Ce mémoire de thèse confidentiel porte sur la valorisation phytochimique et biologique de plantes tropicales. Il s’inscrit dans le cadre d’une procédure de validation des acquis de l’expérience et retrace 14 ans de travaux de recherche appliquée pour la mise sur le marché de nouveaux actifs végétaux destinés à l’industrie dermo cosmétique ainsi que des recherches fondamentales. Ce travail a permis le développement de nouveaux actifs, à forte valeur ajoutée, issus de plantes de Madagascar par la valorisation de nombreux métabolites secondaires tels que les polyphénols (flavonoïdes, tannins, dérivés d’acide chlorogénique) et les triterpènes pentacycliques. Cette activité centrale de recherche s’accompagne d’activités essentielles liées à la maitrise de la ressource végétale en lien avec les actions de développement durable, de la recherche phytochimique, du développement de procédé et du positionnement biologique. Il est illustré entre autre le développement d’extraits issus de Buddleja axillaris, Vernonia appendiculata et les derniers travaux sur la plante Centella asiatica. / This confidential memory thesis focuses on phytochemical and biological enhancement of tropical plants. It is part of a process of validation of experience and retraces 14 years of applied research for the development of new plant extract for cosmetics industry and elemental research.This work enabled the development of new actives, with high value, from Madagascar plants by enhancement of secondary metabolites such as polyphenols (flavonoids, tannins, chlorogenic acid derivatives) and pentacyclic triterpenes. This important activity goes along with essential activities related to the mastery of plant resources in line with the sustainable development actions, phytochemical research, process development and biological positioning. It is illustrated, among other developing, extracts from Buddleja axillaris, Vernonia appendiculata and the latest work on the plant Centella asiatica.

Neste trabalho o estudo fitoquímico foi guiado por dois bioensaios visando o fracionamento e o isolamento de substâncias com atividades antitumoral e antifúngica potenciais. Os bioensaios utilizados são específicos e foram realizados com três cepas modificadas da levedura Saccharomyces cerevisiae e com duas espécies de fungos: Cladosporium cladosporioides e Cladosporium sphaerospermum. O fracionamento guiado por estes bioensaios foi desenvolvido com duas espécies da Mata Atlântica: Petiveria alliacea L. e Bathysa meridionalis L.; e uma espécie da Floresta Amazônica: Psichotria spectabillis S. Este trabalho resultou no isolamento de vinte e duas substâncias. Da espécie P. alliacea foram isolados dois sulfetos, dois dissulfetos, três polissulfetos e um esteróide. A espécie P. spectabillis forneceu três cumarinas, dois diterpenos e dois flavonóides. Da espécie B. meridionalis foram isolados sete triterpenos. Além do estudo químico guiado por bioensaios, os óleos essenciais obtidos das espécies estudadas foram analisados por cromatografia gasosa e trinta substâncias foram identificadas como polissulfetos, mono, sesqui e diterpenos. As substâncias 1, 3, 4, 5, 13 e 22 apresentaram forte atividade antifúngica. As substâncias 1, 4, 6, 9, 13, 22 e a mistura 20-21 foram capazes de inibir seletivamente o crescimento dos mutantes de S. cerevisiae indicando que a atividade citotóxica destas substâncias está relacionada com as vias de reparo do DNA celular. O sulfeto 3, o dissulfeto 4 e os polissulfetos 6 e 8 até então não haviam sido descritos na literatura como substâncias de origem natural. / In this work the phytochemical guided-fractionation, using two bioassays was performed aiming the fractionation and the isolation of potential antifungal and antitumoral compounds. The bioassays used are specific and were performed with three mutants strains of the yeast Saccharomyces cerevisiae, and with two species of fungi: Cladosporium cladosporioides and Cladosporium sphaerospermum. The bioassays guided-fractionation were clone using two plant species: Petiveria alliacea L. and Bathysa meridionalis L. from Atlantic forest: and Psychotria spectabillis S. from Amazon forest: This study resulted in the isolation of 22 substances. From P. alliacea were isolated 2 sulfydes, 2 disulfydes, 3 polissulfydes and 1 steroid. From P. spectabillis supplied 3 cumarins, 2 diterpens and 2 flavonoids. From B. meridionallis were isolated 7 triterpens. Besides the chemical guided-fractionation study, the essential oils obtained of these species were also analyzed by gaseous chromatography and 30 compounds were identified as polisulfydes, mono, sesqui and diterpens. The substances 1, 3, 4, 5, 13 and 22, showed strong antifungal activity. The substances 1, 4, 6, 9, 13, 22 and the mixture 20-21 showed DNA-damaging activity, which was evidenced by selective inhibition of the growth of the mutants of S. cerevisiae. The sulfyde 3, the disulfyde 4 and the polisulfydes 6 and 8 have been described as natural derivatives for the time in this work.

MA (African Studies) / Centre for African Studies / This study explored indigenous medicinal knowledge of Phonda in the Vhembe District. It has been noticed that phonda is becoming a scarce crop. The objectives entail seeking to solicit information on the uses of phonda, to understand the attitudes of local households towards phonda and to establish what can be done to restore the cultivation of phonda. The study used qualitative method involving unstructured interviews to collect and thematically analyse data. Purposive sampling and snowballing methods were used to make up the study sample. From literature, it is known that traditional health practitioners used phonda for treatment of certain diseases and illnesses. Phonda is no longer common, but the study sought to encourage the cultivation of phonda. The study employed an Afrocentric paradigm of social change as the conceptual framework. The study found that many households no longer plough phonda as they used to in the past. The study recommends that people should be educated on the importance of phonda to encourage them to plough it. Additionally, the researcher recommends further studies into different purposes of phonda and areas to boost its farming.