Halogenated phlorethols and fucophlorethols from the brown alga Cystophora retroflexa.

From an ethyl acetate fraction of the brown alga Cystophora retroflexa several halogenated phlorotannins were isolated. Most of the compounds are derivatives of diphlorethol penta-acetate and triphlorethol-A hepta-acetate. The majority turned out to be chlorinated and/or brominated. Only one iodinated substance, 2-iodophloroglucinol triacetate, was isolated. The structure of this derivative and the following compounds have been characterized previously: 2([D])-bromodiphlorethol penta-acetate, 3([A1])-bromodiphlorethol penta-acetate, 4([D])-bromo-diphlorethol penta-acetate, 4([D])-chlorodiphlorethol penta-acetate, 3([A1])-chlorotriphlorethol-A hepta-acetate, 4([D])-bromotriphlorethol-A hepta-acetate and 4([D])-chlorobisfucopentaphlorethol-A nonadeca-acetate. Ten halogenated phlorethols and two chlorinated fucophlorethols are described for the first time and characterized as their acetates: 2([B])-bromotriphlorethol-A hepta-acetate, 2([D])-bromotriphlorethol-A hepta-acetate, 2([B]), 2([D])-dibromotriphlorethol-A hepta-acetate, 3([A1]), 5([A1])-dichlorotriphlorethol-A hepta-acetate, 3([A1]), 4([D])-dichlorotriphlorethol-A hepta-acetate, 3([A1])-chloro-4([D])-bromotriphlorethol-A hepta-acetate. 2([B]), 4([D])-dichlorotriphlorethol-A hepta-acetate, 2([D]), 3([A1])-dibromotriphlorethol-A hepta-acetate, 3([A1])-bromo-2([D])-chlorotriphlorethol-A hepta-acetate, 2([D])-bromotetraphlorethol-C nona-acetate, 4([D])-chlorofucotriphlorethol-B dodeca-acetate and 4([D])-chlorobisfucotetraphlorethol-A heptadeca-acetate. Copyright 1999 John Wiley & Sons, Ltd.