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Marine Natural Products for Human Health Care
Published in Hafiz Ansar Rasul Suleria, Megh R. Goyal, Health Benefits of Secondary Phytocompounds from Plant and Marine Sources, 2021
More than 1000 different NMR experiments have been developed to provide spectra to deliver information about the examined nuclei and can either be one-dimensional (1D) or two-dimensional (2D) [179]. The 1D experiment is spectroscopic analysis of a single nucleus. The most commonly used NMR experiment is 1H-NMR, providing information about chemical shifts, multiple structures, homonuclear coupling constants and integrations of all protons present in the sample.
Drug Design, Synthesis, and Development
Published in Nathan Keighley, Miraculous Medicines and the Chemistry of Drug Design, 2020
Chromatography can be coupled to mass spectrometry, MS, which enables the relative molecular mass of the analytes to be accurately determined and help to characterise product and contaminants. However, this will not give information on isomers. Spectroscopic techniques are required for complete characterisation. Infra-red spectroscopy is a quick and useful technique for identifying functional groups that are present in the molecule, but does not yield complete structural information and this is where nuclear magnetic resonance (NMR) spectroscopy is needed. This enables accurate structural characterisation, and information from coupling constants and integration can determine the proportion of each isomer present.
Structure-Function Elucidation of Flavonoids by Modern Technologies
Published in Dilip Ghosh, Pulok K. Mukherjee, Natural Medicines, 2019
Ritu Varshney, Neeladrisingha Das, Rutusmita Mishra, Partha Roy
Nuclear magnetic resonance (NMR) spectroscopy is an important tool for the structural elucidation of flavonoids (Wenkert and Gottlieb 1977; Markham et al. 1982; Andersen and Fossen 2003; Agrawal 2013). It used to be quite complex to elucidate the complete structure of the flavonoids due to poor sensitivity, slow throughput and difficulties in analysing the mixtures. Recent advancement in NMR spectroscopy techniques have made it arguably the most potent technology to analyse the complete structure of flavonoids even with low sample concentration. The chemical shift and J-coupling parameters obtained from the NMR data are used for structural elucidation of the compounds. Chemical shift (δ) – expressed in parts per million (ppm) – gives a measure of the resonant frequency of a nucleus relative to that of a reference compound, such as tetramethylsilane (TMS) at a given magnetic field (Kemp 1991; Wishart et al. 1992; Balci 2005; Silverstein et al. 2014). The coupling constant (J) gives information about the bonding framework (Kessler et al. 1988; Massiot et al. 2003) because it is mediated through chemical bonds connecting the two spins (Hahn and Maxwell 1952). Although several variations are used for structural elucidation, due to the limitation of space some important NMR experiments used in evaluating flavonoid structures are described below.
Elucidating the structure and cytochrome P450-mediated mechanism for novel metabolites of GDC-0575 in rats
Published in Xenobiotica, 2022
Chenghong Zhang, Sungjoon Cho, José G. Napolitano, David Russell, Christine Gu, Alan Deese, Chong Han, Yuan Chen, Shuguang Ma
NMR experiments were recorded at 600.43 or 500.13 MHz (1H frequencies) on Bruker AVANCE spectrometers equipped with a 5-mm triple resonance (CP TCI) inverse cryoprobe and a 5-mm room-temperature broadband (PABBO) probe, respectively (Bruker BioSpin GmbH, Rheinstetten, Germany). All NMR experiments were acquired at room temperature using standard pulse sequences provided by the instrument manufacturer. Hexadeuterodimethyl sulfoxide (DMSO-D6) and deuterochloroform (CDCl3) were used as diluents for the analysis of metabolites M12 and M17, respectively. Chemical shifts (δ) are expressed in parts per million (ppm) with reference to the corresponding solvent signals and relative to the tetramethylsilane scale. Spin-spin coupling constants (J) are reported in hertz (Hz).
Structure–activity relationship, in vitro and in vivo evaluation of novel dienyl sulphonyl fluorides as selective BuChE inhibitors for the treatment of Alzheimer's disease
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2021
Chengyao Wu, Guijuan Zhang, Zai-Wei Zhang, Xia Jiang, Ziwen Zhang, Huanhuan Li, Hua-Li Qin, Wenjian Tang
All reactions were carried out under air atmosphere, unless otherwise specified. Reactions were checked by TLC on precoated silica gel plates, and spots were visualised by UV at 254 nm. Melting points of the products were measured on a micro melting point apparatus (SGW X-4) and uncorrected. 1H NMR and 13 C NMR spectra were recorded in CDCl3 on a 500 MHz (for 1H), 471 MHz (for 19 F), and 126 MHz (for 13 C) spectrometer. All chemical shifts are reported in parts per million (δ) downfield from the signal of TMS as internal standards. Coupling constants are reported in Hz. The multiplicity is defined by s (singlet), d (doublet), t (triplet), or m (multiplet). MS experiments were performed on a TOF-Q ESI or CI/EI instrument. Reagents and solvents used in the reactions were all purchased from commercial sources and used without further purification, unless otherwise noticed. The purity (relative content) of active compounds was determined by HPLC on an Agilent 1200 instrument (column: Elite, RP-C18, 5 µm, 4.6 × 150 mm) through area normalisation method.
Bioorganometallic derivatives of 4-hydrazino-benzenesulphonamide as carbonic anhydrase inhibitors: synthesis, characterisation and biological evaluation
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2020
Jeremie Brichet, Rodrigo Arancibia, Emanuela Berrino, Claudiu T. Supuran
All manipulations were conducted under an N2 atmosphere using Schlenk techniques. The compounds (η5-C5H4CHO)Re(CO)321, (η5-C5H4COCH3)Re(CO)322, (η5-C5H4CHO)Mn(CO)323 and 4-hydrazinyl-benzenesulphonamide24 were prepared according to published procedures. Ferrocene carboxaldehyde (98%), acetyl ferrocene (95%), acetylcymantrene (98%) and sulphanilamide (99%) were obtained from Sigma-Aldrich (Chicago, IL) and used without additional purification. Solvents such as CH2Cl2, hexane, acetone, EtOH, DMSO and THF were obtained commercially and purified using standard methods. Infra-red spectra were recorded in solid state (KBr pellet) on a Jasco FT-IR 4600 spectrophotometer. 1H NMR spectra were measured on a Bruker spectrometer model ASCEND TM 400 MHz. All NMR spectra are reported in parts per million (ppm, δ) relative to tetramethylsilane (Me4Si), with the residual solvent proton resonances used as internal standards. Coupling constants (J) are reported in Hertz (Hz), and integrations are reported as number of protons. The following abbreviations were used to describe the peak patterns: s = singlet, d = doublet, t = triplet and m = multiplet. Mass spectra were obtained on a Shimadzu model QP5050A GC-MS at the Laboratorio de Servicios Analíticos, Pontificia Universidad Católica de Valparaíso. Elemental analyses were measured on a Perkin Elmer CHN Analyser 2400.