| dc.description.abstract | Polygonum species enjoys a wide distribution In
the highland regions of Kenya. Eleven species are
reported as present in this country with four species
among these being most common. The four include;
P.senegalense Meisn, P.salicifolium Willd, P. pulchrum
Blume and P.setosulum A. Rich. and have found use in
traditional medicine.
Cold extraction of the leaves of the four species,
through washing technique with acetone, followed by thin
layer chromatographic analysis of the respective
extracts found P. senegalense as the richest in
flavonoid aglycones. Unlike in the three others, the
leaves of P. senegalense species are either covered with
resinous material (glabrous) in which flavonoid
aglycones are dissolved or are covered by
quasi-crystalline farina (tomentose) which also contain
an almost identical set of flavonoid aglycones as the
former. In either case, or variations in between (leaves
both tomentose and glabrous), the flavonoid aglycones
are restricted to the leaf surface with younger leaves
having higher concentration.
Petroleum ether wash of the leaf surface led to a
flavonoid concentrate which was completely toxic to Aedes
aegyti mosquito larvae at 10 ppm. Furthermore, 10 ppm of
such a solution sprayed on a sugar coated Whatman No.1
filter paper completely protected it from being fed on
by Schistocerca gregaria (desert locust) previously
starved for 24 hours. Broad fractionation of this
petroleum ether wash concentrate on silica gel using
solvents; petroleum ether (40 - 60), benzene, chloroform
and methanol concentrated the activities in the
chloroform fraction. Complete resolution of this
fraction followed by spectroscopic analysis revealed
several flavonoid aglycones, among them:
2' ,6'-dihydroxy-3' ,4'-dimethoxychalcone -2-/ 2',6'-
dihydroxy-4'-methoxydihydrochalcone 2;
2',4'- dihydroxy-3',6'-dimethoxychalcone 4
2' ,6'-dihydroxy-4'-methoxychalcone 2
2' ,4'-dihydroxy-6'- methoxychalcone 6; and
2' ,5'-dihydroxy-3' ,4' ,6'-trimethoxychalcone 8.
Fractional crystallization of the benzene fraction
yielded 2'-hydroxy-4' ,6'-dimethoxychalcone and
5-hydroxy-7-methoxyflavanone 2. Acid hydrolysate of
the methanol fraction Ii yielded 7-hydroxy-5,8-
dimethoxyflavanone 10 and 7 hydroxy-5-methoxyflavanone
Antifeedant and larvicidal bioassay tests on these
compounds found compound 2 to be toxic to the Aedes
aegypti mosquito larva at 0.8 ppm. Compound 1 was found
to be phago-stimulatory to Schistocerca gregaria while
compound 2 showed high toxicity at 2 ppm towards Aedes
aegypti mosquito larvae.
Compound A, previously reported as showing
molluscicidal activity, was found to be toxic towards
Aedes aegypti larvae at concentrations of about 2 ppm . | en |
