated xanthones in the present study suggests the presence of methylating enzymes in the root of Calophyllum thwaitesii, contrary to previous reports