Letteratura scientifica selezionata sul tema "13C NMR identification"

Characteristic 1H NMR parameters of 88 acyl groups, hitherto found as ester substituents in natural sesquiterpenic lactones, were determined from the measured spectra as well as literature data. Characteristic 13C NMR chemical shifts for 45 acyl groups were obtained in the same way; for the remaining acyls with hitherto unknown 13C NMR data the values were calculated on the basis of semiempirical relationships.

Carbon-13 nuclear magnetic resonance is used to identify components of the distillation residue from the manufacture of cyclohexanone. 13C NMR spectra of rectification fractions provide the data utilized in an algorithm to extract subspectrum resonances specific to each component of the mixture. The subspectra are then subjected to search in 13C NMR library of potential components. A number of components were unambiguously identified in original sample even if moderate peak overlaps occurred. Generated subspectra made also possible identification of substances which are not present in 13C NMR libraries.

Background: Metabolism is essential for cell survival and proliferation. A deep understanding of the metabolic network and its regulatory processes is often vital to understand and overcome disease. Stable isotope tracing of metabolism using nuclear magnetic resonance (NMR) and mass spectrometry (MS) is a powerful tool to derive mechanistic information of metabolic network activity. However, to retrieve meaningful information, automated tools are urgently needed to analyse these complex spectra and eliminate the bias introduced by manual analysis. Here, we present a data-driven algorithm to automatically annotate and analyse NMR signal multiplets in 2D-1H,13C-HSQC NMR spectra arising from 13C -13C scalar couplings. The algorithm minimises the need for user input to guide the analysis of 2D-1H,13C-HSQC NMR spectra by performing automated peak picking and multiplet analysis. This enables non-NMR specialists to use this technology. The algorithm has been integrated into the existing MetaboLab software package. Methods: To evaluate the algorithm performance two criteria are tested: is the peak correctly annotated and secondly how confident is the algorithm with its analysis. For the latter a coefficient of determination is introduced. Three datasets were used for testing. The first was to test reproducibility with three biological replicates, the second tested the robustness of the algorithm for different amounts of scaling of the apparent J-coupling constants and the third focused on different sampling amounts. Results: The algorithm annotated overall >90% of NMR signals correctly with average coefficient of determination ρ of 94.06 ± 5.08%, 95.47 ± 7.20% and 80.47 ± 20.98% respectively. Conclusions: Our results indicate that the proposed algorithm accurately identifies and analyses NMR signal multiplets in ultra-high resolution 2D-1H,13C-HSQC NMR spectra. It is robust to signal splitting enhancement and up to 25% of non-uniform sampling.

Abstract The cyanogenic glycoside of young fronds and fiddleheads of the fern Davallia trichomanoides Blume was identified as (R)-vicianin (the β-vicianoside of (R)-mandelonitrile) by acid and enzymic hydrolysis, 1H-NMR and 13C-NMR spectroscopy, and by comparison with an authentic sample isolated from Vicia angustifolia seeds.

A direct structural identification, and quantitative assessment below the 50 nmol/ml level, of the full pattern of renally excreted metabolites is made possible by 13C NMR measurements of untreated urine samples when stable isotope-labelled (13C) drug analogues are administered to humans. The full potential of the new ex vivo NMR approach is exemplified by a study, for a group of volunteers, of S-carboxymethyl-ʟ-cysteine metabolism. The metabolic sulphoxidation pathway of S-Carboxymethyl-ʟ-cysteine in man, accepted so far, needs to be profoundly revised on the basis of the 13C NMR results.

Several studies have reported the presence of amine and imine tautomeric forms for hydrogenated 1,3-thiazine derivatives. However, identification of their tautomeric forms by UV, FTIR and mass-spectral methods does not yield expected results. Here, we report the synthesis of 2-phenylaminodihydro-1,3-thiazine and 2-phenyliminotetrahydro-1,3-thiazine and the analysis of their UV, FTIR and NMR (1H and 13C) spectral data. An identical picture of UV spectra was recorded for both compounds. However, distinctive characteristics were found in the FTIR, 1H and 13C NMR spectra. The C=N band of amine form was observed in higher frequency region relative to imine form. The signal of C2 carbon of amine form in 13C NMR spectrum was occurred in more downfield (δ 165.3 ppm) relative to C2 signal of imine form (δ 152.1 ppm). In addition, the difference between C2 and C8 carbon signals of amine form was very high (Δδ = 30.6 ppm) relative to imine form (δ 5.4 ppm). The position of C2 and C8 signals and the difference between them in 13C NMR spectrum was found to be more promising in identification of tautomeric forms in case of hydrogenated 1,3-thiazine derivatives.

The work is a continuation of the research on the use of NMR spectroscopy in the quality control of natural peptide hormone-based active substances and their synthetic analogues.The aimof the paper was to develop identification test methods for triptorelin acetate and goserelin acetate substances using NMR spectroscopy that does not require reference standards ‒ with the aim of using the newly developed test methods in pharmacopoeial analysis.Materials and methods:the procedure was developed using two-dimensional NMR spectroscopy (1H-1H gCOSY,1H-13C gHSQC,1H-13C gHMBC).Results:thestudy made it possible to assign1H and13C NMR signals to a specific molecular fragment, and to determine the amino acid composition of each oligopeptide.Conclusions:the authors drew up a table showing structural assignment of NMR signals, which makes it possible to use the NMR method for identification testing of triptorelin acetate and goserelin acetate substances without the use of pharmacopoeial reference standards. The study helped to determine the optimal temperature conditions for recording13C NMR spectra (27 °С and 50 °С for triptorelin acetate and goserelin acetate, respectively). It was demonstrated that13C NMR spectroscopy could be used for identification testing in pharmacopoeial analysis.

L’objectif de ce travail de thèse était de déterminer la composition chimique d’extraits de plantes de Corse encore peu ou pas étudiées et susceptibles d’avoir des activités biologiques valorisables. Cette étude a été menée en mettant en œuvre la méthodologie d’analyse des mélanges complexes par RMN 13C, développée depuis une trentaine d’années par l’équipe « Chimie et Biomasse » de l’UMR CNRS 6134 Sciences pour l’Environnement de l’université de Corse. Dans une première partie, nous avons étudié la composition chimique d’extraits de houx commun (Ilex aquifolium L.). Deux extraits de feuilles (obtenus à l’hexane et au dichlorométhane) ont chacun subi deux fractionnements successifs par chromatographie sur colonne ouverte de silice. L’analyse par RMN 13C (CPG(Ir) et CPG-SM également dans certains cas) des extraits bruts et des fractions de chromatographie a permis l’identification de onze triterpènes dont l’α-amyrine et la β-amyrine et certains de leurs esters. Parallèlement, deux acides triterpéniques d’intérêt (acide ursolique et acide oléanolique) ont été quantifiés par RMN 1H au sein de l’extrait brut au dichlorométhane via une méthode rapide mise au point et validée (justesse, linéarité, précision des mesures). Ces deux composés représentent respectivement 55,3% et 20,8% de l’extrait. Nous avons également réalisé, en collaboration avec l’équipe « Biochimie et Biologie Moléculaire du Végétal » de l’université de Corse, des tests antimicrobiens sur les extraits et certaines fractions de chromatographie. Les deux acides triterpéniques précédemment cités ont montré une activité antimicrobienne comparable à celle du chloramphénicol (antibiotique de référence) vis-à-vis de trois bactéries à Gram positif, Staphylococcus aureus, Staphylococcus epidermidis et Bacillus cereus (CMI = 4 et 8 mg.L-1 vs. 2 et 4 mg.L-1). Par ailleurs, nous avons préparé des extraits de baies de houx en utilisant différents solvants : hexane, dichlorométhane, dichlorométhane/acétate d’éthyle (50/50, v/v). Les deux derniers extraits (dichlorométhane et dichlorométhane/acétate d’éthyle) ont subi des fractionnements successifs et l’étude des spectres RMN 13C des extraits bruts et des fractions de chromatographie a permis d’identifier neuf triterpènes (précédemment identifiés), cinq dérivés phénoliques, six monosaccharides ainsi que quatre lactones (la ménisdaurilide, l’aquilégiolide, la 7-épi-griffonilide et la dasycarponilide) non encore répertoriées dans le houx commun. Dans une seconde partie, nous avons étudié la composition chimique d’extraits de fleurs et de racine de Calicotome villosa (Poir.) Link. Les extraits de fleurs obtenus au dichlorométhane et à l’acétate d’éthyle ont été soumis à des chromatographies successives. L’analyse par RMN 13C des extraits bruts et des fractions de chromatographie a permis l’identification de trois flavonoïdes, cinq dérivés glucosylés de flavonoïdes et quatre phénylpropanoïdes. Dans cette partie, nous nous sommes également intéressés à la composition chimique d’un extrait méthanolique de racine de C. villosa qui n’a fait l’objet d’aucune étude de ce type au préalable. Cet extrait a été soumis à plusieurs fractionnements successifs et dix-huit composés, notamment des stérols, des flavonoïdes, un polyphénol et des ptérocarpanes ont été identifiés par RMN 13C
The aim of this work was to determine chemical composition of wild growing corsican understudied plant species, with potential biological activities. This study was realized using the computerized NMR method developed over the past thirty years by the University of Corsica “Chimie et Biomasse” group, UMR CNRS “Sciences Pour l’environnement”. Identified secondary metabolites were then undertaken to evaluate their antimicrobial properties. As part of this study, we selected on the first place commun holly (Ilex aquifolium L.). After two successive column chromatography, hexane and dichloromethane leaves crude extracts and all chromatography fractions were analyzed by 13C NMR (GC(RI) and GC-MS sometimes) to allow the identification of eleven triterpens and α- and β-amyrin esters. Among identified compounds, ursolic acid and oleanolic acid were also quantified by 1H NMR in the dichloromethane crude extract using a reliable method developped and validated (accuracy, linearity precision of measurements). Ursolic acid accounted for 55.3% of the extract, followed by oleanolic acid, 20.8%. Evaluation of previous identified compounds antimicrobial activities has been performed in collaboration with « Biochimie et Biologie Moléculaire du Végétal » group (University of Corsica). Triterpen acids and chloramphenicol (reference antibiotic) displayed similar antibacterial activities against three Gram-positive bacteria, Staphylococcus aureus, Staphylococcus epidermidis and Bacillus cereus (MIC = 4 and 8 mg.L-1 vs. 2 and 4 mg.L-1). Moreover, dichloromethane and dichloromethane/ethyl acetate (50/50, v/v) berries extracts were submitted to successive column chromatography. Crude extracts and chromatography fractions 13C NMR spectra revealed presence of nine triterpens previously identidied, five phenolics derivatives, six monosaccharides and four lactones (menisdaurilide, aquilegiolide, dasycarponilide and 7-epi-griffonilide) were first time identified in berries holly extracts. On the second place, we determined chemical compositions of Calicotome villosa (Poir.) Link flowers and root extracts. 13C NMR analysis of dichloromethane and ethyl acetate flowers extracts and their chromatography fractions, allowed the identification of three flavonoids, five glycosyl flavonoids and four phenylpropanoids. We also studied chemical composition of a methanol root extract which has never been submitted to any chemical composition study. After successive column chromatography, eighteen compounds were identified by 13C NMR including sterols, flavonoids, a polyphenol and pterocarpans

博士
國立臺灣大學
化學研究所
105
A cyclotriveratrylene-based molecular cage forms hemicarceplexes that significantly increase the solubility of commercially available Sc3N@C80 in CDCl3. When incarcerated within the molecular cage, the two structural isomers of this metallofullerene, Sc3N@D5h-C80 and Sc3N@Ih-C80, displayed characteristic signals in both 1H and 13C NMR spectra, allowing direct identification of each isomer without the need to enrich the sample with 13C atoms.

Most of the NMR spectra shown in this book and in the literature have been recorded at 250 or 300 MHz, with a few being obtained at 500 MHz for 1H NMR (the equivalent for 13C NMR). No special pulse sequences are necessary, just standard one-dimensional (1D) spectra although two-dimensional (2D) experiments (e.g., correlation spectroscopy; COSY) may be necessary in some cases in order to get an unambiguous identification of the signals relevant for the assignment. In general, 5–10 mg or less of CDA derivative dissolved in 0.5 mL of deuterated solvent are sufficient to obtain a good NMR spectrum. Temperature, solvent, and concentration used in the NMR experiments should be adequate for each CDA-substrate pair and methodology, because the method is based on the conformational composition of the AMAA derivatives in precise conditions. With the exception of the low-temperature procedure (single derivatization), a NMR probe temperature around 300 K has always been used. In general, the spectra for double-derivatization assignments should be taken in deuterated chloroform. Different NMR solvents are required only in two of the single-derivatization methods. In the assignment by low-temperature NMR, the most convenient solvent is a CS2/CD2Cl2 (4:1) mixture, which allows the use of temperatures low enough (i.e., 213 K) to obtain relevant shifts. In the procedure based on the complexation with Ba2+, the NMR solvent should be deuterated acetonitrile. The barium salt is anhydrous Ba(ClO4)2, which can be added directly to the tube by using a spatula. No weighing is necessary after shaking, as the excess salt will remain at the bottom of the NMR tube and will not disturb the experiment. (R)- and (S)-MPA, MTPA, and Boc-phenylglycine (BPG) are commercially available and can be used without further purification. The first two (MPA and MTPA) can also be purchased as acid chlorides. When using MTPA or the corresponding acid chloride [85] for the derivatization of an alcohol or amine, it should be noted that the Cahn-Ingold-Prelog priority rules assign different R/S descriptors to the acid and to the corresponding chloride; this is due to the different priority order generated by the substituents [i.e., (R)-MTPA generates the (S)-acid chloride and vice versa].

Alkaloids are secondary metabolites, present in plants, which have been exhibiting a series of biological activities, a fact that highlights the importance of research with this theme. The work developed from August/2019 to August/2020, in the laboratories of the IFSC - Campus Criciúma, aimed to isolate, purify and evaluate antimicrobial activities of extracts, fractions and substances isolated from species of Psychotria genus. The extracts were obtained by maceration of the species leaves in methanol. The fractions were obtained by liquid-liquid extraction and the isolation processes by chromatographic methods. The identification of the tested metabolite was performed by NMR of1 H,13 C and high resolution mass spectrometry. The antimicrobial tests were made with the alkaloid 5-carboxy-strictosidine, extracted from Psychotria nuda, against the following microorganisms: Escherichia coli, Staphylococcus epidermidis and Pseudomonas aeruginosa. Sample did not show any activity when compared to the positive control.

Earlier we reported induction of neurotoxicity and neurodegeneration by tryptophan metabolites that link the metabolic alterations to Alzheimer’s disease (AD). Tryptophan is a product of the Shikimate pathway (SP). Human cells lack SP, which is found in human gut bacteria exclusively using SP to produce aromatic amino acids (AAA). This study is a first attempt toward gene-targeted analysis of human gut microbiota in AD fecal samples. The oligonucleotide primers newly-designed for this work target SP-AAA in environmental bacteria associated with human activity. Using polymerase chain reaction (PCR), we found unique gut bacterial sequence in most AD patients (18 of 20), albeit rarely in controls (1 of 13). Cloning and sequencing AD-associated PCR products (ADPP) enables identification of Na(+)-transporting NADH: Ubiquinone reductase (NQR) in Clostridium sp. The ADPP of unrelated AD patients possess near identical sequences. NQR substrate, ubiquinone is a SP product and human neuroprotectant. A defici in ubiquinone has been determined in a number of neuromuscular and neurodegenerative disorders. Antibacterial therapy prompted an ADPP reduction in an ADPP-positive control person who was later diagnosed with AD-dementia. We explored the gut microbiome databases and uncovered a sequence similarity (up to 97%) between ADPP and some healthy individuals from different geographical locations. Importantly, our main findin of the significan difference in the gut microbial genotypes between the AD and control human populations is a breakthrough.