Chemical constituents of two oriental orchids, Calanthe discolor and C-liukiuensis: Precursor indole glycoside of tryptanthrin and indirubin

Two indole glycosides, calanthoside and glucoindican, were isolated from tw o oriental orchids, Calanthe discolor LINDL. and C. liukiuensis SCHLTR., to gether with calaphenanthreol, calaliukiuenoside, and bioactive known alkalo ids, tryptanthrin, indirubin, and isatin. The structures of calanthoside, g lucoindican, calaphenanthreol, and calaliukiuenoside were determined on the basis of physicochemical and chemical evidence. Furthermore, it was found that enzymatic hydrolysis of calanthoside furnished tryptanthrin as the mai n product, whereas indirubin and isatin were obtained by acid hydrolysis of calanthoside.