Six novel dibenzyl bromophenols (1-6) with different dimerization patterns and two propyl bromophenol derivatives (7 and 8), together with 11 known bromophenol derivatives, were isolated from the ethanolic extract of the brown alga Leathesia nana. On the basis of spectroscopic methods the structures of the new compounds were determined as 5,6'-diethyloxymethyl-3,4,2'-tribromo-2,3',4'-trihydroxydiphenyl ether (1), 2-(2,3-dibromo-4,5-dihydroxybenzyl)-3,5-dihydroxy-4-methoxybenzyl alcohol (2), 6-(2,3-dibromo-4,5-dihydroxybenzyl)-2,3-dibromo-4,5-dihydroxy benzyl methyl ether (3), 9,10-dihydro-9,10-dimethoxy-3,4,7,8-tetrabromo-1,2,5,6-tetrahydroxyanthracene (4), (+)-3-(2,3-dibromo-4,5-dihydroxyphenyl)-4-bromo-5,6-dihydroxy-1,3-dihydroisobenzofuran (5), rel-(4aS,10aR)-(+/-)-6,7-dibromo-4a-hydroxy-3,8-dihydroxymethyl-10a-methoxy-1,4,4a,10a-tetrahydrodibenzo[b,e][1,4]dioxin-1-one (6), (E)-2-methyl-3-(2,3-dibromo-4,5-dihydroxyphenyl)propenal (7), and 2-methyl-3-(2,3-dibromo-4,5-dihydroxyphenyl)-1-propanol (8). Some compounds including 3 showed in vitro selective cytotoxicity against several human cancer cell lines. This is the first brown alga to be reported containing bromophenols.

Eight new bromophenol derivatives, 2,3-dibromo-4,5-dihydroxybenzyl methyl sulfoxide (1), 4-(2,3-dibromo-4,5-dihydroxyphenyl)-3-butene-2-one (2), 2-(3-bromo-5-hydroxy-4-methoxyphenyl)-3-(2,3-dibromo-4,5-dihydroxyphenyl)propionic acid (3), 2-(3-bromo-5-hydroxy-4-methoxyphenyl)-3-(2,3-dibromo-4,5-dihydroxyphenyl)propionic acid methyl ester (4), 2-phenyl-3-(2,3-dibromo-4,5-dihydroxyphenyl)propionic acid (5), 4'-methoxy-2'',3',3''-tribromo-4'',5',5''-trihydroxydiphenylacetic acid (6), and 3-bromo-5-hydroxy-4-methoxyphenylacetic acid (7) and its methyl ester (8), together with a known bromophenol, 3-bromo-5-hydroxy-4-methoxybenzoic acid (9), were isolated from the red alga Rhodomela confervoides. Their structures were elucidated by spectroscopic methods including IR, EIMS, FABMS, ESIMS, HRFABMS, HRESIMS, 1D and 2D NMR, and single-crystal X-ray structure analysis. Compounds 1-4, 8, and 9 were found inactive against several human cancer cell lines and microorganisms.

Four new bromophenols C-N coupled with methyl gamma-ureidobutyrate (1-4), a phenylethanol bromophenol (5), and three phenylethanol sulfate bromophenols (6-8) have been isolated from polar fractions of an ethanolic extract of the red alga Rhodomela confervoides. On the basis of spectroscopic evidence including HRMS and 2D NMR data, the structures of the new compounds were determined as methyl N'-(2,3-dibromo-4,5-dihydroxybenzyl)-gamma-ureidobutyrate (1), methyl N,N'-bis(2,3-dibromo-4,5-dihydroxybenzyl)-gamma-ureidobutyrate (2), methyl N'-[3-bromo-2-(2,3-dibromo-4,5-dihydroxybenzyl)-4,5-dihydroxybenzyl]-gamma-ureidobutyrate (3), methyl N'-(2,3-dibromo-4,5-dihydroxybenzyl)-N'-[3-bromo-2-(2,3-dibromo-4,5-dihydroxybenzyl)-4,5-dihydroxybenzyl]-gamma-ureidobutyrate (4), 2,3-dibromo-4,5-dihydroxyphenylethanol (5), 2,3-dibromo-4,5-dihydroxyphenylethanol sulfate (6), 3-bromo-4,5-dihydroxyphenylethanol sulfate (7), and 3-bromo-2-(2,3-dibromo-4,5-dihydroxybenzyl)-4,5-dihydroxyphenylethanol sulfate (8). The cytotoxicity of all compounds was evaluated against several human cancer cell lines including human colon cancer (HCT-8), hepatoma (Bel7402), stomach cancer (BGC-823), lung adenocarcinoma (A549), and human ovarian cancer (A2780). Among them, the phenylethanol and the phenylethanol sulfate bromophenols (5-8) showed moderate cytotoxicity against all tested cell lines.