Isobrassinin (2-(S-methyldithiocarbamoylaminomethyl) indole (7a), a regioisomer of the cruciferous phytoalexin brassinin (1), exerted marked antiproliferative effects on the HeLa, A431 and MCF7 cell lines (> 78.6% inhibition at 30μM). For structure–activity relationships, further analogues were synthesized. The highest cytotoxic effect was displayed by 2- phenylimino-1, 3-thiazino [5, 6-b] indole (10)(10μM, 76.8%—HeLa and 46.3%—MCF7). ...