Two-dimensional NMR Spectroscopy Research Articles

Daphnetin: A novel blue-green photonic switch for disodium phosphates that allows monitoring of polymerase chain reactions

This paper describes the very simple and robust ratiometric photonic switching properties of daphnetin (DP) toward HPO42− ions selectively in complex biological fluids, without any interference from other relevant anions under physiological conditions. The sensing ability of DP toward HPO42− ions was first demonstrated using UV–Vis and fluorescence spectroscopy, dynamic light scattering (DLS), and one- and two-dimensional NMR spectroscopy. DP can detect HPO42− ions at concentrations up to the sub-micromolar/nanomolar level very effectively, with a ratiometric response resulting from intramolecular charge transfer aided by aggregated-induced emission. The interactions between DP and HPO42− ions resulted in new bands appearing in the UV–Vis (at 385 nm) and emission (at 535 nm) spectra. The noncovalently held HPO42− ions induced pronounced specific aggregation of DP molecules, resulting in the new excimer band at 535 nm while retaining the monomer band centered at 445 nm. In contrast, reciprocal absorptivity changes were observed at 320 and 385 nm, with exponential decrements and increments, respectively. This probe could effectively monitor the consumption of dNTPs during various cycles of the polymerase chain reaction performed with relatively short oligonucleotides as well as genomic DNA from Agrobacterium tumefaciens (AcH5α strain).

Dissymmetric Bay-Functionalized Perylenediimides

We report the synthesis of perylenediimide (PDI)-based ­donor–acceptor hybrids through dissymmetric bay functionalization of PDIs. The dissymmetric bay-functionalized di- and trisubstituted PDIs were characterized by using one- and two-dimensional NMR spectroscopy. Density functional theory calculations revealed (i) an energy gap between the HOMO and LUMO in the range 2.14–2.34 eV, beneficial for charge-transfer properties; and (ii) a twist angle between the two naphthalene units in the range 17–26°, which might be beneficial for disruption of co-facial stacking of the PDI.

Solution equilibria of aromatic dinitroso compounds: a combined NMR and DFT study

Solution-state nitroso monomer-azodioxide equilibria and conformational freedom of several aromatic dinitroso derivatives, differing in the spacer group between the aromatic rings, were studied by one- and two-dimensional variable temperature 1H NMR spectroscopy and by quantum chemical calculations. The proton signals of nitroso monomer-azodioxide mixtures revealed by low-temperature NMR were assigned and validated using B3LYP-D3/6-311+G(2d,p)/SMD level of theory. In almost all cases, a preference towards the formation of only one azodioxy isomer of aromatic dinitroso compounds was found, which was assigned to Z-dimer according to computational data. Nevertheless, the computed small energy difference between the Z- and E-isomer could not account for the extreme preference for Z-dimer formation, indicating an influence of entropic or solvent effects. The formation of shorter oligomers in solution was excluded based on integrated 1H NMR signal intensities. The experimental results indicated an average dimerization Gibbs energy of about − 5 kJ/mol at 223 K and were found to be in very good correlation with dimerization energies obtained by solution-phase optimization.

Three-Component Condensation of 1,2,4-Triazol-3-amine with Cyclohexanone and ortho-Substituted Benzaldehydes

Three-component condensation of 1,2,4-triazol-3-amine with cyclohexanone and ortho-substituted benzaldehydes afforded mixtures of angularly and linearly fused aryl-substituted hexahydrotriazoloquinazolines and octahydrotriazoloquinazolines whose structure was determined by using one- and two-dimensional NMR spectroscopy. A probable scheme of product formation was proposed.

Synthesis of Bis(Isoxazol-4-Ylmethylsulfanyl)Alkanes and Some Metal Complexes as a Hepatoprotective Agents.

Purpose: This research is devoted to designing the synthesis of sulfanyl-substituted 3,5-dimethylisoxazoles, which contain structural analogues of the SAM drug in the molecule. SAM (S-adenosyl-L-methionine), formed in the biosynthetic process, is used as an effective hepatoprotective drug. Complexation and hepatoprotective properties of the combinatorial series of bis(isoxazolylsulfanyl)ethane have been studied.Methods: Bis(isoxazol-4-ylmethylsulfanyl)alkanes were synthesized using the one-pot method. The structures of compounds were established by one-dimensional (1H,13C) and two-dimensional (COSY, HCQS, HMBC) NMR spectroscopy, mass-spectrometry and X-ray diffraction. The biological activity of the combinatorial series of sulfanyl derivatives of diketones, azoles and their metal complexes has been studied by in vivo method. Simulation of the animal associated processes was carried out in accordance with the principles of bioethics. Screening studies of hepatoprotective activity were carried out in a model of acute CC14 intoxication after a single injection intraperitoneally as a 50% solution in olive oil. The pharmacologically known hepatoprotective drug SAM served as a control.Results: Two-step synthesis of novel α,ω-bis(isoxazol-4-ylmethylsulfanyl)alkanes was carried out via the multicomponent reaction between 2,4-pentandione, CH2O and α,ω-dithiols, then the resulting α,ω-bis(1,3-diketone-2-ylmethylsulfanyl)alkanes were transformed by hydroxyl amine to obtain bis-isoxasole derivatives. Promising precursor 1,2-bis(isoxazol-4-ylmethylsulfanyl)ethane was converted to metal complexes by interaction with PdCl2 or CuCl. The obtained compounds were found to be practically non-toxic compounds (1001 – 3000 mg/kg) according to the classification of K.K. Sidorov, but copper complex refers to low-toxic compounds substances (165 mg/kg). Compounds of sulfanyl ethane series demonstrate hepatoprotective activity.Conclusion: Palladium(II) complex being almost non-toxic possesses hepatoprotective activity comparable to the drug like SAM.

Induced secondary metabolites from the endophytic fungus Aspergillus versicolor through bacterial co-culture and OSMAC approaches

Two new cryptic 3,4-dihydronaphthalen-(2H)-1-one (1-tetralone) derivatives, aspvanicin A (1) and its epimer aspvanicin B (2), as well as several known cryptic metabolites (3–8), were obtained from the ethyl acetate extract of the co-culture of the endophytic fungus Aspergillus versicolor KU258497 with the bacterium Bacillus subtilis 168 trpC2 on solid rice medium. When A. versicolor was cultured axenically in liquid Wickerham medium supplemented with 3.5% DMSO, an additional three known secondary metabolites (9–11) were isolated that were lacking when the fungus was fermented on rice medium. The structures of the new compounds were elucidated using one- and two-dimensional NMR spectroscopy as well as HRESIMS. The relative and absolute configurations of 1 and 2 were determined by the combination of NMR and electronic circular dichroism (ECD) analysis aided by DFT conformational analysis and TDDFT-ECD calculations. The ECD calculations revealed that although the sign of the blue-shifted overlapping n-π∗ ECD transition follows the helicity rule of cyclic aryl ketones, the calculation of low-energy conformers and ECD spectra was necessary to determine the stereochemistry. All metabolites were assessed for their antibacterial and cytotoxic activities; one of the new diastereomers, compound 2, showed moderate cytotoxic activity against the mouse lymphoma cell line L5178Y.

Stereoselective synthesis of new rac-quercitols containing hydroxymethyl groups as glucosidase inhibitors

Stereoselective and efficient synthesis of hydroxymethyl-substituted rac-quercitols (13–15) was achieved, starting from cis-furan (Kobayashi, 2008) with photooxygenation reaction, which is readily available by the reduction of cis-phtalic anhydride. α- and β-Glucosidase enzyme activity of the target molecules was evaluated and good inhibitor activity was seen. One- and two-dimensional NMR spectroscopy, IR spectroscopy and X-ray crystallography were utilized in the structure characterization of products.

Tanzawaic acid derivatives from freshwater sediment-derived fungus Penicillium sp.

Chemical investigation of a freshwater sediment-derived fungus, Penicillium sp. (S1a1), led to the isolation of three new tanzawaic acid derivatives, including penitanzchroman (1), tanzawaic acids Y (2) and Z (3), along with six known tanzawaic acid analogues (4-9), three known isochromans (10-12) and two known benzoquinones (13 and 14). The structures of the new compounds were established based on high-resolution mass spectrometry, and detailed analysis of one- and two-dimensional NMR spectroscopy. The relative configuration of the new compounds was assigned on the basis of NMR spectroscopic data including ROESY spectra. The absolute configuration was determined based on the specific optical rotation, in addition to biogenetic considerations in comparison with related co-isolated known metabolites. Penitanzchroman (1) constitutes a hitherto unprecedented skeleton, formed of tanzawaic acid A (5) and (3S)-6-hydroxy-8-methoxy-3,5-dimethylisochroman (10) linked by a CC bond. Moreover, all compounds were evaluated for their antibacterial and cytotoxic activities.

Structure of the Exopolysaccharide Secreted by a Marine Strain Vibrio alginolyticus.

Vibrio alginolyticus (CNCM I-4151) secretes an exopolysaccharide whose carbohydrate backbone is decorated with amino acids, likely conferring its properties that are appreciated in cosmetics. Here, the secreted polysaccharide of another strain of V. alginolyticus (CNCM I-5034) was characterized by chromatography and one- and two-dimensional NMR spectroscopy experiments. The structure was resolved and shows that the carbohydrate backbone is made of four residues: D-galactose (Gal), D-galacturonic acid (GalA) D-N-acetylglucosamine (GlcNAc) and D-glucuronic acid (GlcA), forming a tetrasaccharide repetition unit [→4)-β-d-GlcA-(1→3)-α-d-Gal-(1→3)-α-d-GalA-(1→3)-β-GlcNAc(1→]. GlcA is derivatized with a lactate group giving ‘nosturonic acid’, and GalA is decorated with the amino acid alanine.

Anticancer Gold(III) Peptidomimetics: From Synthesis to in vitro and ex vivo Biological Evaluations

Five new AuIII -peptidodithiocarbamato complexes of the type [AuIII Br2 (dtc-AA1 -AA2 -OR] (in which AA1 =N-methylglycine (Sar), l/d-Pro; AA2 =l/d-Ala, α-aminoisobutyric acid (Aib); R=OtBu, triethylene glycol methyl ether), differing with regard to the amino acid sequence and/or the chiral amino acid configuration, were designed to enhance tumor selectivity and bioavailability. The gold(III)-based moiety was functionalized to exploit the targeting properties of the peptidomimetic ligand toward two peptide transporters (namely PEPT1 and PEPT2), which are upregulated in several tumor cells. The compounds were synthesized and fully characterized, mainly by means of elemental analysis, one- and two-dimensional NMR spectroscopy, FT-IR, and UV/Vis spectrophotometry. The crystal structures of three compounds were also solved by X-ray diffraction. In vitro cytotoxicity studies using a panel of human tumor cell lines (A549 [non-small-cell lung carcinoma], MCF-7 [breast cancer], A2780 [ovarian carcinoma], H1975 [non-small-cell lung carcinoma], H460 [large-cell lung carcinoma], and A431 [human epidermoid carcinoma]) showed the dtc-Pro-Aib-OtBu derivative to be very effective, with GI50 values much lower than those of cisplatin. This complex was thus selected for evaluating stability under physiological conditions and possible interactions with serum albumin, as well in PARP-1 enzyme inhibition assays and preliminary ex vivo toxicity experiments on healthy rat tissues.

Supramolecular Properties of a Monocarboxylic Acid-Functionalized "Texas-Sized" Molecular Box.

A new carboxylic acid-functionalized "Texas-sized" molecular box TxSB-CO2H has been prepared by combining two separate building blocks via an iodide-catalyzed macrocyclization reaction. A single-crystal X-ray diffraction analysis revealed a paired "clip-like" dimer in the solid state. Concentration-dependent behavior is seen for samples of TxSB-CO2H as prepared, as inferred from 1H NMR spectroscopic studies carried out in DMSO- d6. However, in the presence of excess acid (1% by weight of deuterated trifluoracetic acid; TFA- d1), little evidence of aggregation is seen in DMSO- d6 except at the highest accessible concentrations. In contrast, the conjugate base form, TxSB-CO2-, produced in situ via the addition of excess triethylamine to DMSO- d6 solutions of TxSB-CO2H acts as a self-complementary monomer that undergoes self-assembly to stabilize a formal oligomer ([TxSB-CO2-] n) with a degree of polymerization of approximately 5-6 at a concentration of 70 mM. Evidence in support of the proposed oligomerization of TxSB-CO2- in solution and in the solid state came from one- and two-dimensional 1H NMR spectroscopy, X-ray crystallography, dynamic light scattering (DLS), and scanning electron microscopy (SEM). A series of solution-based analyses carried out in DMSO and DMSO- d6 provide support for the notion that the self-assembled constructs produced from TxSB-CO2- are responsive to environmental stimuli, including exposure to the acetate anion (as its tetrabutylammonium, TBA+, salt), and changes in overall concentration, temperature, and protonation state. The resulting transformations are thought to reflect the reversible nature of the underlying noncovalent interactions. They also permit the stepwise interconversion between TxSB-CO2H and [TxSB-CO2-] n via the sequential addition of triethylamine and TFA- d1. The present work thus serves to illustrate how appropriately functionalized molecular box-type macrocycles may be used to develop versatile stimuli-responsive materials. It also highlights how aggregated forms seen in the solid state are not necessarily retained under competitive solution-phase conditions.

Functional Polyesters with Pendant Double Bonds Prepared by Coordination–Insertion and Cationic Ring-Opening Copolymerizations of ε-Caprolactone with Renewable Tulipalin A

The synthesis of functional copolyesters that contain pendant double bonds in their structures is reported by ring-opening copolymerization of renewable monomer Tulipalin A (α-methylene-γ-butyrolactone, MBL) and e-caprolactone (CL) using either coordination–insertion or monomer activated mechanisms. Aluminum tris(isopropoxide) (Al(OiPr)3) was successfully used as a cheap and commonly available catalyst for the coordination–insertion ring-opening copolymerization, and functional copolyesters with dispersities below 1.2 and with contents of MBL units in the copolymer up to 25 mol % were prepared. In addition, linear or multiarm copolymers of MBL with CL were synthesized by cationic ring-opening copolymerization that was conducted using protic acid as a “metal-free” catalyst in combination with mono- or multihydroxyl alcohols as initiators. The molecular characteristics and composition of the functional copolyesters were determined by GPC, NMR, two-dimensional NMR, and MALDI-TOF spectroscopy. The effect of M...

Protein-solvent interfaces in human Y145Stop prion protein amyloid fibrils probed by paramagnetic solid-state NMR spectroscopy

The C-terminally truncated Y145Stop variant of prion protein (PrP23-144), which is associated with heritable PrP cerebral amyloid angiopathy in humans and also capable of triggering a transmissible prion disease in mice, serves as a useful in vitro model for investigating the molecular and structural basis of amyloid strains and cross-seeding specificities. Here, we determine the protein-solvent interfaces in human PrP23-144 amyloid fibrils generated from recombinant 13C,15N-enriched protein and incubated in aqueous solution containing paramagnetic Cu(II)-EDTA, by measuring residue-specific 15N longitudinal paramagnetic relaxation enhancements using two-dimensional magic-angle spinning solid-state NMR spectroscopy. To further probe the interactions of the amyloid core residues with solvent molecules we perform complementary measurements of amide hydrogen/deuterium exchange detected by solid-state NMR and solution NMR methods. The solvent accessibility data are evaluated in the context of the structural model for human PrP23-144 amyloid.

Synthesis and inhibitory activity of mechanism-based 4-coumaroyl-CoA ligase inhibitors

4-Coumaroyl-CoA ligase (4CL) is ubiquitous in the plant kingdom, and plays a central role in the biosynthesis of phenylpropanoids such as lignins, flavonoids, and coumarins. 4CL catalyzes the formation of the coenzyme A thioester of cinnamates such as 4-coumaric, caffeic, and ferulic acids, and the regulatory position of 4CL in the phenylpropanoid pathway renders the enzyme an attractive target that controls the composition of phenylpropanoids in plants. In this study, we designed and synthesized mechanism-based inhibitors for 4CL in order to develop useful tools for the investigation of physiological functions of 4CL and chemical agents that modulate plant growth with the ultimate goal to produce plant biomass that exhibits features that are beneficial to humans. The acylsulfamide backbone of the inhibitors in this study was adopted as a mimic of the acyladenylate intermediates in the catalytic reaction of 4CL. These acylsulfamide inhibitors and the important synthetic intermediates were fully characterized using two-dimensional NMR spectroscopy. Five 4CL proteins with distinct substrate specificity from four plant species, i.e., Arabidopsis thaliana, Glycine max (soybean), Populus trichocarpa (poplar), and Petunia hybrida (petunia), were used to evaluate the inhibitory activity, and the half-maximum inhibitory concentration (IC50) of each acylsulfamide in the presence of 4-coumaric acid (100 µM) was determined as an index of inhibitory activity. The synthetic acylsulfamides used in this study inhibited the 4CLs with IC50 values ranging from 0.10 to 722 µM, and the IC50 values of the most potent inhibitors for each 4CL were 0.10–2.4 µM. The structure–activity relationship observed in this study revealed that both the presence and the structure of the acyl group of the synthetic inhibitors strongly affect the inhibitory activity, and indicates that 4CL recognizes the acylsulfamide inhibitors as acyladenylate mimics.

Diastereoselective One-Pot Tandem Synthesis of Chromeno­pyri­dodiazepinones through 1,4- and 1,6-Aza-Conjugate ­Additions/ Heterocyclizations

We report an efficient one-pot synthesis of a novel series of chromenopyridodiazepinone polyheterocycles by a catalyst-free nucleo­philic addition of ethane-1,2-diamine to (E,E)-3-[3-(2-hydroxyphenyl)-3-oxoprop-1-en-1-yl]-2-styrylchromones at room temperature under mild conditions. The reaction proceeds by a tandem process involving 1,4- and 1,6-aza-conjugate additions of one amino group of ethane-1,2-diamine to the α,β-unsaturated (3-oxoprop-1-en-1-yl) and the α,β,γ,δ-diunsaturated (2-styrylchromone) carbonyl system of the precursor, followed by imine condensation of the remaining amino group to generate the chromenopyridodiazepinone polyheterocycle. All compounds were characterized by means of one- and two-dimensional NMR spectroscopy and single-crystal X-ray crystallography.

Structural characterization of the exopolysaccharides from water kefir

Water kefir is a beverage which is produced by initiating fermentation of a fruit extract/sucrose solution with insoluble kefir grains. Exopolysaccharides that are formed from sucrose play a major role in the kefir grain formation, but the exopolysaccharides in the kefir beverage and the detailed structural composition of the whole kefir grains have not been studied yet. Therefore, kefir grains and the corresponding kefir beverage were analyzed for exopolysaccharides by multiple chromatographic approaches and two-dimensional NMR spectroscopy. Furthermore, different fractionation techniques were applied to obtain further information about the exopolysaccharides. The exopolysaccharide-fraction of the investigated kefir beverage was predominantly composed of O3- and O2-branched dextrans as well as lower amounts of levans. The insoluble dextrans from the kefir grains were mostly O3-branched and contained an elevated portion of 1,3-linked glucose units compared to the soluble dextrans. The structurally different exopolysaccharides in water kefir suggest the involvement of multiple bacteria.

Synthesis of condensed pregnano[17,16-d]triazolines under high pressure

Condensed pregnano[17,16-d]triazolines were produced in 1,3-dipolar cycloaddition of 16-dehydropregnenolone acetate with organic azides at 10 kbar. The structure of the synthesized compounds was determined by using two-dimensional NMR spectroscopy (1H—1H COSY, NOESY, HSQC, and HMBC).

Two-site jumps in dimethyl sulfone studied by one- and two-dimensional 17O NMR spectroscopy

Polycrystalline dimethyl sulfone is studied using central-transition oxygen-17 exchange NMR. The quadrupolar and chemical shift tensors are determined by combining quantum chemical calculations with line shape analyses of rigid-lattice spectra measured for stationary and rotating samples at several external magnetic fields. Quantum chemical computations predict that the largest principal axes of the chemical shift anisotropy and electrical field gradient tensors enclose an angle of about 73°. This prediction is successfully tested by comparison with absorption spectra recorded at three different external magnetic fields. The experimental one-dimensional motionally narrowed spectra and the two-dimensional exchange spectrum are compatible with model calculations involving jumps of the molecules about their two-fold symmetry axis. This motion is additionally investigated by means of two-time stimulated-echo spectroscopy which allows for a determination of motional correlation functions over a wider temperature range than previously reported using carbon and deuteron NMR. On the basis of suitable second-order quadrupolar frequency distributions, sin-sin stimulated-echo amplitudes are calculated for a two-site model in the limit of vanishing evolution time and compared with experimental findings. The present study thus establishes oxygen-17 NMR as a powerful method that will be particularly useful for the study of solids and liquids devoid of nuclei governed by first-order anisotropies.

Diastereoselective One-Pot Tandem Synthesis of Chromenopyridodiazepinones through 1,4- and 1,6-Aza-Conjugate Additions/Heterocyclizations

We report an efficient one-pot synthesis of a novel series of chromenopyridodiazepinone polyheterocycles by a catalyst-free nucleo­philic addition of ethane-1,2-diamine to (E,E)-3-[3-(2-hydroxyphenyl)-3-oxoprop-1-en-1-yl]-2-styrylchromones at room temperature under mild conditions. The reaction proceeds by a tandem process involving 1,4- and 1,6-aza-conjugate additions of one amino group of ethane-1,2-diamine to the α,β-unsaturated (3-oxoprop-1-en-1-yl) and the α,β,γ,δ-diunsaturated (2-styrylchromone) carbonyl system of the precursor, followed by imine condensation of the remaining amino group to generate the chromenopyridodiazepinone polyheterocycle. All compounds were characterized by means of one- and two-dimensional NMR spectroscopy and single-crystal X-ray crystallography.

Application of high-speed counter-current chromatography and HPLC to separate and purify of three polyacetylenes from Platycodon grandiflorum.

Three polyacetylenes were isolated and purified from Platycodon grandiflorum A. DC for the first time by high-speed counter-current chromatography using a two-phase solvent system composed of hexane/ethyl acetate/methanol/water (1:31:1:31, v/v/v/v) and high-performance liquid chromatography with an Agilent ZORBAX® SB-C18 column (4.6mm × 150mm, 5 μm). After separation by high-speed counter-current chromatography and high-performance liquid chromatography, we obtained 3.5mg of platetyolin A, 4.1mg of platetyolin B, and 18.1mg of lobetyolin with purities of 97.2, 96.7, and 96.9%, respectively. The purity of each compound was assessed by high-performance liquid chromatography and the chemical structures were evaluated by high-resolution electrospray ionization time-of-flight mass spectrometry and one- and two-dimensional NMR spectroscopy. Among the isolated compounds, platetyolin A and platetyolin B are newly reported compounds.