The solvent extracts from the algae Sargassum thunbergii (Sargassaceae) and Odonthalia corymbifera (Rhodomelaceae) were subjected to soybean lipoxygenase inhibitory screening. Two hydrophobic inhibitors were obtained from the extracts of S. thunbergii through inhibitory assay-guided fractionation. The inhibitors were identified as known exo-methylenic alkapolyenes (6Z,9Z,12Z,15Z)-1,6,9,12,15-henicosapentaene (1) and (6Z,9Z,12Z,15Z,18Z)- 1,6,9,12,15,18-henicosahexaene (2). The alkapolyenes 1 and 2 showed higher inhibitory activity than the known inhibitor nordihydroguaiaretic acid (NDGA). Pheophytin a (3) was obtained from the extract of O.corymbifera. The inhibitor 3 also showed higher inhibitory activity than NDGA. This is the first report on lipoxygenase inhibition of exo-methylenic alkapolyenes and a chlorophyll a-related substance. Many studies have been carried out on highly unsaturated fatty acids, leukotrienes, and LOX activity originated from macroalgae, 6-9 whereas a few studies were performed on LOX inhibitors. 10,11 During our screening of enzyme inhibitors derived from algal extracts, we disclosed potent LOX inhibitory activity of the extracts from the brown alga Sargassum thunbergii and the red alga Odonthalia corymbifera. In the present study, we isolated two exo-methylenic alkapolyenes from S. thunbergii and a chlorophyll a-related substance from O. corymbifera.S. thunbergii (2.85 kg, air-dried) was collected at the coast of Otobe, south-western Hokkaido, Japan. Fresh alga washed with tap water was extracted with MeOH-water (9:1, v/v) for a week. LOX inhibitory activity was assayed by a modified absorptiometry method 12-14 for the extract and at a series of separation steps. An ethyl acetate-soluble fraction (8.46 g) partitioned from the extract (69.5 g) was chromatographed on silica gel column with hexane-EtOAc (3:1, v/v) as eluent. Further chromatography was employed on silica gel column with n-hexane-EtOAc (19:1, v/v). The active fraction was twice separated on preparative thin-layer chromatography with n-hexane-EtOAc (3:1, v/v) and 100% hexane as developing solvent to afford inhibitors 1 (7.9 mg, 2.8 ppm yield) and 2 (2.8 mg, 1.1 ppm yield). Inhibitors 1 and 2were identified as (6Z,9Z,12Z,15Z)-1,6,9,12,15-henicosapentaene 15 (HEP, Figure 1) and (6Z,9Z,12Z,15Z,18Z)--1,6,9,12,15,18-henicosahexaene 14 (HEH, Figure 1), respectively, by their spectral data, 16 compared with the literature data. [17][18][19][20] Stereostructures of double bonds of 1 and 2 were deduced to be all Z configurations from the 13 C NMR data (δ 25.63-25.64 for 1; δ 25.52-25.64 for 2) for the allylic positions in 1,4-pentadiene moieties of them. Pfeffer et al. 21 reported that the 13 C NMR data of δ 25.7, 30.5, and 35.7 for the allylic positions in 1,4-pentadiene moieties of polyunsaturated fatty acid residues were assigned as Z,Z-, Z,E-, and E,E-isomers, respectively. HEP (1) and HEH (2) inhibited soybean LOX in concentration-dependent manners (Figure 2). The IC 50 values of 1 and 2 were calculated 40 µM and 5...
