The cumbiasins, structurally novel diterpenes possessing intricate carbocyclic skeletons from the West Indian sea whip Pseudopterogorgia elisabethae (Bayer)

From the hexane extract of the West Indian gorgonian Pseudopterogorgia elisabethae, two diterpenes, cumbiasins A (1) and B (2), having a novel tetracyclic carbon skeleton named cumbiane, have been isolated. In addition, we have isolated cumbiasin C (3), a ring cleavage product of cumbiasin B that possesses an unusual carbocyclic framework named seco-cumbiane. The structures and relative configurations of metabolites 1-3 were elucidated by interpretation of overall spectral data, which included 2D NMR correlation methods, IR, UV, and accurate mass measurements (HREI-MS and HRFAB-MS). The carbocyclic skeletons of the cumbiasins are unprecedented and represent new classes of C20 rearranged diterpenes. Cumbiasins A and B display mild in vitro anti-tuberculosis activity.