Structures and aldose reductase inhibitory effects of bromophenols from the red alga Symphyocladia latiuscula

Three new bromophenols, 2,2',3,6,6'-pentabromo-3',4,4',5-tetrahydroxydibenzyl ether (1), bis(2,3,6-tribromo-4,5-dihydroxyphenyl)methane (2), and 2,2',3,5',6-pentabromo-3',4,4',5-tetrahydroxydiphenylmethane (3), were isolated from the red alga Symphyocladia latiuscula. Two bromophenols, 2,3,6-tribromo-4,5-dihydroxymethylbenzene (4) and 2,3,6-tribromo-4,5-dihydroxybenzaldehyde (5), were also reported for the first time as natural products. Their structures were elucidated on the basis of chemical and spectroscopic methods including HREIMS, HRFABMS, and 1D and 2D NMR spectral techniques. Compounds 1-5 exhibited significant aldose reductase inhibitory activity.