Bioassay-guided fractionation of extracts of Toddalia asiatica, a plant used by the Pokot tribe of Kenya to treat fevers, has yielded the alkaloid nitidine as the major antimalarial component. Fractions containing nitidine have in vitro 50% inhibitory concentrations against Plasmodium falciparum in the range of 9 to 108 ng/ml for a range of chloroquine-susceptible and -resistant strains. The results show a lack of cross-resistance between chloroquine and nitidine.Although malaria is in principle preventable and curable, in practice the majority of the population at risk cannot pay for modern treatment and the disease remains a major cause of childhood mortality in the developing world. Recent results with the vaccine sPf66 show a mean protective effect of only 30%, with very wide confidence limits (1). The rapid spread of resistance to chloroquine and related quinoline-based antimalarial agents has greatly increased the risk of malaria to many rural populations, so that there is an urgent need for affordable treatment. One possible source of such treatment lies in the traditional herbal remedies used by ethnic groups, but treatment with these remedies has suffered from a number of deficiencies. Diagnosis is often a problem, identification of plant material may be insecure, and the chemical content of extracts may vary considerably. We have set out to overcome these barriers to effective treatment by systematically evaluating the effectiveness of some of the remedies used by an ethnic group of Kenyan farmers.The Pokot traditionally inhabit a highland plateau, west of the Rift Valley in Kenya. However, the present study concerned a group of Pokot who live on Ol Ari Nyiro Ranch, Laikipia, Kenya, a plateau to the east of the Rift Valley, and who have previously been described in some detail (5).In interviews, the Pokot herbalist Cheptosai Selale, who is 90 years old, described the use of 26 plants for the treatment of malaria and fever, of which only 14 were available at the time of collection (see Table 1). Two of the 14 plants produced extracts with significant antimalarial activity against laboratory strains of Plasmodium falciparum. Bioassay-guided fractionation of the extract from Toddalia asiatica gave a pure alkaloid, nitidine, which has potentially useful antimalarial activity. MATERIALS AND METHODSPlant material. Plant material was collected from Ol Ari Nyiro Ranch and was botanically authenticated by Christine Kabuye and Joshua Muasya of the Herbarium, National Museums of Kenya, where voucher specimens were deposited. Information provided by the herbalist included the required part of the plant, the precise locality for collection, and the time when curative potency was maximal. Plant material for study was dried at room temperature, pulverized, and stored dry in plastic bags until extracts were obtained.Preparation of aqueous crude extracts for preliminary analysis. Aqueous crude extracts (10%) were prepared in a manner analogous to that used by the herbalist. Powdered plant material (10 g) was weighed in...

Two antiprotozoal compounds have been isolated from the roots of Asparagus africanus Lam. (Liliaceae), a new sapogenin, 2 beta, 12 alpha-dihydroxy-(25R)-spirosta-4,7-dien-3-one (1), which was named muzanzagenin, and the lignan (+)-nyasol (2), (Z)-(+)-4,4'-(3-ethenyl-1-propene-1,3-diyl)-bisphenol. The structure of the sapogenin was elucidated by MS and by 1D and 2D NMR methods and established by a single crystal X-ray analysis. (+)-Nyasol potently inhibits the growth of Leishmania major promastigotes, the IC50 being 12 microM, and moderately inhibits Plasmodium falciparum schizonts with the IC50 49 microM. These concentrations only moderately affect the proliferation of human lymphocytes. Muzanzagenin showed a moderate in vitro activity in all three tests, the IC50 against leishmania promastigotes was 70 microM, and against four different malaria schizont strains the IC50 values were 16, 163, 23, and 16 microM, respectively.

Two new isomeric 5-methylcoumarins, 2'-epicycloisobrachycoumarinone epoxide (1) and cycloisobrachycoumarinone epoxide (2), have been isolated from the roots of Vernonia brachycalyx by means of bioactivity-guided fractionation. The structures were elucidated by MS and NMR spectroscopic methods. Compounds 1 and 2 showed in vitro activity against Leishmania major promastigotes and against Plasmodium falciparum schizonts and demonstrated an inhibition on the proliferation of human lymphocytes, which was significantly weaker than the antiparasitic effects.

Extracts of the leaves from Vernonia brachycalyx showed in vitro activity against Plasmodium falciparum and promastigotes of Leishmania major. The germacrane dilactone 16,17-dihydrobrachycalyxolide (1) which was previously isolated from the aerial parts of the plant was shown to be the major antiplasmodial principle. An X-ray crystallographic analysis established the absolute configuration and some signals in the NMR spectra were reassigned. 16,17-Dihydrobrachycalyxolide (1) elicited a strong antiplasmodial and antileishmanial activity but also a high toxicity against human lymphocytes.

Seventeen mostly new, skin irritant diterpene esters (DTE) of the daphnane and 1 alpha-alkyldaphnane types were isolated from roots of Synaptolepis kirkii and Synaptolepis retusa. The parent alcohols of the daphnane types are shown to be 5 beta-hydroxyresiniferonol-6 alpha,7 alpha-oxide [1] and 5 beta, 12 beta-dihydroxyresiniferonol-6 alpha,7 alpha-oxide [2]. Ten of the daphnane types are 9,13,14-orthoesters and three are conventional esters involving tertiary or secondary hydroxyl groups at C-13 or C-14, respectively. The latter may be considered immediate precursors of corresponding orthoesters. The four 1 alpha-alkyldaphnane types are intramolecular 9,13,14-ortho-(2-hexadecenoic acid)-esters in which, formally, the second to last C atom of the orthoester moiety is linked covalently to C-1 alpha of the diterpene parent alcohols 1 or 2. Thus, in the new structure, a macrocyclic ring bridges the alpha side of the diterpene moiety in an "ansa" type manner. The irritancies on the mouse ear of the DTE obtained cover a wide range (I24 = 0.05-670 nmole-1). Some of them are considerably more irritant than the daphnane type standard simplexin. Structure/activity investigations reveal that an ester group instead of a free hydroxyl group at C-20 ("cryptic types"), or presence of a hydroxy or an acetoxy group in position 12 diminishes the irritancies of the daphnane types isolated, similar to what is known in corresponding tigliane types. In the standardized initiation/promotion protocol on the back skin of mice, some of the irritant DTE exhibit tumor-promoting activities higher than that of simplexin.