NOE Difference Spectra Research Articles

Isolation and structure of clematine, a new flavanone glycoside from Clematis armandii franch

A novel flavanone glycoside has been isolated from the Chinese crude drug “ mu tong” which is used in Hunan province, China. The structure of this new natural product is identified as 5,4′-dihydroxy-3′-methoxyflavanone-7-(6″- o-β- l-rhamnopyranosyl)-β- d-glucopyranoside by 1H, 13C NMR, COSY, 1H, 13C HETCOR, LOCOR and 1D NOE-difference spectra.

Miscibility and Inter-Polymer Interactions of the Poly(methyl acrylate)/Poly(vinyl acetate) Blend as Studied by NMR in Solution

To study the miscibility of poly(methyl acrylate)/poly(vinyl acetate) (PMA/PVAc) blend, we observed 1H NOE difference spectra. Inter-polymer NOEs are observed, indicating that PMA and PVAc are mixed on a molecular level. The intermolecular distance between the CH3 protons of PMA and CH proton of PVAc is estimated to be 3.4 A The temperature dependence of spin-lattice relaxation time of 13C nuclei was examined to investigate the interpolymer interaction. The motion of polymer-chain is found more hindered in blend, indicating that there exists an inter-polymer interaction in solution.

Determination by NMR methods of the structure and stereochemistry of astellatol, a new and unusual sesterterpene

AbstractThe full structure of astellatol, a new complex sesterterpene isolated from Aspergillus variecolor, was determined solely by the use of one‐ and two‐dimensional NMR techniques. The carbon skeleton was deduced from a two‐dimensional INADEQUATE spectrum, and the proton shifts were deduced from a two‐dimensional CH correlation (HMQC) experiment. Analysis of a two‐dimensional proton DQFCOSY spectrum and a series of homonuclear NOE difference spectra allowed the determination of the full stereochemistry.

Synthesis of new N-substituted imidazolyl and 1 H-1,2,4-triazolyl derivatives of (η 6-arene)(η 5-cyclopentadienyl)iron(II) salts

A series of new imidazolyl and 1 H-1,2,4-triazolyl derivatives of (η 6-arene)(η 5cyclopentadienyl)iron(II) salts have been prepared by reaction of the corresponding chloroarene complexes with the sodium salts of the heterocycles. Good yields of N-substituted products were obtained in all cases under very mild conditions. In contrast to substitution by primary and secondary amines, both chlorines were displaced from [(η 5-1,2-dichlorobenzene)(η 5-Cp)Fe][PF 6], indicating electron withdrawal by the imidazolyl and triazolyl groups. Detailed 1H and 13C NMR analysis confirmed this point. NOE difference spectra were used for 13C assignments, and evidence for conformational isomers in the 1,2-disubstituted complexes is presented.

Steroidal glycosides from the bulbs of Lilium dauricum

The bulbs of Lilium dauricum yielded 11 compounds, including six new steroidal glycosides. The structures have been determined by spectral analysis and hydrolysis to be (25 R,26 R)-26-methoxyspirost-5-en-3β-ol 3- O-α- l-rhamnopyranosyl-(1→2)- O-[α- l-arabinopyranosyl-(1→3)]-β- d-glucopyranoside, (25 R,26 R)-26-methoxyspirost-5-en-3β-ol 3- O-α- l-rhamnopyranosyl-(1→2)- O-[β- d-glucopyranosyl-(1→4)]-β- d-glucopyranoside, (25 R)-spirost-5-en-3β-ol (diosgenin) 3- O-α- l-rhamnopyranosyl-(1→2)- O-[α- l-arabinopyranosyl-(1→3)]-β- d-glucopyranoside, (25 R)-3β,17α-dihydroxy-5α-spirostan-6-one 3- O-α- l-rhamnopyranosyl-(1→2)-β- d-glucopyranoside, (25 R)-3β,17α-dihydroxy-5α-spirostan-6-one 3- O-α- l-rhamnopyranosyl-(1→2)- O-[α- l-arabinopyranosyl-(1→3)]-α- d-glucopyranoside and (20 R,22 R)-3β,20,22-trihydroxy-5α-cholestan-6-one (tenuifoliol) 3- O-α- l-rhamnopyranosyl-(1→2)-β- d-gluco-pyranoside. The absolute configurations of C-20 and C-22 of tenuifoliol were further confirmed by detailed analysis of the NOE difference spectrum of the corresponding isopropylidene derivative. Several known compounds were also isolated and identified.

Chemical Studies on New Stemona Alkaloids, IV. Studies on New Alkaloids from Stemona tuberosa

Four new alkaloids, tuberostemonone {1}, tubetostemonol {2}, stemoamide {3}, and tuberostemospironine {4}, together with two known alkaloids, tuberostemonine and didehydrotuberostemonine, were isolated from the roots of Stemona tuberosa (Stemonaceae). Their structures were elucidated by ir, ms, and 1D- and 2D-nmr techniques including difference nOe spectra and homonuclear and heteronuclear spectral analyses

Total assignment of the 1H and 13C spectra of peridinin

AbstractComplete 1H and 13C spectral assignments are reported for peridinin, the major dinoflagellate carotenoid responsible for ‘red tides’ in the ocean. These assignments were made with the aid of HETCOR, FLOCK and COSY 2D spectra and NOE difference spectra.

Synthesis and Conformational Studies ofO5′, 6-Methanouridine—A New Type of Pyrimidine Cyclonucleoside

Abstract The 5-oxo-6-methylene-pyrimidine-2,4-dione intermediate (6) that is formed when 5-acetoxy-6-acetoxymethyl-1-β-D-(5-O-acetyl-2,3-O-isopropylidene)-ribofuranosyluracil (5) is treated with sodium hydroxide undergoes cyclization at pH 14 to give 2′,3′-O-isopropylidene-5-hydroxy- O 5, 6-methanouridine (8) in good yield. Conversion of 8 into the 5-triflate ester 14 followed by reduction with [(Ph)3P]4Pd/Bu3SnH and deblocking with acetic acid then affords O 5′, 6-methanouridine (4) Conformational studies (NOE difference spectra, vicinal 1H-13C coupling constants, NOESY and CD spectra, molecular modeling) indicate that the C7-methylene group of 4 projects towards the furanose ring oxygen atom, producing a glycosyl rotation angle of about − 160°.

Formation of Through-Ring α-Cyclodextrin Complexes with α,ω-Alkanedicarboxylate Anion.Effects of the Aliphatic Chain Length and Electrostatic Factors on the Complexation Behavior

Abstract α,ω-Alkanedicarboxylic acid anions with a long spacer methylene chain were observed to form dynamically and statically stable complexes with α-cyclodextrin (α-CD) at an NMR time scale in both neutral and basic media. The structures of these complexes were confirmed to be a “through-ring” type CD complex by measurements of the intermolecular NOESY and NOE difference spectra. From the thermodynamic data in basic media (pD 13), the dynamical stability of these type complexes were attributed not to the steric interaction, but to an electrostatic interaction between the dicarboxylate anion and ionized-CD.

Gamahonolides A, B, and Gamahorin, Novel Antifungal Compounds from Stromata of Epichloe typhina on Phleum pratense.

Four novel antifungal compounds, gamahonolides A and B, gamahorin, and 5-hydroxyl-4-phenyl-2(5H)-furanone, were isolated from stromata of Epichloe typhina on Phleum pratense. Their structures were determined by spectroscopic methods. The absolute configuration of gamahonolide A was determined by its ORD spectrum and (1)H-NMR shift difference between the diastereomeric pair of its O-methylmandelates. The stereochemistry of gamahorin was determined by NOE difference spectra and its CD spectrum.

Secondary mould metabolites. Part 36. Isolation and structure elucidation of sulcatines C–E, novel norsesquiterpenes from Laurilia sulcata, and 7-epi-sulcatine D

Three novel norsesquiterpenes, sulcatines C–E (5, 6 and 11), have been isolated from still liquid cultures of Laurilia sulcata. Their structures were elucidated by 1H and 13C NMR spectroscopic studies, including 1H–13C heteronuclear correlation spectra (HETCOR and COLOC), and the relative configurations were established through a series of NOE difference spectra and the magnitude of the 1H–1H coupling constants. The absolute configuration of these metabolites was deduced by the application of the exciton chirality method to the pivalate dibenzoate of sulcatine D, compound 9. Sulcatines C and E (5 and 11) were shown to exist in solution as an equilibrating mixture of ring-closed hemiketal (5a and 11b) and ring-opened keto (5c and 11a) forms. By reduction with NaBH4 sulcatine C 5 afforded a separable mixture of sulcatine D 6 and its C–7 epimer 10.

Three new bioactive styryllactones from goniothalamusgiganteus (Annonaceae)

Three new styryllactones, goniobutenolides A ( 1) and B ( 3) and goniofupyrone ( 5), have been isolated from the bark of Goniothalamus giganteus (Annonaceae). The structures were elucidated by ir, ms, 1H nmr, 13C nmr, 1H- 1H COSY, nOe difference, and NOESY spectra. These compounds are marginally cytotoxic to human tumor cells in culture.

New β‐dihydroagarofuran sesquiterpenoids from Celastrus paniculatus

AbstractTwo new β‐dihydroagarofuran sesquiterpene polyesters were isolated from Celastrus paniculatus. The structures were deduced using various 2D NMR techniques (HH COSY, CH COSY, COLOC, NOESY), NOE difference spectra and mass spectra. The positions of the ester moieties were located by 2D heteronuclear correlated spectra via long‐range coupling, or combined with NOE experiments. Their stereochemical structures were studied and the complete assignments of the 1H and 13C chemical shifts were made.

Assignment of active‐site protons in the 1H‐NMR spectrum of reduced human Cu/Zn superoxide dismutase

600-MHz 1H-NMR and nuclear Overhauser enhancement spectroscopy (NOESY) spectra in 2H2O and H2O, as well as truncated driven NOE difference spectra in H2O of reduced human Cu(II)2Zn(II)2 superoxide dismutase (Cu/Zn SOD) have been recorded and used to assign the active-site proton signals. A derivative with histidines selectively deuteriated in the C2 position has been used for the detection of the HC2 histidine protons, 16 out of 17 observed signals of the 18 active-site histidine ring protons have been assigned. The results are compared with previous proposals based on more limited data sets. The numerous cross peaks confirm that the structure in solution is essentially similar to the crystallographic data obtained on the oxidized form. Probably this holds also for His63 which in the reduced form is not bridging any more the two metal ions. The effects of azide binding on the exchangeable 1H-NMR signals of the reduced protein are also reported.

Complete 1H and 13C NMR spectral assignment of some polynitropolycyclic cage molecules by 2D NMR spectroscopy

AbstractThe 1H and 13C NMR spectra of several saturated polynitropolycyclic molecules were unambiguously assigned using aromatic solvent‐induced shifts, NOE difference spectra, 1H–1H COSY spectra and 2D 13C–1H shift correlated spectra, optimized either for one‐bond or long‐range 13C–1H couplings.

A Stilbene derivative from Gnetum parvifolium

Gnetifolin F, a novel stilbene derivative, was isolated from the lianas of Gnetum parvifolium. The structure was deduced mainly by the use of 1H- 1H COSY, 13C- 1H COSY, 13C- 1H COLOC and NOE difference spectrum, and verified with X-ray crystallographic analysis.

Syn-anti conformational analysis of regular and modified nucleosides by 1D 1H NOE difference spectroscopy: a simple graphical method based on conformationally rigid molecules

The 1D 1 H NOE difference spectra of 50 base- and/or sugar-modified nucleosides were measured in (CD 3 ) 2 SO with irradiation of various protons. The resulting NOE data were used for a conformational analysis with respect to their syn-anti conformer equilibrium. Measurement of the NOE spectra of sterically hindered nucleosides implied that both the chemical properties as well as the van der Waals radius of nucleobase substituent are of decisive importance for the conformation around the N-glycosylic bond

NMR methods for determining the structures of enzyme/inhibitor complexes as an aid in drug design

Four approaches are described for providing detailed structural information on large enzyme/ inhibitor complexes to aid in the design of improved enzyme inhibitors. In one approach, proton NMR spectra are simplified by isotope-editing procedures in which only those protons that are attached to isotopically labeled nuclei (e.g. 13C or 15N) and their scalar or dipolar coupled partners are observed. Using this strategy, the conformation of an inhibitor bound to porcine pepsin can be determined and structural information on the active site obtained. In another approach, two-dimensional nuclear Overhauser effect (2D NOE) difference spectra are obtained by subtracting NOE spectra of two enzyme/ inhibitor complexes prepared with either a protonated or a deuterated inhibitor. Only NOEs arising from protons of the inhibitor substituted with deuterium appear in the 2D NOE difference spectra as illustrated for a pepsin/inhibitor complex. In a third strategy, deuterated enzymes are employed to eliminate the many proton NMR signals of the enzyme and allow the selective detection of the resonances corresponding to the bound ligand as demonstrated for CTP bound to CMP-3-deoxy d-manno-octulosonic acid (KDO) synthetase. Finally, a fourth approach is described using heteronuclear three-imensional NMR spectroscopy in which homonuclear 2D NMR spectra are edited with respect to the heteronuclear chemical shifts. Using these methods the complete three-dimensional structures of large enzyme/inhibitor complexes can potentially be obtained. Examples of the spectral simplification that can be achieved using 3D NMR are given for 15N-labeled CMP-KDO synthetase complexed with an inhibitor and CTP.

Metall-π-komplexe von benzolderivaten: XXXV. Bis(η 6-bimesityl)chrom. Magnetische Abschirmung und konformative Beweglichkeit

Metal-atom ligand-vapor cocondensation affords the complexes bis(η 6-bimesityl)chromium ( 2), (η 6-bimesityl)(η 6-benzene)chromium ( 5) and bis(η 6-2,4,8,10-tetramethylbiphenyl)chromium ( 4), and conventional carbonyl substitution yields the compounds (η 6-bimesityl)(tricarbonyl)chromium ( 7) and μ(η 6:η 6-bimesityl)bis[(tricarbonyl)chromium] ( 8). 1H NMR data for 2 suggest that in the rotamer of lowest energy the two bimesityl ligands with regard to the sandwich axis have a twist angle, α, of about 90 or 270°, respectively. These two rotamers undergo torsional interconversion with an activation barrier of Δ G c ≠ 75 kJ/mol. The 1H NMR spectra of 2, 5, 7 and 8 are assigned and the large chemical shift differences are traced to the unique positions the protons adopt in the periphery of the bis(η 6-arene)metal core. The NOE difference spectrum of 2 is temperature dependent; rapid exchange on the T 1 scale is achieved at 53°C, a temperature at which, on the chemical shift time scale, slow exchange still prevails. In 4, the ortho-methyl groups of the 8,10-dimethyl substituent relative to the central metal, exclusively occupy exo-positions. Correspondingly, the activation barrier for the conformational interconversion is decreased in 4 compared to 2. Owing to the lower symmetry of the ligand o, o′, p, p′-tetramethylbiphenyl ( 3), the binary complex ( 3) 2Cr is formed as a mixture of the forms meso- 4 and rac- 4. Although 4 is already in the fast exchange region at room temperature, the 1H NMR spectrum still displays a marked temperature dependence. The latter is caused by the fact that for meso- 4 the two equilibrating rotamers are enantiomers, whereas for rac- 4 they are diastereomers. Thus, in contrast to meso- 4, for rac- 4 the population ratio of the interconverting rotamers is temperature dependent.

ChemInform Abstract: 13C NMR Studies. Part 141. The Isolation, Structure, and Stereochemistry of Traversiadiene. The Precursor Hydrocarbon of Traversianal Biosynthesis.

AbstractDetailed 1H and 13C NMR studies as well as a series of NOE difference spectra establish structure (I) for traversiadiene.