Long-range Heteronuclear Coupling Research Articles

1H-detected measurements of long-range heteronuclear coupling constants. Application to a trisaccharide

1H-detected measurements of long-range heteronuclear coupling constants. Application to a trisaccharide

Selective inverse multiple bond analysis. A simple 1D experiment for the measurement of long-range heteronuclear coupling constants

The general concept of selective excitation is well established and the methodology has been utilized on numerous occasions in a wide range of applications. An interesting application of selective pulses has been in the development of selective analogues of two-dimensional NMR experiments. The first such effort germane to our work was that of Bax and Freeman ( 1)) in which they described the selective heteronuclear 2D J spectrum. Davis applied semiselective proton pulses to the Ha resonances of peptides (2) to establish long-range correlations to carbonyl resonances with high resolution in both frequency domains. In a paper published very shortly thereafter, Bermal and co-workers (3) described a group of two-dimensional pulse sequences intended to provide access to heteronuclear coupling constants that employed semiselective Gaussian 13C pulses. Kessler and colleagues have employed semiselective 13C pulses to improve the Fi resolution in proton-detected heteronuclear long-range correlation experiments (4). Supportive ancillary work has addressed the problem of extracting coupling constants from complex cross-peak multiplets observed in proton-detected heteronuclear correlation spectra (5, 6). The importance of measuring small heteronuclear coupling constants has not waned, as evidenced by recently reported heteronuclear two( 7, 8) and three-dimensional (9) studies designed to determine and utilize small heteronuclear coupling constants of biologically important molecules. In a departure from existing multidimensional methods, we report a simple, one-dimensional pulse sequence designed to allow the measurement of long-range heteronuclear coupling constants and to provide the means for establishing long-range heteronuclear connectivities. The earliest reports of one-dimensional analogs of two-dimensional NMR experiments were those of Berger ( IO, II), which were followed by the work of Kessler and colleagues (12, 13). In an extension of these efforts, we describe a one-dimensional analogue of the HMBC experiment ( 14)) for which we propose the acronym SIMBA (selective inverse multiple bond analysis). With this new experiment, each proton with a resolved long-range coupling to the selected carbon simultaneously appears in the resultant spectrum with an apparent

Measurement of long-range heteronuclear coupling constants

A method for the measurement and assignment of long-range heteronuclear coupling constants is described. The technique uses an established pulse sequence to generate a proton-detected two-dimensional correlation spectrum whose cross peaks are analyzed with a simple data fitting procedure. In this way, accurate values of the magnitudes of the couplings are extracted from highly distorted cross-peak multiplets in the correlation spectrum.

Accurate measurements of long-range heteronuclear coupling constants from homonuclear 2D NMR spectra of isotope-enriched proteins

Accurate measurements of long-range heteronuclear coupling constants from homonuclear 2D NMR spectra of isotope-enriched proteins

Determination and assignment of heteronuclear long-range coupling constants. Methods based on semiselective INEPT

One-dimensional methods for the determination and assignment of heteronuclear 1H-X (X = rare spin-z) coupling constants based on the semiselective polarization transfer via INEPT pulse sequence are proposed. Here the selectivity of the polarization transfer plays a positive role with respect to the sensitivity of the measurement and purity of the observed multiplets. In nonrefocused experiments the acquired antiphase multiplets enable an unambiguous assignment of long-range couplings of a preselected proton. The analysis of such multiplets is also discussed. In the refocused version the purging pulse (INEPT+) was used to provide pure in-phase multiplets. The spectral editing technique DISCO was applied to simplify the spectra and to extract the couplings from complex multiplets. Finally, the modified INEPT experiments which combine semiselective polarization transfer with selective proton decoupling are proposed.

Direct observation of long-range heteronuclear splittings in proton 2D J spectra

It has long been recognized that one can obtain from long-range IC-‘H coupling constants conformational information similar, but often complementary, to that obtained from vicinal proton coupling constants (J-3). For peptides, the unambiguous assignment of side-chain rotamer populations cannot be made exclusively from 3J(H,, H,) values. However, in combination with 3J(‘3C0, H,) values, the vicinal proton couplings will provide a definitive assignment (3). At present, most peptide conformation elucidation procedures ignore the potential stereochemical information in the NOES to the nonequivalent protons of the P-methylenes since definitive pro-R/S assignments are rarely available. We and others (2) have recognized that three-bond 13C-‘H couplings provide a means for making such assignments. Determination of the values of these long-range heteronuclear coupling constants has most often been accomplished using methods which involve detection of the low sensitivity 13C spins (2-5), although it has also been pointed out (2) that some qualitative long-range J information may also be gained from the relative peak intensities of a long-range inverse detected HETCOR (HMBC (6)) experiment. In our view, the ideal experiment would provide both three-bond homoand heteronuclear scalar couplings in a single 2D experiment. Here we show that a ‘H-detected heteronuclear 2D J-resolved experiment allows observation of heteronuclear J splittings superimposed on proton J couplings. The proton J couplings may then be removed by a 45” projection of the 2D data matrix (in the weak coupling limit), while the heteronuclear couplings may be preserved by proper experimental design. As a starting point, we take the proton 2D J-resolved experiment (Fig. la). In order to allow evolution of heteronuclear couplings (J& during I~, one need only add a 13C 180” pulse in the middle of tl. In this experiment, 13C information appears as small (~0.55%) satellites on the main peaks of the 2D .I spectrum and is likely lost as a result of dynamic range problems. There are several ways to select only the protons which have 13C coupling partners; they all involve modulating a 13C pulse (meaning the pulse is switched off on alternate scans, or the net rotation of the pulse cancels on alternate scans as in 90,“90&) along with alternate addition and subtraction of the proton FID. Possible pulses to modulate are (i) the 180“ pulse in the middle oft,; (ii) a 180” pulse which is added at the end of cl; or (iii) an added 180’ pulse placed at the

Determination of heteronuclear long-range coupling constants by soft-H,C-COSY

Determination of heteronuclear long-range coupling constants by soft-H,C-COSY

A convenient technique for the measurement and assignment of long-range carbon-13 proton coupling constants

A new technique is described which enables accurate values of heteronuclear long-range coupling constants to be obtained from highly distorted multiplets in two-dimensional correlation spectra. The technique uses a simple data fitting of the distorted multiplet with a model obtained from the conventional proton spectrum, and achieves high sensitivity by detecting the signals at the proton frequency.

Heteronuclear filters for two-dimensional proton NMR. Identification of the metal-bound amino acids in metallothionein and observation of small heteronuclear long-range couplings

Heteronuclear filters for two-dimensional proton NMR. Identification of the metal-bound amino acids in metallothionein and observation of small heteronuclear long-range couplings

Relayed-NOE experiments in the rotating frame for sequence analysis of peptides

Proton spectra of peptides consist of a set of spin systems for the individual amino acid residues, which are usually identified via their characteristic J-coupling patterns (I) in 2D correlation spectra. However, the examination of a peptide with unknown amino acid sequence or the presence of several amino acids with identical spin systems requires an assignment of each spin system to its position in the peptide chain. The sequence analysis of a peptide makes use of correlations across the peptide bonds between a-protons and the amide protons of the following amino acid, either via heteronuclear long-range couplings to carbonyl carbons (favorably by COLOC (2) or its inverse variant (3)) or directly via NOE effects (I) (NOESY (4)). However, especially in linear peptides the H, resonances are often not sufficiently resolved for an unambiguous assignment. This serious problem can be circumvented by the use of the Relayed-NOESY experiment (5), advantageously with double-quantum filter (6), where the magnetization transfer via NOE between NH’+’ and HL is followed by a transfer through J coupling from HL to NH’ within the same amino acid residue. This results in a cross peak between NH’ and NH’+’ which appears only on one side of the diagonal due to the asymmetry of the mixing sequence (7) (cf. Fig. 1). Unfortunately, many oligopeptides with molecular weights of about 1000 show only very weak NOE effects in high-field spectrometers due to their unfavorable correlation times. Instead of conventional NOE spectra, ROESY (8, 9) experiments can be used to measure NOE effects in the rotating frame (ROE effects), which are almost independent of the correlation time. We describe here the recently proposed (IO) possibility of using spin-lock sequences in Relayed-NOESY experiments for both the NOE and the Jtransfer part of the mixing time. Figure 2 shows the pulse sequences which are discussed in this paper. The DQF-Relayed-NOESY experiment exists in two versions, which differ in the order of NOE transfer and J trandkr. Since the desired cross peaks always show antiphaae s&uctaue in one dime i$ seems to be favoraMe to have antiphase in w2 because of’tlte bd%cs resduhta in that dimension. This can be achieved by placing ~JVrans~&z&eNOEtrans&ass&owninF~ Z?a.Tbecorrespondingsequence wi~theJ~r~~eNOE~(givingrise~bo~inwl)is~f~ omitted in Fig. 2.

ChemInform Abstract: The Solid‐State and Solution Conformation of Some 1,2‐O‐Alkylidene Xylopyranoses. Application of Heteronuclear Long‐Range Coupling Constants to the Conformational Analysis of Dioxolane Rings

ChemInformVolume 18, Issue 40 Physical Organic Chemistry ChemInform Abstract: The Solid-State and Solution Conformation of Some 1,2-O-Alkylidene Xylopyranoses. Application of Heteronuclear Long-Range Coupling Constants to the Conformational Analysis of Dioxolane Rings F. H. CANO, F. H. CANO Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorC. FOCES-FOCES, C. FOCES-FOCES Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorJ. JIMENEZ-BARBERO, J. JIMENEZ-BARBERO Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorA. ALEMANY, A. ALEMANY Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorM. BERNABE, M. BERNABE Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorM. MARTIN-LOMAS, M. MARTIN-LOMAS Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this author F. H. CANO, F. H. CANO Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorC. FOCES-FOCES, C. FOCES-FOCES Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorJ. JIMENEZ-BARBERO, J. JIMENEZ-BARBERO Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorA. ALEMANY, A. ALEMANY Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorM. BERNABE, M. BERNABE Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this authorM. MARTIN-LOMAS, M. MARTIN-LOMAS Inst. Quim. Org. Gen., CSIC, E-28006 Madrid, SpainSearch for more papers by this author First published: October 6, 1987 https://doi.org/10.1002/chin.198740049Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue40October 6, 1987 RelatedInformation

Response-intensity modulation in long-range heteronuclear two-dimensional NMR chemical-shift correlation

Two-dimensional NMR spectroscopy has had a very significant impact on the way in which structure elucidation and spectral assignment studies are performed. Investigators have begun to exploit long-range heteronuclear coupling constants by utilizing delays in the conventional 2D NMR heteronuclear chemical-shift correlation experiment optimized for long-range magnetization transfer through two, three, and/or four bonds (‘Jcu, 3JcH, and “J,,) (1-16). Alternatively, several new experiments specifically for the observation of long-range heteronuclear spin-coupling information (14, 15, 2 7-22) have been reported. Despite the now numerous applications of longrange heteronuclear chemical-shift correlation contained in the literature, factors affecting the magnetization transfer step in these experiments have not been carefully investigated. Most long-range experiments are optimized for a 10 Hz magnetization transfer based upon the work of Reynolds and co-workers (2) or that of Wemly and Lauterwein (9), although other optimizations have also been used with success (I, 4, 10). As a consequence of the absence of responses in some of our own work despite optimization of the experiment at or near the magnitude of the coupling in question we now wish to communicate the results of our preliminary investigation into factors affecting response intensity in long-range heteronuclear chemical-shift correlation. Schenker and von Philipsborn (23) have reported a systematic investigation of the optimization of the INEPT and DEPT experiments in weakly coupled spin-f systems. They have shown that when magnetization is transferred via small heteronuclear couplings, that the transfer may be modulated by other homoand/or heteronuclear spin couplings which are experienced by those nuclei involved in the polarization transfer. Population transfer involved in the long-range heteronuclear chemical-shift correlation experiments may also be modulated in similar fashion, as recently suggested by Freeman (18) and Bax (21).

The solid-state and solution conformation of some 1,2-O-alkylidene xylopyranoses. Application of heteronuclear long-range coupling constants to the conformational analysis of dioxolane rings

The molecular structures of 3,4-di-O-acetyl-1,2-O-[(R)-1-cyanoethylidene]-α-D-xylopyranose (1) and its (S)-isomer (2) have been determined from X-ray diffraction data. The pyranoid ring adopts a 1C4 chair conformation for both compounds and the dioxolane ring presents E1 and 2E distorted envelope conformations for (1) and (2) respectively. The solution conformation of (1) and (2), and the ethylidene analogues (3) and (4), have been determined by n.m.r. spectroscopy. Proton–proton coupling constants, variable-temperature and n.O.e. experiments, and molecular mechanics calculations indicate that the major conformation of the pyranoid ring can be described as 1C4 for (1), ∘S2 for (2) and (4), and as an equilibrium among 4C1, 1C4, and ∘S2 forms for (3). Long-range carbon–proton coupling constants can be interpreted in terms of E1 and EO2 conformations for the dioxolane ring of (1) and (2) respectively.

The Elucidation of the Constitution of Glycopeptides by the NMR Spectroscopic COLOC Technique

The structure elucidation of the disaccharide-serine derivative 1 demonstrates how the two-dimensional NMR spectroscopic COLOC technique may be used to assign heteronuclear long-range couplings and thus answer the following questions: (1) How are the sugar residues linked? (2) Is the sugar indeed linked to the amino acid through a urethane unit? (3) At which positions are the various protecting groups?

Hydrogen-bonded 2-hydroxybenzalazines: Complete assignment of1H and13C NMR spectra

The 80 MHz 1H NMR and 20 MHz 13C NMR spectra of eleven substited benzalazines (subsituenst: α-methyl, α,α′-dimethyl, 2-hydroxy, 2,2′-dihydroxy, 4-n-octyloxy, 4,4′-di-n-octyloxy) possessing mesogenic acivity have been assigned using a variety of one-dimensional techniques. These include homonuclear NOE measurements, selective heteronuclear 13C{1H} NOE difference spectroscopy, singlefrequency off-resonance decoupling, spin—echo multiplicity sorting (SEFT) and long-range heteronuclear coupling constant determintion via both gated decoupling and selective excitation (DANTE).

ChemInform Abstract: MICROBIAL METABOLITES. 13. DEMONSTRATION OF AN ALTERNATIVE CHAIN FOLDING IN THE PYRANONAPHTHALENE FONSECIN. USE OF LONG‐RANGE HETERONUCLEAR COUPLINGS IN THE NAPHTHALENE RING FOR STRUCTURAL ASSIGNMENT

Chemischer InformationsdienstVolume 16, Issue 28 Heterocyclic Compounds ChemInform Abstract: MICROBIAL METABOLITES. 13. DEMONSTRATION OF AN ALTERNATIVE CHAIN FOLDING IN THE PYRANONAPHTHALENE FONSECIN. USE OF LONG-RANGE HETERONUCLEAR COUPLINGS IN THE NAPHTHALENE RING FOR STRUCTURAL ASSIGNMENT J. L. BLOOMER, J. L. BLOOMERSearch for more papers by this authorC. A. SMITH, C. A. SMITHSearch for more papers by this authorT. J. CAGGIANO, T. J. CAGGIANOSearch for more papers by this author J. L. BLOOMER, J. L. BLOOMERSearch for more papers by this authorC. A. SMITH, C. A. SMITHSearch for more papers by this authorT. J. CAGGIANO, T. J. CAGGIANOSearch for more papers by this author First published: July 16, 1985 https://doi.org/10.1002/chin.198528204AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume16, Issue28July 16, 1985 RelatedInformation

Microbial metabolites. 13. Demonstration of an alternative chain folding in the pyranonaphthalene fonsecin. Use of long-range heteronuclear couplings in the naphthalene ring for structural assignment

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMicrobial metabolites. 13. Demonstration of an alternative chain folding in the pyranonaphthalene fonsecin. Use of long-range heteronuclear couplings in the naphthalene ring for structural assignmentJames L. Bloomer, Christopher A. Smith, and Thomas J. CaggianoCite this: J. Org. Chem. 1984, 49, 26, 5027–5035Publication Date (Print):December 1, 1984Publication History Published online1 May 2002Published inissue 1 December 1984https://doi.org/10.1021/jo00200a001RIGHTS & PERMISSIONSArticle Views129Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

2-Dimensional NMR in Carbohydrate Structural Analysis

Abstract 2-Dimensional FT NMR techniques have greatly expanded the power of NMR to unravel complex chemical structures. Homonuclear 2D J-resolved experiments can be helpful in sorting out complex over lapping coupling patterns, while homonuclear chemical shift correla tion experiments can be used to determine the homonuclear coupling networks. Heteronuclear chemical shift correlation experiments can indicate the source of direct or long-range heteronuclear couplings, and hence can be used to relate the proton spectrum to the carbon spectrum. Carbon-carbon connectivity experiments reflect carbon homonuclear couplings, and, while the most insensitive of all the techniques, can be the most powerful in directly revealing the molecular framework. Techniques such as these can be used either individually or in combination to reveal part or all of the structural features of both simple and complex carbohydrates. The general features of 2D experiments are discussed in the context of their application to carbohydrates.

Determination of heteronuclear coupling constants via semiselective two-dimensional J spectroscopy

The earliest types of two-dimensional NMR experiments that received widespread attention were the proton-flip and the gated-decoupler experiments (Z-8). Concep tually those early experiments are rather simple to understand, but the use of those experiments in practical cases often is complicated by data storage requirements and sensitivity considerations. Only in the case where the spectroscopist is interested in determining the multiplicity of a certain carbon13 site is the use of the two-dimensional experiment straightforward, in such cases only a very low resolution of the carbon13 multiplet structure along the F, axis is necessary, and hence the data matrix can be kept small. The sensitivity will be fairly good in this application because the carbon13 intensity is spread over a maximum number of only four multiplet components. However, this application of two-dimensional J spectroscopy has been outdated by even more sensitive and experimentally more convenient “spectral editing” experiments (9-Z I). The use of the original 2D J-spectroscopy experiments for the exact determination of coupling constants requires a very fine digitization along the F, frequency axis; this leads to a very large size of the required data matrix, unless the acquisition time along the t2 axis is made very short, which in turn decreases the sensitivity of the experiment dramatically. The intensity of a certain carbon13 nucleus in this highF1-resolution application will generally be spread over a large number of multiplet components, which decreases the sensitivity even further. All problems mentioned above can be overcome by using a modified version of the proton-flip experiment in which only one proton is “flipped” by the proton pulse (which in this case is selective) in the center of the evolution period (12). This allows the accurate determination of all heteronuclear long-range couplings with this particular proton. In this communication we describe two experiments which rely on the same principle as the selective proton-flip experiment and which allow the accurate determination of either all direct ‘H-13C coupling constants by removal of the long-range splittings or the determination of all long-range couplings while removing all the direct ‘H-13C splittings. The experimental pulse scheme is set out in Fig. 1. As in the original proton-flip experiment (3, 4), broadband low power ‘H irradiation during the preparation period provides a NOE effect, enhancing the sensitivity, and high power proton noise decoupling is employed during the detection period. A carbon13 180” pulse is applied

Demonstration of an alternative chain folding in the pyranonapthalene fonsecin

Using recently reported heteronuclear long-range couplings for naphthalene the CMR spectrum of fonsecin has been assigned. Acetate double-label experiments indicated a biosynthesis from a polyketide chain folding previously unreported for napththalene ring formation.