Unexpected Formation of Indenoisoquinoline Derivatives from Thia Analogues of Protoberberine Alkaloids

Treatment of thia analogues of protoberberine alkaloids, 13-carboxy-13,13a-dihydro-6H,8H-isoquinolino [2,3-c][1,3]benzothiazin-8-ones, with thionyl chloride, followed by ethanol, unexpectedly provided 5,11-dioxoindeno [1,2-c]isoquinoline derivatives containing a novel ring system. Elucidation of their structures is presented in this paper. The antiproliferative effects of thiaprotoberberines and indenoisoquinolines were determined by MTT assay against a set of human adherent cancer cell lines (Hela, MCF7 and A431).