Crambescidin 826 and dehydrocrambine A: new polycyclic guanidine alkaloids from the marine sponge Monanchora sp. that inhibit HIV-1 fusion.

Two new polycyclic guanidine alkaloids, crambescidin 826 (1) and dehydrocrambine A (2), and the known compounds crambescidin 800 (3) and fromiamycalin (4) were isolated from the marine sponge Monanchora sp. The structures of 1 and 2 were elucidated by 2D NMR and mass spectrometry, and relative stereochemistry was established by analysis of coupling constants and ROESY spectra. The pentacyclic guanidine alkaloids 1, 3, and 4 inhibit HIV-1 envelope-mediated fusion in vitro with IC(50)'s of 1-3 microM, while compound 2, a tricyclic guanidine alkaloid, showed weaker inhibition, with an IC(50) of approximately 35 microM.