| dc.description.abstract | The aim of this study was to modify three naturally occurring flavonoids namely: abyssinone V-4'~methyl ether (5), (+)-usararotenoid-A (6) and (+)_12a-epimilletosin (7) in a bid to enhance their larvicidal and antioxidant activities. Five modified analogues including abyssinone V-4'-methyl ether oxime (59), tetrahydro-abyssinone V-4'-methyl ether (60), 7- acetyl-abyssinone V-4'-methyl ether (61), 5,7-diacetyl-abyssinone V-4'-methyl ether (62) and dehydromilletosin oxime (63) were prepared. The compounds were characterized by thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR) spectroscopic techniques.
The reaction of abyssinone V -4' -methyl ether (5) with hydroxylamine hydrochloride in the presence of pyridine gave an oxime in 99% yield, while that with hydrogen gas in the presence of 5% palladium on carbon yielded 99% of the hydrogenated compound. The reaction of abyssinone V-4'-methyl ether (5) with acetic anhydride in the presence of pyridine yielded a mixture of 5% of the monoacetate and 45% of the diacetate.
The reaction of (+ )_12a-epimilletosin (7) with hydroxylamine hydrochloride in the presence of pyridine gave 50% of dehydromilletosin oxime (63) whereas the hydrogenolysis of the 9- hydroxyhomoisoflavanone (8) on 5% palladium on carbon yielded 58% of the corresponding 9_deoxylhomoisoflavanone (64). The reaction of (+)-usararotenoid-A (6) with hydroxylamine hydrochloride in the presence of pyridine gave 99% of a mixture of diastereoisomers.
Abyssinone V -4' -methyl ether (5), (+)_12a-epimilletosin (7), (+)_12a-usararotenoid-A (6), and their analogues were tested for larvicidal activity against 2nd, 3rd and 4th instar larvae of Aedes aegypti and compared with the standard - Rotenone. Potent larvicidal activities were observed against the 2nd instar larvae of Aedes aegypti with LC50 values of 0.46, 4.08, 1.68 and 13.4 Ilg/ mL at 24 hours for rotenone (9), abyssinone V -4' -methyl ether (5), abyssinone V-4'-methyl ether oxime (59) and hydrogenated abyssinone V-4'-methyl ether (60) respectively. Compounds 9 and 59 showed 100% mortality at all concentrations tested whereas compounds 5 and 60 had LC50 values of2.78 and 7.07 Ilg/ mL respectively at 48 hours.
Rotenone (9), degeulin (15), (+)-12a-epimilletosin (7), (+)-12a-usararotenoid-A (6), oximes 59, and 63 showed larvicidal activity against the late third and early fourth instar larvae of Aedes aegypti with LCso values of 1.31, 10.4, 38.4, 13.9, 18.5, and 20.8 ~g/ mL respectively at 24 hours. Rotenone (9) showed 100% mortality at 48 hours while compounds 15, 7, 6, 59 and 63 had LCso values of 2.42, 27.6,5.29,9.63, and 10.8 ~g/ mL at 48 hours and 1.43, 19.1 2.8,4.52, and 7.99 ~g/ mL respectively at 72 hours.
Rotenone (9) showed 100% mortality at 24 hours against the late third and early fourth instar larvae of Anopheles gambiae, whereas (+)-12a-usararotenoid-A (6) exhibited strong larvicidal activity with LCso value of 1 0 ~g/ mL at 24 hours and achieved 100% mortality at 72 hours. No antioxidant activity was observed for abyssinone V-4'-methyl ether and its analogues towards 2,2_diphenyl-l-picrylhydrazyl radical (DPPH) when compared with quercetin as a standard. | en_US |
