Extraction of vernonia oil from vernonia galamensis seeds and its aminolysis to vernolamides

Citation:
Extraction of vernonia oil from vernonia galamensis seeds and its aminolysis to vernolamides.; 2001.

Abstract:

Vernonia galamensis grows as a common weed and is widely distributed in Africa,
and its center of diversity is found in East Africa. The dry seeds of Vernonia galamensis
contains a naturally epoxidized oil that is rich in trivernolin, which constitutes about 80% of
the seeds oil. The vernonia oil has a unique structure that makes it attractive for the
preparation of novel and useful products.
This study reports on the extraction of vernonia oil and its conversion to vernolamides
with higher added value. The oil was extracted from the seeds of Vernonia galamensis ssp.
nairobensis using soxhlet extraction. About 31.6% of crude oil was obtained which after
refining gave about 25.2% of oil. The oil was then reacted with 1,6-diaminohexane, 1,8-
diaminooctane, 2-aminopyridine, 2-(aminomethyl)pyridine and 2-(2-aminoethyl)pyridine to
give the corresponding vernolamides under two varied conditions, temperature (25,70 and
80°C) and solvents (neat, chloroform, dichloromethane and dimethylformamide). In all
~
reactions a mole ratio of vernonia oil to amine (1 :3) was used at the reaction time of 12 h.
!
In all cases, highest yields of the vernolamides (4l.2-72.3%) were obtained at 70°C in
chloroform, while the lowest yields (21-53.3%) were recorded at 80°C. The reactions at 25°C
gave reasonably high yields (17-62.8%), thus aminolysis proceeds even at room temperature.
Aminolysis carried under neat conditions also gave relatively high yields (41-64.2%).
The vernolamides were analyzed by thin-layer chromatography (TLC), infrared (IR),
electron impact mass spe~ctroscopy (ElMS) and nuclear magnetic resonance (NMR)
spectroscopic techniques.
The antimicrobial activities of the products were investigated at concentrations of
~
100)..lg, 50)..lg and 25)..lg by the disc diffusion method. The vernolamides exhibited only
antibacterial activity and was greater against gram-positive (Bacillus subtilis) than in gramIX
negative (Escherichia coli) bacteria. There was no antifungal activity shown on all the fungi
that were investigated.

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