Unprecedented Polyketides from a Marine Sponge-Associated Stachylidium sp.
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Abstract:
From the marine sponge-derived fungus Stachylidium sp. six novel phthalide-related compounds, cyclomarinone (1), maristachones A–E (2–5), and marilactone (6), were isolated. The structure of compound 1 comprises a hydroxycyclopentenone ring instead of the furanone ring characteristic for phthalides and represents a new carbon arrangement within polyketides. In the epimeric compounds 5a and 5b the phthalide (=isobenzofuranone) nucleus is modified to an isobenzofuran ring with ketal and acetal functionalities. Biosynthetically the structural skeletons of cyclomarinone (1) and maristachones A (2), C (4), D (5a), and E (5b) are most unusual due to the presence of an additional carbon atom when compared to the basic polyketide skeleton. This special biosynthetic feature also holds true for the likewise isolated polyketide marilactone (6).Keywords:
Phthalide
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Isocoumarins
First asymmetric synthesis of the marine natural product (-)-gracilioether F is described from a d-mannitol derived known compound. The key step involves intramolecular 1,4-conjugate addition of a hydroxymethyl radical generated from Ti (III) mediated ring opening of a terminal epoxy ring tethered to a butenolide to produce stereoselectively a five-membered ring fused bicyclic lactone, the core structure present in gracilioether F.
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The strategies for the synthesis of naturally occurring ten-membered-ring lactones, which are the most abundant of the medium-ring lactones, are discussed. According to their structures and/or biosynthesis, the molecules are classified in monocyclic polyketides, monocyclic oxylipins, aliphatic bicyclic and aromatic bicyclic lactones. In each subsection, the lactones are presented in chronological order of their isolation. Representative complex systems bearing multiple functionalities in addition to the lactone moiety, as well as a selection of recent synthetic approaches to non-natural medium-ring lactones, are briefly presented.
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The title compound, 4a,5,6,8a,9,9a-hexahydro-9a-hydroxy-4,4,7-trimethylnaphtho[2,3-b]furan-2(4H)-one, C15H20O3, is a sesquiterpenoid isolated from the marine sponge Dysidea fragilis. The furodysinin lactone skeleton consists of two six-membered rings, which adopt chair and half-chair conformations, and a furan ring. The molecules are arranged in a helical pattern through O—H⋯O hydrogen bonds.
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The chemical study of a sponge of the genus Axinyssa collected in the Gulf of California has led to the isolation of the new bicyclic sesquiterpenes axinisothiocyanates A−L (1−12) together with the known compounds (1R,6S,7S,10S)-10-isothiocyanato-4-amorphene (13), (4R*,5R*,7S*,10R*)-4-isocyanoeudesm-11-ene, (−)-epipolasin A, and (+)-aristolone. The structures of the new metabolites have been established by spectroscopic techniques, including the analysis of pyridine-induced 1H NMR chemical shifts. The cytotoxic activity has been tested against three human tumor cell lines.
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From the marine sponge-derived fungus Stachylidium sp. six novel phthalide-related compounds, cyclomarinone (1), maristachones A–E (2–5), and marilactone (6), were isolated. The structure of compound 1 comprises a hydroxycyclopentenone ring instead of the furanone ring characteristic for phthalides and represents a new carbon arrangement within polyketides. In the epimeric compounds 5a and 5b the phthalide (=isobenzofuranone) nucleus is modified to an isobenzofuran ring with ketal and acetal functionalities. Biosynthetically the structural skeletons of cyclomarinone (1) and maristachones A (2), C (4), D (5a), and E (5b) are most unusual due to the presence of an additional carbon atom when compared to the basic polyketide skeleton. This special biosynthetic feature also holds true for the likewise isolated polyketide marilactone (6).
Phthalide
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Sponge
Isocoumarins
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Two new five-membered-ring polyketide endoperoxides, epiplakinic acid F methyl ester (1) and epiplakinidioic acid (3), and a peroxide-lactone, plakortolide J (2), were isolated from the Puerto Rican sponge Plakortis halichondrioides, along with two previously reported cyclic peroxides, 4 and 5. The structures of the new metabolites were determined by spectroscopic and chemical analyses. The absolute stereostructures of 1, 2, and 5 were determined by degradation reactions followed by application of Kishi's method for the assignment of absolute configuration of alcohols. Biological screening of cycloperoxides 1−5 and semisynthetic analogues 7−12 for cytotoxic activity against various human tumor cell lines revealed that compounds 3, 4, and 11 are very active. Upon assaying for antimalarial and antitubercular activity, some of the compounds tested showed strong activity against the pathogenic microbes Plasmodium falciparum and Mycobacterium tuberculosis.
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Chondropsin D (2), a new 37-membered-ring macrolide lactam, was isolated as a minor constituent of an aqueous extract of the marine sponge Chondropsis sp. This sponge sample had previously been the source of chondropsins A (1) and B, two novel polyketide-derived macrolides with potent cytotoxic activity. The structure of 2 was initially deduced from analysis of spectral data. This assignment was supported by the observation that chondropsin A (1), which contains a 35-membered macrocyclic ring, could be converted to chondropsin D (2) by a base-catalyzed intramolecular transesterification reaction. Rearrangement of the methylated derivative of chondropsin A (3) to the corresponding methylated analogue of chondropsin D (4) confirmed the structure of 2.
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Abstract Chemical investigation of the fungus Trichoderma sp., isolated from the Caribbean sponge Agelas dispar led to four novel sorbicillinoid polyketide derivatives ( 1 – 4 ) with an unprecedented tricyclic ring system. The structures of all compounds, including the absolute configuration, were determined by interpretation of their spectroscopic data (1D and 2D NMR, CD, MS, UV and IR), and molecular modeling calculations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
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