Four new flavonoids (1-4), along with 13 known compounds, were isolated from the heartwood of Dalbergia louvelii by following their potential to inhibit in vitro the growth of Plasmodium falciparum. Of the isolated compounds, four known compounds showed antiplasmodial activity with IC(50) values ranging from 5.8 to 8.7 microM, namely, (R)-4' '-methoxydalbergione (5), obtusafuran (6), 7,4'-dihydroxy-3'-methoxyisoflavone (7), and isoliquiritigenin (8). The structures of the new compounds were determined using spectroscopic techniques as 1-(3-hydroxyphenyl)-3-(4-hydroxy-2,5-dimethoxyphenyl)propane (1), spirolouveline (2), (3R)-7,2'-dihydroxy-4',5'-dimethoxyisoflavanone (3), and 3-(2,4-dihydroxy-5-methoxy)phenyl-7-hydroxycoumarin (4), respectively.

One hundred and ninety plants, of which 51 are used to treat malaria in traditional medicine, were collected in five different ecosystems of Madagascar for a screening programme devoted to the search of naturally-occurring antimalarial compounds. Thirty-nine plants, of which 12 are used as herbal antimalarials, were found to display in vitro activity against Plasmodium falciparum with a median inhibitory concentration (IC50) lower than 5 microg/ml while 9 had an IC50 ranging from 5 to 7.5 microg/ml. Seventeen of them exhibited cytotoxic effects on murine P388 leukemia cells with an IC50 < 10 microg/ml. The biological activities were mostly located in the ethyl acetate fractions. Bioassay-directed fractionation is underway to isolate the active constituents.

From stem barks of Isolona guesquiereina three known bisbenzylisoquinolines were isolated and identified as (-)-curine, chondrofoline and isochondodendrine. Structures were established mainly on the basis of comparison of their physical and spectral data with published data for them and their methylated derivatives. Cleavage with sodium in liquid ammonia was necessary to unambiguously determine the stereochemistry of (-)-curine and subsequently establish its stereochemical link with chondrofoline, erroneously assigned as 7-O-methyl-(+)-curine. Complete and unambiguous 1H-, 15N- and 13C-NMR assignments of the three alkaloids were made by means of 2D-NMR techniques namely, COSY, HMQC, gs-HMQC, HMBC and NOESY. (-)-Curine, isochondrodendrine and their methylated derivatives were shown to exhibit strong in vitro antiplasmodial activity and in vivo activity was also observed for (-)-curine.

Piptadenia pervillei Vatke (Fabaceae) was selected from a screening programme devoted to the search of naturally-occuring antimalarial compounds from plants of Madagascar. Bioassay-guided fractionation of the ethyl acetate extract of the leaves led to the isolation of four phenolic compounds, (+)-catechin ( 1), (+)-catechin 5-gallate ( 2), (+)-catechin 3-gallate ( 3) and ethyl gallate ( 4). Structures were determined by NMR and mass spectroscopy. Compounds 2 and 3 displayed the highest in vitro activity against the chloroquine-resistant strain FcB1 of Plasmodium falciparum with IC (50) values of 1.2 microM and 1.0 microM, respectively, and no significant cytotoxicity against the human embryonic lung cells MRC-5 was measured (IC (50) values > 75 microM). Five analogues ( 5 - 9) of (+)-catechin 5-gallate ( 2) were synthesized and evaluated for their antiplasmodial activity.

Uapaca bojeri is an endemic Malagasy plant used by the local population. This work aimed to evaluate antioxidant, anti-inflammatory, and antidiabetic activities of the methanol extracts of U. bojeri leaves and stems and to report their total phenolic content and the bioactive compound content by HPLC methods. Antioxidant capacity was determined by DPPH and ferric reducing antioxidant power (FRAP) assays. An in vivo carrageenan-induced paw oedema and acetic acid-induced writhing test in mice were used for anti-inflammatory activity evaluation. An oral glucose tolerance test was performed in mice to evaluate antidiabetic activity. The total bioactive compound content of leaves was higher than that of stems. Stem methanol extract inhibited the free radical DPPH more than the leaf methanol extract. Leaf methanol extract inhibited, in a dose-dependent manner, the carrageenan-induced paw oedema more than the stem extract, but their inhibition of the pain symptoms caused an acetic acid-induced decrease similar to the number of writhes in the dose-dependent case. The leaf and stem methanol extracts significantly reduced blood glucose levels after 30 min of glucose loading in mice compared to the control group blood glucose reduction. The presence of several bioactive compounds in U. bojeri contributed to the different biological activities, but isolation and identification of these bioactive molecules are necessary to confirm these pharmacological properties.