Bromophenolics from the Red Alga Polysiphonia decipiens

The isolation and the structure determination of a new bromophenolic compound, polysiphonol (10), as well as five previously reported compounds, (4–8), from the red alga Polysiphonia decipiens is reported. In addition, the absolute configuration of the natural product rhodomelol (8) could be unequivocally confirmed for the first time, and on biosynthetic grounds, the absolute configuration of polysiphonol (10) was tentatively suggested. Compounds 4–8 were evaluated for their antibacterial activity against both Gram-positive and Gram-negative bacteria, but none of the compounds showed any appreciable activity.