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The DEPTQ + Experiment: Leveling the DEPT Signal Intensities and Clean Spectral Editing for Determining CH n Multiplicities. Molecules 2021; 26:molecules26123490. [PMID: 34201221 PMCID: PMC8228129 DOI: 10.3390/molecules26123490] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 05/27/2021] [Accepted: 05/27/2021] [Indexed: 11/16/2022] Open
Abstract
We propose a new 13C DEPTQ+ NMR experiment, based on the improved DEPTQ experiment, which is designed to unequivocally identify all carbon multiplicities (Cq, CH, CH2, and CH3) in two experiments. Compared to this improved DEPTQ experiment, the DEPTQ+ is shorter and the different evolution delays are designed as spin echoes, which can be tuned to different 1JCH values; this is especially valuable when a large range of 1JCH coupling constants is to be expected. These modifications allow (i) a mutual leveling of the DEPT signal intensities, (ii) a reduction in J cross-talk in the Cq/CH spectrum, and (iii) more consistent and cleaner CH2/CH3 edited spectra. The new DEPTQ+ is expected to be attractive for fast 13C analysis of small-to medium sized molecules, especially in high-throughput laboratories. With concentrated samples and/or by exploiting the high sensitivity of cryogenically cooled 13C NMR probeheads, the efficacy of such investigations may be improved, as it is possible to unequivocally identify all carbon multiplicities, with only one scan, for each of the two independent DEPTQ+ experiments and without loss of quality.
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Bigler P, Furrer J. Simplifying LR-HSQC spectra using a triple-quantum filter: The LR-HTQC experiment. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2021; 59:52-60. [PMID: 33411358 DOI: 10.1002/mrc.5078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Revised: 07/14/2020] [Accepted: 07/19/2020] [Indexed: 06/12/2023]
Abstract
Long-range heteronuclear single quantum correlation (LR-HSQC) experiments may be applied for detecting long-range correlations but suffer from two disadvantages, common to all heteronuclear long-range correlation experiments: (i) The information density in LR-HSQC spectra may be too high to be used directly without "filtering out" shorter range correlations, and (ii) often, substantial differences in intensity among cross peaks exist, potentially hampering the visualization of weak, often crucial cross peaks. In this contribution, we propose a modified LR-HSQC experiment, the LR-HTQC experiment (Long-Range Heteronuclear Triple Quantum Correlation) that partially solves the problems aforementioned. We show theoretically and experimentally that the LR-HTQC experiment removes the intense cross peaks of CH spin pairs, substantially reduces the medium intensity of cross peaks originating from CHH' spin systems, whereas the typically weak intensity of cross peaks of CHH'H″ and C(H)n, n > 3 spin systems is less affected. Consequently, the LR-HTQC experiment affords simplified long-range heteronuclear shift correlation spectra and scales down large intensity differences among different types of cross peaks, although a certain general reduction of signal intensities has to be accepted.
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Affiliation(s)
- Peter Bigler
- Departement für Chemie und Biochemie, Universität Bern, Bern, Switzerland
| | - Julien Furrer
- Departement für Chemie und Biochemie, Universität Bern, Bern, Switzerland
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Joyce LA, Schultz DM, Sherer EC, Neill JL, Sonstrom RE, Pate BH. Direct regioisomer analysis of crude reaction mixtures via molecular rotational resonance (MRR) spectroscopy. Chem Sci 2020; 11:6332-6338. [PMID: 32953028 PMCID: PMC7472927 DOI: 10.1039/d0sc01853h] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 05/30/2020] [Indexed: 01/05/2023] Open
Abstract
Direct analyses of crude reaction mixtures have been carried out using molecular rotational resonance (MRR) spectroscopy. Two examples are presented, a demonstration application in photocatalytic CH-arylation as well as generation of an intermediate in a natural product synthesis. In both cases, the reaction can proceed at more than one site, leading to a mixture of regioisomers that can be challenging to distinguish. MRR structural parameters were calculated for the low lying conformers for the desired compounds, and then compared to the experimental spectra of the crude mixtures to confirm the presence of these species. Next, quantitation was performed by comparing experimentally measured line intensities with simulations based on computed values for the magnitude and direction of the molecular dipole moment of each species. This identification and quantification was performed without sample purification and without isolated standards of the compounds of interest. The values obtained for MRR quantitation were in good agreement with the chromatographic values. Finally, previously unknown impurities were discovered within the photocatalytic CH-arylation work. This paper demonstrates the utility of MRR as a reaction characterization tool to simplify analytical workflows.
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Affiliation(s)
- Leo A Joyce
- Department of Process Research & Development , Merck & Co., Inc. , Rahway , NJ 07065 , USA .
| | - Danielle M Schultz
- Department of Process Research & Development , Merck & Co., Inc. , Rahway , NJ 07065 , USA .
| | - Edward C Sherer
- Department of Computational and Structural Chemistry , Merck & Co., Inc. , Rahway , NJ 07065 , USA
| | - Justin L Neill
- BrightSpec, Inc. , 770 Harris St., Suite 104b , Charlottesville , VA 22904 , USA .
| | - Reilly E Sonstrom
- Department of Chemistry , University of Virginia , McCormick Road , Charlottesville , VA 22904 , USA
| | - Brooks H Pate
- Department of Chemistry , University of Virginia , McCormick Road , Charlottesville , VA 22904 , USA
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Motiram-Corral K, Nolis P, Saurí J, Parella T. LR-HSQMBC versus LR-selHSQMBC: Enhancing the Observation of Tiny Long-Range Heteronuclear NMR Correlations. JOURNAL OF NATURAL PRODUCTS 2020; 83:1275-1282. [PMID: 32155071 DOI: 10.1021/acs.jnatprod.0c00058] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The detection of ultra-long-range (4JCH and higher) heteronuclear connectivities can complement the conventional use of HMBC/HSQMBC data in structure elucidation NMR studies of proton-deficient natural products, where two-bond and three-bond correlations are usually observed. The performance of the selHSQMBC experiment with respect to its broadband HSQMBC counterpart is evaluated. Despite its frequency-selectivity nature, selHSQMBC efficiently prevents any unwanted signal phase and intensity modulations due to passive proton-proton coupling constants typically involved in HSQMBC. As a result, selHSQMBC offers a significant sensitivity enhancement and provides pure in-phase multiplets, improving the detection levels for short- and long-range cross-peaks corresponding to small heteronuclear coupling values. This is particularly relevant for experiments optimized to small nJCH values (2-3 Hz), referred to as LR-selHSQMBC, where key cross-peaks that are not visible in the equivalent broadband LR-HSQMBC spectrum can become observable in optimum conditions.
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Affiliation(s)
- Kumar Motiram-Corral
- Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Catalonia, Spain
| | - Pau Nolis
- Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Catalonia, Spain
| | - Josep Saurí
- Structure Elucidation Group, Analytical Research & Development, Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States
| | - Teodor Parella
- Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Catalonia, Spain
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Motiram-Corral K, Souza AA, Saurí J, Nolis P, Parella T. LR-selHSQMBC: Simultaneous Detection and Quantification of Very Weak Long-Range Heteronuclear NMR Correlations. Chemphyschem 2020; 21:280-283. [PMID: 31951093 DOI: 10.1002/cphc.201901142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 01/10/2020] [Indexed: 11/08/2022]
Abstract
The optimum detection and accurate measurement of longer-range (4 J and higher) heteronuclear NMR correlations is described. The magnitude and/or the sign of a wide range of large and small long-range couplings can be simultaneously determined for protonated and non-protonated 13 C and 15 N nuclei using the LR-selHSQMBC experiment.
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Affiliation(s)
- Kumar Motiram-Corral
- Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona (Catalonia, Spain
| | - Alexandre A Souza
- Departamento de Química, Universidade Federal de Piauí, 64049-550, Teresina" PI, Brazil
| | - Josep Saurí
- Structure Elucidation Group, Analytical Research & Development, Merck & Co., Inc., 33 Av. Louis Pasteur, Boston, MA, 02215, USA
| | - Pau Nolis
- Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona (Catalonia, Spain
| | - Teodor Parella
- Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona (Catalonia, Spain
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Knowles SL, Vu N, Todd DA, Raja HA, Rokas A, Zhang Q, Oberlies NH. Orthogonal Method for Double-Bond Placement via Ozone-Induced Dissociation Mass Spectrometry (OzID-MS). JOURNAL OF NATURAL PRODUCTS 2019; 82:3421-3431. [PMID: 31823607 PMCID: PMC7004233 DOI: 10.1021/acs.jnatprod.9b00787] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Most often, the structures of secondary metabolites are solved using a suite of NMR techniques. However, there are times when it can be challenging to position double bonds, particularly those that are fully substituted or when there are multiple double bonds in similar chemical environments. Ozone-induced dissociation mass spectrometry (OzID-MS) serves as an orthogonal structure elucidation tool, using predictable fragmentation patterns that are generated after ozonolysis across a carbon-carbon double bond. This technique is finding growing use in the lipidomics community, suggestive of its potential value for secondary metabolites. This methodology was evaluated by confirming the double-bond positions in five fungal secondary metabolites, specifically, ent-sartorypyrone E (1), sartorypyrone A (2), sorbicillin (3), trichodermic acid A (4), and AA03390 (5). This demonstrated its potential with a variety of chemotypes, ranging from polyketides to terpenoids and including those in both conjugated and nonconjugated polyenes. In addition, the potential of using this methodology in the context of a mixture was piloted by studying Aspergillus fischeri, first examining a traditional extract and then sampling a live fungal culture in situ. While the intensity of signals varied from pure compound to extract to in situ, the utility of the technique was preserved.
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Affiliation(s)
- Sonja L. Knowles
- Department of Chemistry and Biochemistry, University of North Carolina at Greensboro, Greensboro, NC 27412
| | - Ngoc Vu
- Department of Chemistry and Biochemistry, University of North Carolina at Greensboro, Greensboro, NC 27412
| | - Daniel A. Todd
- Department of Chemistry and Biochemistry, University of North Carolina at Greensboro, Greensboro, NC 27412
| | - Huzefa A. Raja
- Department of Chemistry and Biochemistry, University of North Carolina at Greensboro, Greensboro, NC 27412
| | - Antonis Rokas
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235
| | - Qibin Zhang
- Department of Chemistry and Biochemistry, University of North Carolina at Greensboro, Greensboro, NC 27412
- Center for Translational Biomedical Research, University of North Carolina at Greensboro, Kannapolis, NC 28081
| | - Nicholas H. Oberlies
- Department of Chemistry and Biochemistry, University of North Carolina at Greensboro, Greensboro, NC 27412
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Bigler P, Furrer J. Why is HMBC superior to LR-HSQC? Influence of homonuclear couplings J HH' on the intensity of long-range correlations. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2018; 56:1101-1116. [PMID: 29907970 DOI: 10.1002/mrc.4762] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Revised: 05/16/2018] [Accepted: 06/05/2018] [Indexed: 06/08/2023]
Abstract
Long-range heteronuclear single quantum correlation (LR-HSQC) experiments may be applied as an alternative to heteronuclear multiple-bond correlation (HMBC) experiments for detecting long-range correlations but has never enjoyed popularity for that purpose. To the best of our knowledge, the exact reasons have not yet been fully established. For both experiments, it is widely accepted that the evolution of proton-proton homonuclear couplings JHH' during the polarization transfer delays Δ leads to significant losses, and that the intensity of the observable coherence is zero when JHH' matches the condition Δ = 0.5/JHH' . Here, we analyze the influence of JHH' on the intensity of long-range correlations in HMBC and LR-HSQC spectra. We show that for both experiments long-range correlations will not be canceled because of homonuclear couplings JHH' . Our theoretical and experimental results definitely establish and validate the superiority of HMBC-based experiments among the family of heteronuclear long-range correlation experiments: (a) the overall cross peak's intensity is higher, and (b) in LR-HSQC experiments, the intensity of the long-range cross peaks is additionally influenced in an unwanted way by the magnitude and number of passive homonuclear proton-proton couplings JHH' .
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Affiliation(s)
- Peter Bigler
- Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012, Bern, Switzerland
| | - Julien Furrer
- Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012, Bern, Switzerland
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Koskela H, Kilpeläinen I, Heikkinen S. ME-CAGEBIRD r,X-CPMG-HSQMBC. A phase sensitive, multiplicity edited long range HSQC with absorptive line shapes. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 272:114-122. [PMID: 27689530 DOI: 10.1016/j.jmr.2016.09.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Revised: 09/15/2016] [Accepted: 09/15/2016] [Indexed: 06/06/2023]
Abstract
ME-CAGEBIRDr,X-CPMG-HSMBC pulse sequence is a phase sensitive, carbon multiplicity edited 2D-experiment for detecting heteronuclear correlations originating from long-range 1H, 13C-couplings, nJCH. The presented method allows measurement of nJCH-values as well as is capable of separating different carbon types in subspectra (13C/13CH2 and 13CH/13CH3) with minimal amount of cross talk i.e. cross peaks from wrong carbon multiplicity. Pure lineshapes and clean subspectra are achieved by utilizing CPMG in polarization transfer period, CRISIS-approach in multiplicity editing period and zero-quantum filtration. The obtained spectral properties together with simple setup of the experiment make ME-CAGEBIRDr,X-CPMG-HSMBC a useful addition into synthetic organic chemistry oriented NMR-tool collection.
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Affiliation(s)
- Harri Koskela
- VERIFIN, Department of Chemistry, University of Helsinki, P.O. Box 55, FIN-00014 Helsinki, Finland
| | - Ilkka Kilpeläinen
- Department of Chemistry, University of Helsinki, P.O. Box 55, FIN-00014 Helsinki, Finland
| | - Sami Heikkinen
- Department of Chemistry, University of Helsinki, P.O. Box 55, FIN-00014 Helsinki, Finland.
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