HETCOR Experiments Research Articles

Complete assignment of1H and13C NMR data and establishment of the relative stereochemistry of C-1-functionalized 2,4-dimethyl-8-oxabicyclo[3.2.1] oct-6-en-3-one derivatives

The total assignment of the 1H and 13C NMR spectra of 24 cis-endo and 15 cis-exo diastereoisomers of C-1-substituted 2,4-dimethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one derivatives was deduced from the concerted application of DEPT, COSY, HETCOR, HMBC, HMQC and PS-NOESY experiments. The relative stereochemistry of major (cis-endo) and minor (cis-exo) diastereoisomers was established on the basis of correlation studies of their 1H and 13C NMR data. Copyright © 1999 John Wiley & Sons, Ltd.

Complete assignment of 1H and 13C NMR data and establishment of the relative stereochemistry of C‐1‐functionalized 2,4‐dimethyl‐8‐oxabicyclo[3.2.1] oct‐6‐en‐3‐one derivatives

The total assignment of the 1H and 13C NMR spectra of 24 cis-endo and 15 cis-exo diastereoisomers of C-1-substituted 2,4-dimethyl-8-oxabicyclo[3.2.1]oct-6-en-3-one derivatives was deduced from the concerted application of DEPT, COSY, HETCOR, HMBC, HMQC and PS-NOESY experiments. The relative stereochemistry of major (cis-endo) and minor (cis-exo) diastereoisomers was established on the basis of correlation studies of their 1H and 13C NMR data. Copyright © 1999 John Wiley & Sons, Ltd.

A novel trisaccharide glycolipid biosurfactant containing trehalose bears ester-linked hexanoate, succinate, and acyloxyacyl moieties: NMR and MS characterization of the underivatized structure

A Gram-positive actinomycete growing on n-hexadecane secreted a family of anionic glycolipid surfactant homologs. The major homolog, with a molecular weight of 1210.6347, had the formula C 58H 98O 26. Following mild alkaline saponification, 1H and 13C NMR spectroscopy were used to characterize the non-reducing trisaccharide backbone: β-Glc p-(1→3)-α-Glc p-(1↔1)-α-Glc p (‘laminaratrehalose’). Hexanoate, succinate, 3-hydroxyoctanoate, and 3-hydroxydecanoate were found in 3:1:1:1 molar ratio using GC–EIMS analysis of fatty acid methyl esters (FAME) prepared by transesterification. We found that the β-hydroxy acids bore secondary hexanoate chains in 3- O-ester linkage, giving acyloxyacyl anions of appropriate m/ z in FABMS and FABMS/MS spectra. COSY, HETCOR, HMBC, and HMQC NMR experiments established the acylation pattern: succinate at C-2 of the terminal α-glucopyranose ring; hexanoate at C-3′′ of the β-glucopyranose ring; 3-hexanoyloxyoctanoate and 3-hexanoyloxydecanoate at the 2′- and 4-positions. In FABMS spectra, the homologs flanked the molecular ion by ±14 and ±28 amu, suggesting heterogeneity in acyl chain length.

Briarane diterpenes from the gorgonian octocoral erythropodium caribaeorum from the northern caribbean

An investigation of the gorgonian octocoral Erythropodium caribaeorum collected off the north coast of Jamaica has yielded three new briarane diterpenes. In addition, the six known diterpenes, erythrolides A, B, D, E, F, and I were isolated. The structures of these diterpenes were established by 1H and 13C NMR spectroscopy utilizing DEPT, COSY, and HETCOR experiments.

13C NMR assignments and conformational evaluation of diterpenes fromCroton sarcopetalus Muell.

The known diterpenes junceic acid (1) and the stress metabolite derivatives 2–4 were isolated from the hexane extracts of the roots of Croton sarcopetalus Muell. The complete 13C NMR chemical shift assignments of these compounds were achieved with the aid of DEPT and HETCOR experiments. © 1998 John Wiley & Sons, Ltd.

Chromones and flavanones from artemisia campestris subsp. maritima

From the acetone extract of Artemisia campestris subsp. maritima six flavanones, two chromones and the coumarin scopoletin were isolated. 5-Hydroxy-7-methoxychromone and 5,7-dimethoxychromone are new compounds, while the flavanone eriodictyol-7,3′-dimethyl ether is reported for the first time in this species. The structures were elucidated by 1D and 2D NMR techniques. The unequivocal assignments of carbon resonances, mainly made by using 1D selective INEPT and 2D HETCOR experiments, allowed us to correct some 1H and 13C resonances of the isolated flavanones and also to differentiate between the flavanone isomers sakuranetin⧹isosakuranetin and eriodictyol-7,3′-dimethyl ether⧹eriodictyol-7,4′-dimethyl ether.

Reactivity ratios and sequence determination of acrylonitrile/hexyl methacrylate copolymers by one and two dimensional NMR spectroscopy

Acrylonitrile/hexyl methacrylate copolymers of different monomer composition were prepared by photopolymerization using uranyl ions as photosensitizer. The copolymer composition data were used to calculate the comonomer reactivity ratios according to the Kelen Tüdős (KT) and the error-in-variables model (EVM) method. The reactivity ratios obtained from the EVM method are rA = 0.14 ± 0.03 and rH = 1.32 ± 0.17. The microstructure was obtained in terms of distribution of A and H centred triad sequences from 13C{1H} NMR spectra of the copolymers. The copolymerization mechanism was determined by using Cheng's methodology. It was found that the Markov second order model gave a good fit to the experimental data. The complex and overlapping proton and carbon signals of A/H copolymers were assigned to various compositional and configurational sequences with the help of inverse HETCOR experiments.

Antibacterial constituents from the rhizomes ofFerula communis

The rhizomes of Ferula communis yielded three antibacterial sesquiterpenes, namely, the new daucane ester 14-(o-hydroxycinnamoyloxy)-dauc-4,8-diene (1), ferulenol (2) and ferchromone (3). Compound 1 exhibited significant activity against Gram-positive bacteria, while 3 was found to be less active. Compound 2, on the other hand, demonstrated potent activity against Mycobacterium organisms, and its corresponding C-4-acetoxy derivative 9 was found to retain the same activity as well. In addition, the rhizomes yielded a number of inactive compounds, including 2-nor-1,2-secoferulenol, elemicin, colladonin, feselol and compounds 4 and 5. Structural assignments were largely based on the spectral data, especially the 2D NMR COSY and HETCOR experiments. © 1998 John Wiley & Sons, Ltd.

Structure Elucidation and Assignment of 1H and 13C Spectra of the New Fused Cyclobutane-Naphthofuran Derivative by Two-Dimensional NMR in Different Solvents

One of the major product from the photodimerization of 2-[2-(2-methyl-phenyl)ethenyl)]naphtho[2. 1-b]furan (1) is a new fused cyclobutane-naphthofuran derivative, 6-(2-methylphenyl)-1-[2-(2-methylphenyl)ethenyl]-7-(2-naphtho-[2,1-b]furyl)-3-[2,1]naphtho-2-oxabicyclo[3.2.0]hept-3-ene (2). Its 1H and 13C NMR spectra were fully assigned by the application of COSY, LR COSY, NOESY, APT and HETCOR experiments in deuterated chloroform, acetone and benzene solutions.

NMR and Structural and Conformational Features of 2′-Hydroxychalcones and Flavones

New 2′-hydroxychalcone and flavone derivatives have been synthesised. Their [1H] and [13C] NMR spectra were assigned by the application of COSY and HETCOR experiments and allowed the discussion of some structural aspects. It was shown on the basis of NOE experiments some configurational and conformational features of both type of compounds.

Reaction of 4‐hydroxy‐5‐oximino‐3‐thiophenecarboxylates with hydrazines. Formation of pyrazolylthiohydroxamic acids

AbstractThe reactions of 4‐hydroxy‐5‐oximino‐3‐thiophenecarboxylates with hydrazine and substituted hydrazines have been investigated. The products of the reactions have been shown to be pyrazole‐3‐ or 5‐thiohydroxamic acids rather than the hydrazones previously described by Benary and Silberstrom. Two alternate mechanisms are proposed which account for the regiochemical outcome. The structures of the pyrazole‐3‐ and 5‐thiohydroxamic acids and corresponding nitriles have been proven by independent synthesis, comparison to known compounds, and by proton and carbon magnetic resonance and long range HETCOR experiments.

Research on heterocyclic compounds. XXXVII. Synthesis and antiinflammatory activity of methyl-substituted imidazo[1,2- a]pyrazine derivatives

Summary A series of methyl-substituted imidazo[1,2- a ]pyrazines 8 bearing a carboxylic acid group on the imidazole ring were synthesized. The structures of new compounds were confirmed by 1 H- and 13 C-NMR spectral data; the correct assignment of carbon resonances was made by means of HETCOR and COLOC experiments. Antiinflammatory, analgesic and ulcerogenic activities in vivo were evaluated and compared with those of antiinflammatory imidazopyrazines ( 2 and 3 ) and indomethacin. The inhibitory action on cyclooxygenase activity was evaluated in vitro. Compounds 8 were found to be less potent than indomethacin in these assays. SARs are discussed.

Additional Antibacterial Diterpenes from the Bark of Juniperus procera

The bark of Juniperus procera yielded the diterpene 7β-hydroxyabieta-8,13-dien-11,12-dione (1) with strong activity against Mycobacterium species, and the hitherto unreported bisnorlabdane derivative 14,15-bisnor-13-oxolabd-8(17),11(E)-dien-19-oic acid (4). In addition, the bark yielded the known compounds crypotrienolic acid, isocupressic acid and sugiol. Structural assignments were largely based on the spectral data, including those derived from 2D NMR COSY and HETCOR experiments.

NMR spectral studies of dimedone-aldehyde adducts Part 2. 1H and 13C NMR studies of the adducts

A detailed study of the 270 MHz 1H and 67 MHz 13C NMR spectra of four series of dimedone adducts and “anhydrides” is presented. A valuable 5 J HH homoallylic coupling has been identified which has facilitated signal locations utilising 2D HETCOR and COLOC experiments. Some earlier spectral assignments are revised.

Carbon-13 Assignments and Revision of the Stereostructures of the Cadinanes 2-Hydroxy-8α-angeloyloxycalamenene and 2-Hydroxy-8α-hydroxycalamenene

Abstract The two known cadinanes 2-hydroxy-8α-hydroxycalamenene and 2-hydroxy-8α-angeloyloxycalamenene were isolated from a Louisiana population of Heterotheca subaxillaris. Their 13C NMR spectra were fully assigned by the application of HETCOR, COLOC, COSY, NOESY and DEPT experiments. It was shown on the basis of NOESY experiments that both cadinanes require revision at the stereogenic centre C-7.

C-10 oxygenated neo-clerodane diterpenes from Teucrium sandrasicum

From the aerial parts of Teucrium sandrasicum, three new C-10 oxygenated neo-clerodane diterpenes were isolated. The structures of the compounds were established by spectral data including spin decoupling, 1H 1H COSY, HETCOR, COLOC and NOESY experiments.

Sch 53823 and Sch 53825, novel fungal metabolites with phospholipase D inhibitory activity

Two novel phospholipase D (PLD) inhibitors, Sch 53823 ( 1) and Sch 53825 ( 2), were isolated from a fungal culture. The acetylated derivatives, Sch 53827 ( 3) and Sch 53829 ( 4), were prepared for the purpose of structure determination. The extensive NMR studies of 3 and 4 including DEPT, COSY, NOESY, HETCOR, and selective INEPT experiments permitted the establishment of their structures, as well as relative stereochemistries. Among these compounds, 3 exhibited the most potent inhibitory activity in the phospholipase D assay with the IC 50 = 17 μM.

Rearranged abietane diterpenes from Salvia limbata

Six new rearranged abietane diterpenes were isolated from the roots of Salvia limbata. Their structures were established by 1D and 2D NMR techniques including spin decoupling, COSY, APT, HETCOR and COLOC experiments

Analysis of1H and13C NMR Spectra ofcis- andtrans-10-Chlorodecal-2-ones by 2D NMR Techniques

The 1H and 13C NMR chemical shift assignments of trans- and cis-10-chlorodecal-2-ones were based on 2D COSY and HETCOR experiments. The spectra were measured either in CDCl3 or in C6D6 to optimize the spectral dispersion (ASIS effect). Selective spin decoupling experiments were also performed.

Multinuclear magnetic resonance study of N,N′,N″‐tris(trimethylsilyl)borazine

AbstractThe nuclear spin relaxation rate of the quadrupolar 14N nuclei in N,N′,N″‐tris(trimethylsilyl)borazine (1) is surprisingly slow [T1(14N)=0.1 s]. This allows one to measure 1J(29Si14N) (9.6 Hz) directly from the 29Si NMR spectra and also to compare signs of coupling constants 1J(29Si14N) (<0) and 3J(14NSiC1H) (>0) by 2D 29Si/1H HETCOR experiments. Since the transverse relaxation time T2(14N) in 1 is governed by scalar relaxation of the second kind, the magnitude of 1J(14N11B) can be evaluated (23 ± 0.5 Hz). 11B, 14N and 29Si NMR data for N,N′‐bis(trimethylsilyl)borazine (2) were also obtained, and 11B and 14N NMR spectra of the parent borazine [HBNH]3 (3), and of [HBNMe]3 (4) were remeasured. Calculation of the tensor components of the 14N electric field gradient shows that eqzz in 1 and in 2 for 14N(Si) is significantly smaller than for other borazines [HBNR]3, e.g. with R=H (3) or Me (4), in agreement with the experimental results.