A marine diterpene with a novel tetracyclic framework from the West Indian gorgonian octocoral Pseudopterogorgia elisabethae.

[structure: see text] Colombiasin A (1) was isolated from an extract of the West Indian gorgonian octocoral Pseudopterogorgia elisabethae that showed strong inhibitorial activity against Mycobacterium tuberculosis H37Rv. Structure elucidation by interpretation of 2D-NMR spectroscopic data, IR, UV, and accurate mass measurements (HREI-MS) revealed that colombiasin A belongs to a previously undescribed class of C20 rearranged diterpenes possessing an intricate tetracyclic framework.