Isolation of a New Phlorotannin, Fucodiphlorethol G, from a Brown Alga Ecklonia cava

Ecklonia cava is a brown alga (Alariaceae), widely distributed offshore in Jeju Island.In search of anti-oxidative and anti-tyrosinase components from natural products in Jeju, we have been working on E. cava.1During the phytochemical study on the methanol extract of E. cava, a new phlorotannin-type compound 1, which we named fucodiphlorethol G, was isolated.Phlorotannins are oligo meric compounds using phloroglucinol (1,3,5-trihydroxybenzene) as a basic unit.Some phlorotannins have been identified as the bioactive components in Ecklonia species such as E. cava,2 E. kurome?and E. stolonifera.Described here are the isolation and structure identification of the compound 1.The seaweed, E. cava was collected offshore in Jeju Island, and air dried and cut into small pieces.The dried E. cava powder (4.0 kg) was extracted using 80% MeOH to provide the oily material (1.0 kg).The extract was partition ed between water and ethyl acetate.The obtained ethyl acetate fraction was successively column chromatographed using celite and then sephadex LH-20 to give 11 fractions.The eighth fraction was further purified by using Prep-LC (LC-9104, JAI) system, yielded compound 1 (140 mg) as off-white amorphous powder.By analysis of the 1H and 13C NMR spectra in 1, only aromatic proton and carbon peaks were observed.Therefore it was tentatively assumed that this compound is a phloro glucinol oligomer, a class of common compounds detected in this alga.Further investigation of 13C and DEPT NMR data suggest that 1 has a structure of phloroglucinol tetramer.The molecular formular of 1 was determined as C24H18O12 (unsaturation number 16) on the HR-FAB-MS data [m/z 499.0860 (M+H)+, calcd for C24H19O12 499.0877,A -1.7 mmu].However, investigation of the 13C NMR spectrum showed only 20 carbon signals, which implies that two symmetric benzene units are involved in compound 1.By the examination of 1H and 13C NMR data, it was found that structure of compound 1 is similar to that of triphlorethol-A (3), a trimeric phlorotannin previously isolated.1dIn the case of 1, it was assumed that one additional phloroglucinol unit was attached to triphlorethol-A framework.Comparative examination of NMR 3 values revealed that A an B rings in 1 are relatively unchanged compared to 3.However, some difference was observed in C ring in 1.For example, 1H