| In order to search for new active lead compounds from marine organisms and make good use of marine resources, the ethanolic extract, EtOAc portion, n-BuOH portion and water portion of thirteen marine algae were screened for antitumor activity against ten human cancer cell lines. The EtOAc portion of the brown alga Leathesia nana S. et G. was further studied. Fractions L1~L24 obtained by normal phase silica gel chromatography of the EtOAc soluble extract were screened for antitumor activity against six human cancer cell lines to search for active portions. On the basis of bioactivity and sample quantity, the brown alga Leathesia nana was subjected to bioassay-guided purification and identification.Twenty-five compounds, including bromophenol, alkaloid, glyceride and steroid, were isolated from the EtOAc portion of the ethanolic extract of the brown alga Leathesia nana by means of recrystallization, normal phase silica gel chromatography, Bio-Beads SX3 chromatography, Sephadex LH-20 chromatography, reverse phase MPLC and HPLC. Their structures were elucidated by spectroscopic methods, including IR, MS, HRMS, NMR and X-ray single crystal diffraction experiments, and comparison of their physical and spectral data with those in literatures. Among these twenty-five compounds, eight new were named as (E)-2-methyl-3-(2,3-dibromo- 4,5-dihydroxyphenyl)-propenal (1), (+)-2-methyl-3-(2,3-dibromo-4,5-dihydroxyphenyl) -1-propanol (2), 5,6(-diethyloxymethyl-3,4,2(-tribromo-2,3(,4(-trihydroxydiphenyl ether (3), 2-(2,3-dibromo-4,5-dihydroxybenzyl)-3,5-dihydroxy-4-methoxybenzyl alcohol (4), 6-(2,3-dibromo-4,5-dihydroxybenzyl)-2,3-dibromo-4,5-dihydroxybenzyl methyl ether (5), 9,10-dihydro-9,10-dimethoxy-3,4,7,8-tetrabromo-1,2,5,6- tetrahydroxyanthracene (6), (+)-3-(2,3-dibromo-4,5-dihydroxy-phenyl)-4-bromo-5,6- dihydroxy-1,3-dihydroiso -benzofuran (7) and rel-(4aS*,10aR*)-(()-6,7- dibromo-4a-hydroxy-3,8-dihydroxy-methyl-10a-methoxy-1,4,4a,10a-tetrahydrodibenzo[b,e][1,4]dioxin-1-one (8); and seventeen known were named as 3-bromo- 4-hydroxybenzoic acid (9), 2-bromo-4,5-dihydroxybenzaldehyde (10), 3-bromo- 4,5-dihydroxybenzaldehyde (11), 2,3-dibromo-4,5-dihydroxybenzaldehyde (12), 2,3-dibromo-4,5-dihydroxybenzyl alcohol (13), 2,3-dibromo-4,5-dihydroxybenzyl methyl ether (14), 2,3-dibromo-4,5-dihydroxybenzyl ethyl ether (15), bis(2,3- dibromo-4,5-dihydroxybenzyl) ether (16), 2,2(,3,3(-tetra-bromo-4,4(,5,5(- tetrahydroxydiphenyl methane (17), 2-(2,3-dibromo-4,5-dihydroxy-benzyl)- 3-bromo-4,5-dihydroxybenzyl methyl ether (18), 2-(2,3-dibromo-4,5-di- hydroxybenzyl)-3-bromo-4,5-dihydroxybenzyl ethyl ether (19), 1H-indole-3- carboxylic acid (20), 3-hydroxyacetyl-1H-indole (21), 3,5-dihydroxy- 4-methoxyl benzyl alcohol (22), 4-hydroxybenzoic acid (23), 1-O-hexanoyl-glycerol ester (24) and fucosterol (25). Compounds 1~25 were screened for antitumor activity against six human tumor cell lines HCT-8, Bel7402, BGC823, A549, A2780 and MCF-7, enzymatic inhibitory activity against three enzymes AChE, COX-2 and PTP1B, immune modulatory activity toward T and B lymphocyte, antifungal activity against Canidia albicans and antibacterial activity against Staphylococcus aurens and Escherichia coli. In the in vitro activity test, new compound 5 and known compounds 16~19 and 24 exhibited strong antitumor activity. Especially, IC50 value of compound 5 was found to be 2.83, 5.21, 1.49 and 1.58 μg/mL against four human tumor cell lines Bel7402, BGC823, A549 and A2780, respectively. Compounds 16, 17 and 19 showed significant enzymatic inhibitory activity against protein tyrosine phosphatase PTP1B with an IC50 value of 1.5, 2.4 and 0.84 μmol/L, respectively. Compounds 16~19 exhibited powerful immune modulatory activity toward T and B lymphocyte while they displayed toxicity against normal cells. All compounds do not show significant antifungal and antibacterial activity.It has been reported marine sponge is one of the marine organisms that are studied most for marine natural products. They have proven to be a rich source for novel organic com...
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