Magnetic Resonance in Chemistry

Rimaz, Mehdi; Noroozi Pesyan, Nader; Khalafy, Jabbar

doi: 10.1002/mrc.2573pmid: 20169579

The tautomerism of the synthesized 3‐arylpyrimido(4,5‐c)pyridazine‐5,7(6H,8H)‐diones (1a–d) and 3‐aryl‐7‐thioxo‐7,8‐dihydro‐6H‐pyrimido(4,5‐c)pyridazine‐5‐ones (2a–d) was studied in dimethyl sulfoxide (DMSO)‐d6. 1H NMR spectra of 1a–d showed a clustered water molecule in the structure backbone that is attached by strong intermolecular H bonding. The relation between the temperature and H bonding of the clustered water molecule with 1a was also studied as representative. The relation between the electronegativity (χ) of the substituent on phenyl ring and the chemical shifts of clustered water protons in 1a–d was also studied. All of 1a–d and also 2d compounds existed in lactam (I) form, whereas 2a–c compounds have two distinguished tautomers in DMSO‐d6 (lactam (I) and lactim (II) forms). The solvent‐substrate proton exchange was examined in compounds 1a–d and 2a–d by adding one drop of D2O. All compounds (except 1d) showed proton/deuterium exchange of the clustered water protons in DMSO by adding one drop of D2O. Some compounds (but not all of them) that are easily soluble in DMSO‐d6 containing D2O showed isotopic splitting (β‐isotope effect) in their 13C NMR spectra. Among them, compound 1a was the best evidence to help the spectral assignments and structure determination of predominant tautomer by carbon‐13 splitting (β‐isotope effect). Copyright © 2010 John Wiley & Sons, Ltd.

Przybylski, Piotr; Pyta, Krystian; Stefańska, Joanna; Brzezinski, Bogumil; Bartl, Franz

doi: 10.1002/mrc.2574pmid: 20186698

Four new hydroxy‐aminoalkyl derivatives of α,β‐unsaturated macrolide‐josamycin (2–5) have been synthesised and their structures have been studied by means of 1H and 13C NMR and FT‐IR methods. Complete assignment of resonances in the 1H and 13C NMR spectra has been made on the basis of 1H13C HSQC, 1H13C HMBC, 1H1H COSY, 1H1H NOESY 2D experiments. Spectroscopic data indicated that for the derivatives 3 and 4 some equilibrium between two different structures exists in contrast to derivatives 2 and 5. The lowest‐energy structures of the new derivatives of josamycin have been calculated and visualised by PM5 method at semi‐empirical level of theory, taking into account the NMR and FT‐IR data. The most significant differences between the structures of josamycin and its newly synthesised derivatives' were found in the conformation of the macrolide aglycone part and in the mutual orientation of the 4‐O‐isovalerylmycarosylmycaminose moiety relative to the aglycone part. PM5 semi‐empirical calculations indicated that the structures of the new macrolide derivatives are stabilised by rather weak intramolecular hydrogen bonds in agreement with spectroscopic data. Antimicrobial properties of the new derivatives 2–5 as well as those having an acetate group at C‐3 (6 and 7) were determined and compared to that of the parent macrolide antibiotic josamycin (1). Copyright © 2010 John Wiley & Sons, Ltd.

Gobet, Mallory; Rondeau‐Mouro, Corinne; Buchin, Solange; Le Quéré, Jean‐Luc; Guichard, Elisabeth; Foucat, Loïc; Moreau, Céline

doi: 10.1002/mrc.2576pmid: 20198610

The feasibility of solid‐state magic angle spinning (MAS) 31P nuclear magnetic resonance (NMR) spectroscopy and 23Na NMR spectroscopy to investigate both phosphates and Na+ ions distribution in semi‐hard cheeses in a non‐destructive way was studied. Two semi‐hard cheeses of known composition were made with two different salt contents. 31P Single‐pulse excitation and cross‐polarization MAS experiments allowed, for the first time, the identification and quantification of soluble and insoluble phosphates in the cheeses. The presence of a relatively ‘mobile’ fraction of colloidal phosphates was evidenced. The detection by 23Na single‐quantum NMR experiments of all the sodium ions in the cheeses was validated. The presence of a fraction of ‘bound’ sodium ions was evidenced by 23Na double‐quantum filtered NMR experiments. We demonstrated that NMR is a suitable tool to investigate both phosphates and Na+ ions distributions in cheeses. The impact of the sodium content on the various phosphorus forms distribution was discussed and results demonstrated that NMR would be an important tool for the cheese industry for the processes controls. Copyright © 2010 John Wiley & Sons, Ltd.

Ahmad, Viqar Uddin; Bader, Sadia; Arshad, Saima; Ahmed, Amir; Khan, Afsar; Iqbal, Shazia; Rasheed, Munawwer; Tareen, Rasool Bakhsh

doi: 10.1002/mrc.2578pmid: 20186701

Two new acylated flavonol glycosides, 3‐O‐{(2‐O‐β‐D‐glucopyranosyl)‐3‐(O‐β‐D‐glucopyranosyl)‐4‐((6‐O‐p‐coumaroyl)‐O‐β‐D‐glucopyranosyl)}‐α‐L‐rhamnopyranosyl‐kaempferol 7‐O‐α‐L‐rhamnopyranoside and 3‐O‐{2‐((6‐O‐p‐coumaroyl)‐O‐β‐D‐glucopyranosyl)‐3‐(O‐β‐D‐glucopyranosyl)‐4‐((6‐O‐p‐coumaroyl)‐O‐β‐D‐glucopyranosyl)}‐α‐L‐rhamnopyranosyl‐kaempferol 7‐O‐α‐L‐rhamnopyranoside, trivially named as brauhenefloroside E (1) and F (2), respectively, were isolated from the fruits of Stocksia brauhica and their structures were elucidated using spectroscopic methods, including 2D NMR experiments. Copyright © 2010 John Wiley & Sons, Ltd.

Afonin, Andrei V.; Vashchenko, Alexander V.

doi: 10.1002/mrc.2579pmid: 20198609

According to the density functional theory calculations, the X···H···N (XN, O) intramolecular bifurcated (three‐centered) hydrogen bond with one hydrogen donor and two hydrogen acceptors causes a significant decrease of the 1hJ(N,H) and 2hJ(N,N) coupling constants across the NH···N hydrogen bond and an increase of the 1J(N,H) coupling constant across the NH covalent bond in the 2,5‐disubsituted pyrroles. This occurs due to a weakening of the NH···N hydrogen bridge resulting in a lengthening of the N···H distance and a decrease of the hydrogen bond angle at the bifurcated hydrogen bond formation. The gauge‐independent atomic orbital calculations of the shielding constants suggest that a weakening of the NH···N hydrogen bridge in case of the three‐centered hydrogen bond yields a shielding of the bridge proton and deshielding of the acceptor nitrogen atom. The atoms‐in‐molecules analysis shows that an attenuation of the 1hJ(N,H) and 2hJ(N,N) couplings in the compounds with bifurcated hydrogen bond is connected with a decrease of the electron density ρH···N at the hydrogen bond critical point and Laplacian of this electron density ∇2ρH···N. The natural bond orbital analysis suggests that the additional NH···X interaction partly inhibits the charge transfer from the nitrogen lone pair to the σ*NH antibonding orbital across hydrogen bond weakening of the 1hJ(N,H) and 2hJ(N,N) trans‐hydrogen bond couplings through Fermi‐contact mechanism. An increase of the nitrogen s‐character percentage of the NH bond in consequence of the bifurcated hydrogen bonding leads to an increase of the 1J(N,H) coupling constant across the NH covalent bond and deshielding of the hydrogen donor nitrogen atom. Copyright © 2010 John Wiley & Sons, Ltd.

Vícha, Jan; Maloň, Michal; Veselá, Petra; Humpa, Otakar; Strnad, Miroslav; Marek, Radek

doi: 10.1002/mrc.2575pmid: 20198611

The 1H and 13C NMR resonances of 16 purine glucosides were assigned by a combination of one‐ and two‐dimensional NMR experiments, including gs‐COSY, gs‐HSQC, and gs‐HMBC, in order to characterize the effect of substituent and the position of glucose unit on the NMR chemical shifts. In addition, 15N NMR chemical shifts for selected derivatives were investigated by using 1H15N chemical shift correlation techniques. To map the influence of sugar moiety on the directly bonded nitrogen atom, selected N9‐glucosides and their ribose analogs were compared. Characteristic long‐range 1H15N coupling constants, measured by using 1H15N gradient‐selected single‐quantum multiple bond correlation (GSQMBC), are also reported and discussed. All compounds investigated here belong to cytokinins, an important group of plant hormones. Copyright © 2010 John Wiley & Sons, Ltd.

Carvalho, Luísa R.; Corvo, Marta C.; Enugala, Ramu; Marques, M. Manuel B.; Cabrita, Eurico J.

doi: 10.1002/mrc.2583pmid: 20222070

The solid‐phase synthesis (SPS) of a structurally complex glycopeptide, using Sieber amide resin, was monitored by high resolution magic angle spinning NMR, demonstrating the further application of this technique. A synthetic peptidoglycan derivative, a precursor of a biologically active PGN, known to be involved in the cellular recognition, was prepared by SPS. The synthesis involved the preparation of an N‐alloc glucosamine moiety and the synthesis of a simple amino acid sequence L‐Ala‐D‐Glu‐L‐Lys‐D‐Ala‐D‐Ala. Last step consisted the coupling, on solid‐phase, of the protected muramyl unit to the peptide chain. Proton spectra with good suppression of the polystyrene signals in swollen resin samples were obtained in DMF‐d7 as a solvent and by using a nonselective 1D TOCSY/DIPSI‐2 scheme, thus allowing to follow the SPS without losses of compound and cleavage from the resin. The assignment of the proton spectra of the resin‐bound amino acid sequence and of the bound glycopeptide was achieved through the combination of MAS COSY, TOCSY and NOESY. Copyright © 2010 John Wiley & Sons, Ltd.

doi: 10.1002/mrc.2591pmid: N/A

The original article to which this Erratum refers was published in Magnetic Resonance in Chemistry 2010, 48: 210–218