The structure of tubingensin B: a cytotoxic carbazole alkaloid from the sclerotia of aspergillus tubingensis

Tubingensin B (4), a cytotoxic carbazole alkaloid with a novel ring system, was isolated from the sclerotia of the fungus . The structure was assigned primarily on the basis of selective INEPT, homonuclear decoupling, and COSY experiments