Complete assignment of the 1H and 13C NMR spectra of garciniaphenone and keto-enol equilibrium statements for prenylated benzophenones

This article reports the structural elucidation by IR, UV and MS spectroscopic data along with 1H and 13C NMR chemical shift assignments of two benzophenones isolated from the fruit pericarp of Garcinia brasiliensis Mart. (Clusiaceae): garciniaphenone, (1R,5S,7S)-3-benzoyl-4-hydroxy-6,6-dimethyl-5,7-di(3-methyl-2-butenyl)bicyclo[3.3.1]non-3-ene-2,9-dione, a novel triprenylated benzophenone; and 7-epi-clusianone, a tetraprenylated benzophenone that has already been extracted from another species of the same family. Furthermore, the keto-enol tautomeric equilibrium at solution-state was described for these compounds by 1D and 2D NMR spectral methods and one attempt to rationalize the different ratios between the noted tautomers was based on stereochemical features.     

Characterization of bixin by LC-MS and LC-NMR

An overview upon modern analytical techniques for the isolation, separation, and structural identification of the essential bioactive carotenoid bixin is given. Isolation from biological matrices is performed by matrix solid phase dispersion (MSPD). The extract is separated with shape-selective C(30 )columns. Structural assignment of the separated compounds is done by online LC-MS and capillary HPLC-NMR.     

A novel method for quantitative analysis of acetylacetone and ethyl acetoacetate by fluorine‐19 nuclear magnetic spectroscopy

A new method utilization of NMR spectra was developed for structural and quantitative analysis of enol forms of acetylacetone and ethyl acetoacetate. Acetylacetone and ethyl acetoacetate were determined by ¹⁹F NMR upon derivatisation with р‐fluorobenzoyl chloride. The base‐catalyzed derivatives of acetylacetone and ethyl acetoacetate reaction with р‐fluorobenzoyl chloride were analyzed by ¹H and ¹³C NMR spectroscopies. E and Z configurations of acetylacetone and ethyl acetoacetate were separated and purified by thin layer chromatography. In addition, the ability of ¹⁹F NMR for quantitative analysis of acetylacetone by integration of the appropriate signals of the derivatives were tested and compared. The results further testified the enol forms of acetylacetone and ethyl acetoacetate and the feasibility of ¹⁹F NMR method. This method can be potentially used to characterize E and Z isomers and quantitatively analyze E/Z ratio of β‐diketone and β‐ketoester homologues. Copyright © 2015 John Wiley & Sons, Ltd.     

The design of a multi-dimensional LC-SPE-NMR system (LC(2)-SPE-NMR) for complex mixture analysis

In this communication, we describe the design of an online multi-chromatographic approach to the routine NMR analyses of low-level components ( approximately 0.1%) in complex mixtures. The technique, termed LC(2)-SPE-NMR, optimally combines multi-dimensional liquid chromatography with SPE technology for isolating, enriching and delivering trace analytes to the NMR probe. The fully automated LC(2)-SPE-NMR system allows for maximal loading capacity (in the first, preparative LC dimension), close to optimal peak resolution (in the second, analytical LC dimension) and enhanced sample concentration (through SPE). Using this system, it is feasible to conveniently conduct a wide range of NMR experiments on, for example, drug impurities at the low microgram per milliliter level, even for components poorly resolved in the first dimension. Such a sensitivity gain significantly elevates the analytical power of online NMR technology in terms of the level at which substances of pharmaceutical significance can be structurally characterized.     

Synthesis,Antimicrobial Activity,and 77Se NMR of Some New Pyrrole Derivatives Containing a Diphenyl Selenide Moiety

A simple and mild synthesis for pyrrolyl and pyrrolo[2, 3]pyrimidinyl diphenyl selenides is described based on the reaction of active methylene compounds with 4′-nitro-4-acetylaminodiphenyl selenide. The sensitivity of ⁷⁷Se NMR spectra allowed differentiating the rather similar pyrrole compounds. The synthesized compounds were screened for their antifungal and antibacterial activities.     

Atomistic understanding of the C·T mismatched DNA base pair tautomerization via the DPT: QM and QTAIM computational approaches

It was established that the cytosine·thymine (C·T) mismatched DNA base pair with cis‐oriented N1H glycosidic bonds has propeller‐like structure (|N3C4C4N3| = 38.4°), which is stabilized by three specific intermolecular interactions–two antiparallel N4H…O4 (5.19 kcal mol^?1) and N3H…N3 (6.33 kcal mol^?1) H‐bonds and a van der Waals (vdW) contact O2…O2 (0.32 kcal mol^?1). The C·T base mispair is thermodynamically stable structure (ΔG_int = ?1.54 kcal mol^?1) and even slightly more stable than the A·T Watson–Crick DNA base pair (ΔG_int = ?1.43 kcal mol^?1) at the room temperature. It was shown that the C·T ? C*·T* tautomerization via the double proton transfer (DPT) is assisted by the O2…O2 vdW contact along the entire range of the intrinsic reaction coordinate (IRC). The positive value of the Grunenberg's compliance constants (31.186, 30.265, and 22.166 Å/mdyn for the C·T, C*·T*, and TS_{C·T ? C*·T*}, respectively) proves that the O2…O2 vdW contact is a stabilizing interaction. Based on the sweeps of the H‐bond energies, it was found that the N4H…O4/O4H…N4, and N3H…N3 H‐bonds in the C·T and C*·T* base pairs are anticooperative and weaken each other, whereas the middle N3H…N3 H‐bond and the O2…O2 vdW contact are cooperative and mutually reinforce each other. It was found that the tautomerization of the C·T base mispair through the DPT is concerted and asynchronous reaction that proceeds via the TS_{C·T ? C*·T*} stabilized by the loosened N4? H? O4 covalent bridge, N3H…N3 H‐bond (9.67 kcal mol^?1) and O2…O2 vdW contact (0.41 kcal mol^?1). The nine key points, describing the evolution of the C·T ? C*·T* tautomerization via the DPT, were detected and completely investigated along the IRC. The C*·T* mispair was revealed to be the dynamically unstable structure with a lifetime 2.13·× 10^?13 s. In this case, as for the A·T Watson–Crick DNA base pair, activates the mechanism of the quantum protection of the C·T DNA base mispair from its spontaneous mutagenic tautomerization through the DPT. © 2013 Wiley Periodicals, Inc.     

Complete assignment of NMR data of 22 phenyl‐1H‐pyrazoles' derivatives

Complete assignment of ¹H and ¹³C NMR chemical shifts and J(¹H/¹H and ¹H/¹⁹F) coupling constants for 22 1‐phenyl‐1H‐pyrazoles' derivates were performed using the concerted application of ¹H 1D and ¹H, ¹³C 2D gs‐HSQC and gs‐HMBC experiments. All 1‐phenyl‐1H‐pyrazoles' derivatives were synthesized as described by Finar and co‐workers. The formylated 1‐phenyl‐1H‐pyrazoles' derivatives were performed under Duff's conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Structure and folding of glucagon-like peptide-1-(7–36)-amide in aqueous trifluoroethanol studied by NMR spectroscopy

The conformational changes of free, monomeric glucagon-like peptide-1-(7–36)-amide (GLP-1) in aqueous solution with increasing concentrations of 2,2,2-trifluoroethanol (TFE) were monitored by NMR spectroscopy. It was found that GLP-1 gradually assumes a stable, single-stranded helical structure in water solution when the TFE concentration is increased from 0 to 35% (v/v). No further structural changes were observed at higher TFE concentrations. The structure of GLP-1 in 35% TFE was determined from 292 distance restraints and 44 angle restraints by distance geometry, simulating annealing and restrained energy minimization. The helical structure extends from T7 to K28, with a less well-defined region around G16 and a disordered six-residue N-terminal domain. The folding process of GLP-1 from random coil (in water) to helix (in 35% TFE) is initiated by the formation of the C-terminal segment of the helix that is extended gradually towards the N-terminus of the peptide with increasing concentration of TFE. The exchange rates of the slow exchanging amide protons indicate that the C-terminal part of the helix is more stable than the N-terminal part. Copyright © 2001 John Wiley & Sons, Ltd.     

Unexplained acidosis of malnutrition: a study by ion-exchange chromatography/mass spectrometry

Keto-acidosis is usually associated with uncontrolled diabetes and typically poses few diagnostic problems when presenting as hyperglycaemia, metabolic acidosis and a high anion gap. An emaciated patient suffering from Duchenne Muscular Dystrophy and volume depletion presented with acidosis of unknown origin. Preliminary investigations appeared to rule out lactic acidosis, diabetic keto-acidosis and acidosis due to base loss. We have previously reported a technique utilizing liquid chromatography coupled to mass spectrometry (LC-MS) which can be used to characterize the underlying aetiology of acidosis and applied it to ultrafiltrate derived from a blood sample taken from this patient. The anion profile obtained on the chromatogram showed elevated levels of acetoacetate and hydroxybutyrate but no evidence of lactic acidosis, nor was the profile typical of that seen in 'unexplained' acidosis. We concluded that the patient was suffering from keto-acidosis associated with starvation and dehydration, the biochemical features being obscured by both the patient's chronic malnutrition and minimal muscle mass. A combination of enteral feeding and rehydration led to prompt resolution of the patient's metabolic acidosis.     

A simple flowcell for reaction monitoring by NMR

A simple, cheap and flexible flowcell based on a standard 5 mm NMR tube, designed for the monitoring of reactions but of wide applicability, is described. No modification of the NMR instrument is needed, allowing the system to be employed with any conventional NMR probe and magnet. The system is robust and economical in use of reagents, and can be used for studying both homogeneous and heterogeneous reactions. Copyright © 2010 John Wiley & Sons, Ltd.     

Radical copolymerization of 2‐trifluoromethylacrylic monomers. I. Kinetics of their copolymerization with norbornenes and vinyl ethers as studied by in situ 1H NMR analysis

Radical copolymerizations of electron‐deficient 2‐trifluoromethylacrylic (TFMA) monomers and electron‐rich norbornene derivatives and vinyl ethers with azobisisobutyronitrile were investigated by analyzing the kinetics in situ with ¹H NMR. Although none of the monomers underwent radical homopolymerization under normal conditions, they copolymerized readily, producing a copolymer containing 60–70 mol % TFMA. Terpolymerization involving these monomers was also investigated. The rates of copolymerization and kinetic chain lengths were determined in some cases on the basis of the in situ kinetics analysis. These radial copolymerizations of TFMA provide a basis for the preparation of chemical‐amplification resist polymers for emerging 157‐nm lithography. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1468–1477, 2004     

Structural determination of two new triterpenoids biotransformed from glycyrrhetinic acid by Mucor polymorphosporus

Five hydroxylated derivatives of glycyrrhetinic acid by Mucor polymorphosporus were isolated. Among them, 6β, 7β‐dihydroxyglycyrrhentic acid (2) and 27‐hydroxyglycyrrhentic acid (3) are new compounds. Their chemical structures were identified by spectral methods including 2D‐NMR. Copyright © 2009 John Wiley & Sons, Ltd.     

Nuclear magnetic resonance spectroscopic analysis of ethyl ester yield in the transesterification of vegetable oil: an accurate method for a truly quantitative analysis

Biodiesel has recently gained importance as an alternative to fossil diesel. However, the development of more efficient biodiesel formation processes still depends on the use of fast and accurate analytical techniques to evaluate the conversion degree of the transesterification reaction. Nuclear magnetic resonance (NMR) spectroscopy has been used for this purpose, but some experimental details still need to be addressed. Therefore, in this communication, the experimental conditions for a truly quantitative NMR analysis of biodiesel formation are presented. The longitudinal relaxation time (T₁), which is the determining factor for quantitative analysis, was measured using an inversion‐recovery method, and a maximum value of 2.35 s was obtained for a biodiesel sample. A linear determination coefficient of r² = 0.99 was obtained when a time delay between pulses longer than 5T₁ =15 s was used, whereas strong deviations were observed when using shorter delays. Copyright © 2012 John Wiley & Sons, Ltd.     

Determination of the content of fatty acid methyl esters (FAME) in biodiesel samples obtained by esterification using 1H-NMR spectroscopy

Three different calibration curves based on (1)H-NMR spectroscopy (300 MHz) were used for quantifying the reaction yield during biodiesel synthesis by esterification of fatty acids mixtures and methanol. For this purpose, the integrated intensities of the hydrogens of the ester methoxy group (3.67 ppm) were correlated with the areas related to the various protons of the alkyl chain (olefinic hydrogens: 5.30-5.46 ppm; aliphatic: 2.67-2.78 ppm, 2.30 ppm, 1.96-2.12 ppm, 1.56-1.68 ppm, 1.22-1.42 ppm, 0.98 ppm, and 0.84-0.92 ppm). The first curve was obtained using the peaks relating the olefinic hydrogens, a second with the parafinic protons and the third curve using the integrated intensities of all the hydrogens. A total of 35 samples were examined: 25 samples to build the three different calibration curves and ten samples to serve as external validation samples. The results showed no statistical differences among the three methods, and all presented prediction errors less than 2.45% with a co-efficient of variation (CV) of 4.66%.     

2-vinyloxy ethyl phthalimide polymerization initiated by 1-(isobutoxy) ethyl acetate in the presence of ethyl aluminum dichloride and either ethyl acetate or ethyl benzoate

2-Vinyloxy ethyl phthalimide (ImVE) was polymerized using 1-(isobutoxy) ethyl acetate as the initiator in the presence of ethyl aluminum dichloride and either ethyl acetate or ethyl benzoate. The resulting polymers have a narrow molecular weight distribution, and their molecular weight can be controlled within a narrow range by varying the monomer and initiator concentrations. Diblock copolymers with n-butyl vinyl ether can also be formed. The behavior of the polymerization is consistent with a living cationic mechanism. A brief comparison of the title system with other initiating systems is also presented. © 1996 John Wiley & Sons, Inc.     

NMR analysis of mono‐ and difructosyllactosucrose synthesized by 1F‐fructosyltransferase purified from roots of asparagus (Asparagus officinalis L.)

Two novel oligosaccharides, mono‐ and difructosyllactosucrose {[O‐β‐D ‐fructofuranosyl‐(2 → 1)]_n‐β‐D ‐fructofuranosyl‐O‐[β‐D ‐galactopyranosyl‐(1 → 4)]‐α‐D ‐glucopyranoside, n = 1 and 2} were synthesized using 1^F‐fructosyltransferase purified form roots of asparagus (Asparagus officinalis L.). Their ¹H and ¹³C NMR spectra were assigned using several NMR techniques. The spectral analysis was started from two anomeric methines of aldose units, galactose and glucose, since they showed separate characteristic signals in their ¹H and ¹³C NMR spectra. After assignments of all the ¹H and ¹³C signals of two units of aldose, they were discriminated as galactose and glucose using proton–proton coupling constants. The HMBC spectrum revealed the galactose residue attached to C‐4 of glucose, fructose residue attached to the C‐1 of glucose, and further fructosyl fructose linkage extended from the glucosyl fructose residues. Copyright © 2002 John Wiley & Sons, Ltd.     

Optimising reaction performance in the pharmaceutical industry by monitoring with NMR

Quality assurance and process understanding are assuming increasing importance in the production of Active Pharmaceutical Ingredients (APIs). NMR has the potential to report on physical processes, quantities, structures, and speciation as chemical reactions progress. Following the progression of chemical reactions by placing the sample in an NMR tube, one can perform a large number of useful studies that provide chemical and mechanistic insight. But this simple approach can have limitations, and we have therefore constructed an apparatus comprising a laboratory reactor coupled with an NMR flow cell. The reactor duplicates the exact reaction conditions that will apply with large-scale production. This reaction mixture is sampled and pumped to a high-resolution NMR flow cell where the spectrum is recorded through the course of the reaction. We demonstrate the utility of reaction monitoring using NMR both for simple cases where tubes can be used, and describe the design of the on-flow apparatus and highlight its utility with an example.     

Towards the automatic analysis of 1H NMR spectra: Part 4--additional requirements of flow-NMR

Flow-NMR allows more rapid and convenient acquisition of NMR spectra. Its main application area has therefore been in multiple parallel synthesis or combinatorial chemistry. At the same time, there is a significant need to automate the analysis of the resultant spectra. However, flow-NMR brings spectral imperfections, which compromise attempts to automate this analysis. This study proposes experimental and computational expedients to accommodate the effects of residual solvent peaks, 13C satellites, finite signal-to-noise ratio, impurities, presaturation on integral calculations, the 'silent' region and how multiplet areas can be scaled to numbers of protons in this environment.     

Free‐radical copolymerization of styrene and itaconic acid studied by 1H NMR kinetic experiments

The free‐radical copolymerization of itaconic acid (IA) and styrene in solutions of dimethylformamide and d₆‐dimethyl sulfoxide (50 wt %) has been studied by ¹H NMR kinetic experiments. Monomer conversion versus time data were used to estimate the ratio k_p · k_t^−0.5 for various comonomer mixture compositions. The ratio k_p · k_t^−0.5 varies from 5.2 · 10⁻² for pure styrene to 2.0 · 10⁻² mol^0.5 L^−0.5 s^−0.5 for pure IA, indicating a significant decrease in the rate of polymerization. Individual monomer conversion versus time traces were used to map out the comonomer mixture–composition drift up to overall monomer conversions of 60%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed can be observed. This depletion becomes more pronounced at higher levels of IA in the initial comonomer mixture. The kinetic information is supplemented by molecular weight data for IA/styrene copolymers obtained by variation of the comonomer mixture composition. A significant decrease in molecular weight of a factor of 2 can be observed when increasing the mole fraction of IA in the initial reaction mixture from 0 to 0.5. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 656–664, 2001