Unprecedented spirocyclization of 3-methyleneindoline-2-thiones during hydrolysis of the phytoalexin cyclobrassinin

The phytoalexin cyclobrassinin is a plant defense that has additional importance since it inhibits brassinin hydrolase, a phytoalexin detoxifying enzyme produced by the plant pathogen Alternaria brassicicola. Hence, the 1,3-thiazino[6,5-b]indole scaffold of cyclobrassinin has great application as a lead structure to design potential inhibitors of brassinin detoxification. For this reason, it is necessary to determine whether A. brassicicola is able to transform cyclobrassinin. During this work new reactions of 1,3-thiazino[6,5-b]indoles and indoline-2-thiones and their unique [4+2] cycloaddition products were discovered and characterized.