Halicloic Acids A and B Isolated from the Marine Sponge Haliclona sp Collected in the Philippines Inhibit Indoleamine 2,3-Dioxygenase

Two new merohexaprenoids, halicloic acids A (1) and B (2), have been isolated from the marine sponge Haliclona (Halichoclona) sp. collected in the Philippines. The glycolic acids 1 and 2 slowly decomposed during acquisition of NMR data to aldehydes 3 and 4, respectively, via an oxidative decarboxylation. Halicloic acid B (2) has the new rearranged haliclane meroterpenoid carbon skeleton. The halicloic acids 1 and 2 are indoleamine 2,3-dioxygenase inhibitors that are significantly more active than the decomposition products 3 and 4.