Chromatographic fractionation of the CH2Cl2/MeOH extract of the Red Sea red alga Laurencia obtusa gave two new hexahydrofuro[3,2-b]furan-based C15-acetogenins, namely, isolaurenidificin (1) and bromlaurenidificin (2). The chemical structures were elucidated based on extensive analyses of their spectral data. Compounds 1 and 2 showed no toxicity (LC50 > 12 mM) using Artemia salina as test organism. Both compounds showed weak cytotoxicity against A549, HepG-2, HCT116, MCF-7, and PC-3 cells, however, they exhibited a relatively potent cytotoxic activity against peripheral blood neutrophils. This can be attributed partly to induction of apoptosis.
