Depuis des décennies, les plantes sont utilisées en pharmacopée traditionnelle pour le soin de plusieurs maladies. Ceci en raison des résistances que présentent certains microorganismes vis-à-vis des produits pharmaceutiques. On notera aussi le manque de moyen financier pour l'accès au soin en médecine moderne. Voilà pourquoi le présent travail porte sur l'extraction, l'isolement, l'élucidation des structures, les transformations chimiques et les tests biologiques des métabolites secondaires des variétés sauvage et cultivée de l'espèce Triumfetta cordifolia A Rich (Tiliaceae). Les chromatographies successives de l'extrait organique des tiges et des feuilles de la variété sauvage ont conduit à l'isolement de quatre produits nouveaux dont deux céramides isolés des tiges et deux triterpènes obtenus des feuilles. Ces composés ont été identifiés à (2R, 6Z)-2-hydroxy-N-[(2S,3S,4R)-1,2,4-trihydroxyhexacosan-2-yl]heptadec-6enamide, {(2R)-N-(1S,2R,3E,6Z,9Z,12Z,15Z)-1-[(beta-D-glucopyranosyloxy)methyl]-2-hydroxy heneicosa-3,6,9,12,15-pentaen-1-yl}-2-hydroxytetradecanamide, 3-O-propanoyl-29-O-triacontanoylstigmasta-5,22-diene-3beta,29-diol et l'acide 2alpha,3beta,19alpha-trimethoxyurs-12-ene-24,28-dioique-24-[(2alpha,3beta)-24,28-bis(beta-D-glucopyranosyloxy)-2-hydroxy-24,28-dioxours-12-en-3-yl] ester. En plus de ces composés, onze autres de structures connues ont été isolés et identifiés à l'acide heptadecanoïque, au glucopyranoside de bêta-sitostérol, à la friedeline, au lupéol, à la bétuline, à l'acide oléanolique, à l'acide maslinique, à l'acide corosolique, au mélange de stigmastérol et bêta-sitostérol, à l'acide heneisanoïque et au trans-tiliroside. De l'extrait organique des tiges et des feuilles de l'espèce cultivée de Triumfetta cordifolia dix produits ont été isolés parmi lesquels trois n'ont pas encore été identifiés, quatre ont été déjà isolés de l'espèce sauvage (mélange de stigmastérol et bêta-sitostérol, glucopyranoside de bêta-sitostérol, triumfettamide) et les trois derniers de structures connues ont été identifiés à l'acide tormentique, à la bêta-carotène et à l'acide 24-hydroxytormentique. Les structures de ces composés ont été élucidées grâce aux données de RMN (1 et 2D) et elles ont été confirmées en comparant ces données à celles décrites dans la littérature. Le stigmastérol a été soumis à plusieurs réactions d'oxydation et en plus des produits obtenus, certains composés isolés en grande quantité ont été soumis au test de cytotoxicité sur une lignée de cellules HT1080. La méthode utilisée est la cytométrie à flux et certaines de ces drogues ont présenté une grande activité cytotoxique bien que induisant à la fois la mort nécrotique et non nécrotique des cellules cancérigènes. L'activité antioxydante des fractions issues du flash des deux plantes et certains composés a été évaluée par la méthode FRAP. Le travail révèle ici le caractère préventif et curatif de nos plantes comestibles ; car ces espèces peuvent bien utiliser contre les stress oxydatifs et les études biologiques pourront être approfondies sur certains composés isolés pour mettre en valeur leur propriétés anticancer / From decade, plants are used in traditional healer to treat many diseases. This could be explained by microorganism pharmaceutical drug resistance. Beside, the poverty limits also access to modern treatment. That is why the present work deals with extraction, isolation, structural elucidation, chemical transformation and biological evaluation of secondary metabolites isolated from the wild and cultivated species of Triumfetta cordifolia A Rich (Tiliaceae). From the organic extract of twigs and leaves of wild T. cordifolia, four new compounds were characterized (two ceramides and two triterpens) by successive chromatography methods and identified as (2R, 6Z)-2-hydroxy-N-[(2S,3S,4R)-1,2,4-trihydroxyhexacosan-2-yl]heptadec-6enamide, {(2R)-N-(1S,2R,3E,6Z,9Z,12Z,15Z)-1-[(beta-D-glucopyranosyloxy)methyl]-2-hydroxy heneicosa-3,6,9,12,15-pentaen-1-yl}-2-hydroxytetradecanamide, 3-O-propanoyl-29-O-triacontanoylstigmasta-5,22-diene-3beta,29-diol et l'acide 2alpha,3beta,19alpha-trimethoxyurs-12-ene-24,28-dioique-24-[(2alpha,3beta)-24,28-bis(beta-D-glucopyranosyloxy)-2-hydroxy-24,28-dioxours-12-en-3-yl] ester acid..These compounds were obtained together with eleven known compounds identified as heptadecanoic acid, beta-sitostérol glucopyranoside, friedelin, lupeol, betulin, oleanolic acid, maslinic acid, corosolic acid, the mixture of stigmasterol and beta sitosterol, heneicosanoic acid and trans-tiliroside. From the organic extract of twigs and leaves of cultivated species, ten products were isolated ; three among of them have not yet been identified, four of them were already obtained from the wild species and the rest were identified as Tormentic acid, beta-carotene and 24-hydroxytormentic acid. The structures of these compounds were determined on the basis of NMR data(1H, 13C, two dimensional NMR analyses), mass spectrometry structure of new compounds were confirmed by chemical transformations while those of known compounds were confirmed by comparison of their physical and spectral data with those reported in the literature and with authentic samples for some of them. Stigmasterol was subjected to different oxidation reactions. The cytotoxic activities of the products and some isolated compounds against human fribosarcoma cell line HT1080 were evaluated. The flow cytometry was used to carry out this assay and some drugs showed good cytotoxic activities although inducing at the same time the apoptopic and necrotic dead of cells. The antioxidant properties of some fractions and compounds were also evaluated by FRAP method. Trans-tiliroside and its fraction showed good antioxidant activity. This work reveals the preventive and curative character of both eatable plants since these species could be used against oxidative stress. Other biological studies could be deepened to highlight the anticancer property of some isolated compounds

Ingestion of extracts prepared from various medicinal plants to induce or augment labour is common amongst Black South African women during the late stages of pregnancy. This applies particularly to the rural areas where modern health care facilities are often lacking. Many of these plants have not been investigated scientifically and one needs to substantiate claims of quality, safety and efficacy. Furthermore, it is believed that the consumption of these plant extracts can result in foetal meconium staining at delivery. An investigation into the uterotonic properties of three plants viz. Ekebergia capensis Sparrm. Clivia miniata (Lindl.) Regel. and Grewia occidentalis L. were carried out using guinea pig uterine smooth muscle in vitro. Supercritical fluid extraction was performed with water modified supercritical carbon dioxide to extract the uterotonic components. An attempt was also made to couple supercritical fluid extraction directly on-line to the bioassay so that on line screening of crude plant extracts could be performed within short periods of time. The effects of supercritical CO2 decompression on temperature and pH of the muscle bathing solution were considered since these factors affect muscle contractility. The direct effects of excess CO2 on intracellular mechanisms were eliminated by constructing a CO2 reduction interface together with passage of carbogen which aided in the rapid displacement of excess CO2, As samples of these extracts were found to induce muscle contraction, supercritical fluid fractionation (SFF) was performed by sequentially increasing the fluid density. Extracted fractions were obtained by sequentially increasing the pressure at constant temperature and modifier concentration in an attempt to identify the active fractions. Extractions were performed at 200 atm, 300 atm and 400 atm respectively. Subsequent testing of these fractions enabled the detection of active and inactive fractions as well as a fraction that had a spasmolytic effect on uterine muscle. The 400 atm extracts of E. capensis and C. miniata displayed maximum activity while only the 300 atm extract of G. occidentalis induced uterine muscle contraction. Subsequent analysis of the sequentially extracted fractions, by high performance liquid chromatography and micellar electrokinetic capillary chromatography revealed that certain compounds present in the fractions that stimulated muscle contraction, were sensitive to the extraction pressure hence making it possible to determine the compounds that were likely to be active. Column chromatography followed by various spectroscopic techniques were performed in an attempt to isolate and elucidate the structures of the compounds that were present in the plant extracts. The extract of Ekebergia capensis yielded five known compounds (B-sitosterol, oleanonic acid, 3-epioleanolic acid, 2,3,22,23-tetrahydroxy-2,6,1 0, 15,19 ,23-hexamethyl-6, 10, 14, 18- tetracosatetrene and 7-hydroxy-6-methoxy coumarin. The extract of Clivia miniata yieded linoleic acid and 5-hydroxymethyl-2-furancarboxaldehyde while the extract of Grewia occidentalis yielded 3-(4-hydroxy-3-methoxyphenyl)-2-propenal, a novel compound 2,2' ,6,6'-tetramethoxy-4'-al-4-(w-oxo-E-propenyl)-biphenyl and oleanonic acid. The pure compounds were further evaluated pharmacologically to identify the active components and assess the physiological mode of action by the use of various receptor blockers. Oleanonic acid, 3-epioleanolic acid, linoleic acid and 5- hydroxymethyl-2-furancarboxaldehyde and 3-(4-hydroxy-3-methoxyphenyl)-2-propenal were found to induce an agonistic muscle response. All these compounds were observed to mediate their effects through the cholinergic receptors. The results obtained in this study supports the claim of these plants possessing uterotonic properties. / Thesis (Ph.D.)-University of Natal, Durban, 1997.