Expanding the Phytoalexin Chemical Space: Tropalexins a and B from Tropaeolum Majus Suggest Evolutionary Conservation of Biosynthetic Enzymes

Tropalexins A and B, the first phytoalexins isolated from Tropaeolum majus (Brassicales order, Tropaeolaceae family), together with their antifungal activity and biosynthetic precursors are disclosed. These plant defenses contain a 1,3-benzothiazine ring and are shown to derive from Phe via the glucosinolate glucotropaeolin, which indicates that T. majus employs a phytoalexin biosynthetic pathway closely related to the pathway operating in Brassica spp. (Brassicales order, Brassicaceae family) and suggests an evolutionary conservation of key biosynthetic enzymes