Abstract Indirubin, present in extracts of Isatis tinctoria and some other plant species, has promising cytotoxicity against a variety of cell lines by inhibition of cyclin-dependent kinases. Chemical synthesis of its derivatives relies on the combination of isatins and 2, 3-dihydro-1H- indol-3-one ('indoxyl') derivatives and usually yields indigo as well as other by-products. Inspection of the hydrolysis of the long-known condensation products of 2- ...
