ISOLATION AND CHARACTERISATION OF BIOACTIVE PRINCIPLES FROM Raphia africana (OTEDOH)
ISOLATION AND CHARACTERISATION OF BIOACTIVE PRINCIPLES FROM Raphia africana (OTEDOH)
No Thumbnail Available
Date
2018-01
Authors
ANYAM, John Vershima
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Raphia africana (Otedoh) is a member of the palm family Arecaceae. The plant was collected from banks of the creeks Ukoko and Uertsor in Buruku Local Government Area of Benue State. The fruit mesocarp was extracted and subjected to phytochemical and antimicrobial screenings. The ethyl acetate extracts, obtained via different extraction protocols (soxhlet extraction, microwave assisted extraction and maceration) were subjected to Artemia salina lethality assay. Extracts (ethyl acetate and methanol) were subjected to Gas Chromatography Mass Spectrometry (GCMS) and High-Performance Liquid Chromatography (HPLC) as part of pre-isolation analysis. Phytochemical screening showed the presence of steroids, triterpenes, alkaloids, anthroquinones, cardiac glycosides and flavonoids. Antimicrobial screening of the extracts showed the ethyl acetate extract to have the broadest and highest activity against the test microbes, having lower minimum inhibitory concentration (0.625 mg/mL) and a wider zone of inhibition diameter (27 mm) on Klebsiella pneumoniae. The ethyl acetate extract also showed good minimum bactericidal/fungicidal concentration values on Staphylococcus aureus (2.5 mg/mL), Klebsiella pneumoniae (1.25 mg/mL) and Candida albicans (2.5 mg/mL). The hexane extract was the least active against the test microbes with chloroform and methanol extracts showing intermediate activity. Extracts obtained by soxhlet extraction and microwave assisted extraction showed toxicity at a concentration of 269.2 mg/mL, while the extract obtained through maceration showed the lowest toxicity (467.7 mg/mL). The GCMS profiles showed the extracts to consist of lipids and diterpene alcohols while the selectively targeted HPLC showed traces of sterols (campesterol, cholestanol, cholesterol, ß-sitosterol, stigmasterol and tocopherol) and flavonoids (isovitexin,
xxx
kaempferol and orientin). Crude extracts were extensively purified using vacuum liquid chromatography (VLC) and gel filtration (GF). Fractions from VLC and GF sessions were characterised using Nuclear Magnetic Resonance Spectroscopy (NMR) and found to be mainly lipids. Extensive chromatography allowed the isolation of saturated fatty acids (margaric and myristic acids), a monounsaturated fatty acid methyl ester (methyl oleate), triglycerides, a sterol methyl ether, tentatively identified diosgenin-type steroidal saponins, tentatively identified monogalactosyl diacylglycerides, monoacyl glycerides and diacylglycerides. This is the first time these substances have been identified in the mesocarp of this plant. The isolated compounds were tested against microbes and they showed higher but similar activity compared to the crude extracts. Ja 83 (a monogalactosyldiacylglyceride) showed the largest zone of inhibition against Staphylococcus aureus (30 mm), against Klebsiella pneumoniae (31 mm) and 32 mm against Shigella dysenteriae while showing the least zone against Microsporum sp. Isolated compounds were inactive towards Aspergillus fumigatus and Aspergillus niger. Relatively mild behaviour of the crude extracts against Artemia salina, and the lipidic nature of the phytoconstituents reaffirm its use as a food source and it is recommended that this, now increasingly neglected tropical fruit tree, be actively cultivated for human use provided the toxicity studies allow them for such purpose.
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF DOCTOR OF PHILOSOPHY IN ORGANIC CHEMISTRY DEPARTMENT OF CHEMISTRY, FACULTY OF PHYSICAL SCIENCES AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA
Keywords
ISOLATION,, CHARACTERISATION,, BIOACTIVE PRINCIPLES,, Raphia africana (OTEDOH),