Dragmacidin f, a new antiviral bromoindole alkaloid from the Mediterranean sponge Halicortex sp.

A new bromoindole alkaloid, named dragmacidin F (1) and structurally related to other dragmacidins previously described, was isolated from a marine sponge of the genus Halicortex collected off the southern coast of Ustica Island (Italy). Structural elucidation of 1 was achieved by an extensive spectroscopic study (mainly by 1D/2D-NMR and MS techniques). Compound 1, containing an unprecedented carbon skeleton that is very likely derived from cyclization of a partially oxidized form of dragmacidin D (2), showed in vitro antiviral activity against HSV-1 (EC50=95.8 mu M) and HIV-1 (EC50=0.91 mu M), thus proving to be responsible for the antiviral property exhibited by Halicortex extracts.