Homonuclear COSY Research Articles

Synthesis and spectral study of (2R,11R)‐2,11‐bis{[(2‐methoxyethoxy)methoxy]methyl}‐1,10‐dibenzyl‐4,7,13,16‐tetraoxa‐1,10‐diaza‐cyclooctadecane

AbstractA new C2‐symmetric chiral lariat ether has been prepared by 1 : 1 cyclocondensation of a contrafunctional amine easily obtained from L‐serine. Its 1H and 13C spectra were completely assigned using the two‐dimensional gradient enhanced one‐bond (HMQC) and multiple‐bond (HMBC) heteronuclear techniques together with the homonuclear DQF COSY correlation technique. Copyright © 2001 John Wiley & Sons, Ltd.

Identification of amino acids in wines by one- and two-dimensional nuclear magnetic resonance spectroscopy.

Amino acids are minor compounds in wines, but they have a profound influence on wine quality, and amino acids composition can be used to differentiate wines according to the vine variety, geographical origin, and year of production. The NMR signals of amino acids in NMR spectra are overlapped by the signals of other compounds present and especially by the signals of dominant compounds such as water, ethanol, and glycerol. In this work we used 1D (1)H and (13)C, 2D homonuclear COSY, TOCSY, and 2D heteronuclear HSQC and HMQC pulse sequences, also with an incorporated WET pulse sequence element that allows the simultaneous suppression of several frequencies. Complete (1)H and (13)C NMR assignments for 17 amino acids commonly present in wine and of gamma-aminobutyric acid at pH 3 have been achieved in wine sample of Sauvignon from the Coastal wine-growing region of Slovenia, vintage 1994.

The virtual NMR spectrometer: a computer program for efficient simulation of NMR experiments involving pulsed field gradients.

This paper presents a software program, the Virtual NMR Spectrometer, for computer simulation of multichannel, multidimensional NMR experiments on user-defined spin systems. The program is capable of reproducing most features of the modern NMR experiment, including homo- and heteronuclear pulse sequences, phase cycling, pulsed field gradients, and shaped pulses. Two different approaches are implemented to simulate the effect of pulsed field gradients on coherence selection, an explicit calculation of all coherence transfer pathways, and an effective approximate method using integration over multiple positions in the sample. The applications of the Virtual NMR Spectrometer are illustrated using homonuclear COSY and DQF COSY experiments with gradient selection, heteronuclear HSQC, and TROSY. The program uses an intuitive graphical user interface, which resembles the appearance and operation of a real spectrometer. A translator is used to allow the user to design pulse sequences with the same programming language used in the actual experiment on a real spectrometer. The Virtual NMR Spectrometer is designed as a useful tool for developing new NMR experiments and for tuning and adjusting the experimental setup for existing ones prior to running costly NMR experiments, in order to reduce the setup time on a real spectrometer. It will also be a useful aid for learning the general principles of magnetic resonance and contemporary innovations in NMR pulse sequence design.

Tryptophan glycoconjugates in food and human urine

Evaluating the formation of tryptophan glycoconjugates other than well-established Amadori rearrangement products, HPLC-tandem MS (MS/MS) analysis of human urine collected from several healthy individuals proved the presence of one distinct tryptophan C-glycosyl compound [Horiuchi, Yonekawa, Iwahara, Kanno, Kurihara and Fujise (1994) J. Biochem. (Tokyo) 115, 362-366]. After isolation, unambiguous identification of this novel tryptophan metabolite as 2-(alpha-mannopyranosyl)-l-tryptophan was achieved by tandem MS combined with NMR spectroscopy including homonuclear COSY, heteronuclear multiple-bond connectivity and (1)H-detected heteronuclear multiple-quantum coherence experiments. Remarkably, a thorough evaluation of vicinal proton-proton coupling constants in different solvents and nuclear Overhauser effect experiments demonstrate the predominant axial orientation of the hydroxymethyl group of the hexopyranosyl residue. Likewise this spatial arrangement indicates that the respective alpha-anomeric C-mannosylhexopyranose is preferentially adopting a (1)C(4) conformation in acidic methanol. Whereas only one distinct tryptophan mannoconjugate could be observed in human urine, HPLC-MS/MS analysis of food samples for the first time led to the identification of numerous N(1)-(beta-d-hexopyranosyl)-l-tryptophan, 2-(beta-d-hexopyranosyl)-l-tryptophan and 1-(1,2,3,4,5-pentahyd- roxypent-1-yl)-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid derivatives derived from the condensation of tryptophan with aldohexoses. Taking into consideration the significant differences between profiles and configurations of tryptophan glycoconjugates originating from dietary sources and human urine, C-2 mannosylation of tryptophan residues [de Beer, Vliegenthart, Loeffler and Hofsteenge (1995) Biochemistry 34, 11785-11789] represents a novel enzymic pathway in tryptophan metabolism in humans.

2D NMR characterization of poly(ethylene-co-5-vinyl-2-norbornene)

Unsaturated poly(ethylene-co-5-vinyl-2-norbornene) was synthetized using the [Ph2C(Flu)(Cp)]ZrCl2 metallocene/methylaluminoxane (MAO) catalyst system. 1H and 13C NMR spectra of the copolymer were assigned by means of DEPT, homonuclear 2D 1H-1H COSY, and heteronuclear 2D 1H-13C correlation NMR experiments. The used catalyst system produces mainly isolated 5-vinyl-2-norbornene (VNB) sequences. VNB is incorporated selectively via the cyclic double bond. The unreacted double bond of the copolymer exists in the 5-endo: 5-exo positions (3 : 1). Both isomers of VNB are polymerized with the same propability.

2D NMR characterization of poly(ethylene-co-5-vinyl-2-norbornene)

Unsaturated poly(ethylene-co-5-vinyl-2-norbornene) was synthetized using the [Ph2C(Flu)(Cp)]ZrCl2 metallocene/methylaluminoxane (MAO) catalyst system. 1H and 13C NMR spectra of the copolymer were assigned by means of DEPT, homonuclear 2D 1H-1H COSY, and heteronuclear 2D 1H-13C correlation NMR experiments. The used catalyst system produces mainly isolated 5-vinyl-2-norbornene (VNB) sequences. VNB is incorporated selectively via the cyclic double bond. The unreacted double bond of the copolymer exists in the 5-endo: 5-exo positions (3 : 1). Both isomers of VNB are polymerized with the same propability.

Solution structure of a non-palindromic 16 base-pair DNA related to the HIV-1 κb site: evidence for BI-BII equilibrium inducing a global dynamic curvature of the duplex

1H and 31P NMR spectroscopy have been used together with molecular modelling to determine the fine structure of a non-palindromic 16 bp DNA containing the NF-κB binding site. Much emphasis has been placed upon NMR optimization of both two-dimensional 31P NMR techniques to extract structural information defining the phosphodiester backbone conformation and selective homonuclear 2D COSY experiments to determine sugar conformations. NMR data show evidence for a dynamic behaviour of steps flanking the ten base-pairs of the NF-κB binding site. A BI-BII equilibrium at these steps is demonstrated and two models for each extreme conformation are proposed in agreement with NMR data. In the refined BII structures, the NF-κB binding site exhibits an intrinsic curvature towards the major groove that is magnified by the four flanking steps in the BII conformation. Furthermore, the base-pairs are translated into the major groove. Thus, we present a novel mode of dynamic intrinsic curvature compatible with the DNA curvature observed in the X-ray structure of the p50-DNA complex.

An NMR study of ligand binding by maltodextrin binding protein

Proton NMR spectra of maltodextrin binding protein from Escherichia coli were used to monitor conformational changes that accompany ligand binding. Chemical shift changes associated with the binding of different maltodextrins to maltodextrin binding protein were studied using one-dimensional difference spectra. Line-shape analysis of an isolated upfield methyl resonance was used to measure the kinetics of maltose binding at several temperatures. Maltose and linear maltodextrins caused similar changes to the upfield protein spectrum with no detectable differences between alpha and beta sugar anomers. Binding of a cyclic ligand, beta-cyclodextrin, caused smaller chemical shift changes than binding of linear maltodextrins. Two maltodextrin derivatives were also studied. Both maltohexaitol and maltohexanoic acid gave one-dimensional difference spectra that were intermediate between those of linear maltodextrins and beta-cyclodextrin. The methyl resonances at -1 and -0.35 ppm were assigned to leucine 160 on the basis of homonuclear COSY and TOCSY experiments and theoretical chemical shift calculations using the X-ray crystal structure of maltodextrin binding protein.Key words: maltose binding protein, chemical shifts, chemical exchange, sugar anomer specificity.

Norditerpenoid alkaloids from Delphinium pyrimadale

From the aerial parts of Delphinium pyrimadale a new norditerpenoid alkaloid, 8-acetylcondelphine, has been isolated, together with the known alkaloids isotalatizidine, condelphine and senbusine C. The structure of the new alkaloid was established on the basis of 1H, 13C, APT, DEPT homonuclear COSY, HETCOR and COLOC NMR spectral studies and by chemical reactions.

Selective Demethylation of Some Aconitine-Type Norditerpenoid Alkaloids

Demethylation of some aconitine-type norditerpenoid alkaloids was carried out with trimethylsilyl iodide and with HBr in glacial AcOH. Aconitine (10), cammaconine (23), delphinine (3), falconerine (18), lappaconitine (22), and talatizamine (24) afforded partially demethylated products. When methoxyl groups are present at the C-16 and C-18 positions, these are demethylated, and the methoxyl group at the C-1 position underwent demethylation in none the alkaloids studied except falconerine (18). With HBr-AcOH, in the case of alkaloids possessing a C-3 hydroxyl group, the methoxymethyl at C-18 formed a tetrahydrofuran, cyclizing at the C-6 position. Detailed NMR spectral studies (1H, 13C, 1H homonuclear COSY, HETCOR, and selective INEPT) carried out on the demethylation products have enabled accurate chemical shift assignments to be made for the demethylated alkaloids.

Structural Assignment of the Opium Alkaloid, Codeine via 2D NMR Techniques

Two dimensional inverse detected heteronuclear correlation experiments HMQC and HMBC and the homonuclear correlation experiment COSY were performed on the natural alkaloid, codeine enabling complete assignments of the 1H and 13C spectra. The assignments presented follow directly from observed internuclear interactions without the need for arguments based on relative chemical shifts and relaxation rates.

The Application of 2D NMR Techniques in the Structural Assignment of the Diterpenoid Alkaloid, Delphinine

The two dimensional inverse detected heteronuclear correlation experiment HMQC and the homonuclear correlation experiments COSY and ROESY were performed on the natural alkaloid, delphinine enabling complete assignments of the 1H and 13C spectra. The stereochemistry of ring A and B have been determined in solution. The results suggest that the application of direct correlation multipulse NMR techniques allows for unambiguous structural assignment of delphinine.

NMR Studies of Hindered Rotation. The Diels-Alder Adduct of Phencyclone withN-n-Propylmaleimide: Restricted Motion of Bridgehead Phenyls

Abstract The Diels-Alder adduct of phencyclone and N-n-propylmaleimide has been studied in CDCl3 solution at ambient temperatures by one-and two-dimensional 1H NMR (300 MHz) and 13C NMR (75 MHz) techniques. Clear evidence is presented from slow exchange limit (SEL) spectra for hindered rotation of the bridgehead phenyls in the adduct. Full 1H spectral assignments have been made via selective homonuclear decoupling and high resolution COSY experiments. The number of signals in the aryl region of 13C NMR spectra also indicated slow rotation about the C(sp2)-C(sp3) bond to the unsubstantiated bridgehead phenyls. Striking evidence of magnetic anisotropic effects, seen from 1H NMR, permits stereochemical assignment of the adduct as endo.

Isolation and structure of wightional and wightiolide from Andrographis wightiana

Two new ent-labdane-type diterpenoids, wightional and wightiolide have been isolated from the leaves of Andrographis wightiana. Their structures were determined on the basis of extensive 1H and 13C, 1H homonuclear COSY, and HMBC NMR spectroscopic studies. To correlate the newly isolated diterpenes with wightionolide, a number of derivatives of wightionolide have been prepared and characterized.

Determination of the Stereochemistry of Four Spirodiastereoisomers by One- and Two-Dimensional NOE Studies

The stereochemistries of four cycloadducts obtained by 1,3-dipolar reactions were investigated with one-and two-dimensional NMR techniques. Analysis of a series of homonuclear NOE difference spectra and COSY and NOESY spectra recorded in a variety of solvents and at various temperatures allowed the determination of the full stereochemistry of each adduct.

Long-Range4Jand5J, IncludingInterglycosidic Correlations in Gradient-Enhanced Homonuclear COSY Experiments of Oligosaccharides

Gradient-enhanced, two-dimensional, homonuclear correlation techniques (GCOSY) of carbohydrates provide numerous correlations based on4Jand5Jlong-range interactions.Intraresidue correlations, involving all1H resonances of a given pyranose ring with its anomeric proton, are consistently observed in α-pyranosyl residues at approximately 5 to 10 times lower intensities than vicinal3Jcorrelation cross peaks. β-Anomers, pyranosyl residues with axial H1 protons, show very few such effects. Both α and β anomers do, however, exhibitinterresidue4Jcorrelations across the glycosidic linkage as shown for several linear and branched oligosaccharides ranging from three to five residues and are especially useful for spectral assignments in the envelope of pyranosyl ring protons located in the typically very crowded 3 to 4 ppm region. These effects depend on the strength and duration of the applied gradients.

Polyester Biosynthesis Characteristics of Pseudomonas citronellolis Grown on Various Carbon Sources, Including 3-Methyl-Branched Substrates

Forty-two different carbon sources were tested for the polyester synthesis of a citronellol-utilizing bacterium, Pseudomonas citronellolis (ATCC 13674). These included linear C(2) to C(10) monocarboxylic acids, C(3) to C(10) dicarboxylic acids, saccharides, alpha,omega-diols, hydrocarbons, and 3-methyl-branched substrates such as 3,7-dimethyl-6-octen-1-ol (citronellol), 3-methyl-n-valerate, 3-methyl-1-butanol, and 3-methyladipate. Isolated polymers were characterized by gas chromatography, infrared spectroscopy, H- or C-nuclear magnetic resonance spectroscopy, H-C heteronuclear correlation spectroscopy (H-C COSY), H-H homonuclear COSY, and differential scanning calorimetry. Polyesters from nine monocarboxylic acids and two related carbon sources could be metabolically divided into three groups. The first group of C(2) to C(4) carbon sources resulted in copolyesters composed of 61 to 70 mol% 3-hydroxydecanoate, 23 to 33 mol% 3-hydroxyoctanoate, 3.6 to 9.0 mol% 3-hydroxy-5-cis-dodecenoate, and 1.8 to 2.6 mol% 3-hydroxy-7-cis-tetradecenoate. Carbon sources in group II (C(7) to C(10)) produced copolyesters composed of 3-hydroxyacid monomer units with the same number of carbon atoms as the substrate (major constituent) and monomer units with either two less or two more carbons. Negligible amounts of 3-hydroxy-5-cis-dodecenoate and 3-hydroxy-7-cis-tetradecenoate were detected in copolyesters from this group. Copolyesters from group III (C(5) and C(6)) had a monomer unit distribution that could be said to be between those of groups I and II. In addition, a novel copolyester, poly(3-hydroxy-7-methyl-6-octenoate-co-3-hydroxy-5-methylhexanoate), was synthesized when grown on citronellol. The H-C heteronuclear COSY spectrum for monomer unit II revealed that both methylene and isopropyl groups, proximately connected in series to a single chiral center, had magnetically diastereotopic natures.

Revision of the NMR Assignments of Pterostilbene and of Dihydrodehydrodiconieferyl alcohol: Cytotoxic Constituents fromAnogeissus acuminata

Abstract Further phytochemical work on Anogeissus acuminata var. lanceolata (Combretaceae) led to the isolation of pterostilbene (1), dihydrodehydrodiconiferyl alcohol (2), and conocarpan (3). The structure of these compounds were determined by spectroscopic means, mainly through 1D and 2D NMR experiments. A revision of some of the 13C NMR chemical shifts of 1 and 2 were made possible by HETCOR, FLOCK, and selective INEPT experiments. Homonuclear spin-decoupling and 1H-1H COSY experiments also enabled the precise assignment of the 1H NMR chemical shifts of 2. Compounds 1–3 exhibited in vitro cytotoxicity in various cancer cell lines. This is the first isolation of 1–3 from Anogeissus.

Measurement of Homonuclear Long-Range J Couplings by Relayed E.COSY

Abstract A pulse sequence is presented that extends the E.COSY concept to homonuclear relayed COSY experiments for the accurate measurement of homonuclear long-range J coupling constants. The method is applied to the measurement of coupling constants between HN and side-chain protons in proteins.

Norditerpenoid Alkaloids from the Aerial Parts of Aconitum balfourii Stapf

From the aerial parts of Aconitum balfourii Stapf nine norditerpenoid alkaloids: condelphine (1), bullatine C (2), neoline (3), isotalatizi- dine (4), 1-O-methyldelphisine (5), pseudaconitine (6), yunaconitine (7), bikhaconitine (8), and indaconitine (9), were isolated. The iden- tity of these alkaloids was determined by comparison of mp, tlc and ir spectra with those of authentic samples and the carbon-13 nmr spectra of 2, 5, 6, 7 and 8 with the published chemical shifts. Detailed nmr spectral studies ( 1 H, 13 C, 1 H homonuclear COSY, HETCOR, and selective INEPT) carried out on (1), (3), (4) and (9) have provided accurate chemical shift assignments for these alkaloids