Chemistry Weekly Seminar - Quang Huy To
PhD student, Quang Huy To, will present a seminar on his PhD research
Speaker: Quang Huy To
Department of Chemistry, University of Saskatchewan
Title: Phytoalexins from Crucifers: Structures, Syntheses and Biosyntheses
Phytoalexins are antimicrobial natural products that play important roles in the defence mechanisms of plants. Crucifers are a diverse family of plants containing species employed globally as oilseeds, horticultural and condiment crops, as well as wild species of great interest as model-systems. My Ph.D. thesis work involved the isolation, synthesis and biosynthesis of phytoalexins from crucifer species. Highlights of this work will be presented and discussed.
Elicitation of leaves of crucifers induced the production of several metabolites that were isolated and their structures determined. Cyclonasturlexin, a tryptophan-derived phytoalexin with an unprecedented indole-fused thiazepine scaffold, was characterized and synthesized. Nasturlexins, a group of phenylalanine-derived phytoalexins were discovered, being the first non-indolyl phytoalexins reported from crucifers. The antifungal activities of all new plant metabolites against important fungal pathogens of crucifers were evaluated. Biosynthetic studies using stable isotope labelling revealed the primary precursors and biosynthetic intermediates of cyclonasturlexin and nasturlexins. That is, cyclonasturlexin is derived from brassinin, an important precursor of several cruciferous phytoalexins, which in turn is derived from (S)-tryptophan. By contrast, nasturlexins are derived from (S)-phenylalanine, via gluconasturtiin, a glucosinolate abundant in a few wild crucifer species. The discovery of new biosynthetic intermediates and pathways should facilitate the discovery of the corresponding biosynthetic enzymes and genes present in specific crucifer species.