Assignment Of 13C NMR Signals Research Articles

Isolation and Characterization of An Allergic Dimer Impurity in Cefmenoxime Hydrochloride by NMR and HR-MS Method

Background: We systematically characterized an allergic dimer impurity in cefmenoxime hydrochloride raw material by UV, IR, HR-MS, 1D, and 2D NMR for the first time. Methods: The dimer stock solution of cefmenoxime hydrochloride was obtained by the degradation method. The target dimer impurity in the stock solution was separated by preparative RP-HPLC and purified by the freeze-drying method. By comparing the dimer to cefmenoxime hydrochloride, the functional groups corresponding to the characteristic peaks of UV and IR spectra were identified, and the molecular formula and mass fragmentation pattern were determined using HR-MS. Results: Then, based on the full assignment of 1H and 13C NMR signals， the dimerized position was confirmed and its absolute configuration was identified by 1D and 2D NMR. Conclusion: This study provided a structural basis for the allergic study of dimer impurities in cephalosporin drugs.

Determination of the absolute stereochemistry of ( +)-solaniol

The absolute stereochemistry of ( +)-solaniol (5,8-dihydroxy-7-(2-hydroxypropyl)-2-methoxy-6-methyl-1,4-naphthoquinone) (1) was deduced to be S using Mosher’s method. Our result did not accord with the R configuration of ( +)-solaniol recently proposed by Maharjan et al., but agreed with the S configuration determined by X-ray crystallographic analysis by Kyekyeku et al. In addition, complete and unambiguous assignments of 13C NMR signals for 1 are reported.

Factors influencing green strength of commercial natural rubber

Abstract The factors influencing the green strength of commercial solid rubbers were investigated in the present study through characterization of commercial natural rubber (NR). Various solid commercial rubbers such as standard Vietnam rubber (SVR10), standard Indonesia rubber (SIR10), India standard natural rubber (ISNR10), ribbed smoked sheets (RSS3), and FNR (commercial Sumitomo Rubber) were used as a source. Purification of the samples was carried out through acetone extraction and purified samples were characterized by nuclear magnetic resonance (NMR) and Fourier-Transform infrared spectroscopy. Degradation was found for SVR10, ISNR10, and SIR10 but not for RSS3 and FNR through the assignment of 13C-NMR signals. Acetone extraction was found to improve the green strength of commercial NR due to the removal of impurities. Linked fatty acids and proteins contributed to the upturn of stress at small strain. However, the network structure of degraded rubbers had an insignificant role in enhancing the green strength of commercial NR.

Structural elucidation of a novel transglycosylated compound α-glucosyl rhoifolin and of α-glucosyl rutin by NMR spectroscopy

We report the full assignment of 1H and 13C NMR signals belonging to α-glucosyl rhoifolin (Rhf-G), a novel transglycosylated compound synthesized from a flavone glycoside, rhoifolin, as well as its chemical structure. Furthermore, we report the complete NMR signal assignment for another transglycosylated compound, α-glucosyl rutin (Rutin-G), as the signals corresponding to its sugar moieties had not been identified. Electrospray ionization-mass spectrometry along with multiple NMR methods revealed that Rhf-G possesses three sugar moieties in its chemical structure. The additional glucose was bound directly via a transglycosylation to rhoifolin at position 3a of the sugar moiety. Interestingly, intramolecular hydrogen bonds in the basic Rhf-G and Rutin-G skeletons were confirmed by HMBC experiments. These findings will be helpful for comprehensive NMR studies on transglycosylated compounds in food, cosmetic, and pharmaceutical fields.

13C NMR assignments of regenerated cellulose from solid-state 2D NMR spectroscopy

From the assignment of the solid-state 13C NMR signals in the C4 region, distinct types of crystalline cellulose, cellulose at crystalline surfaces, and disordered cellulose can be identified and quantified. For regenerated cellulose, complete 13C assignments of the other carbon regions have not previously been attainable, due to signal overlap. In this study, two-dimensional (2D) NMR correlation methods were used to resolve and assign 13C signals for all carbon atoms in regenerated cellulose. 13C-enriched bacterial nanocellulose was biosynthesized, dissolved, and coagulated as highly crystalline cellulose II. Specifically, four distinct 13C signals were observed corresponding to conformationally different anhydroglucose units: two signals assigned to crystalline moieties and two signals assigned to non-crystalline species. The C1, C4 and C6 regions for cellulose II were fully examined by global spectral deconvolution, which yielded qualitative trends of the relative populations of the different cellulose moieties, as a function of wetting and drying treatments.

Structure and Spectroscopy of o-anisidine Investigated by Density Functional Theory in Comparison with Experiments

The molecular structures, vibrational spectra (IR and Raman), UV-Vis electronic absorption spectra, and NMR spectra (13C and 1H) of o-anisidine have been investigated in terms of density functional theory by using B3LYP as a density functional and 6-311++G** as a basis set. Two stable and virtually degenerate conformers arising from non-planarity of the amino group of o-anisidine have been located at the room temperature. All normal modes of o-anisidine have been assigned in terms of percent contributions of the internal motions. All main electronic transitions in the UV-Vis spectrum of o-anisidine have been assigned. Solution that increases ionization potential of o-anisidine but decreases its electron affinity has been shown to affect the unoccupied orbitals of o-anisidine drastically, which shift all electronic absorption bands to longer wavelengths. The frontier molecular orbital, molecular electrostatic potential map, and atomic charge (Mulliken, ESP, and NBO) analyses have been shown useful in estimating both global and atom-inmolecule characteristics of o-anisidine. The present chemical shift calculations allow certain assignments of the experimental 13C and 1H NMR signals of o-anisidine. The high correlations between the experimental and the present computational spectral data indicate that the computational route presented in this study can be extended for the spectroscopic calculations of analogous compounds.

Unambiguous assignment of 13C NMR signals in epimeric 4,5-epoxy-3-oxo-steroids assisted by X-ray diffraction and gauge invariant atomic orbitals calculation of absolute isotropic shieldings

Complete assignments of the 13 C signals of diastereomeric 4,5-epoxy-3-oxo steroids based on a combination of 1D and 2D NMR techniques are described The assignments were corroborated or corrected by calculation of the absolute isotropic 13 C NMR shieldings using the Gauge Invariant

Synthesis, structure, absorption and fluorescence of Pechmann dye heteroanalogues

Abstract Three N-analogues of Pechmann dye with identical aryl groups in the 5, 5′-positions (aryl = phenyl, 2-naphthyl, 2-thienyl) and carboxy ester groups in the 3,3′-positions were synthesized by oxidative dimerization of the corresponding 5-aryl-pyrrolinone esters. Derivatives with improved solubility in most organic solvents were prepared by subsequent N-methylation. The dyes were confirmed as E isomers, i.e. holding an all-trans 1,6-diaryl-1,3,5-hexatriene backbone, with slight torsion of central C C bond by X-ray diffraction and density functional theory (DFT) calculations. No E/Z photoisomerization was observed. Full assignment of 1H and 13C NMR signals was performed. The absorption spectra are quite similar with the maxima in the range 572 nm (aryl = phenyl)–643 nm (aryl = 2-thienyl) in accordance with time dependent DFT calculations of excitation energies. No fluorescence was observed in solution, while all compounds fluoresce in low temperature solvent glass (77 K) and a weak solid-state fluorescence of phenyl and 2-naphthyl derivatives in red/IR region was detected.

13C NMR identification in crude oils of hydrocarbons bearing ethyl and n-alkyl substituents on their main chain

Assignment of 13C NMR signals of compounds with ethyl, n-propyl, n-butyl, n-amyl, and n-C6+ alkyl substituents in different positions of carbon chains in the spectra of saturated hydrocarbon fractions of crude oils and in the spectra of crude oils, taking into account the dependence of chemical shifts on the recording temperature, the concentration of the test solution. and the composition of the object of study, has been proposed. The capabilities of the 13C NMR technique as applied to determination of this almost unexplored group of hydrocarbons in crude oils have been discussed.

One-pot efficient synthesis of novel fused pentacyclic indolopyridobenzimidazoles and pyridoimidazopyridoindoles from the reaction of pyranoindolones with 1,2-diaminobenzenes and 2,3-diaminopyridines

The synthesis of a number of novel, fully conjugated, planar pentacyclic 5H-indolo[3′,2′:4,5]pyrido[1,2-a][1,3]benzimidazoles (8) and 11H-pyrido[3″,2″:4′,5′]imidazo[1′,2′:1,6]pyrido[3,4-b]indoles (12) by a one-pot reaction of pyranoindolones with substituted o-phenylenediamines or 2,3-diaminopyridines is described. In the case of 2,3-diaminopyridines the reaction proceeds regioselectively affording only regioisomers 12. Structural assignments of the new compounds as well as complete assignment of 1H and 13C NMR signals were based on the analysis of their 1H and 13C NMR (1D and 2D), IR, MS and elemental analysis data. Plausible mechanisms are proposed.

Isolation and characterization of ellagitannins as the major polyphenolic components of Longan (Dimocarpus longan Lour) seeds

Longan (Dimocarpus longan Lour, syn. Euphoria longan Lam.) represents an important fruit in Northern Thailand and has significant economic impact. The fruit is either consumed fresh or as commercially prepared dried and canned products. The canning industry in Thailand produces considerable quantities of waste products, in particular Longan seeds. Because these seeds may be an exploitable source of natural phenolic antioxidants, it was of interest to identify, purify and quantitate the major potential antioxidant phenolics contained therein. The polyphenolic fraction from ground Longan seeds was obtained by extraction with methanol after delipidation with hexane. The hexane extract contained predominantly long-chain fatty acids with major contributions from palmitic (35%) and oleic (28%) acids. The polyphenolic fraction (80.90g/kg dry weight) was dominated by ellagic acid (25.84g/kg) and the known ellagitannins corilagin (13.31g/kg), chebulagic acid (13.06g/kg), ellagic acid 4-O-α-l-arabinofuranoside (9.93g/kg), isomallotinic acid (8.56g/kg) and geraniin (5.79g/kg). Structure elucidation was performed with mass spectrometry and complete assignment of 1H and 13C NMR signals. The methanol extracts exhibited strong antioxidant capacities with an IC50 of 154μg/ml for reactive oxygen species attack on salicylic acid and 78μg/ml for inhibition of xanthine oxidase in the hypoxanthine/xanthine oxidase assay. The extracts were less effective in the 2-deoxyguanosine assay (IC50=2.46mg/ml), indicating that gallates along with ellagic acid and its congeners exert their potential antioxidant effects predominantly by precipitation of proteins such as xanthine oxidase. This was confirmed for the pure compounds gallic acid, methyl gallate, ellagic acid and corilagin.

Synthesis and structural, spectroscopic, and electrochemical characterization of benzo[c]quinolizinium and its 5-aza-, 6-aza, and 5,6-diaza analogues

Four heterocyclic salts 1a– d were prepared by Ca 2+-assisted cyclization of fluoro derivatives 3, and investigated by spectroscopic (NMR and UV), electrochemical, and computational (DFT and MP2) methods. The mechanism for the formation of the cations was investigated at the DFT level of theory. 2-D NMR spectroscopy for 1[ ClO 4 ] in DMSO­ d 6 aided with DFT results permitted the assignment of 1H and 13C NMR signals in cations 1. The molecular and crystal structures for 1a[ ClO 4 ] [C 13H 10ClNO 4 triclinic, P−1, a=9.6517(12) Å, b=11.0470(13) Å, c=12.2373(15) Å, α=67.615(1)°, β=78.845(2)°, γ=87.559(2)°; V=1183.0(2) Å 3, Z=4] and 1d[ ClO 4 ] [C 12H 9ClN 2O 4 triclinic, P−1, a=5.9525(6) Å, b=8.3141(9) Å, c=12.2591(13) Å, α=73.487(1)°, β=83.814(1)°, γ=83.456(1)°; V=576.07(10) Å 3, Z=2] were determined by X-ray crystallography and compared with results of DFT and MP2 calculations. Electrochemical analysis gave the reduction potential order ( 1b> 1c∼ 1d> 1a), which is consistent with computational results.

One-pot microwave assisted synthesis under green chemistry conditions, antioxidant screening, and cytotoxicity assessments of benzimidazole Schiff bases and pyrimido[1,2-a]benzimidazol-3(4H)-ones

The synthesis of a number of benzimidazole Schiff bases 3 and 3-oxo-pyrimido[1,2-a]benzimidazoles 4 in excellent yields by a one-step sequence from the reaction of 2-aminobenzimidazole under green chemistry conditions is described. Structural assignments of the new compounds as well as complete assignment of 1H and 13C NMR signals have been unambiguously achieved based on the analysis of their 1H and 13C NMR (1D and 2D), IR, MS and elemental analysis data. To the synthesized Schiff bases the E-configuration was assigned on the basis of comparison of experimental and calculated (DFT) 13C NMR chemical shifts. Compounds 3 and 4 were evaluated as inhibitors of lipoxygenase (LOX) and of lipid peroxidation (LPO). All the tested derivatives showed inhibition of lipid peroxidation, whereas most of them were found to have higher activation than the reference compound trolox; The Schiff bases 3e, 3h, and 3i, and the pyrimidobenzimidazoles 4a, 4e and 4f were found to be the most potent. The most potent LOX inhibitor within the subset of Schiff bases was found compound 3i, followed by 3f, whereas compounds 4a and 4g were found the most potent of the 3-oxo-pyrimido[1,2-a]benzimidazole group. Moreover, some cytotoxicity assessments were undertaken, whereupon it was found that Schiff base 3i and pyrimidobenzimidazoles 4e and 4f did not exhibit cytotoxicity at similar concentrations resembling thus the inhibitory activity of lipid peroxidation. The most cytotoxic Schiff base and pyrimidobenzimidazole were found to be 3d and 4c, respectively.

1,5-Benzoxazepines vs 1,5-Benzodiazepines. One-Pot Microwave-Assisted Synthesis and Evaluation for Antioxidant Activity and Lipid Peroxidation Inhibition

Amino-1,5-benzoxazepines 2 and 5 and hydroxyl-1,5-benzodiazepines 3 and 6 have been synthesized in one-pot solvent-free conditions from 2,3-diaminophenol and ketones through microwave assisted acid catalysis, the benzoxazepine/benzodiazepine ratio depending on the R(1) and R(3) aryl substituents. The otherwise inaccessible and unknown 2,2-dimethyl-4-aryl-1,5-benzodiazepines 8 were also prepared in an analogous manner. The reaction mechanism was investigated by means of DFT calculations. Structural assignments of the new compounds as well as complete assignment of (1)H and (13)C NMR signals have been unambiguously achieved on the basis of the analysis of their (1)H and (13)C NMR (1D and 2D), IR, MS, and elemental analysis data, whereas the presence of an amino group in 5 and of a hydroxyl in 6 was confirmed by derivatization. Compounds 2, 3, 5f, 6a, 6c, 6d, 6f, 6h, 8c, and 12 were evaluated as antioxidants and lipid peroxidation inhibitors in vitro. Compound 6f was also evaluated as anti-inflammatory agent in vivo. Compounds 2 and 6f were found to be the most potent as inhibitors of lipoxygenase and of lipid peroxidation, respectively.

ChemInform Abstract: Oxidation of Spiroketones with DDQ - Synthesis of Tropone Derivatives and DDHQ Diesters.

Abstract Oxidation of spiroketones 3a–f with DDQ in dry benzene gave tropone derivatives 4a–f and DDHQ esters 5a–f ( cis - cis isomer 6a–f, trans - trans isomer 7a–f). While the aryl substituted spirokeone 17a gave a 2:1 mixture of 19a and the corresponding trans - trans isomer, the aryl substituted spiroketones 17b–d gave exclusively cis - cis isomers 19b–d. Heating acid chloride of acid 9c with DDHQ resulted in compounds 4a and 7a, thus confirming the structures assigned. Mechanism of formation of these compounds has been rationalised. A detailed study of 2D 1H-1H COSY, 1H-13C COSY, HMBC and 2D NOESY of compound 7d led to complete assignment of 1H and 13C NMR signals and its solution conformation.

Expeditious one-pot synthesis of highly substituted thiazolo[3,2- a]pyridines involving chromones

The 1,4-zwitterion derived from 4,5-dimethylthiazole and acetylenedicarboxylates has been shown to react at low temperature readily with 3-formylchromones (chromone-3-carboxaldehydes) resulting, after an unusual rearrangement, in the facile synthesis of thiazolo[3,2- a]pyridine derivatives; in the case of electron-donating substituents in the chromone ring tetracyclic chromenothiazolopyridines are isolated as the main reaction products. However, at higher temperature after an unexpected 1,2-aroyl migration 8-formyl-5 H-[1,3]thiazolo[3,2- a]pyridines are formed as a mixture of two rotamers. Structural assignments of the new compounds as well as complete assignment of 1H and 13C NMR signals were based on the analysis of their 1H and 13C NMR (1D and 2D), IR, MS and elemental analysis data. Plausible mechanisms are proposed.

A combinatorial access to 1,5-benzodiazepine derivatives and their evaluation for aldose reductase inhibition

Aryldiazepinothiophenones 4 were prepared from the reaction of o-phenylenediamines with acetone in the presence of 2-mercaptocarboxylic acids along with thiazolobenzodiazepines 6, thiazolobenzimidazoles 7 and 1,5-benzodiazepines 5, which were obtained as by-products. The benzodiazepinothiophenones 4a– d and the benzodiazepines 5a– d were also isolated from the reaction of o-phenylenediamines 1a– c with phorone. Structural assignments of the new compounds as well as complete assignment of 1H and 13C NMR signals were based on the analysis of their 1H and 13C NMR (1D and 2D), IR, MS and elemental analysis data. Compounds 4 were evaluated for aldose reductase inhibition and also as antioxidants.

Structure elucidation and complete NMR spectral assignment of two triterpenoid saponins from Radix Hedysari

A new oleanane-type triterpenoid saponin with a carbonyl group at C-15, named polybosaponin A (1), together with a known triterpenoid saponin, dehydrosoyasaponin I (2), were isolated from Radix Hedysari. On the basis of one- and two-dimensional NMR and high resolution electrospray ionization mass spectrometry, the structure of 1 were elucidated and the (1)H and (13)C NMR spectral signals were assigned totally. In addition, the complete assignment of (1)H NMR signals and revision of incorrect assignment of (13)C NMR signals for 2 were also achieved based on one- and two-dimensional NMR spectrometry.

2D Selective-TOCSY–DQFCOSY and HSQC–TOCSY NMR experiments for assignment of a homogeneous asparagine-linked triantennary complex type undecasaccharide

The assignment of 1H and 13C NMR signals of a complex type triantennary asialooligosaccharide was examined using 2D selective-TOCSY–DQFCOSY and HSQC–TOCSY experiments. The 2D selective-TOCSY–DQFCOSY experiment exhibits a 2D DQFCOSY spectrum of an individual monosaccharide in the undecasaccharide, although the NMR signals of several monosaccharides in the triantennary undecasaccharide are heavily overlapped. Selective excitation of each anomeric proton signal and subsequent TOCSY experiment afforded transverse magnetization corresponding to all of the proton signals of the monosaccharide. This magnetization was then developed with the corresponding DQFCOSY pulse sequence to afford the DQFCOSY spectrum of the individual monosugars. In this case, four GlcNAc-b, -e, -j, and -h residues were excited as a mixture. In order to assign 13C signals, a conventional 2D HSQC–TOCSY spectrum was examined and compared with an unambiguous assignment of 2D selective-TOCSY–DQFCOSY thus obtained. This systematic analysis made it possible to obtain an assignment of the 1H and 13C NMR signals of the triantennary undecasaccharide. In addition, these experiments also revealed all of the glycosyl positions in the triantennary undecasaccharide.

1,3,2-Diazaalumina-[3]ferrocenophanes with Alkyn-1-yl Substituents at Aluminum

The 1,3,2-diazaalumina-[3]ferrocenophane-ethyl(dimethyl)amine adduct 2, containing an Al-H function, reacts with terminal alkynes R-C≡C-H [R = nBu (a), tBu (b), Ph (c), SiMe3 (d)] by elimination of H2 to the amine adducts 4a - d containing an Al-C≡C-R function. Addition of pyridine leads to the corresponding pyridine adducts 5a - d, of which the molecular structure of 5d could be determined by single crystal X-ray diffraction. The formation of 4 is accompanied by side reactions such as trimerization of the alkynes to the 1,3,5-trisubstituted benzene derivatives 6a, c, and some polymerization of the alkynes. The solution-state structures of 4 and 5 were confirmed by multinuclear magnetic resonance spectroscopy (1H, 13C, 27Al, 29Si NMR). Structural features and molecular dynamics were investigated by appropriate 1H/1H NOE and magnetization transfer experiments, and particular attention was paid to the correct assignment of 13C(Al-C≡C-R) NMR signals.