Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Ethnobotany, phytochemistry and antimicrobial activity of Combretum, Terminalia and Anogeissus species (Combretaceae) growing naturally in Sudan

Auteur : Salih, Enass Yousif Abdelkarim

Université de soutenance : University of Helsinki,

Grade : Doctoral dissertation (article-based) / Doctoral Programme in Interdisciplinary Environmental Sciences 2019

Résumé
A variety of tree species, belonging to the genera Combretum, Anogeissus and Terminalia (Combretaceae) are well known for their uses in African traditional medicine for the treatment of infectious diseases and wounds. In this study, Anogeissus leiocarpus, Terminalia brownii and Terminalia laxiflora were selected based on ethnopharmacological information for in-depth studies on their antimicrobial effects and phytochemical constituents. The mentioned species were collected from the Blue Nile and Kordofan regions in Sudan. The main objectives of this research were (1) to perform ethnobotanical and ethnopharmacological documentation of the medicinal plants found in the study areas in Sudan, (2) to study the in vitro antibacterial and antifungal effects of extracts, obtained from A. leiocarpus, T. brownii and T. laxiflora, (3) to elucidate the chemical structures of compounds in extracts with promising antimicrobial activity and to (4) isolate fractions with antibacterial activity using preparative TLC and column chromatography. Ethnopharmacological and ethnobotanical information was collected from seven villages during three expeditions. According to this information species belonging to the family Combretaceae could be especially prospective as sources for antimicrobial extracts and compounds. Therefore various parts of the studied plants were subjected to antimicrobial testing using Staphylococcus aureus ATCC 25923, S. epidermidis ATCC 12228, Micrococcus luteus ATCC 4698 and Mycobacterium smegmatis ATCC 14468. In addition the plant pathogenic fungi, Aspergillus niger ATCC 9763, Aspergillus flavus ATCC 9763, Nattrassia mangiferae ATCC 96293 and Fusarium verticilloides (syn. F. moniliformis) ATCC 24378 were used. Compounds in the active extracts were characterised using HPLC-DAD, GC-MS, UHPLC/QTOF-MS and LC-MSn Tandem Mass Spectrometry. In studies I, II and III the ethnopharmacological data of the uses of Terminalia brownii, T. laxiflora and Anogeissus leiocarpus in traditional medicine in the villages in Sudan against diarrhoea and cough and for wound inflammation, could be verified. Our results demonstrate that especially extracts of the studied plants are active in vitro against the growth of human pathogenic bacteria, including a model bacterium for tuberculosis, with the lowest MIC values of 39 µg/ml. Pure compounds, such as punicalagin and corilagin, present in these active extracts, did not give as low MIC values and demonstrate that the antimicrobial compounds in the studied plants could act in concert. However, purification using Sephadex LH-20 of a root extract of T. brownii resulted in a significant reduction of the MIC against M. smegmatis from 5000 to 62,5 µg/ml. The chemical profiling of the most active extracts demonstrated the presence of a high variety of chemical classes, including ellagitannins, gallotannins, condensed tannins, flavonoids, stilbenes and fatty compounds. Methyl-(S)-flavogallonate was characterized for the first time from the roots of T. brownii and corilagin and its isomer, sanguiin H-4, and punicalagin have not been found before in the roots of T. laxiflora. Among the compounds in the studied species both antibiotic scaffolds and adjuvants could be found. Moreover, our in vitro results against phytopathogenic fungi demonstrate that T. brownii could be used for the protection of crop plants against fungal contamination.

Présentation

Version intégrale (12,4 Mb)