| || || Sharma, Sujlesh.|
| || || Chemical and biological investigations of metabolites from Mammea Odorata |
Institution: University of the South Pacific.
Call No.: pac In Process
Copyright:Under 10% of this thesis may be copied without the authors written permission
Abstract: This thesis focuses on the chemical and biological investigations of Mammea odorata (Clusiaceae), a plant indigenous to the South Pacific. Cold extraction of the stem bark collected from Deuba, Fiji Islands, resulted in methanol, ethyl acetate and dichloromethane extracts. Fractionation of the three extracts by employing flash chromatography and reverse phase HPLC separation techniques yielded a total of eleven compounds. A combination of spectral data mainly obtained through 1D and 2D NMR experiments (1H and 13C NMR and gradient COSY, HMBC, HSQC and ROESY) and mass spectroscopy (HRESIMS and LRESIMS) were instrumental in structure elucidation of the isolated compounds. Two new xanthone glycosides, 2,3-dihydroxyxanthone; 3-O-β-D-glucopyranoside (116) and 1,6,7-trihydroxyxanthone; 6-O-β-D-glucopyranoside (117) together with a known flavonol, (-)-epicatechin (115) were isolated from the methanol extract. Ethyl acetate extract yielded a new natural product, 2,3-dihydroxyxanthone (118) and six known xanthones, 2- and 4-hydroxyxanthones (83 and 84), 2,6-dihydroxyxanthone (94), 2-hydroxy-3-methoxyxanthone (119), 1,6,7-trihydroxyxanthone (88), and 1,6,7- trihydroxy-3-methoxyxanthone (120). A known coumarin, surangin B (34) was isolated from the dichloromethane extract. In vitro antimalarial assays of the eleven compounds using 3D7 (chloroquinesensitive) line of Plasmodium falciparum identified 34 to be the most potent of all the test compounds with an IC50 of 2.5 (±1.6) μM. Other compounds exhibited antimalarial activity in the range of 14.5% to 43.2% at 25.0 μM. In vitro antimicrobial susceptibility assays of the extracts (50 mg/mL) and the eleven compounds (10 mg/mL) against nine human pathogenic bacteria was performed using the disc diffusion method. The extracts were shown to inhibit the growth of Gram positive bacteria, Staphylococcus aureus, Methicillin Resistant Staphylococcus aureus and Enterococcus faecalis, with the dichloromethane extract displaying the greatest zone of inhibition. The isolated compounds did not show any activity at the tested concentration. iv Finally, this thesis reports the sole occurrence of xanthone glycosides 116 and 117 in the genus Mammea. The antimalarial activity of some compounds especially 34 has also been reported for the first time.