Diterpenoids isolated from the Samoan marine sponge Chelonaplysilla sp. inhibit Mycobacterium tuberculosis growth

Crude extracts of the marine sponge Chelonaplysilla sp. collected in Samoa, that were obtained from the NCI Open Repository (NCS 21903), inhibited Mycobacterium tuberculosis growth. Assay-guided fractionation of the extract led to the isolation and structural elucidation of the known diterpenoid macfarlandin D (1) and three new diterpenoids macfarlandins F (2), G (3), and H (4). Macfarlandin D (1) exhibited potent antimicrobial activity against M. tuberculosis with an MIC of 1.2 ± 0.4 µg mL−1. Macfarlandins F (2), G (3), and H (4) exhibited significantly weaker antitubercular activities, revealing SAR for the macfarlandin antitubercular pharmacophore. The structures of compounds 2, 3, and 4 were elucidated via detailed analysis of NMR and MS data.