| This is the first time to apply Pyricularia oryzae bioassay to marine organisms for screening bioactive natural products. Among 66 ethanolic and aqueous extracts belonging to 33 species inhabiting East China Sea and South China Sea, twenty ethanolic extracts and five aqueous extracts belonging to fifteen families induced morphological deformation of P. oryzae mycelia or exhibited inhibition against conidia germination and mycelia growth of P. oryzae. Two species of brown algae-Sargassum carpophyllum and Ishige okamurai, and a species of sea hare-Natarchus leachii freeri were selected for further investigation and bioassay-guided fractionation led to the isolation of 85 compounds. Fifty-six of them were identified, among which twenty-eight compounds showed activity causing morphological abnormality of P. oryzae mycelia.The brown algae of Sargassaceae are abundant seaweeds growing along the coast of South China Sea and East China Sea. Sheu and co-workers have reported the isolation of six new cytotoxic oxygenated fucosterols from a species of the family, Turbinaria conoides. However, only a few phytochemical work have been performed on the title alga up to date. The whole plant of S. carpophyllum is used as folk medicine for the treatment of tracheitis and goitre in China. From the ethanolic extracts of the alga, twenty-five compounds were isolated and identified, i.e. twelve steroids-fucosterol (1), 24-ethylcholesta-4,24(28)-dien-3-one (2), 24-ethylcholesta-4,24(28)-dien-3,6-dione(3), saringosterol(4), 24-hydroperoxy-24-vinyl-cholesterol(5), 24R, 28R- and 24S',28S'-epoxy-24-ethylcholesterol(6), 24-ketocholesterol(7),stigmasterol-3-O- 3 -D-glucopyranoside(8), daucosterol(9), 3 ,28 -dihydroxy-24-ethylcholesta-5,23Z-dien (10), 24-ethyl-3-carbethoxy-3-hydroxy-A-nor-cholesta-5,24(28)-dien-2-one (11) and 24-ethyl-2a-oxa-2-oxo-5 a -hydroxy-3,4-dinor-cholesta-24(28)-ene (12); two chlorophyll derivates: 132S-hydroxypheophytin a(13) and pheophytin a(14); a lignan: gomisin N(15); two glycerides: l-O-palmitoyl-3-O-(l3Z-octadecenoyl) glycerol (16) and 1, 2, 3-O-tri(10Z, 13Z-octadecadienoyl)glycerol (17); three glycolipids: (2S)-1-O-palmitoyl-2-O-myristoyl-3-O- 3 -D-galactopyranosyl glycerol (18), (2S)-1-O-palmitoyl-2-O-palmitoyl-3-O- b-D-galactopyranosyl glycerol (19) and (2S)-1-O-palmitoyl-2-O-(11Z-octadecenoyl)-3-O-b-D-galactopyranosyl glycerol (20); and five other type compounds: palmitic acid (21), trans-butene diacid (22), p-hydroxy-benzoic acid (23), vanillin (24) and mannitol (25). Compounds 2-25 are first reported from the species and 10, 11, 12, 16, 20 are novel compounds or new natural products, according to the best of our knowledge. Fourteen compounds(1, 3, 4, 5, 6, 7,10,13,14,15,17,18,19 and 20) showed activity against P. oryzae. The preliminary cytotoxic assay of 1, 3, 5, 10 and 15 indicated that all the compounds exhibit cytotoxicity against cultured tumor cell line of HL-60 or P388. In the antitumor screen with sulforhodamine B microtitre plate assay, compound 6 showed cytotoxicity against six HTCLs while 4, 7, 12,13, 14, 17,18, 19 and 20 exhibited weak cytotoxicity against MCF-7 and A549 tumor cell lines in vitro. In the anti-fungus screen, 1, 3, 6 and 10 were confirmed as active against Fonsecaea pedrosoi in vitro. In the anti-HIV screen, 7 showed moderate activity against HIV-1 in vitro. However, the low therapeutic index might limit its further utilization as anti-AIDS agent.The whole alga of I. okamurai has been used as folk remedy for the treatment of laryngitis, lymphnoditis and goitre in China. From the ethanolic extracts of the alga, eighteen compounds were isolated and identified, i.e. six steroids: 5 a ,8 a -epidioxy-ergosta-6,22-dien-3 b-ol (1), saringosterol (2), fucosterol (3), stigmasterol (4), daucosterol (5) and 3, 28 -dihydroxy-24-ethylcholesta-5,23Z-dien (6); two chlorophyll derivates: 132S-hydroxypheophytin a (7) and pheophytin a (8); three glycerides: 1-O-cerotoylglycerol (9),1-O-palmitoylglycerol (10) and 1-O-(8Z-tetradecenoyl)glycerol (11); aMGDG: (2S)-1-O-palmit...
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