Novel antimycobacterial benzoxazole alkaloids, from the west Indian Sea whip Pseudopterogorgia elisabethae

[formula: see text] Our screening for marine natural products with anti-tuberculosis activity from the West Indian gorgonian coral Pseudopterogorgia elisabethae resulted in the isolation of two active diterpenoid alkaloids, pseudopteroxazole (1) and seco-pseudopteroxazole (2). Their structures were elucidated by NMR spectral analysis, including a variety of two-dimensional techniques. Compounds 1 and 2 are previously undescribed diterpenoids containing the uncommon benzoxazole moiety. Biological screening studies indicated that pseudopteroxazole (1) is a potent growth inhibitor of Mycobacterium tuberculosis H37Rv, while seco-pseudopteroxazole (2) shows moderate to strong inhibitorial activity.