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Introduction: Natural products and metabolomics are intrinsically linked through efforts to analyze complex mixtures for compound annotation. Although most studies that aim for compound identification in mixtures use MS as the main analysis technique, NMR has complementary advances that are worth exploring for enhanced structural confidence. Objective: This review aimed to showcase a portfolio of the main tools available for compound identification using NMR. Materials and Methods: COLMAR, SMART‐NMR, MADByTE, and NMRfilter are presented using examples collected from real samples from the perspective of a natural product chemist. Data are also made available through Zenodo so that readers can test each case presented here. Conclusion: The acquisition of 1H NMR, HSQC, TOCSY, HSQC‐TOCSY, and HMBC data for all samples and fractions from a natural products study is strongly suggested. The same is valid for MS analysis to create a bridged analysis between both techniques in a complementary manner. The use of NOAH supersequences has also been suggested and demonstrated to save NMR time. This review highlights the tools available for compound identification using NMR in natural product chemistry. The tools discussed include COLMAR, SMART‐NMR, MADByTE, and NMRfilter, and examples are presented using real samples. The acquisition of various NMR data, such as 1H NMR, HSQC, TOCSY, HSQC‐TOCSY, and HMBC data, is strongly recommended for natural product studies. The use of NOAH supersequences is also suggested to save NMR time, and an example is provided to demonstrate this. [ABSTRACT FROM AUTHOR]

Cadinanes are typical plant sesquiterpenes with a broad range of biological functions. We report the isolation of three cadinanes (1–3) from a bacterial endophyte (Streptomyces sp.) of the mangrove plant Bruguiera gymnorrhiza. The structures of two new cadinenes, (+)‐11‐hydroxy‐epicubenol (1) and (+)‐12‐hydroxy‐epicubenol (2) were elucidated by nuclear magnetic resonance (NMR) and mass spectrometry. The bacterial product (+)‐11‐hydroxy‐epicubenol was elucidated to be an enantiomer of the plant product pubinernoid C. (+)‐12‐Hydroxy‐epicubenol was established as a diastereomer of the basidiomycete product trichapargin A. In addition, a crystal structure analysis corroborated the structure and configuration of 5,11‐epoxy‐10‐cadinanol (3), a cadinane cycloether initially described as a natural product from liverwort. The discovery of oxygenated cadinanes from a bacterial endophyte may set the basis for the production of cadinanes by bacterial fermentation. [ABSTRACT FROM AUTHOR]

Abstract: Pure shift techniques have recently attracted much attention, as they have the ability to reduce spectral overlap and thus to simplify the analysis of complex and congested spectral regions. For peptides, band‐selective pure shift approaches are often the most reasonable choice among these, when spectra need to be simplified along proton dimensions. Band‐selective approaches usually offer the highest sensitivity of all pure shift methods, albeit at the cost that signals can only be acquired in a single‐frequency region of the spectrum, in which protons are well isolated in the proton spectrum. For α‐peptides, signals are usually acquired either in the amide‐proton region or in the α‐proton region. Herein, we present experiments, which enable the pure shift acquisition in both the amide‐proton and the α‐proton regions of α‐peptides simultaneously, without sacrificing the characteristics of band‐selective pure shift methods to provide high sensitivity. The “perfectBASH” approach discussed here combines the perfect echo experiment with band‐selective decoupling. It can be used for band‐selective pure shift acquisition of 1H, TOCSY, CLIP‐COSY, relayed CLIP‐COSY, NOESY, and EASY‐ROESY spectra, with proton–proton decoupling over the full backbone region of α‐peptides, which is most interesting for samples prepared without isotopic enrichment. As the utility of this technique is by no means limited to α‐peptides, we further illustrate its utility for 1H‐NMR studies of a peptidomimetic oligourea. [ABSTRACT FROM AUTHOR]

Bioassay guided fractionation of the cytotoxic extract of the plant Cuscuta reflexa, employing cytotoxic assay against a panel of 60 cell lines, led to the isolation of 13 compounds identified as odoroside H ( 1), 21-hydroxyodoroside H ( 2), neritaloside ( 3), strospeside ( 4), 16- β-hydroxydigitoxin ( 5), N-trans and cis feruloyl tyramines ( 6 and 7), ethyl caffeate ( 8), coumarins ( 9 and 10), ursolic acid ( 11), β-sitosterol glucoside ( 12), and 4-O-p-coumaroyl- β-D-glucoside ( 13). Compound 2 was found to be a new natural product while 1, 3, 4, 5, 6, 7, 10, and 11 are known compounds isolated from this source for the first time. Compounds 1, 3, and 4 possessed very good cytotoxic activity against renal and prostate cancer cell lines. Of these compounds, 1 showed a positive hollow fiber test and was selected for in vivo xenograft testing. The structures of compounds 1-5 have been established through chemical and spectral studies including UV, IR, mass, NMR (H and C), and 2D NMR (COSY-45°, NOESY, HMQC, HMBC, and J-resolved) experiments. [ABSTRACT FROM AUTHOR]

The structure of a novel compound from Adansonia digitata has been elucidated, and its 1H and 13C NMR spectra have been assigned employing a variety of one-dimensional and two-dimensional NMR techniques without degradative chemistry. The Advanced Chemistry Development ACD/Structure Elucidator software was important for determining part of this structure that contained a fused bicyclic system with very few hydrogen atoms, which in turn, exhibited essentially no discriminating HMBC connectivities throughout that portion of the molecule. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article discusses a study related to structure elucidation of cycloartane triterpene glycoside from Souliea vaginata by using the nuclear magnetic resonance (NMR) technology. It mentions role of Souliea vaginata as Chinese folk medicine that is used for treatment of conjunctivitis, pharyngitis and enteritis. It also mentions that the isolated compound gave positive Liebermann–Burchard reaction.

The article discusses research on two new sesquiterpenoids from Artemisia annua, a fragrant herb belonging to the family Asteraceae. The study presented the isolation and structural elucidation of the sesquiterpenoids by the anaysis of 1D and 2D nuclear magnetic resonance (NMR), high-resolution electrospray ionisation mass spectrometry (HR-ESI-MS), calculated equivalent circulating density (ECD) and crystal X-ray diffraction. Results showed the presence of a proton spin system.

The effectiveness of hetero-COSY, HETCOR, HMQC, and HSQC two-dimensional NMR pulse sequences for detection of 19F-1H correlations by scalar coupling was evaluated on monofluorinated and polyfluorinated test compounds. All four of these sequences were effective in observing 1H-19F correlations, using either 19F or 1H as the observe nucleus. All four sequences were amenable, to some degree, to adjustment to observe larger or smaller couplings preferentially. A 1/2J echo filter was effectively applied to remove artifacts from 2JFF strong coupling. The HETCOR experiments afforded the best overall combination of sensitivity, resolution and selectivity for JHF. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Urea-formaldehyde resins are bulk products of the chemical industry. Their synthesis involves a complex reaction network. The present work contributes to its elucidation by presenting results from detailed NMR spectroscopic studies with different methods. Besides1H NMR and13C NMR,15N NMR spectroscopy is also applied.15N-enriched urea was used for the investigations. A detailed NMR signal assignment and a model of the reaction network of the hydroxymethylation step of the synthesis are presented. Because of its higher spectral dispersion and the fact that all key reactions directly involve the nitrogen centers,15N NMR provides a much larger amount of detail than do1H and13C NMR spectroscopy. Symmetric and asymmetric dimethylol urea can be clearly distinguished and separated from monomethylol urea, trimethylol urea, and methylene-bridged urea. The existence of hemiformals of methylol urea is confirmed. 1,3,5-Oxadiazinan-4-on (uron) and its derivatives were not found in the reaction mixtures investigated here but were prepared via alternative routes. The molar ratios of formaldehyde to urea were 1, 2, and 4, the pH values 7.5 and 8.5, and the reaction temperature 60 °C. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A new triterpenoid bidesmoside (leptocarposide) possessing an acyl group in their glycosidic moiety (1), together with the known luteolin-8- C-glucoside (2) and 1- O-β- d-glucopyranosyl-(2 S,3 R,8 E)-2-[(2′ R)-2-hydroxypalmitoylamino]-8-octadecen-1,3-diol (3) was isolated from the n-butanol-soluble fraction of whole plant of Ludwigia leptocarpa (Nutt) Hara (Onagraceae). Structure of compound 1 has been assigned on the basis of spectroscopic data (1H and 13C NMR, 1H-1H COSY, HSQC, HMBC, and ROESY), mass spectrometry, and by comparison with the literature. This compound was further screened for its potential antioxidant properties by using the radical scavenging assay model 2,2-diphenyl-1-picrylhydrazyl and reveals non-potent antioxidant activities, while compound 2 shows SC50 of 0,038 mM. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Four new prenylated flavonoids, cudraflavanones E-F (1-2) and cudraflavones F-G (6-7), together with eight known compounds were isolated from the roots of Cudrania tricuspidata. The structures of new compounds were elucidated on the basis of extensive spectroscopic analyses, including 1D and 2D NMR, HRESIMS and CD. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

To find potent new chemotherapy drugs, we designed and synthesized a series of naphthochalcones bearing naphthalenyl-phenyl-pyrazoline moieties. The complete 1H and 13C NMR data for these compounds are reported here and can be used to identify further new naphthochalcones bearing the desired pyrazoline moieties. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Cis and trans isomers of a series of double-decker silsesquioxanes (DDSQ) were characterized by two-dimensional NMR techniques. The 1H NMR spectra of these species have not previously been assigned to a degree that allows for quantification. Thus, 1H-29Si HMBC correlations were applied to facilitate 1H spectral assignment and also to confirm previous 29Si assignments for this class of silsesquioxanes. With the ability to identify all the pertinent resonances of the 1H NMR spectrum, 29Si NMR is no longer required for quantification and required only for characterization. This not only saves time and material but also provides a more accurate quantification, thus allowing for the ratio of cis and trans isomers present in each compound to be determined. A more accurate measure of the cis/ trans ratio enables the investigation of its influence on the physical and chemical properties of DDSQ nanostructured materials. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A one-step method was reported for the synthesis of 6-acetamido-3-( N-(2-(dimethylamino) ethyl) sulfamoyl) naphthalene-1-yl 7-acetamido-4-hydroxynaphthalene-2-sulfonate by treating 7-acetamido-4-hydroxy-2-naphthalenesulfonyl chloride with equal moles of N, N-dimethylethylenediamine in acetonitrile in the presence of K2CO3. The chemical structure of the obtained compounds was characterized by MS, FTIR, 1H NMR, 13C NMR, gCOSY, TOCSY, gHSQC, and gHMBC. The chemical shift differences of 1H and 13C being δ 0.04 and 0.2, respectively, were unambiguously differentiated. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Chalcones are of interest to medicinal chemists because their structures can be easily modified with various functional groups. The syntheses and biological activities of chalcones from natural sources are well known. In this study, 24 2′-hydroxychalcones bearing methoxy substituents were synthesized, among which five are new. The NMR data for all synthesized chalcones are described for the first time. The complete assignments of the 1H and 13C NMR data can be used for the identification of newly discovered and widely isolated, synthesized chalcones. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Four new prenylindole derivatives, ( R)-6-(2,3-dihydroxy-3-methylbutyl)indole (1), ( R)-6-(2,3-dihydroxy-3-methylbutyl)indolin-2-one (2), and an unseparated mixture of ( Z)-6-(4-hydroxy-3-methylbut-2-en-1-yl)indolin-2-one (3a) and ( E)-6-(4-hydroxy-3-methylbut-2-en-1-yl)indolin-2-one (3b) with a ratio of 3 : 2, were isolated from the culture broth of a streptomycete isolated from Ailuropoda melanoleuca feces. Their structures were elucidated on the basis of 1D and 2D NMR spectroscopic techniques. The absolute configuration of 1 was determined by Mosher's method. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

From the branches of Pittosporum senacia Putterlick (Pittosporaceae), two new triterpenoid saponins, senaciapittosides A and B (1, 2), were isolated. Their structures were elucidated by extensive analysis of one- and two-dimensional nuclear magnetic resonance spectroscopy, high-resolution electrospray ionization mass spectrometry (HR-ESIMS) and chemical evidence as 3- O-[ β- d-glucopyranosyl-(1 → 2)]-[ α- l-arabinopyranosyl-(1 → 3)]-[ α- l-arabinofuranosyl-(1 → 4)]- β- d-glucuronopyranosyl oleanolic acid 28- O-β- d-glucopyranosyl ester (1) and 3- O-[ β- d-glucopyranosyl-(1 → 2)]-[ α- l-arabinopyranosyl-(1 → 3)]-[ α- l-arabinofuranosyl-(1 → 4)]- β- d-glucuronopyranosyl-22- O-α- l-arabinopyranosyl-21-acetoxy R1-barrigenol (2). Compound 2 presents an unusual glycosylation at C-22 of its aglycone. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Several types of chalcones containing 2 H-chromen group were synthesized. Claisen-Schmidt condensation of 2 H-chromen-3-carbaldehydes (I) with methoxy substituted acetophenones afforded ( E)-3-(2 H-chromen-3-yl)-1-(methoxyphenyl)prop-2-en-1-ones (chromenylchalcones, 1-7). Other types of chromenylchalcone, ( E)-1-(6-methoxy-2 H-chromen-3-yl)-3-(methoxyphenyl)prop-2-en-1-ones (8-13) were also obtained between reaction of methoxy substituted benzaldehydes and 1-(6-methoxy-2 H-chromen-3-yl)ethanone (II). Dichromenylchalcones (14-16) were also synthesized through the same reaction between aldehydes (I) and ketone (II). Their complete 1H-NMR and 13C-NMR assignments are reported here and more polysubstituted chromenylchalcones synthesized or isolated from the natural sources in the future can be identified on the basis of the NMR data reported here. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The revised structures of avenacosides A and B and a new sulfated steroidal saponin isolated from grains of Avena sativa L. were elucidated. Their structures and complete NMR assignments are based on 1D and 2D NMR studies and identified as nuatigenin 3- O-{ α- l-rhamnopyranosyl-(1→2)-[ β-D-glucopyranosyl-(1→4)]- β- d-glucopyranoside}-26- O-β- d-glucopyranoside (1), nuatigenin 3- O-{ α- l-rhamnopyranosyl-(1→2)-[ β- d-glucopyranosyl-(1→3)- β- d-glucopyranosyl-(1→4)]- β- d-glucopyranoside}-26- O-β- d-glucopyranoside (2), and nuatigenin 3- O-{ α- l-rhamnopyranosyl-(1→2)-[ β- d-6- O-sulfoglucopyranosyl-(1→4)]- β- d-glucopyranoside}-26- O-β- d-glucopyranoside (3). Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The application of common two-dimensional NMR correlation experiments to gaseous analytes for structural elucidation is reported. Standard sequences such as COSY, HSQC, and HMBC are readily applied to volatile hydrocarbons and fluorocarbons. In experiments using 19F or 13C as the observed nucleus, it is possible to take advantage of efficient spin-rotation relaxation to perform common experiments swiftly (a 19F COSY acquired in 6s is shown) or to render insensitive experiments possible on a practical timescale (e.g. a gas phase INADEQUATE at natural isotopic abundance in 14h). NOE-based experiments were not successful on the gaseous systems studied. [Copyright &y& Elsevier]

Abstract: Aqueous phospholipid mixtures that form bilayered micelles (bicelles) have gained wide use by molecular biophysicists during the past 20 years for spectroscopic studies of membrane-bound peptides and structural refinement of soluble protein structures. Nonetheless, the utility of bicelle systems may be compromised by considerations of cost, chemical stability, and preservation of the bicelle aggregate organization under a broad range of temperature, concentration, pH, and ionic strength conditions. In the current work, 31P nuclear magnetic resonance (NMR) and atomic force microscopy (AFM) have been used to monitor the size and morphology of isotropically tumbling small bicelles formed by mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (DIOMPC) with either 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) or 1,2-di-O-hexyl-sn-glycero-3-phosphocholine (DIOHPC), testing their tolerance of variations in commonly used experimental conditions. 1H-15N 2D NMR has been used to demonstrate the usefulness of the robust DMPC–DIOHPC system for conformational studies of a fatty acid-binding protein that shuttles small ligands to and from biological membranes. [Copyright &y& Elsevier]

Abstract: In this paper we present a complete 1H and 13C NMR spectral analysis of three lignan lactones (methylpluviatolide, dimethylmatairesinol and hinokinin) by the use of techniques such as COSY, HMQC, HMBC and J-resolved. Complete assignment and all homonuclear hydrogen coupling constant measurements were performed, providing enough data also to the confirmation of the relative stereochemistry. [Copyright &y& Elsevier]

Products of thermal transformation of substituted N-aryl- o-quinoneimines were studied using NMR spectroscopy. The formation of 4a H-phenoxazine, which was further dimerized by the Diels—Alder reaction, was established. [ABSTRACT FROM AUTHOR]

Two new unusual xanthones, 5-O-β- d-glucopyranosyl-1,3,8-trihydroxy-5,6,7,8-tetrahydroxanthone (1) and 1,3,5,8-tetrahydroxy-5,6,7,8-tetrahydroxanthone (2), were isolated from Lomatogonium carinthiacum (Wulf) Reichb. Their structures were elucidated on the basis of spectroscopic methods including UV, IR, ESI-MS, 1D NMR, and 2D NMR. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study explored the rearrangement process which occurred during Grignard reactions of the pentacycloundecane (PCU) dione, 1. This compound was reacted with vinyl and allyl magnesium bromide to afford PCU-vinyl cyclic ether, 2 , and PCU-allyl cyclic ether, 4 , which upon ozonolysis afforded compounds PCU dilactone, 3 and PCU-cyclic ether monoacid, 5 respectively. This resulted in the discovery of three novel cage compounds, 2 , 4 and 5. The Baeyer-Villiger oxidation of 1 was proposed and investigated experimentally as an alternative synthetic route for the PCU dilactone. The unsymmetrical nature of compounds 2 , 4 and 5 resulted in overlapping signals of the methine protons and carbons observed in the 1H and 13C NMR spectra, however, the complexity of the spectra was resolved by using 2D NMR techniques to successfully elucidate these compounds. Herein, the three novel cage compounds including compound 3 were fully characterized by IR and NMR spectroscopy, HRMS. Single crystal X-ray crystallography analysis was also performed on compounds 3 and 5. • 2D NMR is essential to the elucidation of overlapping polycyclic 'cage' proton NMR signals. • X-ray crystal structure of pentacycloundecane supports 1D and 2D NMR elucidation. • Elucidation of polycyclic molecules using NMR techniques. • NMR Elucidation of Pentacycloundecane and its derivatives. [ABSTRACT FROM AUTHOR]