Phlorethols, fuhalols and their derivatives from the brown alga Sargassum spinuligerum

Abstract The structural elucidation of 14 new phloroglucinol derivatives isolated from the ethanolic extract of the brown alga Sargassum spinuligerum is described. To protect them from rapid oxidation they were peracetylated before isolation. These phlorotannins belong to the classes of phlorethols, hydroxyphlorethols, deshydroxyfuhalols, fuhalols and hydroxyfuhalols. By means of spectral analysis, the following compounds were identified: hydroxytrifuhalol-A and -B nonaacetate, dihydroxytetraphlorethol-A and -B undecaacetate, deshydroxytetrafuhalol-B decaacetate, pentaphlorethol-A undecaacetate, pentafuhalol-B tridecaacetate, hydroxypentafuhalol-B tetradecaacetate, deshydroxy-hexafuhalol-B pentadecaacetate, heptafuhalol-B octadecaacetate, hydroxyheptafuhalol-A and -B nonadecaacetate and nonafuhalol-B tricosaacetate. In addition, the following 14 well known substances were identified: phloroglucinoltriacetate, diphloretholpentaacetate, bifuhalolhexaacetate, triphlorethol-A and -B heptaacetate, trifuhalol-B octaacetate, tetraphlorethol-C nonaacetate, tetrafuhalol-B undecaacetate, hydroxypentafuhalol-A tetradecaacetate, hexafuhalol-B hexadecaacetate, trifuhalol-A octaacetate, hydroxytetraphlorethol-A decaacetate, pentafuhalol-A tridecaacetate and heptafuhalol-A octadecaacetate. An accurate assignment of 1 HNMR chemical shifts was carried out for the last four of these.