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Träfflista för sökning "L773:0040 4020 srt2:(2015-2019)"

Sökning: L773:0040 4020 > (2015-2019)

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1.
  • Angles d'Ortoli, Thibault, et al. (författare)
  • Synthesis of the tetrasaccharide glycoside moiety of Solaradixine and rapid NMR-based structure verification using the program CASPER
  • 2016
  • Ingår i: Tetrahedron. - : Elsevier. - 0040-4020 .- 1464-5416. ; 72:7, s. 912-927
  • Tidskriftsartikel (refereegranskat)abstract
    • The major glycoalkaloid in the roots of Solanum laciniatum is Solaradixine having the branched tetrasaccharide beta-D-Glcp-(1 -> 2)-beta-D-Glcp-(1 -> 3)[alpha-L-Rhap-(1 -> 2)]-beta-D-Galp linked to O3 of the steroidal alkaloid Solasodine. We herein describe the synthesis of the methyl glycoside of the tetrasaccharide using a super-armed disaccharide as a donor molecule. A 2-(naphthyl)methyl protecting group was used in the synthesis of the donor since it was tolerant to a wide range of reaction conditions. The 6-O-benzylated-hexa-O-tert-butyldimethylsilyi-protected beta-D-Glcp-(1 -> 2)-beta-D-Glcp-SEt donor, which avoided 1,6-anydro formation, was successfully glycosylated at O3 of a galactoside acceptor molecule. However, subsequent glycosylation at O2 by a rhamnosyl donor was unsuccessful and instead a suitably protected alpha-L-Rhap(1 -> 2)-beta-D-Galp-OMe disaccharide was used as the acceptor molecule together with a super-armed beta-D-Glcp-(1 -> 2)-beta-D-Glcp-SEt donor in the glycosylation reaction, to give a tetrasaccharide in a yield of 55%, which after deprotection resulted in the target molecule, the structure of which was verified by the NMR chemical shift prediction program CASPER.
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2.
  • Berg, Robert, et al. (författare)
  • Synthesis of thieno[2,3-b]indole-2,3-diones and their ring expansions induced by diazomethane
  • 2017
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 73:38, s. 5654-5658
  • Tidskriftsartikel (refereegranskat)abstract
    • Indole-2-thione 3 reacted quickly with oxalyl chloride to yield thieno[2,3-b]indole-2,3-dione 4 together with the isomer thiazolo[3,2-a]indole-2,3-dione 5. These thieno[2,3-b]indole-2,3diones underwent ring expansions when treated with diazomethane and e.g. thieno[2,3-b]indole-2,3-dione 4 gave the thiopyrano derivative 16, after two insertions.
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3.
  • Bornadel, Amin, et al. (författare)
  • Enhancing the productivity of the bi-enzymatic convergent cascade for ɛ-caprolactone synthesis through design of experiments and a biphasic system
  • 2016
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020. ; 72:46, s. 7222-7228
  • Tidskriftsartikel (refereegranskat)abstract
    • A two-step Design of Experiments (DoE) strategy followed by a two-liquid-phase system (2LPS) was applied to enhance the ɛ-caprolactone yield in the cyclohexanone monooxygenase (CHMO)-alcohol dehydrogenase (ADH) convergent cascade system. The key reaction parameters were identified and optimized for the determination of an optimal operational window for the aqueous media. In the 2LPS system, high partitioning of the lactone product was observed in 2-MeTHF and in toluene; however, these solvents led to drastically reduced enzymatic activity. Dodecane was chosen as the non-miscible organic phase owing to the enzymes’ high residual activity, despite the low partitioning of the lactone. Cyclohexanone concentrations up to 75 mM were applied in the aqueous media. The turnover numbers for the nicotinamide cofactor and for the ADH reached up to 980 and 392,000, respectively whereas a turnover number value of 5600 was achieved for the CHMO. By employing a 2LPS, whereby 91 mM of cyclohexanone was applied in the second phase, turnover numbers were slightly increased.
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4.
  • Brea, Oriana, et al. (författare)
  • Mechanism(s) of thermal decomposition of N-Nitrosoamides : A density functional theory study
  • 2019
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 75:8, s. 929-935
  • Tidskriftsartikel (refereegranskat)abstract
    • The thermal decomposition of N-nitrosoamides has experimentally been demonstrated to depend on several factors, such as temperature, solvent and the substituents on the substrate. Consequently, a number of reaction mechanisms have been proposed for this process in the literature. In this work, we present a comprehensive computational investigation in which we examine the detailed reaction mechanisms for two N-nitrosoamides (with aliphatic and aromatic substituents) in two different solvents (mesitylene and methanol). It is shown that the reaction mechanism can change dramatically with the nature of the substrate and the choice of solvent. Importantly, it is found that the polar solvent stabilizes ion-pairs that are unstable in the non-polar solvent, which can play a key role in the mechanism.
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5.
  • Janson, Pär G., et al. (författare)
  • Effects of B(2)pin(2) and PCy3 on copper-catalyzed trifluoromethylation of substituted alkenes and alkynes with the Togni reagent
  • 2015
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 71:6, s. 922-931
  • Tidskriftsartikel (refereegranskat)abstract
    • The copper-catalyzed oxytrifluoromethylation of phenylacetylenes and C-H trifluoromethylation of quinones were studied. It was found that both reactions are accelerated by B(2)pin(2) and PCy3 additives. The two reactions have different substituent effects. The oxytrifluoromethylation is faster in the presence of electron-donating groups, while the C-H trifluoromethylation is faster with electron-withdrawing substituents. The Hammett plot for oxytrifluoromethylation gave a rho value of 0.76 indicating electron demand in the rate determining step of the reaction. According to the absolute value of rho the reaction probably does not proceed through a rate determining formation of a carbocation intermediate. The kinetic isotope effect measurements indicate that in C-H trifluoromethylation of quinones the cleavage of the C-H bond is not the rate determining step of the reaction.
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6.
  • Khosravi, Kaveh, et al. (författare)
  • 1,1,2,2-Tetrahydroperoxy-1,2-Diphenylethane: An efficient and high oxygen content oxidant in various oxidative reactions
  • 2018
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020.
  • Tidskriftsartikel (refereegranskat)abstract
    • Several oxidative approaches namely thiocyanation of aromatic compounds, epoxidation of alkenes, amidation of aromatic aldehydes, epoxidation of α, β-unsaturated ketones, oxidation of sulfides to sulfoxides and sulfones, bayer-villeger reaction, bromination and iodation of aniline and phenol derivatives oxidative esterification, oxidation of pyridines and oxidation of secondary, allylic and benzyllic alcohols were carried out using 1,1,2,2-Tetrahydroperoxy-1,2-Diphenylethane as the potential solid oxidant which can be stored for several months without any loss in its activity. All of the procedures were accomplished via mild reaction conditions and the products were afforded in high yields and short reaction times.
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7.
  • Rao, M. Suri Appa, et al. (författare)
  • Piscidinols H-L, apotirucallane triterpenes from the leaves of Walsura trifoliata and their insecticidal activity
  • 2015
  • Ingår i: Tetrahedron. - : Elsevier. - 0040-4020 .- 1464-5416. ; 71:9, s. 1431-1437
  • Tidskriftsartikel (refereegranskat)abstract
    • Five new apotirucallane-type terpenoids, Piscidinols H-L (1-5), were isolated from the leaves of Walsura trifoliate and their structures were fully established on the basis of detailed spectroscopic (especially 20 NMR and mass) analysis. These new compounds possessed tetracyclic and acetal rings. All the new isolates were evaluated for their antifeedant activities in tobacco caterpillar (Spodoptera aura) and castor semilooper (Achaea janata) using a no-choice laboratory bioassay and the test compounds (1-6) exhibited moderate insecticidal activities. (C) 2015 Elsevier Ltd. All rights reserved.
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8.
  • Thorsheim, Karin, et al. (författare)
  • Expanding the scope of methyl xanthate esters - From Barton-McCombie reaction auxiliary to versatile protective group
  • 2017
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020. ; 73:44, s. 6329-6333
  • Tidskriftsartikel (refereegranskat)abstract
    • The methyl xanthate ester is presented as a versatile protective group for alcohols. Hydroxyl groups can easily be transformed into methyl xanthate esters by several methods and are commonly used as an auxiliary in the Barton-McCombie reaction. We show that these methyl xanthate esters can readily and chemoselectively be cleaved under mild conditions by the action of diethylenetriamine using microwave heating. This method is orthogonal to many common hydroxyl protective groups that can be introduced and cleaved in the presence of methyl xanthate ester.
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9.
  • Trouillas, Patrick, et al. (författare)
  • Optical properties of wine pigments: theoretical guidelines with new methodological perspectives
  • 2015
  • Ingår i: Tetrahedron. - : Elsevier. - 0040-4020 .- 1464-5416. ; 71:20, s. 3079-3088
  • Tidskriftsartikel (refereegranskat)abstract
    • Wine pigmentation results from the complex chemistry of anthocyanins. Their flavylium cation form is stabilized either by chemical transformation occurring during wine aging (e.g., pyranoanthocyanin formation), or by the formation of non-covalent complexes with (phenolic) copigments. Molecular modeling (quantum mechanics and molecular dynamics) is more and more adapted to understand wine chemistry and pigmentation. The constant developments of theoretical methodologies might get non-specialists easily lost. This manuscript is a review of the theoretical studies dedicated to the field of wine pigments, showing conformational analysis, energetics of the various forms, pigment/copigment (non-)covalent association, and charge transfer excited states. QM/MM calculations are newly performed here, which improve solvent description. The conclusion is a comprehensive guideline for an accurate prediction of light absorption by wine pigments and all related supramolecular processes.
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10.
  • Wakchaure, Prasad B., et al. (författare)
  • Synthesis of enantiopure angiotensin II type 2 receptor [AT(2)R] antagonist EMA401
  • 2015
  • Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 71:38, s. 6881-6887
  • Tidskriftsartikel (refereegranskat)abstract
    • We report a facile synthesis of the angiotensin II type 2 receptor antagonist EMA401, which recently passed phase II clinical trials, in high overall yield. The synthesis of the key phenylalanine intermediate involved the formation of an a-nitro cinnamic ester and its reduction followed by a Pictet-Spengler cyclization, which furnished the tetrahydroisoquinoline core structure. Next, EMA401 was separated from its enantiomer EMA402 by four recrystalizations of a diastereomeric salt in 98% ee. All steps were performed on gram scale with emphasis on avoiding column purification and using readily available low cost starting materials and reagents.
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11.
  • Wallgren, Jakob, et al. (författare)
  • Synthesis and identifications of potential metabolites as biomarkers of the synthetic cannabinoid AKB-48
  • 2018
  • Ingår i: Tetrahedron. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020 .- 1464-5416. ; 74:24, s. 2905-2913
  • Tidskriftsartikel (refereegranskat)abstract
    • AKB-48 belongs to the family of synthetic cannabinoids. It has strong binding affinity to CBI receptor and is psychoactive. It is banned in many countries including USA, Japan, Germany, New Zealand, Singapore and China etc. But the difficulty in detecting the parent compound in urine samples highlights the importance of studies of its metabolites. Here we report the synthesis of 19 potential metabolites of AKB-48, among which, compounds 2, 9, 10, 30 and 31, together with the commercially available substance 5 were identified as metabolites of AKB-48 by comparison with one authentic human urine sample and human liver microsomal data. Compounds 10 and 30 could be of use as biomarkers in detecting AKB-48 in human urine samples. (C) 2018 Elsevier Ltd. All rights reserved.
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12.
  • Wu, Xiongyu, et al. (författare)
  • Synthesis and identification of metabolite biomarkers of 25C-NBOMe and 25I-NBOMe
  • 2017
  • Ingår i: Tetrahedron. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020 .- 1464-5416. ; 73:45, s. 6393-6400
  • Tidskriftsartikel (refereegranskat)abstract
    • Synthetic routes have been developed for synthesis of potential metabolites of 25C-NBOMe and 25I-NBOMe. Nine potential metabolites have been synthesized, among which compounds 8 and 20a could be used as metabolite biomarkers of 25C-NBOMe and 20b of 25I-NBOMe in urinary detection at forensic laboratories to prove intake. (C) 2017 Elsevier Ltd. All rights reserved.
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