Complete assignment of 1H and 13C NMR data of some flavonol derivatives

Nine flavonol derivatives were studied. Previously reported NMR data of three of these derivatives were corrected. We report complete assignments of the NMR data for six flavonol derivatives not previously studied.     

1H and 13C NMR assignments of abietane diterpenes from Aegiphila lhotzkyana

An NMR study of one new and several known abietane diterpenes isolated from the roots of Aegiphila lhotzkyana is described. In addition to 1D NMR, several 2D shift‐correlated NMR pulse sequences (¹H–¹H‐COSY, NOESY, HMQC and HMBC) were used to establish all the structures, and unambiguously perform the ¹H and ¹³C chemical shift assignments of the new natural diterpene and three derivatives, the NMR data for which have not been reported previously. Revision of current data assignment for teuvincenone H is also suggested. Copyright © 2003 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.     

Complete assignments of (1)H and (13)C NMR spectral data of nine surfactin isomers

A new surfactin isomer (1) was isolated from a mangrove bacteria strain 'Bacillus sp'. Its structure was identified, and full assignments of (1)H and (13)C NMR spectral data were achieved for the first time by a combination of mass spectrometry and 1D and 2D NMR experiments including DEPT, (1)H-(1)H COSY, HSQC, HMBC, TOCSY, ROESY, and HSQC-TOCSY. The NMR spectral data of eight known analogs (2-9) are also reported.     

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.     

Complete assignments of (1)H and (13)C NMR spectroscopic data for two new triterpenoid saponins from Ilex pernyi

Ilexpernoside A and ilexpernoside B, two new pentacyclic C(4)-nortriterpenoid saponins, were isolated from the leaves of Ilex pernyi Franch. Their chemical structures were determined by MS, NMR spectroscopy and chemical analysis. Complete assignments of the (1)H and (13)C NMR spectroscopic data were achieved by 1D and 2D NMR experiments (HSQC, HMBC, (1)H-(1)H COSY and NOESY).     

Complete assignments of 1H and 13C NMR data for ten phenylpiperazine derivatives

Ten phenylpiperazine derivatives were designed and synthesized. The first complete assignments of (1)H and (13)C NMR chemical shifts for these phenylpiperazine derivatives were achieved by means of 1D and 2D NMR techniques, including (1)H-(1)H COSY, HSQC and HMBC spectra.     

17O NMR studies on (E)-3-arylidenechromanone and -flavanone derivatives

¹⁷O NMR data for some 3-arylidenechromanones and -flavanones are discussed in terms of mesomeric and steric substituent interactions. The transmission of long-range substituent effects was studied. ¹⁷O NMR chemical shifts were correlated with Hammett σ_p⁺ values for 4′-substituted derivatives. Copyright © 2001 John Wiley & Sons, Ltd.     

1H and 13C spectral assignment of 2(1H)-pyridone derivatives

1H and 13C NMR spectroscopic data for 4-aryl-3,4-dihydro-6-methyl-2(1H)pyridone derivatives were fully assigned by a combination of one- and two- dimensional experiments (DEPT, HMBC, HMQC, COSY, NOE).     

Complete assignment of 1H and 13C NMR data of pravastatin derivatives

The complete ¹H and ¹³C NMR data of 27 pravastatin derivatives are presented. Assignment was achieved by use of 1D and 2D NMR experiments (selective 1D NOE, COSY, NOESY, HSQC, HMBC). Copyright © 2008 John Wiley & Sons, Ltd.     

3‐Methylflavones characterization revisited: complete assignment of 1H and 13C NMR data

Ten 3‐methylflavone derivatives were studied. Previously reported NMR data of some derivatives were corrected and/or completed, including the complete assignment of the two known natural derivatives. The complete ¹H and ¹³C NMR assignments were achieved by combination of one‐dimensional and two‐dimensional NMR experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Automated structure verification based on a combination of 1D (1)H NMR and 2D (1)H - (13)C HSQC spectra

A method for structure validation based on the simultaneous analysis of a 1D (1)H NMR and 2D (1)H - (13)C single-bond correlation spectrum such as HSQC or HMQC is presented here. When compared with the validation of a structure by a 1D (1)H NMR spectrum alone, the advantage of including a 2D HSQC spectrum in structure validation is that it adds not only the information of (13)C shifts, but also which proton shifts they are directly coupled to, and an indication of which methylene protons are diastereotopic. The lack of corresponding peaks in the 2D spectrum that appear in the 1D (1)H spectrum, also gives a clear picture of which protons are attached to heteroatoms. For all these benefits, combined NMR verification was expected and found by all metrics to be superior to validation by 1D (1)H NMR alone. Using multiple real-life data sets of chemical structures and the corresponding 1D and 2D data, it was possible to unambiguously identify at least 90% of the correct structures. As part of this test, challenging incorrect structures, mostly regioisomers, were also matched with each spectrum set. For these incorrect structures, the false positive rate was observed as low as 6%.     

1H and 13C-NMR data of hydroxyflavone derivatives

Many hydroxyflavone derivatives have been found in nature and shown to have many biological functions. Because their function is changed by the position and number of hydroxyl group, their structural identification is a fundamental and necessary step for understanding their functions. In the present study, the complete 1H and 13C NMR spectral assignments were presented for 6 hydroxyflavones, and NMR data of additional 14 hydroxyflavone derivatives were compared with those of the 6 hydroxyflavones. In addition, the partially incorrect NMR data of two of the dihydroxyflavones whose NMR data were previously reported were corrected.     

1H and 13C NMR assignments for new heterocyclic TAM leuco dyes, (2Z,2'E)-2,2'-(2-phenyl propane-1,3-diylidene) bis(1,3,3-trimethylindoline) derivatives. Part II

The (1)H and (13)C NMR spectra of the novel heterocyclic Leuco-TAM dyes, (2Z, 2'E)-2,2'-(2-phenyl propane-1,3-diylidene) bis(1,3,3-trimethylindoline) derivatives 1-4 as precursors of triarylmethane (TAM)(+) (Malachite Green FB-analog) dyes were completely assigned by 1D and 2D NMR experiments, including DEPT, COSY, HSQC, HMBC, and NOESY. Especially, the diastereotopic gem-dimethyl protons at the C3 and C3' positions of the FB rings were definitively assigned. The (Z,E) isomers adopt the energetically favored three-bladed propeller conformation in solution.     

Complete assignments of 1H and 13C NMR data for trypanocidal eremantholide C oxide derivatives

The chemical transformations of eremantholide C (1), a trypanocidal sesquiterpene lactone isolated from Lychnophora trichocarpha Spreng., gave five new oxide derivatives: 3'-hydroxyeremantholide C (2), 1'-formyleremantholide C (3), 1'-carboxyeremantholide C (4), 1'-carbomethoxyeremantholide C (5) and sodium 1'-carboxylate of eremantholide C (6). The (1)H and (13)C NMR data of all these derivatives were assigned based on 1D and 2D techniques. The derivatives were evaluated against Y and CL strains of Trypanosoma cruzi. All of them were inactive against the Y strain. Compounds 2 and 5 displayed 100% activity on the CL strain while compounds 4 and 6 were partially active on the CL strain.     

Structure determination of selaginellins G and H from Selaginella pulvinata by NMR spectroscopy

Selaginellins G ( 1 ) and H ( 2 ), two new selaginellin derivatives, were isolated from the whole plant of Selaginella pulvinata. Their structures were elucidated, and complete assignments of the ¹H and ¹³C NMR spectroscopic data were achieved by 1D and 2D NMR experiments (HSQC, HMBC, COSY and ROESY). Compound 1 displayed good antifungal activity against Candida albicans with an IC₅₀ value of 5.3 µg/ml. Copyright © 2010 John Wiley & Sons, Ltd.     

Detailed assignments of 1H and 13C NMR spectral data of 14 cyclopentane derivatives

Detailed assignments of ¹H and ¹³C NMR spectral data for 14 cyclopentane derivatives are reported. The assignments are based on 1D ¹H and ¹³C NMR and on 2D shift‐correlated [¹H, ¹³C‐HMQC], J‐resolved and NOEDIF experiments. Copyright © 2003 John Wiley & Sons, Ltd.     

Head-to-tail Aggregates of Sulfonatomethylated Calix[4]resorcinarene in Aqueous Solutions

Two amphiphilic water-soluble sulfonatomethylated calix[4]resorcinarene derivatives were studied by various ¹H NMR techniques (¹H NMR titration, 2D NOESY, NMR diffusion measurements). The derivative with methyl moieties at the lower rim (1) was found to be non-aggregated in the range 0–10 mM in aqueous solutions. Lengthening of the lower rim substituent to pentyl (2) results in self-aggregation of 2 in aqueous solutions with the aggregation number varying from 3 at 1 mM to 20 at 10 mM. The 2D NOESY ¹H NMR spectroscopy data reveal an unusual head-to-tail packing mode in aqueous solutions, resulting from the cooperative effect of weak hydrophobic interactions. Binding of guests (tetramethylammonium and N-methylpyridinium) results in additional stabilization of the aggregates whilst the head-to-tail packing mode of the aggregate is retained.     

Complete assignments of 1H and 13C NMR data for three new arylnaphthalene lignan from Justicia procumbens

Three new arylnaphthalene lignans, named neojusticin C (1), procumbenoside C (2) and procumbenoside D (3), have been isolated from the whole plant of Justicia procumbens, together with three known ones, justicidinoside B (4), justicidinoside C (5), and diphyllin-1-O-beta-D-apiofuranoside (6). The complete assignments of 1H and 13C NMR data for three new lignans were first obtained by means of 2D NMR techniques, including HSQC and HMBC.     

(1)H and (13)C NMR assignments for five anthraquinones from the mangrove endophytic fungus Halorosellinia sp. (No. 1403)

We report the unambiguous assignments of the (1)H and (13)C NMR spectra of two new natural products, namely, 1,4,5,6,7,9-hexahydroxy-2-methoxy-7-methyl-5beta,9beta,8abeta, 6alpha,10aalpha-hexahydroanthracen-10 (10aH)-one (1) and 1,4,6-trihydroxy-2-methoxy-7-methylanthracene-9, 10-dione (2), together with three known anthraquinones. These compounds were all isolated from the marine endophytic fungus No. 1403 collected from the South China Sea. Compounds 3 and 4 were isolated from the marine fungus for the first time. The structures were elucidated by the spectroscopic methods 1D and 2D NMR including COSY, HMQC, HMBC and NOE, and HREIMS. In our cytotoxicity assays, compound 5 showed cytotoxicity toward KB and KBv-200 cells with IC(50) of 1.40 and 2.58 microg/ml, respectively. In addition, the plausible biogenic relationship of compounds 1, 2, 3 and 4 is discussed.