Studies On Chemical Constituents And Antioxidant Activity Of The Marine Red Alga Symphyocladia Latiuscula

The extracts obtained from 28 species of marine algae collected along the coastline of Qingdao were evaluated for their antioxidant activity (AA) versus the positive controls butylated hydroxytoluene (BHT), gallic acid (GA), and ascorbic acid (AscA) by using two methods both scavenging DPPH (α,α-diphenyl-β-picrylhydrazyl) radical assay andβ-carotene-linoleate assay. Most of the tested samples displayed antioxidant activity in various degrees. Among them, the extract of Symphyocladia latiuscula exhibited the strongest AA.In addition, the ethyl acetate-soluble fraction isolated from the crude extract of S. latiuscula exhibited the highest antioxidant activity in both assay systems. This fraction was further fractionated into seven subfractions (F1–F7) by vacuum liquid chromatography (VLC). F1 and F4 were found to be the most effective subfractions in scavenging DPPH radical assay and inβ-carotene-linoleate assay, respectively.The total phenolic content (TPC) and reducing power (RP) in all of the extracts, fractions, and subfractions F1-F7 were also determined. The TPC of the 28 extracts ranged from 0.10 to 8.00 of gallic acid equivalents (mg/g seaweed dry weight) while the RP ranged from 0.07 to 11.60 of ascorbic acid equivalents (mg/g seaweed dry weight). Highly positive relationships between AA and TPC as well as between AA and RP were found for the extracts and fractions. The results obtained from this study will be helpful to further analyze those marine algal species that contain the most antioxidant activity in order to identify the active principals.The extract of the S. latiuscula had the strongest antioxidant activity. Therefore this species was selected for further chemical investigation. 19 compounds were isolated by the combination of column chromatography on silica gel, preparative thin layer chromatography (PTLC), and Sephadex LH-20, RP-18, semi-preparative HPLC, and recrystallization, and were elucidated by means of spectroscopic methods including IR, UV, ESI-MS, EI-MS, FAB-MS, HR-FAB-MS, 1D-NMR and 2D-NMR, including four new compounds, namely, 1-(2,3,6-tribromo-4,5-dihydroxybenzyl)-pyrrolidin-2-one (S1), 1,2-bis(2,3,6-tribromo-4,5-dihydroxyphenyl)ethane (S2), 6-(2,3,6-tribromo-4,5-dihydroxybenzyl)-2,5-dibromo-3,4-dihydroxybenzyl methyl ether (S3), and 2,3,6-tribromo-4,5-dihydroxybenzyl methyl sulfone (S4), Five known compounds and ten compounds isolated from S. latiuscula for the first time.The isolated bromophenol compounds S1-S10 showed strong activities, with IC₅₀ values ranging from 8.1 to 24.7μM. These radical scavenging activities were 10- and 3.3-fold more potent than that of butylated hydroxytoluene (IC₅₀ = 81.8μM). Structurally, This result is in good agreement with the former observation that free radical scavenging activity increased significantly with the numbers of hydroxyl groups in related molecules.