Use Of Nuclear Overhauser Effect Research Articles

Modified Biginelli reaction in the synthesis of chromenopyrimidobenzimidazolones

Biginelli reaction of 4-hydroxychromen-2-one with aromatic aldehydes and biazanucleophiles was investigated. The character of the substituent in the aromatic aldehyde and the reaction conditions affect its direction. The possibility to separate two probable regio isomers and the preparation of the chromenopyrimidobenzimidazolone with angular junction was demonstrated. The use of nuclear Overhauser effect (NOE 1D) made it possible to establish the spatial interaction between ortho-protons of chromene and benzimidazole fragments additionally confirming the structure of the obtained compound. The identification of the possible intermediates in the case of reacting 3-methyl-1H-pyrazol-5-amine as the azabinucleophile confirms the assumed scheme of 2H-chromen-2-ones formation under the applied conditions.

The indelible mark of computation on bio-NMR

Computation played an enabling role in the birth of modern NMR spectroscopy, when Ernst and Anderson proposed using the discrete Fourier transform (DFT) to compute the spectrum from measurements of the free induction decay (FID). In retrospect their proposal for speeding up NMR was even more audacious than it appeared at the time, because they were unaware of the nearly contemporaneous publication of the Cooley-Tukey fast Fourier transform (FFT) algorithm (personal communication from R. Ernst to J.H.). With the proposal by Jeener to parametrically sample indirect time dimensions by recording multiple FIDs, the role of computation for obtaining multidimensional spectra was even more firmly entrenched. Invention followed necessity as the ability to resolve individual resonances for complex biomacromolecules that was enabled by multidimensional experiments led to the development of software for computer visualization and analysis of complicated spectra. Systematic use of nuclear Overhauser effects for solving the three-dimensional structure of a protein relied on software for optimizing the fit to an underdetermined set of distance restraints. Richard Ernst summarized the impact of computation in bio-NMR most succinctly in the title of his opening lecture at a 1990 NATO Advanced Research Workshop: “Without Computers, No Biological NMR”. In the proceedings volume, he would broaden this assertion to “No Modern NMR” (Ernst 1991).

Mapping the hydration dynamics of ubiquitin.

The nature of water's interaction with biomolecules such as proteins has been difficult to examine in detail at atomic resolution. Solution NMR spectroscopy is potentially a powerful method for characterizing both the structural and temporal aspects of protein hydration but has been plagued by artifacts. Encapsulation of the protein of interest within the aqueous core of a reverse micelle particle results in a general slowing of water dynamics, significant reduction in hydrogen exchange chemistry and elimination of contributions from bulk water thereby enabling the use of nuclear Overhauser effects to quantify interactions between the protein surface and hydration water. Here we extend this approach to allow use of dipolar interactions between hydration water and hydrogens bonded to protein carbon atoms. By manipulating the molecular reorientation time of the reverse micelle particle through use of low viscosity liquid propane, the T(1ρ) relaxation time constants of (1)H bonded to (13)C were sufficiently lengthened to allow high quality rotating frame nuclear Overhauser effects to be obtained. These data supplement previous results obtained from dipolar interactions between the protein and hydrogens bonded to nitrogen and in aggregate cover the majority of the molecular surface of the protein. A wide range of hydration dynamics is observed. Clustering of hydration dynamics on the molecular surface is also seen. Regions of long-lived hydration water correspond with regions of the protein that participate in molecular recognition of binding partners suggesting that the contribution of the solvent entropy to the entropy of binding has been maximized through evolution.

The solution structure of a cyclic endothelin antagonist, BQ-123, based on 1H1H and 13H1H three bond oupling constants

A cyclic pentapeptide endothelin antagonist, cyclo(dTrp-dAsp-Pro-dVal-Leu), recently reported (K. Ishikawa et al., 13th Am. Pept. Symp., Cambridge MA, 1991) has been studied by NMR spectroscopy and molecular modeling. A stable structure has been determined without the use of nuclear Overhauser effects and is based primarily on homonuclear and heteronuclear three bond coupling constants. The 13C-edited TOCSY experiment is demonstrated at natural abundance and ∼30 mM peptide concentrations. Three bond 13C1H coupling constants obtained by this method are shown to reduce the ambiguity in φ angle determination which exists when only interproton coupling constants are used. Three out of four φ angles were determined uniquely by this method and the fourth was reduced to two possible values. The proline φ angle was determined to be −78° based on the 3JHzHα and 3JHzHβ coupling constants. Comparison of amide proton temperature dependence, chemical shifts and vicinal proton coupling constants in a 20% acetonitrile/80% water solvent mixture and in (CD3)2SO indicates that the structure is similar in both solvents.

Proton nuclear Overhauser effect study of the heme active site structure of chloroperoxidase

Chloroperoxidase, a glycoprotein from the mold Caldariomyces fumago, has been investigated in its ferric low-spin cyanide-ligated form through use of nuclear Overhauser effect (NOE) spectroscopy to provide information on the heme pocket electronic/molecular structure. Spin-lattice relaxation times for the hyperfine-shifted heme resonances were found to be three times less than those in horseradish peroxidase. This must reflect a slower electronic relaxation rate for chloroperoxidase than for horseradish peroxidase as a consequence of axial ligation of cysteine in the former versus histidine in the latter enzyme. Isoenzymes A1 and A2 of chloroperoxidase show the largest chemical shift differences near the heme propionate on the basis of NOE measurements. This suggests that the primary structure differences for the two isoenzymes are communicated to the heme group through the ring propionate substituents. A downfield peak has been detected in chloroperoxidase with chemical shift, T1, and line width characteristics similar to those of the C epsilon-H proton of the distal histidine residue. The NOE pattern and T1's of the peaks in the 0.0 to -5.0 ppm upfield region are consistent with the presence of an arginine amino acid residue in the heme pocket near either the 1-CH3 or 3-CH3 group. Existence of catalytically important distal histidine and arginine amino acid residues in chloroperoxidase shows it to be structurally similar to peroxidases rather than to the often compared monooxygenase, cytochrome P-450. This result supports the earlier conclusions of Sono et al. [Sono, M., Dawson, J.H., Hall, K., & Hager, L.P. (1986) Biochemistry 25, 347-356].

NMR Determination of absolute configurations in 2‐alkylthiazolidine‐4‐carboxylic acids

AbstractThe condensation of L‐cysteine with enantiomerically pure aldehyde 2a and 2b afforded a mixture of 2‐substituted thiazolidine diastereomers 1a‐b and 1c‐d, respectively. The present paper deals with the use of nuclear Overhauser effect (nOe) in determining the absolute configurations of the stereocenters.

Concerted two-dimensional NMR approaches to hydrogen-1, carbon-13, and nitrogen-15 resonance assignments in proteins

When used in concert, one-bond carbon-carbon correlations, one-bond and multiple-bond proton-carbon correlations, and multiple-bond proton-nitrogen correlations, derived from two-dimensional (2D) NMR spectra of isotopically enriched proteins, provide a reliable method of assigning proton, carbon, and nitrogen resonances. In contrast to procedures that simply extend proton assignments to carbon or nitrogen resonances, this technique assigns proton, carbon, and nitrogen resonances coordinately on the basis of their integrated coupling networks. Redundant spin coupling pathways provide ways of resolving overlaps frequently encountered in homonuclear 1H 2D NMR spectra and facilitate the elucidation of complex proton spin systems. Carbon-carbon and proton-carbon couplings can be used to bridge the aromatic and aliphatic parts of proton spin systems; this avoids possible ambiguities that may result from the use of nuclear Overhauser effects to assign aromatic amino acid signals. The technique is illustrated for Anabaena 7120 flavodoxin and cytochrome c-553, both uniformly enriched with carbon-13 (26%) or nitrogen-15 (98%).

Die Busseine C, D, E, F, G, H, J, K, L und M, zehn neue Tetranortriterpene aus Entandrophragma bussei Harms.

The Business C,D,E,F,G,H,J,K,L und M, Ten New Tetranortriterpenes from Entandrophragma Bussei HarmsTen new tetranortriterpenes, busseins C, D, E, F, G., H, J, K, L and M have been isolated from the petroleum ether extract of the timber of Entandrophragma bussei Harms. utilizing separation by high‐pressure liquid chromatography (HPLC). The structural assignments are based mainly on spectral evidence. For the 1H‐NMR spectroscopy extensive use of nuclear Overhauser effects (NOE) was made.

Acridone alkaloids. VI. The constituents of Citrus depressa. Isolation and structure elucidation of new acridone alkaloids from Citrus genus.

Five new acridone alkaloids, citracridone-I (1a), -II (1b), citpressine-I (2a), -II (2b), and prenylcitpressine (3) along with a known acridone alkaloid, 5-hydroxynoracronycine (5), and three known coumarins, clausarin (6), suberosin (7a), and xanthyletin (8) were isolated from the root bark of Citrus depressa (Rutaceae) collected in Taiwan and characterized. This is the first report of isolation of acridone alkaloids from Citrus species. In the structure elucidations, the use of nuclear Overhauser effect (NOE) experiment on the O-methoxymethyl derivatives of phenolic acridone alkaloids was shown to be useful for the determination of the location of the phenolic hydroxyl groups.

Individual assignments of the heme resonances in the 360 MHz 1H NMR spectra of cytochrome c-557 from Crithidia oncopelti

With the use of nuclear Overhauser effects, spin decoupling and saturation transfer experiments individual assignments for numerous resonances of the heme group in the 360 MHz 1H NMR spectra of reduced and oxidized cytochrome c-557 from Crithidia oncopelli were obtained. These data provide direct evidence that the heme substituent in position 2 is a vinyl group. They further show that in spite of the different covalent structures of the heme groups the heme crevice and the electronic heme structure in the oxidized state are nearly identical in cytochrome c-557 and in mammalian cytochromes c.

Use of proton Nuclear Overhauser Effects for the determination of the conformations of amino acid residues in oligopeptides

The use of the Nuclear Overhauser Effect to determine backbone and side-chain conformations of oligopeptides is discussed. The distance between the H α proton of a given residue and the amide proton of the following residue depends only on the dihedral angle ψ. A calibration curve is given for the determination of ψ from the Nuclear Overhauser Effect involving these protons. In amino acids with branched side chains, e.g., threonine, isoleucine, and valine, the Nuclear Overhauser Effect involving the H β proton and the amide proton in either the same or the following residue gives limited information about both χ 1 and either or ψ. The Nuclear Overhauser Effect involving the H α and H γ protons in leucine gives information about χ 1 and χ 2.

A conformational study of some adenosines by use of nuclear Overhauser effect.

Conformations of 8-bromo-2'-[unk]-triisopropylbenzenesulfonyladenosine ([unk]) and its 3'-[unk]-isomer ([unk]) in solution have been determined by the use of intramolecular nuclear Overhauser effects in (1)H NMR spectroscopy. Compound [unk] has been proved to have a conformation in which the adenosine and benzene rings are intramolecularly stacked and compound [unk] an elongated non-stacked conformation in dimethylsulphoxide. The 5'-[unk]-acetyl derivative of [unk] has also been found to adopt the intramolecularly stacked conformation in dimethylsulphoxide, but a non-stacked one in chloroform. Coupling constants observed are discussed in connection with the conformation of the ribose moiety. The (13)C NMR spectra have also been examined, but no effect which could be ascribed to the stacking phenomena was observed in the carbon chemical shifts.

Stereochemistry of ring A in gibberellic acid as indicated by use of nuclear Overhauser effects

Stereochemistry of ring A in gibberellic acid as indicated by use of nuclear Overhauser effects