Phytochemical Evaluation of Some Kenyan Medicinal Plants

11th NAPRECA Symposium Book of Proceedings, Antananarivo, Madagascar Pages 9-19

Midiwo et al. 9

Phytochemical Evaluation of Some Kenyan Medicinal Plants

J. Ogweno Midiwo, A. Yenesew, B.F. Juma

Kerubo L Omosa, Irene L Omosa, Daniel Mutisya.

Department of Chemistry, University of Nairobi,

P.o. Box 30197, Nairobi. Kenya.

Abstract

There are more than 1200 described medicinal plants in Kenya from a flora of approximately

10,000 members. Strong cross-medical information from the 42 ethnic groups points to the high

potential of some of these species.

The Myrsinaceae are well established ethno-anthelmintics and anti-bacterials. They are

harbingers of long alkyl side chain benzoquinones which clearly have a protective function from

their histochemical disposition. The main benzoquinone in the sub-family Myrsinodae is embelin

while for the Maesodae it is maesaquinone together with its 5-acetyl derivative; the distribution

of these benzoquinones by their alkyl side chain length or the presence / absence of 6-methyl

group is in accord with morphological sub-family de-limitation. The benzoquinones showed antifeedant,

anti-microbial, phytotoxic, acaricidal, insecticidal and nematicidal activity. Many other

benzoquinones of medium and minor concentration were also isolated and characterised.

Some plants belonging to the Polygonaceae which are widely used as ethno-anthelmintics have

been studied. The common anthelmintic anthraquinones were obtained from all five Rumex

species while the naphthalenic acetogenin derivative, nepodin was more selectively distributed.

The leaf of Polygonum senegalense is upto 17% surface exudate; about thirteen non polar

flavonoid derivatives (chalcones, dihydrochalcones, flavanones and a flavone) have been isolated

from it. From the internal aerial tissues of this plant, the major flavonoids were common

flavonoids, quercetin, kaempferol, luteolin and their glycosides. The only unique compound

isolated from this plant was 2'-glucosyl-6'-hydroxy-4'-methoxychalcone whose aglycone,

uvangolatin is part of the exudate mixture. Other leaf exudate plants studied included the

stomach-ache medicine, Psiadia punctulata (Compositae) from which novel methylated

flavonoids, kaurene and trachyloban diterpenes have been found.

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African Medicinal Plants