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Results for “Pyrones”

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At least 1,279 records · Page 71Linked to original sources
PubMed2006

Cycloisomerization of activated (2E,4Z)-heptatrienoate and its relevance to crispatene (bio)synthesis. A case of concerted and stepwise uncertainty.

A single transition structure was located on the potential energy surface of the cycloisomerization of protic and Lewis acid activated (2E,4Z)-heptatrienal and the corresponding methyl ester to provide the bicyclo[3.1.0]hexene derivatives, the central skeleton of the crispatene natural products. A two-dimensional scan of the C-C bond-forming reactions revealed a barrierless cyclopropane closure following the pentadienyl cycloisomerization, with preservation of the stereochemical information.

Alkadienes↗
PubMed2006

Total synthesis of gymnoconjugatins A and B.

Convergent and efficient syntheses of the microbial natural products gymnoconjugatin A and B are reported and were based on a linchpin coupling strategy using a boron/tin hetero-bis-metallated butadiene system.

Boron Compounds↗
PubMed2001

Planifolin, a new naphthopyranone dimer and flavonoids from Paepalanthus planifolius.

A new naphthopyranone dimer (1) named planifolin was isolated from a methylene chloride extract of the capitula of Paepalanthus planifolius. The structure of 1 has been determined by chemical and spectroscopic means. In addition, a known dihydronaphthopyranone glycoside and seven known flavonoids were isolated from an ethanolic extract of the leaves of P. planifolius.

Chromatography, Thin Layer↗
PubMed2001

Acetylated analogues of the microtubule-stabilizing agent discodermolide: preparation and biological activity.

A series of eight discodermolide acetates have been prepared using natural (+)-discodermolide and evaluated for in vitro cytotoxicity against the cultured murine P-388 leukemia cells. The acetylated analogues showed a significant variation of cytotoxicity and suggested the importance of C-11 and C-17 hydroxyl groups for potency. The preparation and structure elucidation of the new analogues are described.

Acetylation↗
PubMed2001

Limonoids from Nigerian Harrisonia abyssinica and their stimulatory activity against Striga hermonthica seeds.

Deoxyobacunone (1), a new limonoid with a double bond in ring D, has been isolated from the root bark of Harrisonia abyssinica collected in Nigeria. Also, the known limonoids obacunone (2), harrisonin (3), 12beta-acetoxyharrisonin (4), and pedonin (5) have been isolated. The structure of 1 was assigned unambiguously by spectral data analysis. Under laboratory conditions, 10(-3)-10(-5) M concentrations of compounds 1-5 exhibited significant stimulatory activity (12-98%) against conditioned Striga hermonthica seeds. This study provided useful insight regarding the functionalities required for activity of limonoids against Striga seeds. The variation in activity was rationalized through quantitative structure-activity relationship (QSAR) models based on several molecular descriptors including van der Waals volume (VDW(v)), molecular polarizability (alpha), dipole moment (mu), log P, and the differences between the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO gap).

Benzopyrans↗
PubMed2001

Production of aromatic minimal polyketides by the daunorubicin polyketide synthase genes reveals the incompatibility of the heterologous DpsY and JadI cyclases.

Our investigations into whether the biosynthesis of a linearly fused ring system of an aromatic polyketide (jadomycin) could be modified to produce an angularly fused system (daunorubicin) and vice versa showed that introduction of the respective cyclases did not have the desired effect. Genes from the daunorubicin pathway produced a novel 21-carbon polyketide.

Acetyl Coenzyme A↗
PubMed2001

A new naphthopyrone derivative from Cassia quinquangulata and structural revision of quinquangulin and its glycosides.

A novel naphthopyrone derivative, named quinquangulone (1), has been isolated from Cassia quinquangulata, along with the known compounds quinquangulin (2) and its two glycosides (3 and 4), rubrofusarin (5) and its two glycosides (6 and 7), nor-rubrofusarin (8) and its 6-O-glucoside (9), and three stilbenes (10-12). The structure of quinquangulone was established by spectral interpretation as 5,9-dihydroxy-8-methoxy-2,9-dimethyl-6-oxo-4H,6H,9H-naphtho-[2,3-b]pyran-4-one. Reinvestigation of the NMR spectra of quinquangulin led to revision of its structure as 5,6-dihydroxy-8-methoxy-2,9-dimethyl-4H-naphtho[2,3-b]pyran-4-one (2a). The structures of two quinguangulin glycosides, 3 and 4, were also revised accordingly. Compound 2a exhibited activity against Staphylococcus aureus and methicillin-resistant S. aureus (MIC, 3.125 and 6.25 microg/mL, respectively).

Anti-Bacterial Agents↗
PubMed2002

Cryphonectric acid and other minor metabolites from a hypovirulent strain of Cryphonectria parasitica.

Investigations carried out on secondary metabolites produced in culture by a hypovirulent strain of Cryphonectria parasitica allowed the isolation of several compounds which were characterized by NMR analysis and derivatization reactions. The most abundant metabolite was a new compound, called cryphonectric acid (1). Other metabolites were diaporthin, the only known phytotoxic compound isolated from both virulent and hypovirulent strains of C. parasitica, (+)-orthosporin, and L-p-hydroxyphenyllactic acid (HOPLA). Root growth activity of the purified compounds was evaluated both on tomato seedlings and maize subapical segments.

Ascomycota↗
PubMed2002

Goniolactones A-F, six new styrylpyrone derivatives from the roots of Goniothalamus cheliensis.

Six new styrylpyrone derivatives, goniolactones A-F (1-6), have been isolated from the roots of Goniothalamus cheliensis. The structures and stereochemistry of the new compounds were elucidated by interpretation of spectroscopic data and chemical methods. The relative configuration of goniolactone A (1) was determined by X-ray crystallography analysis, and the absolute configurations of goniolactones A (1) and B (2) were established by Mosher's method. Goniolactone B (2) exhibited significant cytotoxicity against A2780, HCT-8, and KB cells with IC(50) values of 7.40, 4.43, and 7.23 microM, respectively.

Annonaceae↗
PubMed2003

New dimeric naphthopyrones from Aspergillus niger.

Three new dimeric naphthopyrones, asperpyrones A (1), B (2), and C (3), together with two known compounds, fonsecinone A (4) and aurasperone A (5), have been isolated from okara that was fermented with Aspergillus niger JV-33-48. Compounds 1, 4, and 5 showed inhibitory activity on Taq DNA polymerase.

Aspergillus niger↗
PubMed2002

Chemical constituents of the ascomycete Daldinia concentrica.

Four compounds, daldinone A (1), daldinone B (2), daldiniapyrone (4-methoxy-5-carbomethoxy-6-pentyl-2H-pyran-2-one, 3), and daldinialanone (22R-hydroxylanosta-7,9(11),24-trien-3-one, 4), were isolated from an ethyl acetate extract of fruit bodies of Daldinia concentrica collected in Europe. In addition, 11 known compounds, 4:5:4':5'-tetrahydroxy-1:1'-binaphthyl (5), 3,4,5-trihydroxy-1-tetralone (6), (+)-orthosporin (7), curuilignan D (8), (22E)-cholesta-4,6,8(14),22-tetraen-3-one (9), 3beta,22-dihydroxylanosta-7,9(11),24-triene (10), concentricol (11), concentricol B (12), concentricol C (13), concentricol D (14), and phenochalasin B (15), were obtained. The structures of the new compounds were elucidated by 2D NMR, MS, IR, and UV spectra and by X-ray crystallographic analysis. The absolute configurations of 1 and 4 were determined by CD spectroscopy and the modified Mosher's method, respectively. The chemotaxonomic relevance of the compounds obtained in this investigation is discussed.

Ascomycota↗
PubMed2002

Semisynthetic analogues of the microtubule-stabilizing agent discodermolide: preparation and biological activity.

A series of 12 semisynthetic discodermolide analogues, 2-13, have been prepared using natural (+)-discodermolide (1) and evaluated for in vitro cytotoxicity against cultured murine P-388 leukemia and A-549 human adenocarcinoma cells. These semisynthetic analogues showed a significant variation of cytotoxicity and confirmed the importance of the C-7 through C-19 molecular fragment for potency. Specifically, these analogues suggested the importance of the C-11 and C-17 hydroxyl groups and the C-13 double bond for the potency of discodermolide. The preparation, structure elucidation, and biological activity of these new analogues are described.

Adenocarcinoma↗
PubMed2003

Diplopyrone, a new phytotoxic tetrahydropyranpyran-2-one produced by Diplodia mutila, a fungus pathogen of cork oak.

A new phytotoxic monosubstituted tetrahydropyranpyran-2-one, named diplopyrone (1), was isolated from the liquid culture filtrates of Diplodia mutila, a plant pathogenic fungus causing a form of canker disease of cork oak (Quercus suber). Diplopyrone was characterized, using spectroscopic and chemical methods, as 6-[(1S)-1-hydroxyethyl]-2,4a,6,8a-tetrahydropyran[3,2-b]pyran-2-one. The absolute stereochemistry of the chiral secondary hydroxylated carbon (C-9), determined by application of Mosher's method, proved to be S. Diplopyrone assayed at a 0.01-0.1 mg/mL concentration range caused necrosis and wilting on cork oak cuttings. On a nonhost plant, tomato, diplopyrone caused brown discoloration or stewing on the stem.

Italy↗