A new dimeric carbazole alkaloid from Glycosmis stenocarpa roots

A new dimeric pyranocarbazole alkaloid, bisisomahanine (1), was isolated from the roots of Glycosmis stenocarpa (DRAKE) TAN., along with two known monomeric carbazole alkaloids, murrayafoline-A (2) and murrayanine (3). The planar structure of bisisomahanine was determined to be 9,9'-dihydroxy-3,3',8,8'-tetramethyl-3,3'-bis-(4-methyl-3-pentenyl)-3,3',11,11'-tetrahydro-10,10'-(bipyrano[3,2-a]carbazole) from the combination of spectroscopic and chemical evidence. Bisisomahanine is the first dimeric prenylated pyranocarbazole alkaloid with a 1,1' type of linkage; the NMR and CD spectroscopic data indicated it to be a mixture of diastereomers having a dominant configuration at the axis of chirality. (1)H- and (13)C-NMR assignments of murrayafoline-A were made on the basis of 2D-experiments.