A new approach to the synthesis of rare thiazino[6,5-b]indol-4-one derivatives. First total synthesis of the indole phytoalexins cyclobrassinon.

The first synthesis of the indole phytoalexin cyclobrassinon and some of its analogues, possessing a thiazino[6,5-b]indol-4-onetricyclic ring system was performed starting from 1-substitued 2-chloroindole-3-carboxaldehydes. The route employed the intramolecular Et3N-mediated or photochemical nucleophilic substitution of a chlorine atom in the 2-position of the indole ring with a sulfur atom as a key step. Examination of biological activity against the selected tumor cell lines, bacteria and fungi revealed no expressive activity of synthesized compounds.