Complete 1H- and 13C NMR assignments of saponins from roots of Gypsophila trichotoma Wend

The assignments of 1H and 13C NMR spectra of two new aminoacyl triterpene saponins from roots of Gypsophila trichotoma Wend. are reported. In addition to 1D NMR methods, 2D NMR techniques (COSY, TOCSY, ROESY, HSQC, HMBC, and HSQC-TOCSY) were used for the assignments. The structures were completed by analysis of HR-ESI-MS and ESI-MS(n).     

New and old NMR experiments for the resonance assignment of complex oligosaccharides--application to a cyclodextrin derivative

The complete assignment of the (1)H and (13)C sugar resonances in mono-3,6-anhydro-heptakis(2,3-O-methyl)-hexakis(6-O-methyl)-β-cyclodextrin, an asymmetrically functionalized β-cyclodextrin, was carried out by means of 2D NMR experiments. The TOCSY and the homonuclear multiple relay COSY spectra provided most of the (1)H assignments. The multiplicity edited HSQC and a set of F(1) selective HSQC-TOCSY and multiple relay HSQC-COSY spectra gave access to most of the (13)C chemical shifts. The latter were fully and accurately determined by means of a pair of complementary, highly folded HSQC-TOCSY spectra. The TOCSY-ROESY and ROESY-TOCSY spectra yielded the sequential assignment of the sugar units. A high resolution F(1) selective F(1) decoupled version of the TOCSY-ROESY experiment was recorded.     

1H and 13C NMR assignments for four triterpenoid saponins from Albizziae cortex

Four triterpenoid saponins were isolated from Albizziae cortex, and a complete assignment of their (1)H and (13)C NMR spectra was carried out using 1D and 2D NMR ((1)H-(1)H COSY, HSQC, HMBC, and HSQC-TOCSY) methods. Their (1)H NMR assignments were reported for the first time and some of their (13)C NMR spectral data reported in literature were corrected.     

One- and two-dimensional NMR studies of methyl acrylate/vinyl acetate/N-vinyl carbazole terpolymers

Terpolymers of methyl acrylate/vinyl acetate/N-vinyl carbazole (M/A/C) with different compositions were synthesized by solution polymerization using AIBN as an initiator. Composition of terpolymers was determined from quantitative ¹³C{¹H} NMR spectrum. Two-dimensional heteronuclear single quantum correlation (HSQC) and total correlated spectroscopy (TOCSY) were used to assign the methylene and methine carbon resonances by analyzing two and three bond order couplings. Various resonance signals were assigned to different compositional and configurational sequences with the help of one- and two-dimensional NMR spectra. Three and four bond order coupling between carbonyl carbon and other neighboring protons have been investigated with the help of 2D heteronuclear multiple bond correlation (HMBC) spectra. The complex and overlapped ¹H NMR spectrum of terpolymer was analyzed completely with the help of 2D HSQC and TOCSY spectra.     

Poly(acrylonitrile‐co‐methyl methacrylate‐co‐methyl acrylate): Synthesis and stereosequence distribution analysis by 2D NMR

Terpolymers of acrylonitrile (A), methyl methacrylate (B), and methyl acrylate (M) were synthesized under optimized atom transfer radical polymerization conditions using 2‐bromopropionitrile as an initiator and CuBr/dinonyl bipyridine as a catalyst. Variation of the feed composition led to terpolymers with different compositions. Composition of synthesized terpolymers were calculated from quantitative ¹³C{¹H} NMR spectra. Number average molecular weight and polydispersity index were determined by gel permeation chromatography. The overlapping and broad signals of the terpolymers were assigned completely to various compositional and configurational sequences by correlation of one‐dimensional ¹H, ¹³C{¹H}, and distortionless enhancement by polarization transfer and two‐dimensional heteronuclear single quantum coherence (HSQC) and total correlation spectroscopy (TOCSY). 2D HSQC NMR study shows one to one correlation between carbon and proton signals, while 2D TOCSY spectra were used to confirm 1, 2 bond geminal couplings between nonequivalent protons of same methylene group. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 25–37, 2009     

Long-range carbon-carbon connectivity via unsymmetrical indirect covariance processing of HSQC and HMBC NMR data

It was recently demonstrated that an IDR- (Inverted Direct Response) HSQC-TOCSY data set could be decomposed into a negatively phased direct response spectrum and a positively phased relayed response spectrum that could then be subjected to unsymmetrical indirect covariance processing for the removal of artifacts due to response overlap in the proton NMR spectrum of the molecule. Using experimentally discrete HSQC and HMBC data sets, it is shown that unsymmetrical indirect covariance processing of the pair of NMR spectra affords a presentation containing long-range carbon-carbon connectivity information. The method is demonstrated using strychnine as a model compound. The resulting data are largely free of artifacts although artifacts can arise due to proton response overlap, as previously reported.     

Complete assignments of (1)H and (13)C NMR spectral data of nine surfactin isomers

A new surfactin isomer (1) was isolated from a mangrove bacteria strain 'Bacillus sp'. Its structure was identified, and full assignments of (1)H and (13)C NMR spectral data were achieved for the first time by a combination of mass spectrometry and 1D and 2D NMR experiments including DEPT, (1)H-(1)H COSY, HSQC, HMBC, TOCSY, ROESY, and HSQC-TOCSY. The NMR spectral data of eight known analogs (2-9) are also reported.     

Automatic compatibility tests of HSQC NMR spectra with proposed structures of chemical compounds

A recently introduced similarity measure is extended here for comparing two-dimensional spectra. Its applicability is demonstrated with heteronuclear single-quantum correlation (HSQC) NMR spectra. For testing the compatibility of a spectrum with the proposed chemical structure, first, the spectrum is predicted on the basis of that structure and then, the proposed comparison algorithm is applied. In this context, the topics of optimization are peak picking, signal intensity measures, and optimizing the parameters of the two-dimensional comparison method. The performance is analyzed with a test set of 289 structures of organic compounds and their HSQC and ¹H NMR spectra. The results obtained with HSQC spectra are better than those achieved using the previously described one-dimensional similarity test with ¹H NMR spectra alone.     

The NMR studies on two new furostanol saponins from Agave sisalana leaves

The detailed NMR studies and full assignments of the 1H and 13C spectral data for two new furostanol saponins isolated from Agave sisalana leaves are described. Their structures were established using a combination of 1D and 2D NMR techniques including 1H, 13C, 1H-1H COSY, TOCSY, HSQC, HMBC and HSQC-TOCSY, and also FAB-MS spectrometry and chemical methods. The structures were established as (25S)-26-(beta-D-glucopyranosyl)-22 xi-hydroxyfurost-12-one-3beta-yl-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->3)-O-[O-beta-D-glucopyranosyl-(1-->2)]-O-beta-D-glucopyranosyl-(1-->4)-beta-D-galacto- pyranoside (1) and (25S)-26-(beta-D-glucopyranosyl)-22xi-hydroxyfurost-5-en-12-one-3beta-yl-O-alpha-L-rhamno- pyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->3)-O-[O-beta-D-glucopyranosyl-(1-->2)]-O-beta-D-glucopyranosyl- (1-->4)-beta-D-galactopyranoside (2).     

Spectral assignment of poly(vinyl acetate) by one and two dimensional NMR spectroscopy: Revisited

Poly(vinyl acetate) (PVA) prepared by photopolymerization was studied by a combination of one and two dimensional NMR spectroscopy. The ¹³C{¹H} and ¹H NMR spectra of the homopolymer (PVA) were assigned to the configurational pentads (CH region) and tetrads (CH₂ region). These assignments were substantiated by the use of two dimensional heteronuclear single quantum correlation (HSQC), heteronuclear single quantum correlation‐total correlation spectroscopy (HSQC‐TOCSY) and double quantum filtered correlation spectroscopy (DQFCOSY) experiments. The results obtained by the analysis of the area under the resonance signals confirmed that PVA obeys Bernoullian statistics. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 551–556, 1999     

The wewakpeptins, cyclic depsipeptides from a Papua New Guinea collection of the marine cyanobacterium Lyngbya semiplena

Four new depsipeptides have been isolated from the marine cyanobacterium Lyngbya semiplena collected from Papua New Guinea. The amino and hydroxy acid partial structures of wewakpeptins A-D (1-4) were elucidated through extensive spectroscopic techniques, including HR-FABMS, 1D (1)H and (13)C NMR, as well as 2D COSY, HSQC, HSQC-TOCSY, and HMBC spectra. The sequence of the residues was determined through a combination of multifaceted approaches including ESI-MS/MS, HMBC, ROESY, and a modified 1D HMBC experiment. The absolute stereochemistry of each residue was determined by chiral HPLC and chiral GC-MS methods. The wewakpeptins represent an unusual arrangement of amino and hydroxy acid subunits relative to known cyanobacterial peptides and possess a bis-ester, a 2,2-dimethyl-3-hydroxy-7-octynoic acid (Dhoya) or 2,2-dimethyl-3-hydroxyoctanoic acid (Dhoaa) residue, and a diprolyl group reminiscent of dolastatin 15. Wewakpeptin A and B were the most cytotoxic among these four depsipeptides with an LC(50) of approximately 0.4 muM to both the NCI-H460 human lung tumor and the neuro-2a mouse neuroblastoma cell lines.     

The advantages of forward linear prediction over multiple aliasing for obtaining high‐resolution HSQC spectra in systems with extreme spectral crowding

The resolution obtained for the highly crowded ¹³C–¹H HSQC spectrum of a mixture of three trisaccharides using forward linear prediction is compared with that recently reported for the same mixture but using multiple (100‐fold or greater) aliasing of HSQC spectra in combination with a computer program to unfold the aliased spectra. It is shown that forward linear prediction gives slightly superior resolution while avoiding the significant sensitivity loss associated with the very narrow spectral windows and consequent long evolution times required for the multiple aliasing method. Copyright © 2003 John Wiley & Sons, Ltd.     

Unusual sesquiterpene glucosides from Amaranthus retroflexus

Implementing the phytochemical study of the weed Amaranthus retroflexus, four new sesquiterpene glucosides were isolated from the methanolic extract of the plant. The structures of these metabolites are determined on the basis of the mass spectrometry, and 1D and 2D NMR spectroscopies (DQ-COSY, TOCSY, HSQC, HSQC-TOCSY, HMBC, and NOESY). Two compounds are characterized by a new aglycone and differed from the site of glucosylation. The other two compounds are dimeric diastereoisomers.All the glucoside sesquiterpenes were tested on the wild species Taraxacum officinale to evaluate the role of this weed in the habitat and on the seed of A. retroflexus to verify the potential autotoxic effect of the plant.     

Stereochemical and compositional assignment of acrylonitrile/methyl methacrylate copolymers by DEPT and inverse HECTOR NMR spectroscopy

The acrylonitrile/methyl methacrylate copolymers of different monomer concentration were prepared by photo polymerization using uranyl ion as initiator. The carbon 13 and proton spectra of these copolymers are overlapping and complex. The complete spectral assignment of the ¹³C- and ¹H-NMR spectra were done with the help of Distortionless Enhancement by Polarization Transfer (DEPT) and two dimensional ¹³C–¹H Heteronuclear Single Quantum Correlation (HSQC) experiments. The methylene, methine and the methyl carbon resonances show both stereochemical (triad level) and compositional (dyad, triad, tetrad, pentad and hexad level) sensitivity. 2D Double Quantum Filtered Correlated Spectroscopy (DQFCOSY) experiment was used to ascertain the various geminal couplings between the methylene protons. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1081–1092, 1998     

A toolbox of HSQC experiments for small molecules at high 13C‐enrichment. Artifact‐free,fully 13C‐homodecoupled and JCC‐encoding pulse sequences

A set of modified HSQC experiments designed for the study of ¹³C‐enriched small molecules is introduced. It includes an improved sensitivity‐enhanced HSQC experiment eliminating signal artifacts because of high‐order ¹³C magnetization terms generated at high ¹³C enrichment. A broadband homonuclear ¹³C decoupling sequence based on Zangger and Sterk's method simplifies the complex ¹³C–¹³C multiplet structure in the F1 dimension of HSQC. When recording spectra at high resolution, the combination with a multiple‐site modulation of the selective pulse outperforms the constant‐time HSQC in terms of sensitivity and reliability. Finally, two pulse sequences reintroducing selected J_CC couplings with selective pulses facilitate their assignments and measurements either in the splitting of the resulting doublets or by modulation of the signal amplitude. A sample of uniformly 92% ¹³C‐enriched cholesterol is used as an example. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of heteronuclear coupling constants from 3D HSQC-TOCSY experiment with optimized random sampling of evolution time space

An application of 3D version of HSQC-TOCSY experiment for the measurement of heteronuclear coupling constants of organic compounds yielding complex spectra is proposed. The approach presented here is based on the optimized random sampling of the evolution time space followed by Multidimensional Fourier Transform (MFT). In this study, we show that the interpretation of omega(3)-(13)C coupled (1)H-(13)C 3D HSQC-TOCSY spectra with E.COSY-type multiplets allows one to evaluate heteronuclear coupling constants of strychnine with high accuracy, whereas the employment of 2D methods is associated with signal overlap and use of conventionally recorded 3D NMR spectra cannot provide accurate results in an overnight experiment.     

Total assignment of 1H and 13C NMR spectra of three triterpene saponins from roots of Silene vulgaris (Moench) Garcke

The assignments of ¹H and ¹³C NMR spectra for three new triterpene saponins from Silene vulgaris (gypsogenin 3‐O‐glucuronide, quillaic acid 3‐O‐glucuronide, and gypsogenin 3‐O‐glycoside) are reported. In addition to 1D NMR methods, 2D NMR techniques (COSY, HSQC, HMBC, and HSQC‐TOCSY) were used for the assignments. Copyright © 2002 John Wiley & Sons, Ltd.     

2BOB – extracting an H2BC and an HSQC‐type spectrum from the same data set,and H2OBC – a fast experiment delineating the protonated 13C backbone

Two new related methods, 2BOB and H2OBC, for tracking out the backbone of protonated ¹³C nuclei are presented. 2BOB extracts an H2BC and an HSQC‐type spectrum from one and the same data set, and the combined information of these two spectra tracks out the molecular backbone. The faster method, H2OBC, typically requiring only a few minutes of instrument time, yields a single spectrum with distinct and different phases imposed on the H2BC and one‐bond peaks thus obviating the need to separate them in the absence of complicating spectral overlap. Copyright © 2017 John Wiley & Sons, Ltd.     

An unambiguous assignment and structural analysis using solution NMR experiments of O-antigen from Escherichia coli ATCC23505 (Serotype O9)

Bacterial lipopolysaccharide from Escherichia coli O9 (O9 LPS) has various characteristic biological activities other than endotoxic activities. The biological activities exhibited depend on the structure of the O-antigen. The O-antigen region of O9 LPS is composed of the mannose homopolysaccharide (MHP). This structure was reported previously, but not all its proton and carbon signals were assigned. In the present study, we completely assign all proton and carbon signals of the O-antigen of O9 LPS using (1)H- and (13)C-NMR spectroscopy, including the DQF-COSY, TOCSY, NOESY, HSQC, H2BC, HSQC-TOCSY and HMBC methods.     

Proton high‐field NMR study of tomato juice

A detailed analysis of the proton high‐field (600 MHz) NMR spectra of tomato juice and pulp is reported for the first time. A combination of J‐resolved, COSY, TOCSY, DOSY, ¹H–¹³C HSQC and ¹H–¹³C HMBC 2D sequences was used to assign each spin system and to separate the components of the complex patterns in the 1D overlapped proton spectra. To obtain resolved proton spectra of tomato pulps the high‐resolution magic angle spinning technique was used; a comparison with the liquid‐state NMR spectra of the corresponding juices was accomplished. On the basis of the assignments made, the chemical composition of tomato juices from two cultivars (Red Setter and Ciliegino) was determined. Copyright © 2003 John Wiley & Sons, Ltd.