Antimicrobial Phenylpropanoid esters and Sesquiterpene lactones from the leaves of Tarchonanthus camphoratus (asteraceae)

Abstract

The plant Tarchonanthus camphoratus belongs to Asteraceae family. Its common name is wild sage or camphor bush. This study was aimed at isolating bioactive phenypropanoid esters and sesquiterpene lactones from the leaves of this plant. A powdered sample of the leaves weighing 500 g was sequentially extracted with of hexane (1.5 L), dichloromethane (1.5 L) and methanol (3 x 1.5 L). The methanolic extract was partitioned between equal volumes (250 ml each) of distilled water. The n-butanol fraction was concentrated under reduced pressure followed by addition of diethyl ether, precipitating 20 g of a dry crude extract. The extract was successively fractionated using hexane, dichloromethane, chloroform, ethyl acetate, acetone, ethanol and methanol yielding 1.6 g, 1.4 g, 1.6 g, 7.0 g, and 1.4 g, 2 g and 4 g respectively of samples soluble in each solvent. Phytochemical and chemical tests were employed in identifying the fractions that contained phenolic compounds and terpenoids. Antimicrobial activity tests of the extracts soluble in various solvents were then performed on Escharichia coli, Staphylococcus aureus, Pseudomonas aeruginos, Klebsiella pneumoniae, Proteus mirabilis, Salmonella typhi, Candida albicans and Bacillus spp. Ethyl acetate and methanol soluble fractions were found to contain phenolics, while hexane, dichloromethane, chloroform and ethyl acetate fractions contained terpenoids. Ethyl acetate fraction was active against E. coli, P. mirabilis, K. pneumoniae, S. typhi, and Bacillus spp while methanol fraction was active against E. coli, K. pneumoniae, S. typhi, and Bacillus spp. The two fractions were combined and subjected to TLC analysis, Column chromatography, HPLC analysis and sephadex LH-20 reversed phase column chromatography, affording three isomers of dicaffeoyl quinic acids: 4, 5- dicaffeoyl quinic acid, 1 (135 mg), 3, 5-dicaffeoyl quinic acid, 2 (125 mg), and 3, 4-dicaffeoylquinic acid, 3 (90 mg) which are known compounds, and a sesquiterpene lactone, 4 (150 mg). Structural elucidation of the compounds was done using IR, MS, 13C- NMR, 1H- NMR, DEPT, 1H-1H COSY, 1H-13C COSY and HMBC techniques.