Analysis Of Coupling Constants Research Articles

Key role of electron-phonon interactions in the electronic conductivity ofTi3SiC2: Experiment andab initiocalculations

The electronic conductivity anisotropy of $\mathrm{T}{\mathrm{i}}_{3}\mathrm{Si}{\mathrm{C}}_{2}$ is directly evidenced from data collected on (i) a thin film epitaxially grown on a $(11\overline{2}0)$-oriented SiC single crystal and (ii) a single crystal. Density functional theory calculations, including the linear-response approach and coupled to a Bloch-Gr\uneisen model, show that the electron-phonon interactions are mainly responsible for the observed anisotropy. Detailed analysis of the electron-phonon coupling constants allows for the rationalization of these scattering processes in terms of the $\mathrm{T}{\mathrm{i}}_{3}\mathrm{Si}{\mathrm{C}}_{2}$ nanostructure, giving insights into the possibility of modifying the electron-phonon interaction in this system by substitution effects.

Stereochemical Investigations of DiastereomericN-[2-(Aryl)-5-methyl-4-oxo-1,3-thiazolidine-3-yl]-pyridine-3-carboxamides by Nuclear Magnetic Resonance Spectroscopy (1D and 2D)

Some newN-[2-(aryl)-5-methyl-4-oxo-1,3-thiazolidine-3-yl]-pyridine-3-carboxamides were synthesized and their structures were investigated by IR, NMR (1H,13C, and 2D), and mass spectra. The presence of C-2 and C-5 stereogenic centers on the thiazolidinone ring resulted in diastereoisomeric pairs. The configurations of two stereogenic centers were assigned based upon1H NMR analysis of coupling constants and 2D nuclear overhauser enhancement spectroscopy (NOESY) experiment. Resolution of the diastereoisomers was performed by high performance liquid chromatography (HPLC) using a chiral stationary phase.

Conformational analysis of some type XII bisbenzyltetrahydroisoquinoline alkaloids from Thalictrum alpinum assisted by quantitative noe, j coupling constants analysis and anisotropic NMR parameters

Northalrugosidine (1), a type XII bisbenzyltetrahydroisoquinoline alkaloid, exhibits in vivo efficacy in a murine model of visceral leishmaniasis (J. Nat. Prod., 2015, 78, 552 – 556). The conformational space of the macrocyclic moiety in compounds within the same subgroups of this class should provide more clues on their structure-activity relationships, which will be very beneficial for the potential future medicinal chemistry optimization of 1. The solution-state conformation of this molecule was investigated by conducting NMR spectroscopic studies on two naturally occurring analogues in the same subclass, thalrugosidine (2) and thalidasine (3). Residual dipolar couplings (RDCs), collected in compressed PMMA gel, were employed for the determination of relative spatial orientation of 1H-13C bonds, whereas 1H-1H inter-atomic distances were determined by measurement of quantitative nuclear Overhauser effects (qNOEs). The conformation of the studied molecules in solution was determined by simultaneous fitting of these NMR data and 3 J H,H coupling constants with computed molecular models.

Suncheonosides A-D, Benzothioate Glycosides from a Marine-Derived Streptomyces sp.

A marine-derived Streptomyces strain, SSC21, was isolated from the sediment of Suncheon Bay, Republic of Korea. Chemical analysis of the bacterial strain resulted in the isolation of four new metabolites, suncheonosides A-D (1-4, respectively), each bearing a sulfur atom. The planar structures of the suncheonosides were identified as hexasubstituted benzothioate glycosides by combined spectroscopic analyses. Analysis of the configuration of the sugar moieties based on ROESY nuclear magnetic resonance correlations, one-bond (1)H-(13)C coupling constant analysis, and chemical derivatizations indicated that the suncheonosides incorporate only l-rhamnose. Suncheonosides A, B, and D promoted adiponectin production in a concentration-dependent manner during adipogenesis in human mesenchymal stem cells, suggesting antidiabetic potential.

Propylphosphonic anhydride (T3P) mediated synthesis of β-lactams from imines and aryl-substituted acetic acids

β-Lactams were prepared from imines and aryl-substituted acetic acids using T3P as an activating agent. In most cases, good to excellent yields were obtained (up to 93%) and the trans-β-lactam was the exclusive or major diastereoisomer (confirmed through analysis of 1H NMR coupling constants and by X-ray crystallography).

The microwave spectra and molecular structures of 2-chloro-1,1-difluoroethylene and its complex with the argon atom

The microwave spectra of six isotopologues each of 2-chloro-1,1-difluoroethylene and its argon complex are obtained in the 5.6–20.5GHz region using a combination of broadband chirped pulse and Balle–Flygare cavity Fourier transform microwave techniques. The structure of the halogen substituted ethylene has been determined using a combination of theory and experiment. Argon is found to form a nonplanar complex with this haloethylene, locating in the ClCCF cavity, which maximizes its interactions with the heavy atoms in the ethylene subunit. A combined analysis of the chlorine quadrupole coupling constants of the monomer and of the complex allows the sign of the only nonzero off-diagonal component of the quadrupole coupling tensor for the monomer to be determined; thus, the complete tensor for the monomer has been derived.

Spectral characterization and crystal structure of some 2,6-diarylthian-4-one hydrazone derivatives

A series of cis and trans 2,6-diarylthian-4-one hydrazone derivatives (11–16) have been synthesized and characterized by 1H, 13C and two dimensional NMR spectroscopy. For the 2r,6t-diphenylthian-4-one N-isonicotinoylhydrazone (14) X-ray diffraction have also been recorded. The coupling constants suggested that the cis-hydrazones (11–13), which have the phenyl groups in cis orientation, largely exist in chair conformations with equatorial orientation of the phenyl groups 11C. Analysis of the vicinal coupling constants of trans-hydrazones (14–16) suggests that boat forms 14B must make significant contributions to it and the relative population is 58%. Moreover, in solution chair conformations 14C and 14C′, may contribute to 14. The NOESY and X-ray diffraction of 14 gives definite evidence for the contribution of 14C.

A convenient synthesis of fluorinated vinyl ethers derived from di-O-isopropylidenehexofuranose and O-isopropylidenepentofuranose

The synthesis of fluorinated vinyl ethers derived from di- O -isopropylidenehexofuranose and O -isopropylidenepentofuranose has been accomplished using penta- and hexafluoroolefins. Newly obtained compounds could be used as potential building blocks in drug design and substrates for the Claisen rearrangement reactions. • Synthesis of fluorinated vinyl ethers derived from carbohydrates has been studied. • Reactions were accomplished by using fluoroolefins: penta- and hexafluoropropene. • Analysis of 19 F NMR spectra has allowed assignment of Z/E geometry of products. This paper focuses on a convenient synthesis of fluorinated vinyl ethers derived from di- O -isopropylidenehexofuranose and O -isopropylidenepentofuranose allyl alcohols. The structures of new compounds have been confirmed by 1 H, 13 C and 19 F NMR spectroscopic methods. An analysis of coupling constants between vinylic H and F atoms observed in 19 F NMR spectra has allowed assignment of Z/E geometry of the products.

Rotational spectrum of tryptophan.

The rotational spectrum of the natural amino acid tryptophan has been observed for the first time using a combination of laser ablation, molecular beams, and Fourier transform microwave spectroscopy. Independent analysis of the rotational spectra of individual conformers has conducted to a definitive identification of two different conformers of tryptophan, with one of the observed conformers never reported before. The analysis of the (14)N nuclear quadrupole coupling constants is of particular significance since it allows discrimination between structures, thus providing structural information on the orientation of the amino group. Both observed conformers are stabilized by an O-H···N hydrogen bond in the side chain and a N-H···π interaction forming a chain that reinforce the strength of hydrogen bonds through cooperative effects.

Stereochemical determination of new cytochalasans from the plant endophytic fungus Trichoderma gamsii

Three new cytochalasans, trichalasins E (1), F (2) and H (7), together with four known analogues, trichalasin C (3), aspochalasin K (4), trichalasin G (5) and aspergillin PZ (8), were isolated from one endophytic fungus Trichoderma gamsii inhabiting in the traditional medicinal plant Panax notoginseng (BurK.) F.H. Chen. Trichalasins E (1) contains a unique hydroperoxyl group, which is the first report in all known analogues, whereas trichalasin H (7) possesses the rare 6/5/6/6/5 pentacyclic skeleton with 12-oxatricyclo [6.3.1.02,7] moiety as that of aspergillin PZ (8). The relative configurations of the new compounds were characterized by analysis of coupling constants and ROESY correlations, and the absolute configurations of trichalasins E (1), H (7) and aspergillin PZ (8) were determined by modified Mosher’s reaction. In addition, compounds 1–5, 7 and 8 were tested cytotoxic activities against several cancer cell lines.

Regioselective syntheses of [13C]4-labelled sodium 1-carboxy-2-(2-ethylhexyloxycarbonyl)ethanesulfonate and sodium 2-carboxy-1-(2-ethylhexyloxycarbonyl)ethanesulfonate from [13C]4-maleic anhydride.

The entitled monohydrolysis products, also known as α-ethylhexyl and β-ethylhexyl sulfosuccinate (EHSS), of the surfactant diisooctyl sulfosuccinate (DOSS) were synthesized in stable isotope-labelled form from [(13)C]4 -maleic anhydride. Sodium [(13)C]4 -1-carboxy-2-(2-ethylhexyloxycarbonyl)ethanesulfonate (α-EHSS) was prepared by the method of Larpent by reaction of 2-ethylhexan-1-ol with [(13)C]4 -maleic anhydride followed by regioselective conjugate addition of sodium bisulfite to the resulting monoester (38% overall yield). The regiochemical outcome of bisulfite addition was confirmed by a combination of (13)C/(13)C (incredible natural abundance double quantum transfer) and (1)H/(13)C (heteronuclear multiple-bond correlation (HMBC)) NMR spectral correlation experiments. Sodium [(13)C]4 -2-carboxy-1-(2-ethylhexyloxycarbonyl)ethanesulfonate (β-EHSS) was prepared in four steps by reaction of 4-methoxybenzyl alcohol with [(13)C]4 -maleic anhydride, regioselective sodium bisulfite addition, N,N'-dicyclohexylcarbodiimide-mediated esterification with 2-ethylhexan-1-ol, and p-methoxybenzyl ester deprotection with trifluoroacetic acid (13% overall yield). The regiochemical outcome of the second synthesis was confirmed by a combination of (1)JCC scalar coupling constant analysis and (1)H/(13)C (HMBC) NMR spectral correlation. The materials prepared are required as internal standards for the liquid chromatography-mass spectrometry (LC-MS)/MS trace analysis of the degradation products of DOSS, the anionic surfactant found in Corexit, the oil dispersant used during emergency response efforts connected to the Deepwater Horizon oil spill of April 2010.

Conformational Analysis of Geometric Isomers of Pitavastatin Together with Their Lactonized Analogues

Super-statins are synthetic inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, which is the rate-limiting enzyme responsible for the biosynthesis of cholesterol. All of the super-statins with a C=C double bond spacer between the heterocyclic and the dihydroxycarboxylic moiety that are currently on the market exist as E-isomers. To extend the understanding of conformational and thermodynamic preferences of Z-isomeric super-statin analogues, this study focused on analyzing pitavastatin and its lactonized derivatives via NMR spectroscopy and ab initio calculations. Z-isomeric pitavastatin analogues exist in solution as a pair of interconverting rotamers, where the Gibbs free energies between the major and minor rotamers are within 0.12 and 0.25 kcal mol−1 and the rotational energy barriers are between 15.0 and 15.9 kcal mol−1. The analysis of long-range coupling constants and ab initio calculations revealed that rotation across the C5'–C7 single bond is essential for generating a pair of atropisomers. The overall comparison of the results between Z-isomeric pitavastatin and rosuvastatin analogues demonstrated that the former are to some extent more flexible to attain numerous conformations. Demonstrating how structural differences between super-statin analogues induce distinctive conformational preferences provides important insight into the super-statins’ conformational variability and may well improve future drug design.

Addition of “HOBr” to trans-Anethole: Investigation of the Regioselectivity and the Stereoselectivity of an Addition Reaction

In this advanced organic experiment, students used a combination of spectroscopy and molecular modeling to determine the regiochemical and stereochemical outcome of the addition of “HOBr” to trans-anethole. 1H, 13C, and HMQC NMR spectra were used to determine the regiochemistry of the addition reaction, and coupling-constant analysis and molecular modeling were used to determine the stereochemistry. Using a procedurally simple synthetic procedure, students obtained a racemic mixture of (1S,2R)- and (1R,2S)-2-bromo-1-(4-methoxyphenyl)propan-1-ol in 70% quantitative yield from the reaction between trans-anethole and N-bromosuccinimide (NBS) in 95% acetone(aq).

Conformational Analysis of the Anti‐obesity Drug Lorcaserin in Water: How To Take Advantage of Long‐Range Residual Dipolar Couplings

The conformational state of 8-chloro-1-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (lorcaserin) in water has been determined on the basis of one-bond and long-range C-H residual dipolar coupling (RDC) data along with DFT computations and (3)J(HH) coupling-constant analysis. According to this analysis, lorcaserin exists as a conformational equilibrium of two crown-chair forms, of which the preferred conformation has the methyl group in an equatorial orientation.

Stereochemistries of monapinones produced by Talaromyces pinophilus FKI-3864

Monapinones A (1) to E (5), half parts of dinapinones, were produced by fermentation of Talaromyces pinophilus FKI-3864 in seawater-containing medium and have a common dihydronaphthopyranone skeleton with a different long alkyl chain. The relative stereochemistries of 3–5 were elucidated by various NMR experiments including analysis of 1H NMR coupling constants, ROESY and the dihedral angles. The absolute stereochemistries of 3–5 at C-3 were determined by the circular dichroism spectra in comparison to the data of (R)- and (S)-semivioxanthins (6 and 7). Accordingly, total absolute stereochemistries of 3–5 were concluded to be 3S,13R,15R,17R,19R,3S,13R,15R,17R and 3S,13R,15R, respectively.

Thalassospiramide G, a New γ-Amino-Acid-Bearing Peptide from the Marine Bacterium Thalassospira sp.

In the chemical investigation of marine unicellular bacteria, a new peptide, thalassospiramide G (1), along with thalassospiramides A and D (2–3), was discovered from a large culture of Thalassospira sp. The structure of thalassospiramide G, bearing γ-amino acids, such as 4-amino-5-hydroxy-penta-2-enoic acid (AHPEA), 4-amino-3,5-dihydroxy-pentanoic acid (ADPA), and unique 2-amino-1-(1H-indol-3-yl)ethanone (AIEN), was determined via extensive spectroscopic analysis. The absolute configuration of thalassospiramide D (3), including 4-amino-3-hydroxy-5-phenylpentanoic acid (AHPPA), was rigorously determined by 1H–1H coupling constant analysis and chemical derivatization. Thalassospiramides A and D (2–3) inhibited nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated mouse macrophage RAW 264.7 cells, with IC50 values of 16.4 and 4.8 μM, respectively.

Antitubercular diterpenoids from Vitex trifolia

A new halimane diterpenoid, 13-hydroxy-5(10),14-halimadien-6-one (1) and two new labdane diterpenoids, 6α,7α-diacetoxy-13-hydroxy-8(9),14-labdadien (2) and 9-hydroxy-13(14)-labden-15,16-olide (3), were isolated for the first time, along with fifteen known compounds, from the hexane soluble fraction of methanolic extract of Vitex trifolia leaves. The structures of these new diterpenoids were elucidated by spectral analysis. Their relative configurations were established using analysis of NOESY correlations and coupling constants observed in 1H NMR. Compounds 2, 3 and another known diterpenoid, isoambreinolide (4) were evaluated for antitubercular activity. 3 and 4 exhibited antitubercular activity (MIC=100 and 25μg/ml) against Mycobacterium tuberculosis H37Rv in BACTEC-460 assay.

Spin-spin coupling constants 13C-15N and 1H-15N in the investigation of azido-tetrazole tautomerism in a series of 2-azidopyrimidines

A new method was developed for the investigation of an azido-tetrazole equilibrium based on using a complex analysis of 13C-15N and 1H-15N spin-spin coupling constants. The use of this approach became possible due to the selective inclusion of 15N isotopes into the structures of 2-azidopyrimidines and their cyclic analogs tetrazolo[1,5-a]pyrimidines.

Four new sesquiterpenoids from Ligularia cymbulifera

Four new highly oxygenated bisabolane sesquiterpenoids (1–4) were obtained from the EtOH extract from Ligularia cymbulifera, and their structures were elucidated by interpretation of spectroscopic data. Their relative configurations were clarified by a detailed analysis of 1H NMR coupling constants, nuclear overhauser effect (NOE) experiments and two-dimensional NMR spectra. These four new compounds were assayed for their antimicrobial activities against four Gram-positive and Gram-negative bacteria, as well as against one human pathogenic fungus.

(+)-Ascosalitoxin and Vermelhotin, a Calmodulin Inhibitor, from an Endophytic Fungus Isolated from Hintonia latiflora

Chemical investigation of the endophytic MEXU 26343, isolated from the medicinal plant Hintonia latiflora, yielded the known polyketide vermelhotin (1) and a new salicylic aldehyde derivative, namely, 9S,11R-(+)-ascosalitoxin (2). The structure and absolute configuration of the new compound were established through extensive NMR spectroscopy and molecular modeling calculations at the DFT B3LYP/DGDZVP level, which included the comparison between theoretical and experimental optical rotation values. In addition, chemical transformations of 2 yielded suitable derivatives for NOESY and (1)H-(1)H NMR coupling constant analyses, which reinforce the stereochemical assignment. The potential affinity of 1 and 2 with (Ca(2+))(4)-hCaM in solution was measured using the fluorescent biosensor hCaM M124C-mBBr. The results showed that 1 bound to the protein with a dissociation constant (K(d)) of 0.25 ± 0.04 μM, close to that of chlorpromazine (K(d) = 0.64 ± 0.03 μM), a classical CaM inhibitor. The stoichiometry ratio of 1 to (Ca(2+))(4)-hCaM was 1:4, similar to other well-known CaM ligands.