Further New Staurosporine Derivatives from the Ascidian Eudistoma toealensis and Its Predatory Flatworm Pseudoceros sp.

Three new indolocarbazole alkaloids, 3-hydroxy-4‘-N-methylstaurosporine (<BO>3</BO>), 3-hydroxy-4‘-N-demethylstaurosporine (<BO>4</BO>), and 3‘-demethoxy-3‘-hydroxy-4‘-N-demethylstaurosporine (<BO>5</BO>), were isolated from the marine ascidian Eudistoma toealensis and its predatory flatworm Pseudoceros sp. in addition to two known staurosporines. The structures were determined by 1D and 2D homonuclear and ¹H-detected heteronuclear NMR spectroscopy and from comparisons with published data. CD measurements for these five staurosporine derivatives, as well as the previously described seven staurosporines, are reported, confirming that all derivatives possess the 2‘S,3‘R,4‘R,6‘R configuration.