Phytoalexins from crucifers : probing detoxification pathways in Sclerotinia sclerotiorum

Content Provider	Semantic Scholar
Author	Hossain, Mohammad
Copyright Year	2007
Abstract	This thesis investigates two aspects of phytoalexin metabolism by the phytopathogenic fungus Sclerotinia sclerotiorum (Lib) de Bary: (i) determination of detoxification pathways of structurally different molecules; (ii) design and synthesis of potential inhibitors of enzyme(s) involved in detoxification steps. First, the transformations of important cruciferous phytoalexins by the economically important stem rot fungus, S. sclerotiorum, were investigated. During these studies a number of new metabolic products were isolated, their chemical structures were determined using spectroscopic techniques, and further confirmed by synthesis. The metabolic products did not show detectable antifungal activity against S. sclerotiorum which indicated that these metabolic transformations were detoxification processes. Overall, the results of these transformations suggested that S. sclerotiorum produces various enzymes that can detoxify cruciferous phytoalexins via different pathways. While the detoxifications of strongly and moderately antifungal phytoalexins such as brassilexin, sinalexin, and 1-methoxybrassinin were fast and led to glucosylated products, the transformations of the weakly antifungal phytoalexins brassicanal A, spirobrassinin and 1-methoxyspirobrassinin were very slow and yielded nonglucosylated compounds. Next, the design of potentially selective inhibitors of the brassinin detoxification enzyme, BGT, was sought. Two sets of potential inhibitors of BGT were designed: (i) a group was based on the structure of brassinin, where the indole ring of brassinin was replaced with benzofuran, thianaphthene, 7-azaindole and pyrazolo[1,5a]pyridine and/or the position of side chain was changed from C-3 to C-2; and (ii) another group based on the structure of camalexin where the thiazole ring of camalexin was replaced with a phenyl group. The syntheses and chemical characterization of
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Language	English
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