Tenualexin, Other Phytoalexins and Indole Glucosinolates from Wild Cruciferous Species

In general, the chemodiversity of phytoalexins, elicited metabolites involved in plant defense mechanisms against microbial pathogens, correlates with the biodiversity of their sources. In this work, the phytoalexins produced by four wild cruciferous species (Brassica tournefortii, Crambe abyssinica (crambe), Diplotaxis tenuifolia (sand rocket), and Diplotaxis tenuisiliqua (wall rocket)) were identified and quantified by HPLC with photodioarray and electrospray mass detectors. In addition, the production of indole glucosinolates, biosynthetic precursors of cruciferous phytoalexins, was evaluated. Tenualexin, (=2-(1,4-dimethoxy-1H-indol-3-yl) acetonitrile), the first cruciferous phytoalexin containing two MeO substituents in the indole ring, was isolated from D. tenuisiliqua, synthesized, and evaluated for antifungal activity. The phytoalexins cyclobrassinin and spirobrassinin were detected in B. tournefortii and C. abyssinica, whereas rutalexin and 4-methoxybrassinin were only found in B. tournefortii. D. tenuifolia, and D. tenuisiliqua produced 2-(1H-indol-3-yl) acetonitriles as phytoalexins. Because tenualexin appears to be one of the broad-range antifungals occurring in crucifers, it is suggested that D. tenuisiliqua may have disease resistance traits important to be incorporated in commercial breeding programs.