| Marine natural product is one of the most active subfield of natural pharmaceutical discovery. This work describes the chemical investigations of marine brown alga Dictyopteris divaricata and marine invertebrate Amaroucium sp.. Also covered are the isolation, structure elucidation techniques employed in this studies and bioactivities screening of the isolates from the marine organism. Dictyopteris divaricata, a brown alga belonging to the family of Dictyotaceae was collected from the coast of Qingdao, Shandong Province, China. Air-dried sample was extracted with ethanol. Then the ethanol extract was portioned with EtOAc and n-BuOH to yield three fractions. The ethanol extract, EtOAc-soluble fraction, n-BuOH-soluble fraction and H2O-soluble fraction were tested for antitumor activity. The EtOAc-soluble fraction showed strong activity against B16-BL6 and A2780 with the IC50 7.61 and 8.06 μg/mL, respectively. Further chemical constituents investigation into the EtOAc-soluble fraction led to the isolation of 33 compounds by means of normal phase silica gel chromatography, Sephadex LH-20 chromatography, HPLC and recrystallization. Structure elucidation was accomplished by spectroscopic methods including IR, MS, HRMS, 1D NMR, 2D NMR and X-ray single crystal diffraction experiments. 18 of them were new compounds including three novel carbon skeletons and eight new compounds (D9~D16). New compounds were named as (-)-(1R,6S,7S,10R)-1-hydroxycadinan- 3-en-5-one (D1), (+)-(1R,5S,6R,7S,10R)-cadinan-3-en-1,5-diol (D2), (+)-(1R,5R, 6R,7S,10R)-cadinan-3-en-1,5-diol (D3), (+)-(1R,5S,6R,7S,10R)-cadinan-4(11)-en- 1,5-diol (D4), (+)-(1R,5R,6R,7R,10R)-cadinan-4(11)-en-1,5,12-triol (D5), (-)-(1R,4R, 5S,6R,7S,10R)-cadinan-1,4,5-triol (D6), (-)-(1R,6R,7S,10R)-11-oxo-cadinan-4-en- 1-ol (D7), (+)-(1R,6R,9S)-4-acetyl-1-hydroxyl-6-isopropyl-9-methylbicyclo[4.3.0] non-4-en-3-one (D8), (+)-(1R,5R,6S,9R)-3-acetyl-1-hydroxyl-6-isopropyl-9- methylbicyclo[4.3.0]non-3-ene (D9), (+)-(1R,3S,4S,5R,6S,9R)-3-acetyl-1,4- dihydroxyl-6-isopropyl-9-methylbicyclo[4.3.0]nonane (D10), (+)-(1R,3R,4R,5R, 6S,9R)-3-acetyl-1,4-dihydroxyl-6-isopropyl-9-methyl bicyclo[4.3.0]nonane (D11), (+)-(1S,2S,6S,9R)-1-hydroxyl-2-(1-hydroxyethyl)-6-isopropyl-9-methylbicyclo[4.3.0]non-4-en-3-one(D12), (+)-(5S,6R,9S)-2-acetyl-5-hydroxyl-6-isopropyl-9- methylbicyclo[4.3.0]non-1-en-3-one (D13), (+)-(1R,6S,9R)-1-hydroxyl-6-isopropyl- 9-methylbicyclo[4.3.0]non-4-en-3-one (D14), (-)-(1S,6S,9R)-1-hydroxyl-6- isopropyl-9-methylbicyclo[4.3.0]non-4-en-3-one (D15), (+)-(5S,6R,9S)-5-hydroxyl- 6-isopropyl-9-methylbicyclo[4.3.0]non-1-en-3-one (D16), (-)-(1R,7S,10R)- 1-hydroxy-11-norcadinan-5-en-4-one (D17), 3-[(decahydro-2-hydroxy-2,5,5,8a- tetramethyl-1-naphthalenyl)-methyl]-4-hydroxybenzoic acid (D18). The absolute stereochemistry of the new compounds was determined by CD spectra and Biogenesis Biogenetic Origin. 15 known compounds were (-)-torreyol (D19), 4β,5α-dihydroxycubenol (D20), 3-farnesyl-p-hydroxybenzioc acid (D21), chromazonarol (D22), fucosterol (D23), loliolide (D24), isololiolide (D25), 3β-hydroxy-5α,6α-epoxy-7-megastigmen-9-one (D26), dehydrovomifoliol (D27), (3R)-4-[(2R,4S)-dihydroxy-2,6,6-trimethylcyclohexylidene]-3-buten-2-one (D28), (3R)-4-[(2R,4S)-4-acetoxy-2-hydroxy-2,6,6-trimethylcyclohexylidene]-3-buten-2-one (D29), aurantiamide acetate (D30), phenylacetamide (D31), 4-hydroxybenzoic acid (D32), hexadecanoic acid (D33). All the compounds were obtained from this species for the first time. These compounds were belonging to different classes of structure, including sesquiterpene, sesquiterpene-derivative, norsesquiterpene, steroid, ionone derivative, dipeptide, organic acid and so on. Amaroucium sp. was collected from the coast of Qingdao, Shandong Province, China. Minced sample of Amaroucium sp. was extracted with ethanol to yield brown residue. Then the residue was extracted with EtOAc and n-BuOH to give three fractions. The n-BuOH-soluble fraction was subjected to chemical constituents study by means of normal phase silica gel chromatography,...
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