Nuclear Overhauser Effect Difference Research Articles

Controlling the Chain Folding for the Synthesis of Single-Chain Polymer Nanoparticles Using Thermoresponsive Polymers

Synthetic polymer single-chain nanoparticles (SCNPs) are an emerging new class of nanomaterials that possess similar folded structures as natural proteins. However, most SCNPs reported so far are p...

Stereochemical assignment of four diastereoisomers of a maculalactone derivative by computational NMR calculations

Naturally occurring γ-butyrolactones and their synthetic analogues display a wide range of bioactivities. Here, the multicomponent reaction of dimethyl 2-benzyl-3-methylenesuccinate with bromobenzene and benzaldehyde catalyzed by cobalt (II) bromide afforded a maculalactone derivative with three stereogenic centers. This reaction presented moderate diastereoselectivity and yielded different proportions of all the four possible diastereoisomers. The anti:anti (majority), anti:syn, syn:anti, and syn:syn diastereoisomers were isolated and characterized by 1D and 2D NMR experiments. Because the stereochemical assignment of all the diastereoisomers by Nuclear Overhauser Effect Difference (NOEDiff) experiments was not definitive, the 1H and 13C NMR chemical shifts were predicted by theoretical calculations with the density functional theory at the B3LYP/6-31G(d) level. The relative configurations of all the four diastereoisomers were assigned by using the CP3 parameter to compare the experimental and the calculated data and by determining the CP3 probability, which provided high level of confidence.

Chlorinated Dehydrocurvularins and Alterperylenepoxide A from Alternaria sp. AST0039, a Fungal Endophyte of Astragalus lentiginosus.

Investigation of Alternaria sp. AST0039, an endophytic fungus obtained from the leaf tissue of Astragalus lentiginosus, led to the isolation of (-)-(10E,15S)-4,6-dichloro-10(11)-dehydrocurvularin (1), (-)-(10E,15S)-6-chloro-10(11)-dehydrocurvularin (2), (-)-(10E,15S)-10(11)-dehydrocurvularin (3), and alterperylenepoxide A (4) together with scytalone and α-acetylorcinol. Structures of 1 and 4 were established from their spectroscopic data, and the relative configuration of 4 was determined with the help of nuclear Overhauser effect difference data. All metabolites were evaluated for their cytotoxic activity and ability to induce heat-shock and unfolded protein responses. Compounds 2 and 3 exhibited cytotoxicity to all five cancer cell lines tested and increased the level of the pro-apoptotic transcription factor CHOP, but only 3 induced the heat-shock response and caused a strong unfolded protein response.

Imaging human teeth by phosphorus magnetic resonance with nuclear Overhauser enhancement.

Three-dimensional phosphorus MR images (31P MRI) of teeth are obtained at a nominal resolution of 0.5 mm in less than 15 minutes using acquisition pulse sequences sensitive to ultra-short transversal relaxation times. The images directly reflect the spatially resolved phosphorus content of mineral tissue in dentin and enamel; they show a lack of signal from pulp tissue and reduced signal from de-mineralized carious lesions. We demonstrate for the first time that the signal in 31P MR images of mineralized tissue is enhanced by a 1H-31P nuclear Overhauser effect (NOE). Using teeth as a model for imaging mineralized human tissue, graded differences in signal enhancement are observed that correlate well with known mineral content. From solid-state NMR experiments we conclude that the NOE is facilitated by spin diffusion and that the NOE difference can be assigned to a higher water content and a different micro-structure of dentin. Thus, a novel method for imaging mineral content without ionizing radiation is proposed. This method has potential use in the assessment of de-mineralization states in humans, such as caries of teeth and osteoporosis of bones.

Diastereoselective Synthesis of Rotationally Restricted Chiral Phenylpyridines via Intramolecular Cascade Cyclization of N-Acyliminium Ions Containing α-Amino Acid Residues

A series of chiral phenylpyridines possessing a fused chiral bridge were synthesized diastereoselectively via cascade cyclizations, where N-acyliminium ions including an enantiopure α-amino acid residue were involved. The absolute configuration of the synthesized phenylpyridines was identified unambiguously by using nuclear Overhauser effect difference and circular dichroism (CD) measurements on the basis of literature methods. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resources: Full experimental and spectral details.]

The Binding Mode of Second-Generation Sulfonamide Inhibitors of MurD: Clues for Rational Design of Potent MurD Inhibitors

A series of optimized sulfonamide derivatives was recently reported as novel inhibitors of UDP-N-acetylmuramoyl-L-alanine:D-glutamate ligase (MurD). These are based on naphthalene-N-sulfonyl-D-glutamic acid and have the D-glutamic acid replaced with rigidified mimetics. Here we have defined the binding site of these novel ligands to MurD using 1H/13C heteronuclear single quantum correlation. The MurD protein was selectively 13C-labeled on the methyl groups of Ile (δ1 only), Leu and Val, and was isolated and purified. Crucial Ile, Leu and Val methyl groups in the vicinity of the ligand binding site were identified by comparison of chemical shift perturbation patterns among the ligands with various structural elements and known binding modes. The conformational and dynamic properties of the bound ligands and their binding interactions were examined using the transferred nuclear Overhauser effect and saturation transfer difference. In addition, the binding mode of these novel inhibitors was thoroughly examined using unrestrained molecular dynamics simulations. Our results reveal the complex dynamic behavior of ligand–MurD complexes and its influence on ligand–enzyme contacts. We further present important findings for the rational design of potent Mur ligase inhibitors.

Metabolism of the Insecticide Metofluthrin in Cabbage (Brassica oleracea)

The metabolic fate of metofluthrin [2,3,5,6-tetrafluoro-4-(methoxymethyl)benzyl (E,Z)-(1R,3R)-2,2-dimethyl-3-(prop-1-enyl)cyclopropanecarboxylate] separately labeled with (14)C at the carbonyl carbon and the α-position of the 4-methoxymethylbenzyl ring was studied in cabbage ( Brassica oleracea ). An acetonitrile solution of (14)C-metofluthrin at 431 g ai ha(-1) was once applied topically to cabbage leaves at head-forming stage, and the plants were grown for up to 14 days. Each isomer of metofluthrin applied onto the leaf surface rapidly volatilized into the air and was scarcely translocated to the untreated portion. On the leaf surface, metofluthrin was primarily degraded through ozonolysis of the propenyl side chain to produce the secondary ozonide, which further decomposed to the corresponding aldehyde and carboxylic acid derivatives. In the leaf tissues, the 1R-trans-Z isomer was mainly metabolized to its dihydrodiol derivative probably via an epoxy intermediate followed by saccharide conjugation in parallel with the ester cleavage, whereas no specific metabolite was dominant for the 1R-trans-E isomer. Isomerization of metofluthrin at the cyclopropyl ring was negligible for both isomers. In this study, the chemical structure of each secondary ozonide derivative was fully elucidated by the various modes of liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy together with cochromatography with the synthetic standard, and their cis/trans configuration was examined by the nuclear Overhauser effect (NOE) difference NMR spectrum.

Stabilization of a Supersaturated Solution of Mefenamic Acid from a Solid Dispersion with EUDRAGIT® EPO

The stabilization mechanism of a supersaturated solution of mefenamic acid (MFA) from a solid dispersion with EUDRAGIT(®) EPO (EPO) was investigated. The solid dispersions were prepared by cryogenic grinding method. Powder X-ray diffractometry, in vitro dissolution test, in vivo oral absorption study, infrared spectroscopy, and solid- and solution-state NMR spectroscopies were used to characterize the solid dispersions. Dissolution tests in acetate buffer (pH 5.5) revealed that solid dispersion showed > 200-fold higher concentration of MFA. Supersaturated solution was stable over 1month and exhibited improved oral bioavailability of MFA in rats, with a 7.8-fold higher area under the plasma concentration-versus-time curve. Solid-state (1)H spin-lattice relaxation time (T(1)) measurement showed that MFA was almost monomolecularly dispersed in the EPO polymer matrix. Intermolecular interaction between MFA and EPO was indicated by solid-state infrared and (13)C-T(1) measurements. Solution-state (1)H-NMR measurement demonstrated that MFA existed in monomolecular state in supersaturated solution. (1)H-T(1) and difference nuclear Overhauser effect measurements indicated that cross relaxation occurred between MFA and EPO due to the small distance between them. The formation and high stability of the supersaturated solution were attributable to the specifically formed intermolecular interactions between MFA and EPO.

Synthesis and Characterization of Novel Bi- and Tricyclic α-Amino Acids

As part of a medicinal chemistry collaboration, a number of novel bi- and tricyclic α-amino acids were prepared through various routes and characterized by 1H nuclear Overhauser effect difference experiments. The syntheses provide a number of routes to access some highly substituted amino acid derivatives that have not been reported previously. It is envisaged that the chemistry described here could be applied to the synthesis of other unique substrates.

Tigloylshikonin, a New Minor Shikonin Derivative, from the Roots and the Commercial Root Extract of Lithospermum erythrorhizon

Tigloylshikonin, a new shikonin derivative esterified with tiglic acid ((E)-2-methylbut-2-enoic acid), was isolated as a minor pigment from a food colorant "Shikon color," a commercial root extract from Lithospermum erythrorhizon SIEBOLD et ZUCCARINI. The structure of tigloylshikonin was elucidated using (1)H, (13)C, the difference nuclear Overhauser effect (NOE), and 2D NMR techniques. Its stereochemistry was determined by chiral-phase HPLC analysis. Tigloylshikonin was also found in the roots of L. erythrorhizon, which indicated that this new shikonin derivative is a typical component of naphthoquinone pigments in the roots of L. erythrorhizon.

ChemInform Abstract: Oligomeric Stilbenes from Caragana chamlagu Lamark Root

Caraganaphenol A (1), a new tetrameric stibene, was isolated from the root of Caragana chamlagu LAMARK (Leguminosae) along with (+)-α-viniferin (2) and kobophenol A (3). The stereostructure of 1 was suggested using NMR techniques (1H-detected heteronuclear multiple quantum coherence (HMQC), 1H-detected heteronuclear multiple bond connectivity (HMBC), and nuclear Overhauser effect (NOE) difference spectra).

Regioselective Bromination of a Thymine–Acridine Conjugate by N-Bromosuccinimide

A thymine and acridine conjugate (1), containing a benzylic carbon of thymine and an electron-rich aromatic ring (acridine) within the same molecule, was synthesized. Treatment of 1 with N-bromosuccinimide (NBS) in anhydrous chloroform in the presence of azobisisobutylnitrile produced a dibromo-substituted thymine–acridine conjugate (7) as a major product, in which the bromination was only observed on the acridine ring. Nuclear Overhauser effect (NOE) difference spectroscopy revealed that the actual bromination substitution was on C-2 and C-7 of acridine. Our results suggest that electrophilic aromatic substitution, not the expected benzylic radical reaction, takes place predominantly even when 1 is subjected to the NBS reaction condition, which favors radical processes. In addition, such selectivity is clearly solvent dependent.

Chiral interaction between aromatic aldehydes and a polymer bearing large chiral rings obtained by cyclopolymerization of bisacrylamide

This paper describes the investigation of an interaction between chiral induction behavior and a chiral polymer obtained by cyclopolymerization of a bisacrylamide (1) prepared from α-pinene and acrylonitrile. Poly(1) can interact with aromatic aldehydes, as confirmed by infrared (IR), circular dichroism (CD), diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY) and 1-D nuclear Overhauser effect difference (1-D NOE) measurements. The observed induced CD demonstrates that the chiral framework of poly(1) forced aldehydes to remain in chiral environments. IR, DOSY and 1-D NOE measurements on mixtures of poly(1) and aromatic aldehydes suggest that carbonyl groups interacted with the polymer. Interaction between a chiral polymer obtained by cyclopolymerization of a bisacrylamide [poly(1)] and aromatic aldehydes was investigated by CD, NMR and IR measurements. The observed induced CD demonstrated that the chiral frameworks of poly(1) forced aldehydes to remain in a chiral environment. NMR and IR measurements on the mixtures of poly(1) and aromatic aldehydes suggested that carbonyl groups interacted with the polymer.

Substituted 1,3,5-Triazaadamantanes: Biocompatible and Degradable Building Blocks

Substituted 1,3,5-Triazaadamantanes: Biocompatible and Degradable Building Blocks

X-ray crystal structure and nuclear Overhauser effect studies of cerium(IV) complexes with Schiff bases obtained from N, N′-(1 R,2 R)(−)-1,2-cyclohexanediamine and benzaldehyde derivatives

Schiff bases, obtained by condensation of N, N′-(1 R,2 R)-cyclohexanediamine with 2-hydroxy-5-chlorobenzaldehyde or 2-hydroxy-3,5-dichlorobenzaldehyde and of (±)cyclohexanediamine and salicylaldehyde, have been used as ligands for cerium(IV). The complexes were characterized by circular dichroism (CD), 1H NMR, 13C NMR and nuclear Overhauser effect (NOE) studies. X-ray crystal structures determined for: [Ce(IV)((1 R,2 R)(−)chxn(3,5-diClba) 2) 2] and [Ce(IV)(±)(chxn(salal) 2) 2] revealed different orientation of a pair of Schiff base ligands in the coordination sphere. In [Ce(IV)((1 R,2 R)(−)chxn(3,5-diClba) 2) 2] two ligands form a sandwich with the cerium(IV) ion positioned between two layers of dichlorophenolic moieties. CD spectra in acetonitrile solution revealed exciton coupled π → π ∗ and LMCT transitions. CD data are characteristic for distortion of the chelate ring from planarity and λ conformation of the cyclohexane bridge. NOE difference spectroscopy for the Schiff bases (saturated – HC N–) demonstrate correlations of the azomethine protons with the protons of the phenyl ring and the cyclohexane’s CH protons, and a weak correlation with the hydroxyl group. In the case of the cerium(IV) complexes, the strongest NOE (saturated H–C N) was observed with the phenyl ring’s hydrogen atoms, a slightly weaker correlation to the cyclohexane’s CH 2 protons, and a much weaker NOE to the cyclohexyl’s CH 2 protons. Results of spectral analyses suggest central ions in a distorted square antiprism geometry with the two basal N 2O 2 chromophore group. The X-ray crystallography study also confirmed antiprismatic distortion from planarity in obtained complexes.

An NMR study of [formula omitted] ions in polypyrrole

A variety of NMR techniques are employed to examine the abundance, dynamics, and translational diffusion of PF 6 − ions in doped polypyrrole films in various oxidation states. NMR is employed as a non-invasive alternative to elemental analysis for quantifying ion content, which is found to decrease linearly with decreasing electrochemical potential, directly confirming the ion intercalation mechanism of polymer actuation, and demonstrating the capacitive nature of the polypyrrole film/electrolyte system. With known ion content, sample mass, and deposition current, the relative amounts of pyrrole, ions, and solvent in the films can be determined. A T 1 relaxation study along with 1D nuclear Overhauser effect (NOE) difference experiments reveal that the rotational correlation time and solvent accessibility of PF 6 − ions in the oxidized films are similar to those in the solvent, indicating the ions experience a solvated environment, and do not sit at stable sites in the polymer matrix. A drastic decrease of the NOE enhancement, along with changes in relaxation behavior and electrical conductivity in reduced films implies that polypyrrole undergoes a significant structural change when reduced. This change leads to a much less solvated ion environment, and may be responsible for the expansion of films sometimes observed upon reduction. Translational motion of the PF 6 − ions in the oxidized films is probed via diffusion measurements made using pulsed-field gradient NMR. The diffusion coefficients found ( ∼ 5 × 1 0 − 9 cm 2/s) are an order of magnitude smaller than those typically extracted from impedance spectroscopy measurements; this is explained in terms of field driven ion migration in the impedance spectroscopy case.

The Structure of Hypericin in Solution. Searching for Hypericin's 1,6 Tautomer¶

Hypericin in organic solvents displays two types of electronic spectra: one type which shows a distinct solvatochromic effect, the stable form, and the other, the unstable form, which lacks this property. The latter type is formed in dry nonprotic solvents (e.g. tetrahydrofuran, EtOAc) and can be converted to the stable form on addition of protic solvents. In order to establish the tautomeric structure of the unstable form we applied conventional nuclear magnetic resonance techniques as well as two-dimensional gradient-enhanced heteronuclear multiple-quantum correlation, gradient-enhanced ROESY and one-dimensional nuclear Overhauser effect difference experiments. All these techniques pointed to the fact that the unstable form has the 7,14-diketo tautomeric structure, like the stable form, and not the 1,6-diketo structure. Electronic spectroscopy indicated that the unstable form has acidic properties and therefore possesses two free OH groups at C3 and C4 at the bay region of the molecule.

NMR Structural Characterization of Substrates Bound to N-Acetylglucosaminyltransferase V

N-Acetylglucosaminyltransferase V (GnT-V) is an enzyme involved in the biosynthesis of asparagine-linked oligosaccharides. It is responsible for the transfer of N-acetylglucosamine (GlcNAc) from the nucleotide sugar donor, uridine 5’-diphospho-N-acetylglucosamine (UDP–GlcNAc), to the 6 position of the α-1-6 linked Man residue in N-linked oligosaccharide core structures. GnT-V up-regulation has been linked to increased cancer invasiveness and metastasis and, appropriately, targeted for drug development. However, drug design is impeded by the lack of structural information on the protein and the way in which substrates are bound. Even though the catalytic domain of this type II membrane protein can be expressed in mammalian cell culture, obtaining structural information has proved challenging due to the size of the catalytic domain (95 kDa) and its required glycosylation. Here, we present an experimental approach to obtaining information on structural characteristics of the active site of GnT-V through the investigation of the bound conformation and relative placement of its ligands, UDP–GlcNAc and β-d-GlcpNAc-(1→2)-α-d-Manp-(1→6)-β-d-GlcpOOctyl. Nuclear magnetic resonance (NMR) spectroscopy experiments, inducing transferred nuclear Overhauser effect (trNOE) and saturation transfer difference (STD) experiments, were used to characterize the ligand conformation and ligand–protein contact surfaces. In addition, a novel paramagnetic relaxation enhancement experiment using a spin-labeled ligand analogue, 5’-diphospho-4-O–2,2,6,6-tetramethylpiperidine 1-oxyl (UDP–TEMPO), was used to characterize the relative orientation of the two bound ligands. The structural information obtained for the substrates in the active site of GnT-V can be useful in the design of inhibitors for GnT-V.

Use of NMR Binding Interaction Mapping Techniques to Examine Interactions of Chiral Molecules with Molecular Micelles

NMR spectroscopy was used to investigate the association of four chiral molecules with the molecular micelle poly(sodium N-undecanoyl-l-leucylvalinate) (poly(SULV)). Adding poly(SULV) to the background electrolyte in electrokinetic chromatography (EKC) allows enantiomeric resolution to be achieved because enantiomers interact differentially with the chiral centers on the micelle headgroups as they both move in the electric field. Pulsed field gradient diffusion experiments were used to measure molecular micelle association constants for enantiomers of each analyte. These association constants were consistent with EKC elution order for the compounds 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (BNP), 1,1'-bi-2-naphthol (BOH), and Troger's base. In addition, nuclear Overhauser enhancement spectroscopy, nuclear Overhauser effect difference, and intermolecular cross relaxation diffusion experiments were used to generate binding interaction maps for each chiral analyte. These maps showed that BNP and BOH inserted into the surfactant headgroup's major chiral groove and interacted predominately with the leucine chiral center. (+)-Troger's base was also found to insert into the major chiral groove. However, this compound instead interacted with the valine chiral atom. In diffusion experiments with long diffusion times, the linearized diffusion plots for each analyte-molecular micelle mixture showed curvature characteristic of intermolecular cross relaxation. The magnitude of this effect scaled linearly with the analytes' free energies of binding.

Design, synthesis, and biological evaluation of cytotoxic 11-alkenylindenoisoquinoline topoisomerase I inhibitors and indenoisoquinoline-camptothecin hybrids.

The indenoisoquinolines are a novel class of topoisomerase I (top1) inhibitors that are cytotoxic in cancer cell cultures and are therefore under development as potential anticancer agents. As inhibitors of the DNA religation reaction occurring after DNA cleavage by the enzyme, they are classified as top1 poisons, similar to the camptothecins. Two strategies were employed in order to further develop the structure-activity relationships of the indenoisoquinolines and enhance their therapeutic potential. The first strategy involved the synthesis of indenoisoquinoline-camptothecin hybrid molecules to take advantage of a proposed structural analogy between the indenoisoquinolines and camptothecin. The desired hybrids were synthesized by reaction of halogenated phthalides with a dihydropyrroloquinoline. The second strategy involved the attachment of various alkenyl substituents to the C-11 position of the indenoisoquinolines, which were assumed to project into the DNA minor groove. The required C-11-substituted indenoisoquinolines were synthesized by McMurry reactions of 11-ketoindenoisoquinolines with aldehydes, and the geometries of the resulting alkenes were established by nuclear Overhauser effect difference NMR spectroscopy. All of the new indenoisoquinolines were examined for cytotoxicity in human cancer cell cultures as well as for activity vs top1. Although the indenoisoquinoline-camptothecin hybrid molecules proved to be less cytotoxic and displayed less activity against top1, an analogue incorporating a 3'-aminoalkenyl substituent at the C-11 position of the indenoisoquinoline system was significantly more potent than the prototype indenoisoquinoline in both assays. These results indicate that C-11 aminoalkyl substituents that are assumed to project into the minor groove enhance the cytotoxicity and top1 inhibitory activity of the parent indenoisoquinoline system.