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Application of INADEQUATE NMR techniques for directly tracing out the carbon skeleton of a natural product

Ismail, FMD, Nahar, L and Sarker, SD Application of INADEQUATE NMR techniques for directly tracing out the carbon skeleton of a natural product. Phytochemical Analysis. ISSN 0958-0344 (Accepted)

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Abstract

Abstract Introduction: NMR measurement of 1JCC coupling by 2D INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment), which is a special case of double-quantum (DQ) spectroscopy that offers unambiguous determination of 13C-13C spin-spin connectivities through the DQ transitions of the spin system, is especially suited to solving structures rich in quaternary carbons and poor in hydrogen content (Crews rule). Objective: To review published literature on the application of NMR methods to determine structure in the liquid-state, which specifically considers the interaction of a pair of 13C nuclei adjacent to one another, to allow direct tracing out of contiguous carbon connectivity using 2D INADEQUATE. Methodology: A comprehensive literature search was implemented with various databases: Web of Knowledge, PubMed and SciFinder, and other relevant published materials including published monographs. The keywords used, in various combinations, with INADEQUATE being present in all combinations, in the search were 2D NMR, 1JCC coupling, natural product, structure elucidation, 13C-13C connectivity, cryoprobe and CASE (Computer-Assisted Structure Elucidation) /PANACEA (Protons And Nitrogen And Carbon Et Alia). Results: 2D INADEQUATE continues to solve “intractable” problems in natural product chemistry, and using mg quantities with cryoprobe techniques combined with CASE/PANACEA experiments can increase machine time efficiency. 13C-13C-based structural elucidation by dissolution single-scan DNP NMR can overcome disadvantages of 13C insensitivity at natural abundance. Selected examples have demonstrated the trajectory of INADEQUATE spectroscopy from structural determination to clarification of metabolomics analysis and use of DFT (Density Functional Theory) and coupling constants to clarify the connectivity, hybridisation and stereochemistry within natural products. Conclusions: Somewhat neglected over the years because of perceived lack of sensitivity, the 2D INADEQUATE NMR technique has re-emerged as a useful tool for solving natural products structures, which are rich in quaternary carbons and poor in hydrogen content.

Item Type: Article
Uncontrolled Keywords: 03 Chemical Sciences, 06 Biological Sciences, 11 Medical and Health Sciences
Subjects: Q Science > QD Chemistry
Divisions: Pharmacy & Biomolecular Sciences
Publisher: Wiley
Date Deposited: 14 Jul 2020 12:38
Last Modified: 14 Jul 2020 12:45
DOI or Identification number: 10.1002/pca.2976
URI: http://researchonline.ljmu.ac.uk/id/eprint/13293

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