ISOLATION AND CHARACTERISATION OF BIOACTIVE PRINCIPLES FROM Raphia africana (OTEDOH)
ISOLATION AND CHARACTERISATION OF BIOACTIVE PRINCIPLES FROM Raphia africana (OTEDOH)
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Date
2018-01
Authors
ANYAM, John Vershima
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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, 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