Unveiling the first indole-fused thiazepine: structure, synthesis and biosynthesis of cyclonasturlexin, a remarkable cruciferous phytoalexin.

As a mechanism of defense against pathogens and other types of stress, watercress plants produce a variety of elicited chemical defenses generally known as phytoalexins. Herein the chemical structure, synthesis, biosynthesis and antifungal activity of cyclonasturlexin, the most intriguing indolyl phytoalexin isolated to date, are reported.

Divergent reactivity of an indole glucosinolate yields Lossen or Neber rearrangement products: the phytoalexin rapalexin A or a unique ß-d-glucopyranose fused heterocycle.

Transformation of 1-t-Boc-4-methoxyindole-3-glucosinolate under acidic conditions yielded the potent phytoalexin rapalexin A, providing its first biomimetic synthesis via Lossen type rearrangement, while a novel 1-thioimidocarbonyl-ß-d-glucopyranose heterocyclic system was obtained under basic conditions via Neber type rearrangement.