High‐resolution NMR correlation experiments in a single measurement (HR‐PANACEA)Kupče, Ēriks; Freeman, Ray
doi: 10.1002/mrc.2595pmid: 20309871
Three important NMR pulse sequences, INADEQUATE, HSQC and three‐dimensional HMBC have been combined into a single entity called high‐resolution Parallel Acquisition NMR: an All‐in‐one Combination of Experimental Applications (HR‐PANACEA) to provide reliable structural information about a small molecule in a single measurement. This exploits a recent instrumental development that permits simultaneous acquisition of signals from several nuclear species, using multiple receivers. Where high‐precision values of the long‐range heteronuclear splittings are important, selected regions of a large experimental data matrix are extracted and examined with the highest possible resolution. The J‐doubling technique is then applied to derive precise values for these couplings. As proof of principle, the method is applied to the molecule of methyl salicylate, confirming the expected conformation of the COH moiety. Copyright © 2010 John Wiley & Sons, Ltd.
DFT study of nitroxide radicals: explicit modeling of solvent effects on the structural and electronic characteristics of 4‐amino‐2,2,6,6‐tetramethyl‐piperidine‐ N ‐oxylIkryannikova, Larissa N.; Ustynyuk, Leila Yu.; Tikhonov, Alexander N.
doi: 10.1002/mrc.2585pmid: 20225189
An explicit DFT modeling of water surroundings on the electron paramagnetic resonance properties of 4‐amino‐2,2,6,6‐tetramethyl‐piperidine‐N‐oxyl (TA) has been performed. A stepwise hydration of TA is accompanied with certain changes in geometrical parameters (bond lengths and angles) and redistribution of partial electric charges in TA. An aqueous cluster of 45 water molecules can be considered as an appropriate model for a complete aqueous shell around TA, although most of the structural and electronic characteristics of TA already converge at about 10 water molecules. Water surroundings induce an increase in electron spin density on the nitrogen atom of the nitroxide fragment due to stabilization of the polar resonance structure > N+•O− at the expense of less polar structure > NO•. The water‐induced rise of the isotropic splitting constant aiso, calculated from the contact term of the hyperfine interaction, comprises Δaiso(ρN2) = 2.2–2.5 G, which is typical of experimental value for TA. There are two contributions to the solvent effect on the aiso(ρN2) value: the redistribution of spin density in the nitroxide fragment (polarity effect) and water‐induced distortions of TA geometry. Microscopic variations in a hydrogen‐bonded water network cause noticeable fluctuations of the splitting constant aiso(ρN2). Calculations of the atomic spin density (σN2) allowed us to compute the splitting constant from the relationship aiso(σN2) = QσN2, where Q = 36.2 G. A practical advantage of using this relationship is that it gives ‘smoothed’ values of the splitting constant, which are sensitive to the environment polarity but remain tolerant to microscopic fluctuations of the hydrogen‐bonded water network around a spin‐label molecule. Copyright © 2010 John Wiley & Sons, Ltd.
Characterization of three saponins from a fraction using 1D DOSY as a solvent signal suppression tool. Agabrittonosides E–F. Furostane Saponins from Agave brittoniana Trel. spp. BrachypusMacías, Francisco A.; Guerra, José O.; Simonet, Ana M.; Pérez, Andy J.; Nogueiras, Clara
doi: 10.1002/mrc.2590pmid: 20391439
A careful NMR analysis, especially by 1D TOCSY and 1D ROESY, of a refined saponin fraction allowed us to determine the structure of three saponins from a polar extract of Agave brittoniana Trel. spp. Brachypus leaves. The use of 1D DOSY for the suppression of the solvent signal was useful to obtain the chemical shifts of anomeric signals. A full assignment of the 1H and 13C spectral data for the new saponins, agabrittonosides E–F (1–2) and the well‐known Karatavioside C (3) and their methoxyl derivatives, is reported. The structures were established using a combination of 1D and 2D (1H, 1H‐COSY, TOCSY, ROESY, g‐HSQC, g‐HMBC and g‐HSQC‐TOCSY) NMR techniques and ESI–MS. In addition, the methoxylation of these furostane saponins in the presence of MeOH was studied. Copyright © 2010 John Wiley & Sons, Ltd.
Synthesis, 1 H and 13 C NMR assignment and electrochemical properties of novel thiophene–thiazolothiazole oligomers and polymersVan Mierloo, S.; Chambon, S.; Boyukbayram, A. E.; Adriaensens, P.; Lutsen, L.; Cleij, T. J.; Vanderzande, D.
doi: 10.1002/mrc.2593pmid: 20301090
Novel hexyl‐substituted bisthiophene compounds containing a thiazolothiazole(5,4‐d) unit have been explored. The molecules are soluble in common organic solvents, which would enhance their chance of possible integration in printable electronics. Synthesis and complete elucidation of the chemical structures by detailed 1D/2D NMR spectroscopy are described. This provides interesting input for chemical shift prediction software, because few experimental data on this type of compounds are available. Furthermore, the potential n‐type character of these derivatives is verified using electrochemical measurements. In addition, the low‐bandgap character of conjugated polymers containing the thiazolothiazole unit is demonstrated by performing an electropolymerization. Copyright © 2010 John Wiley & Sons, Ltd.
Structure elucidation of new oleanane‐type glycosides from three species of AcanthophyllumTimité, Gaoussou; Mitaine‐Offer, Anne‐Claire; Miyamoto, Tomofumi; Ramezani, Mohammad; Rustaiyan, Abdolhossein; Mirjolet, Jean‐François; Duchamp, Olivier; Lacaille‐Dubois, Marie‐Aleth
doi: 10.1002/mrc.2577pmid: 20209583
From the roots of three species of Acanthophyllum (Caryophyllaceae), two new gypsogenic acid glycosides, 1 and 2, were isolated, 1 from A. sordidum and A. lilacinum, 2 from A. elatius and A. lilacinum, together with three known saponins, glandulosides B and C, and SAPO50. The structures of 1 and 2 were established mainly by 2D NMR techniques as 23‐O‐β‐D‐galactopyranosylgypsogenic acid‐28‐O‐β‐D‐glucopyranosyl‐(1→3)‐(β‐D‐glucopyranosyl‐(1→6))‐β‐D‐galactopyranoside (1) and gypsogenic acid‐28‐O‐β‐D‐glucopyranosyl‐(1→3)‐(β‐D‐glucopyranosyl‐(1→6))‐β‐D‐galactopyranoside (2). The cytotoxicity of several of these saponins was evaluated against two human colon cancer cell lines (HT‐29 and HCT 116). Copyright © 2010 John Wiley & Sons, Ltd.
Trifluoromethylated (tetrahydropyrrolo) quinazolinones by a new three‐component reaction and facile assignment of the regio‐ and stereoisomers formed by NMR spectroscopyDolenský, Bohumil; Kvíčala, Jaroslav; Paleta, Oldřich; Lang, Jan; Dvořáková, Hana; Čejka, Jan
doi: 10.1002/mrc.2580pmid: 20301203
A new three‐component cyclisation reactions of methyl 3,3,3‐trifluoropyruvate, 2‐aminobenzylamine and oxo compounds afforded tetrahydropyrroloquinazolinones of the types 4 and 5 as mixtures of regio‐ and stereoisomers. Whereas standard 1D NMR spectroscopy was used for a facile assignment of the cyclization regioisomers, a combination of homo (proton–proton) and heteronuclear (proton–fluorine) NOE experiments allowed the determination of the relative configuration on stereogenic centres. The structure of some compounds was also confirmed by the X‐ray diffraction. Adaptation of the 1D double‐pulsed field‐gradient spin‐echo NOE for a heteronuclear case is presented. Copyright © 2010 John Wiley & Sons, Ltd.
1 H, 13 C, and 15 N NMR spectra of some pyridazine derivativesKatritzky, Alan R.; El‐Gendy, Bahaa El‐Dien M.; Draghici, Bogdan; Fedoseyenko, Dmytro; Fadli, Aziz; Metais, Eric
doi: 10.1002/mrc.2584pmid: 20213770
1H, 13C, and 15N NMR chemical shifts for pyridazines 4–22 were measured using 1D and 2D NMR spectroscopic methods including 1H1H gDQCOSY, 1H13C gHMQC, 1H13C gHMBC, and 1H15N CIGAR–HMBC experiments. Copyright © 2010 John Wiley & Sons, Ltd.