Regioselective synthesis and structural elucidation of 1,4-disubstituted 1,2,3-triazole derivatives using 1D and 2D NMR spectral techniques

Regioselective synthesis of 2-[1-(2-oxo-2-phenylethyl)-1H-[1,2,3]triazol-4-ylmethoxy]-benzaldehyde derivatives was achieved by [3 + 2] cycloaddition reaction of 2-(prop)-2-ynyloxy-benzaldehyde derivatives with phenacyl azide. The regiochemistry and the spectral assignments of the synthesized triazole derivatives were studied using both 1D and 2D NMR spectral techniques in solution.     

Synthesis and structure elucidation of five series of aminoflavones using 1D and 2D NMR spectroscopy

Twenty-six new aminoflavones have been synthesised by two different methods and the structure elucidation was accomplished using extensive 1D (1H, 13C) and 2D NMR spectroscopic studies (COSY, HSQC and HMBC experiments).     

Synthesis and structure elucidation of five new conjugates of oleanolic acid derivatives and chalcones using 1D and 2D NMR spectroscopy

Five new conjugates of oleanolic acid derivatives and chalcones have been designed and synthesized. The structure elucidation of these conjugates was accomplished by using extensive 1D (¹H, ¹³C) and 2D NMR spectroscopic studies (COSY, HSQC and HMBC); and α‐glucosidase inhibitory activity is reported for these conjugates. Compound 2b (IC₅₀ = 47.5 µm ) displayed much stronger activity than oleanolic acid and acarbose. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and structure elucidation of three series of nitro‐2‐styrylchromones using 1D and 2D NMR spectroscopy

2‐Styrylchromones, although scarce in nature, constitute a group of oxygen heterocyclic compounds which have shown significant biological activities. New nitro‐2‐styrylchromones have been synthesised by the Baker–Venkataraman method, and the structure elucidation was accomplished using extensive 1D (1H, 13C) and 2D NMR spectroscopic studies (COSY, HSQC and HMBC experiments). Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and NMR elucidation of novel penta-cycloundecane amine derivatives as potential antituberculosis agents

The synthesis and NMR elucidation of five novel penta-cycloundecane amine derivatives are reported. These compounds are potential antituberculosis agents. The (1)H and (13)C spectra showed major overlapping of methine signals of the cage skeleton making it extremely difficult to elucidate these compounds. The overlapping occurs as a result of the additions made to the carbonyl carbon (C-8/C-11) of the cage. The two-dimensional NMR technique proved to be a useful tool in overcoming this problem. All compounds reported are meso compounds thereby not only simplifying the NMR structure elucidation, but also making it indeed possible.     

Structural elucidation of a new delta2-pyrazoline derivatives using 1H and 13C NMR spectroscopy

This paper describes the unequivocal structural elucidation of a new kind of Delta2-pyrazoline derivatives carried out by means of monodimensional 1H and 13C NMR spectroscopies, bidimensional ones such as HMBC and HMQC experiments, and NOEDIFF effects. Conformational analysis of this molecule agrees very well with the experimentally NOEDIFF effects found.     

Structure elucidation and NMR assignments for two xanthone derivatives from a mangrove endophytic fungus (No. ZH19)

The structure elucidations and complete ¹H and ¹³C NMR assignments are reported for two new xanthone derivatives: 1,7‐dihydroxy‐2‐methoxy‐3‐(3‐methylbut‐2‐enyl)‐9H‐xanthen‐9‐one (1) and 1‐hydroxy‐4,7‐dimethoxy‐6‐(3‐oxobutyl)‐9H‐xanthen‐9‐one (2). Both of these secondary metabolites were isolated from the fermentation medium of a mangrove endophytic fungus (No. ZH19). High‐resolution electron impact mass spectrometry (HREIMS), Fourier transform infrared (FT‐IR) absorption spectrometry, and NMR experiments including gCOSY, gHMQC, and gHMBC were used for the determination of the structures and NMR spectral assignments. Preliminary pharmacological test showed that compounds (1) and (2) inhibited KB cells with IC₅₀ values of 20 and 35 µmol/ml, and KB_V200 cells with IC₅₀ values of 30 and 41 µmol/ml, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Structure elucidation and NMR assignments for curcuminoids from the rhizomes of Curcuma longa

Thirteen curcuminoids (1–13) were isolated from the rhizomes of Curcuma longa. Among them, 1,5‐dihydroxy‐1,7‐bis(4‐hydroxyphenyl)‐4,6‐heptadiene‐3‐one (1), 1,5‐dihydroxy‐1‐(4‐hydroxy‐3‐methoxyphenyl)‐7‐(4‐hydroxyphenyl)‐4,6‐heptadiene‐3‐one (2), 1,5‐dihydroxy‐1‐(4‐hydroxyphenyl)‐7‐(4‐hydroxy‐3‐methoxyphenyl)‐4,6‐heptadiene‐3‐one (3), and 3‐hydroxy‐1,7‐bis‐(4‐hydroxyphenyl)‐6‐heptene‐1,5‐dione (4) are new compounds, and 1‐(4‐hydroxyphenyl)‐7‐(3, 4‐dihydroxyphenyl)‐1, 6‐heptadiene‐3, 5‐dione (5) is isolated from natural sources for the first time. The structures of these compounds were elucidated by extensive spectroscopic analyses, especially 1D and 2D NMR spectroscopy. The ¹³C NMR data and complete ¹H and ¹³C NMR assignments of some known compounds are reported for the first time. In addition, the errors of ¹H and ¹³C assignments reported in the literature were corrected. Copyright © 2009 John Wiley & Sons, Ltd.     

NMR elucidation of a novel (S)-pentacyclo-undecane bis-(4-phenyloxazoline) ligand and related derivatives

The NMR elucidation of a novel ligand (S)-pentacyclo-undecane bis-(4-phenyloxazoline) and related pentacyclo-undecane (PCU) derivatives is reported. Two-dimensional NMR proved to be a powerful technique in overcoming the difficulties associated with the elucidation of these compounds when only one-dimensional NMR data is utilized. A chiral substituent was introduced to both 'arms' of the PCU skeleton to produce derivatives 1-3. These derivatives display C(1) symmetry with all thecage atoms being nonequivalent. Owing to overlapping of peaks in the (1)H spectra, identification of these diastereomeric protons was very difficult. The (13)C spectra gave rise to clear splitting of the nonequivalent carbons. This is unusual compared to similar PCU derivatives with chiral substituents as splitting of all the diastereomeric cage carbons has not yet been reported. Nuclear Overhauser enhancement spectroscopy (NOESY) correlations of derivatives 1-3 confirm the different conformations of the molecule in which the side 'arms' occupy different orientations with respect to cage moiety.     

2D NMR analysis for unambiguous structural elucidation of phenolic compounds formed through reaction between (+)‐catechin and glyoxylic acid

Various phenolic compounds were synthesized in an aqueous–alcoholic solution containing (+)‐catechin and glyoxylic acid which was used as a model of fruit‐derived food browning that usually occurs during aging. After purification by semi‐preparative HPLC, the isolated compounds were subjected to homo‐ and heteronuclear proton and carbon NMR analysis including COSY, TOCSY, ROESY, HSQC and HMBC techniques. These experiments allowed the structural elucidation and complete ¹H and ¹³C NMR assignment of the isolated compounds. The strategies followed for the assignment of all proton and carbon resonances in addition to the linkage site determination are discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis and structure elucidation of five new pyrimido[5,4-c]quinoline-4(3H)-one derivatives using 1D and 2D NMR spectroscopy

Five new 2-(amino/aroxy)-5-methylpyrimido[5,4-c]quinolin-4(3H)-one derivatives have been designed and synthesized via an aza-Wittig reaction, and the structure elucidation was accomplished using extensive 1D ((1)H, (13)C) and 2D NMR spectroscopic studies (COSY, HSQC and HMBC experiments).     

Structure elucidation and NMR assignments for two amide alkaloids from a Mangrove endophytic Fungus (No. ZZF-22)

The structure elucidations and complete (1)H and (13)C NMR assignments are reported for two new natural products: 3-benzylidene-8,8a-dihydroxy-2-methyl-hexahydro-pyrrolo[1,2-a]pyrazine-1,4-dione(1) and 4-hydroxy-6-(hydroxy-phenyl-methyl)-N-(3-methyl-butyryl)-nicotinamide (2). Both of these secondary metabolites were isolated from the fermentation medium of a Mangrove endophytic fungus. High resolution electron impact mass spectrometry (HREIMS), FT-IR Spectroscopy and NMR experiments including gCOSY, gHMQC, gHMBC and NOE were used for determination of the structures and assignments of the amide alkaloids.     

Structural elucidation and NMR spectral assignment of three new furostanol saponins from the roots of Tupistra chinensis

Three new furostanol saponins (1–3) were isolated from the roots of Tupistra chinensis (T. chinensis). And their structures were elucidated on the basis of NMR and mass spectrometry (MS) spectral analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Structure elucidation and NMR assignments of two unusual monoterpene indole alkaloids from Psychotria stachyoides

Two unusual monoterpene indole alkaloids, stachyoside ( 1 ) and nor‐methyl‐23‐oxo‐correantoside ( 2 ), have been isolated from the aerial parts of Psychotria stachyoides. The structural elucidation of both compounds was performed by the aid of HRESIMS, FT‐IR, and 1D‐ and 2D‐NMR techniques including COSY, HSQC, HMBC, and NOESY. Copyright © 2010 John Wiley & Sons, Ltd.     

Structure elucidation and NMR assignments for three anthraquinone derivatives from the marine fungus Fusarium sp. (No. ZH‐210)

The structure elucidations and complete ¹H and ¹³C NMR assignments are reported for three new anthraquinone derivatives: Fusaquinon A (1), B (2), and C (3) isolated from the fermentation medium of the marine fungus Fusarium sp. (No. ZH‐210). HREIMS, Fourier transform infrared absorption spectrometry (FT‐IR), NMR experiments including gCOSY, gHMQC, gHMBC, and NOESY were used for the determination of the structures and NMR spectral assignments. Preliminary pharmacological test showed that they exhibited low cytotoxic activity towards KB, KBv200, and MCF‐7 cell lines. Copyright © 2009 John Wiley & Sons, Ltd.     

Contribution to Structural Elucidation： Behaviours of Substructures Partially Defined from 2D NMR

Structural elucidation (automatic determination of the structure of a molecule from its spectra) is frequently hampered by com-binatorial explosion when trying to assemble the identified sub-structures. We devised a new method which can avoid this pit-fall by a systematic examination of allowed t3C chemical shifts ranges for all substructures chemically possible and combined with a progressive pruning thanks to neighbouring relationships appearing from 2D NMR. This method is explained by a de-tailed example.     

Structure elucidation and NMR spectral assignment of five new xanthones from the bark of Garcinia xanthochymus

Five new xanthones, namely Garcinexanthones A-E (1-5), were isolated from the barks of Garcinia xanthochymus. Their structures were elucidated by spectral analysis, primarily NMR, MS, and UV. The complete assignments of the (1)H NMR and (13)C NMR chemical shifts for the compounds were achieved by using 1D and 2D NMR techniques, including DEPT, HSQC, and HMBC NMR experiments.     

Complete NMR elucidation of a novel trishomocubane hydantoin and its mono- and bis-t-Boc protected derivatives

The syntheses of a novel trishomocubane hydantoin and its mono- and bis-protected t-Boc derivatives are described. The less nucleophilic N-3' nitrogen of the hydantoin ring is protected first when treated with di-tert-butyl dicarbonate (t-Boc anhydride), possibly owing to steric hindrance by the bulky trishomocubane cage skeleton. More basic conditions were required to form the bis-protected t-Boc hydantoin with the same reagent. The structures of these novel compounds were elucidated with 2D NMR techniques. The proton spectrum of the trishomocubane skeleton is complex owing to major overlap of proton signals. A high-level DFT calculation was used to determine some of the crucial interatomic positions, which assisted with the elucidation of the structures. The assignment of proton and carbon signals of the three structures is described and it differs significantly from each other and also from the trishomocubanol precursor. The bis-Boc hydantoin is required for a more facile hydrolysis to the corresponding trishomocubane amino acid at room temperature.     

Structural and spectral assignment by 2D NMR of a new prenylated benzopyrancarboxylic acid and structural reassignment of a related compound

A new prenylated benzopyrancarboxylic acid, 1a (3,4‐dihydro‐5‐hydroxy‐2,7‐dimethyl‐8‐(2‐methyl‐2‐butenyl)‐ 2‐(4‐methyl‐1, 3‐pentadienyl)‐2H‐1‐benzopyran‐6‐carboxylic acid) was isolated from Peperomia amplexicaulis and fully characterized by 1D and 2D NMR and high‐resolution mass spectrometry. In the course of this investigation, the structure of a related compound (minus the carboxylic acid group) which was previously assigned as 2b was corrected to structure 1b . Copyright © 2003 John Wiley & Sons, Ltd.     

Structural elucidation and complete assignment of a novel class of sulfonamides: bridgehead tricyclic sultams

Endocyclic sulfonamide templates bearing both an exocyclic ketone function and an internal olefin underwent reaction with a variety of hydroxylamines to effect an intramolecular nitrone–olefin cycloaddition to afford a new class of compounds suitable for derivatization by high‐throughput medicinal chemistry. Structural elucidation via complete assignment of the ¹H and ¹³C NMR spectra of this new class of compounds was achieved using gradient‐COSY, gradient heteronuclear multiple quantum‐coherence spectroscopy and gradient heteronuclear multiple bond correlation spectroscopy. Additionally, double pulsed field gradient spin echo–nuclear Overhauser effect experiments were carried out in order to study the spatial conformation of this new type of molecule and assess the stereo‐ and regio‐selectivity of the chemical transformation. The unequivocal molecular framework and structural conformation was confirmed by X‐ray diffraction. Copyright © 2002 John Wiley & Sons, Ltd.