Heteronuclear Multiple Quantum Coherence Research Articles

Sesamolinol Glucoside, Disaminyl Ether, and Other Lignans from Sesame Seeds

The application of a procedure based on XAD-4 adsorption resin permitted the obtainment of an enriched polyphenolic extract from Sesamum indicum seeds. Chemical analysis of the obtained extract led to the identification of 12 lignans. Among them, 2 lignans, (+)-sesamolinol-4'-O-β-D-glucoside and disaminyl ether, are reported for the first time as natural compounds. Their structure has been determined by spectroscopic methods, mainly by the application of one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) techniques [heteronuclear multiple-quantum coherence (HMQC), heteronuclear multiple-bond correlation (HMBC), and nuclear Overhauser effect spectrometry (NOESY)] and mass spectroscopy. The isolated compounds were evaluated for their antimutagenic activity. Among the tested lignans, the most active lignan was found to be sesamolin, followed by sesamolinol and samin, against H(2)O(2). Additionally, some of the tested lignans showed desmutagenic activity against benzo[a]pyrene (BaP).

Practical choice of 1H– 1H decoupling schemes in through-bond 1H–{X} HMQC experiments at ultra-fast MAS

Three 1H– 1H homonuclear dipolar decoupling schemes for 1H indirect detection measurements at very fast MAS are compared. The sequences require the following conditions: (i) being operable at very fast MAS, (ii) a long T 2 ′ value, (iii) a large scaling factor, (iv) a small number of adjustable parameters, (v) an acquisition window, (vi) a low rf-power requirement, and (vii) a z-rotation feature. To satisfy these conditions a modified sequence named TIlted Magic-Echo Sandwich with zero degree sandwich pulse (TIMES 0) is introduced. The basic elements of TIMES 0 consist of one sampling window and two phase-ramped irradiations, which realize alternating positive and negative 360° rotations of 1H magnetization around an effective field tilted with an angle θ from the B 0 axis. The TIMES 0 sequence benefits from very large chemical shift scaling factors at ultra-fast MAS that reach κ cs = 0.90 for θ = 25° at ν r = 80 kHz MAS and only four adjustable parameters, resulting in easy setup. Long κ cs T 2 ′ values, where T 2 ′ is a irreversible proton transverse relaxation time, greatly enhance the sensitivity in 1H–{ 13C} through-bond J-HMQC (Heteronuclear Multiple-Quantum Coherence) measurements with 1H– 1H decoupling during magnetization transfer periods. Although similar sensitivity can be obtained with through-space D-HMQC sequences, in which 13C– 1H dipolar interactions are recoupled, J-HMQC experiments incorporating 1H– 1H decoupling benefit from lower t 1-noise, more uniform excitation of both CH, CH 2 and CH 3 moieties, and easier identification of through-bond connectivities.

A new highly hydroxylated triterpene from Salvia atropatana Bunge

One new triterpenoid olean-18-ene-1β, 2α, 3β-triol (1) along with four known compounds were isolated from the chloroform extract of the aerial part of Salvia atropatana Bunge. The known compounds were two flavonoids, 5-hydroxy-7,4′-dimethoxyflavone (2) and 5-hydroxy-6,7,4′-trimethoxyflavone (3), an abietane-type diterpene namely taxodione (4) and a phytosterol namely γ -sitosterol (5). The structure of (1) was elucidated by comprehensive spectroscopic analysis including electron ionization-mass spectra (EI-MS), 1H NMR, 13C NMR, distortionless enhancement by polarization transfer (DEPT), H,H correlation spectroscopy (COSY), heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond correlation (HMBC). The structure of known compounds 2–5 were identified by comparison of their spectral data with those reported in the literature.

A new triterpene from Salvia xanthocheila Boiss.

From the chloroform extract of the aerial parts of Salvia xanthocheila, one new triterpene, together with two known diterpenes, two known flavonoids and a phytosterol was isolated. On the basis of comprehensive spectroscopic analyses, including electron ionisation mass spectra, 1H-NMR, 13C-NMR, 1-D nuclear Overhauser effect, distortionless enchancement by polarisation transfer, H,H correlation spectroscopy, heteronuclear multiple quantum coherence, rotating frame Overhauser enhancement spectroscopy spectra and comparison with spectral data of known compounds, the structure of new compounds was established as 1β,3β-dihydroxy-olean-9(11),12-dienyl (1). The five known compounds (2–6) were 7α-acetoxyroyleanone, taxodione, salvigenin, apigenin-7,4′-dimethyl ether and β-sitosterol, respectively. These known structures are isolated from the aerial parts of S. xanthocheila for the first time.

Biomass Fractionation for the Biorefinery: Heteronuclear Multiple Quantum Coherence–Nuclear Magnetic Resonance Investigation of Lignin Isolated from Solvent Fractionation of Switchgrass

Two-dimensional heteronuclear multiple quantum coherence and quantitative (13)C nuclear magnetic resonance spectroscopy are used to identify the structural features of lignin isolated from solvent fractionation of switchgrass at several different severities. The spectra are consistent with a progressive deconstruction of the lignin as the fractionation severity increases, with structural units involved in cross-linking and capping of the bulk lignin polymer removed first, followed by increasing levels of acid-catalyzed, solvolytic cleavage of the bulk lignin. The results show that solvent fractionation conditions between about 120 °C and 0.1 M H(2)SO(4) and 160 °C and 0.025 M H(2)SO(4) are optimal for separating biomass in the biorefinery to give process streams most suitable for biobased fuel and chemical production.

English

A new compound was isolated from the ethyl acetate (EtOAc) fraction of the aerial parts of Myrsine africana. The compound was eluted with mobile phase of EtOAc and n-hexane at a ratio of 0.2:9.8. The structure of the compound was identified with the help of 13C-NMR, 1H-NMR, heteronuclear multiple bond correlation (HMBC), heteronuclear multiple quantum coherence (HMQC), nuclear overhauser effect spectroscopy (NOESY) and correlation spectroscopy (COSY). The crude methanolic extract and various fractions of the aerial parts of the plant were also screened for anti-inflammatory activity. The EtOAc and n-hexane fractions of the plant showed moderate (44.8 and 40.9%, respectively) anti-inflammatory activity, while the rest of the fractions and crude extract showed low activity at concentration of 500 µg/ml against human neutrophils.   Key words: Myrsine africana, anti-inflammatory activity, indomethacin.

Deciphering sulfoglycolipids of Mycobacterium tuberculosis

For 4 decades, in vivo and in vitro studies have suggested that sulfoglycolipids (SGLs) play a role in the virulence or pathogenesis of the tubercle bacilli. However, the SGL structure and biosynthesis pathway remain only partially elucidated. Using the modern tools of structural analysis, including MALDI-time-of-flight MS, MS/MS, and two-dimensional NMR, we reevaluated the structure of the different SGL acyl (di-, tri-, and tetra-acylated) forms of the reference strain Mycobacterium tuberculosis H37Rv, as well as those produced by the mmpL8 knockout strains previously described to intracellularly accumulate di-acylated SGL. We report here the identification of new acyl forms: di-acylated SGL esterified by simple fatty acids only, as well as mono-acylated SGL bearing a hydroxyphthioceranoic acid, which were characterized in the wild-type strain. In a clinical strain, a complete family of mono-acylated SGLs was characterized in high abundance for the first time. For the mmpL8 mutant, SGLs were found to be esterified i) by an oxophthioceranoic acid, never observed so far, and ii) at nonconventional positions in the case of the unexpected tri-acylated forms. Our results further confirm the requirement of MmpL8 for the complete assembly of the tetra-acylated forms of SGL and also provide, by the discovery of new intermediates, insights in terms of the possible SGL biosynthetic pathways.

Purification and Properties of a Novel Phenolic Antioxidant from Radix astragali Fermented by Aspergillus oryzae M29

The Chinese herb Radix astragalus (RA) has been widely used as a dietary supplement in Asia, and there are numerous reports on its bioactivities. However, there are no reports to date regarding the use of Aspergillus spp. in the culture medium of the RA plant for the production of phenolic antioxidants. In this study, utilizing the fungus Aspergillus to ferment the native RA has successfully resulted in a significant increase in the phenolic contents of RA, and the fermented RA also revealed much better antioxidant activity toward 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radicals, hydroxyl radical, superoxide radical and peroxyl radical than those of unfermented RA. Among these phenolics, a potent novel antioxidant was isolated and identified as 3,4-di(4'-hydroxyphenyl) isobutyric acid with a molecular weight of 272, by ESI-MS (electrospray ionization mass), ¹H NMR (nuclear magnetic resonance), ¹³C NMR, DEPT (distortionless enhancement by polarization transfer)-NMR, HMQC (heteronuclear multiple quantum coherence), and HMBC (heteronuclear multiple bond correlation) spectra. These data demonstrated that the solid-state bioprocessing strategy could be an innovative approach to enhance the antioxidant activity of RA.

Investigation of grafting sites of acrylic monomers onto alkyd resins via gHMQC two-dimensional NMR: Part 1

Acrylic monomers were grafted onto alkyds via free radical chemistry. The alkyd was a medium oil soya-based alkyd with glycerol, phthalic anhydride, and tetrahydrophthalic anhydride (THPA) as the other components. To identify the specific graft locations, 1D and 2D NMR spectroscopy techniques were utilized. Gradient heteronuclear multiple quantum coherence (gHMQC) 2D NMR was required to assign the chemical shifts of the 1D carbon and proton NMR spectra. Three acrylic monomers, methyl methacrylate (MMA), butyl acrylate (BA), and methacrylic acid (MAA) were grafted to the alkyd, resulting in either MMA, BA, or MAA modified alkyds. Two-dimensional gHMQC spectra for each system confirm grafting at doubly allylic hydrogens located on the fatty acid chains and the polyol segment of the alkyd backbone. The gHMQC spectra show no evidence of grafting across double bonds on either pendant fatty acid groups or THPA unsaturation sites for any of the monomer choices.

Design, synthesis and antifungal activities of novel pyrrole alkaloid analogs

A series of novel analogs of pyrrole alkaloid were designed and synthesized by a facile method and their structures were characterized by 1H NMR, 13C NMR and high-resolution mass spectrometry (HRMS). The structure of compound 2a was identified by 2D NMR including heteronuclear multiple-quantum coherence (HMQC), heteronuclear multiple-bond correlation (HMBC) and H–H correlation spectrometry (H–H COSY) spectra. Their antifungal activities against five fungi were evaluated, and the results indicated that some of the title compounds showed moderate fungicidal activities in vitro against Alternaria solani, Cercospora arachidicola, Fusarium omysporum, Gibberella zeae and Physalospora piricola at the dosage of 50 μg mL −1. Compound 2a and 3a exhibited good activities against P. piricola at low dosage.

Inhomogeneity-free heteronuclear iMQC

Intermolecular dipolar interactions between proton and carbon spins can be used to indirectly detect carbon spectra with high sensitivity. In this communication, we present a modified sequence that, in addition to the high sensitivity of heteronuclear intermolecular multiple quantum coherence (iMQC) experiments, retains the line narrowing capability characteristic of homonuclear zero-quantum coherences. We demonstrate that this sequence can be used to obtain high resolution 13C spectra in the presence of magnetic field inhomogeneities, both for thermal and hyperpolarized samples, and discuss applications to water-hyperpolarized carbon imaging.

Preparation and characterisation of an equatorial para-adduct of (PhCH2)HC70 from the reaction of C702− with benzyl bromide and H2O: addition effects in the polar and equatorial regions of C70

Benzyl(hydro)[70]fullerene regioisomers with the addends in both the equatorial and polar regions of C(70) have been prepared via the reaction of dianionic C(70) with benzyl bromide and H(2)O. HRMS, UV-vis, (1)H, (13)C, HMQC (heteronuclear multiple quantum coherence) and HMBC (heteronuclear multiple bond coherence) NMR characterisations have shown that the addition in the equatorial region of C(70) affords a new (PhCH(2))HC(70) regioisomer with para-positioned addends across a six-membered ring, which is different from the "polar" regioisomers where the addends have an ortho-addition pattern. (1)H NMR characterisations have shown a much stronger shielding effect for the addends in the equatorial region with respect to the counterparts in the polar region of C(70), while cyclic voltammetry study has shown a surprising positive shift for the first reduction potential of the equatorial regioisomer with respect to those of the polar regioisomer and pristine C(70), suggesting that the equatorial region of C(70) is rather electropositive than electronegative. D(2)O experiment has shown a significant difference of the deuterated product distribution between the equatorial and polar regioisomers, which can be justified by the different acidity of the (PhCH(2))HC(70) regioisomers. Computational calculations have been carried out to rationalize the formation of the C(70)HR regioisomers.

Asterosaponins Isolated from the Starfish Asterias amurensis

Three new asterosaponins 1-3 and four known saponins 4-7 have been isolated from the starfish Asterias amurensis LÜTKEN. By means of high magnetic field 1D- and 2D-NMR ((1)H-(1)H correlation spectroscopy (COSY), total correlation spectroscopy (TOCSY), heteronuclear multiple quantum coherence (HMQC), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond correlation (HMBC), and nuclear Overhauser effect spectroscopy (NOESY)) and MS analyses, the chemical structures of new compounds were determined to be 6α-O-[β-D-fucopyranosyl-(1→2)-β-D-galactopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-D-quinovopyranosyl-(1→3)-β-D-galactopyranosyl]-5α-chol-9(11)-en-23-one-3β-yl sodium sulfate (1), 6α-O-[β-D-fucopyranosyl-(1→2)-β-D-galactopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-D-quinovopyranosyl-(1→3)-β-D-galactopyranosyl]-5α-cholesta-9(11),24-dien-23-one-3β-yl sodium sulfate (2), and 6α-O-[β-D-fucopyranosyl-(1→2)-β-D-galactopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-D-quinovopyranosyl-(1→3)-β-D-galactopyranosyl]-5α-cholest-9(11)-en-23-one-3β-yl sodium sulfate (3). In addition, the NMR data for known saponins 4-7 were completely assigned by extensive 2D-NMR analysis without chemical degradation.

Characterization of Chemical Constituents of <i>Luffa operculata</i>(Cucurbitaceae)

A mixture of new ceramides (1, 2, 3, 4 and 5) together with a binary mixture of ceramides with long chain alkyl (6 and 7), triterpenoid (10) and steroids (11 and 12) have been isolated from bark of the fruits and of the stems of Luffa operculata (Cucurbitaceae). The structures were elucidated by comprehensive spectro- scopic analysis including 1H and 13C NMR, DEPT (distortionless enhancement by polarization transfer), COSY (correlated spectroscopy), HMQC (heteronuclear multiple quantum coherence), HMBC (heteronu- clear multiple bond connectivity), IR (infrared), HR-ESI-MS (electrospray ionization-high resolution mass spectra) and LR-MS (low resolution electron ionization mass spectra) experiments. All the ceramides are reported for the first time in Cucurbitaceae and this is the first report of the rare triterpene 10 isolated from Luffa operculata. The ceramides 6 and 7 showed a high acetylcholine esterase inhibitory effect.

Microbial Transformation of Isopimpinellin by Glomerella cingulata

Microbial transformation studies conducted on isopimpinellin (1) by the fungus Glomerella cingulata have revealed that 1 was metabolized to give the corresponding reduced acid, 5,8-dimethoxy-6,7-furano-hydrocoumaric acid (2). The structure of metabolite 2 was elucidated by high-resolution mass spectrometry (HR-MS), extensive NMR techniques, including (1)H NMR, (13)C NMR, (1)H-(1)H correlation spectroscopy (COSY), heteronuclear multiple quantum coherence (HMQC) and heteonuclear multiple bond coherence (HMBC). The biotransformed product 2 showed weak a in vitro β-secretase (BACE1) inhibitory effect.

Chromanols from Sargassum siliquastrum and their antioxidant activity in HT 1080 cells.

Six meroterpenoids (compounds 1-6) of chromene class, including three known compounds (1-3), were isolated from Sargassum siliquastrum. The structure of these compounds was established by extensive 2D-NMR experiments such as (1)H gradient double quantum filtered correlation spectroscopy (gDQCOSY), total correlation spectroscopy (TOCSY), nuclear Overhauser effect spectroscopy (NOESY), gradient heteronuclear multiple quantum coherence (gHMQC), and gradient heteronuclear multiple bond correlation (gHMBC), and by comparison with published spectral data. The antioxidant activity of these compounds was evaluated by various antioxidant tests, such as scavenging effects on generation of intracellular reactive oxygen species (ROS), increments of intracellular glutathione (GSH) level, and inhibitory effects on lipid peroxidation in human fibrosarcoma HT 1080 cells. Compounds (1-6) significantly decreased generation of intracellular ROS and inhibited lipid peroxidation while they increased levels of intracellular GSH at a concentration of 5 µg/ml.

Structural characterisation of phosphate materials: new insights into the spatial proximities between phosphorus and quadrupolar nuclei using the D-HMQC MAS NMR technique

We show in this article how the spatial proximity between phosphorus and quadrupolar nuclei can be efficiently and easily investigated with the D-HMQC (Dipolar Hetero-nuclear Multiple-Quantum Coherences) NMR technique. Compared to the commonly used CP-HETCOR (Cross-Polarisation HETero-nuclear CORrelation) sequence, the D-HMQC pulse scheme exhibits a higher sensitivity and a better robustness with respect to spinning frequency, electronic shielding and quadrupole interaction, and thus does not require time-consuming and complicated optimisation procedures. The advantages of the D-HMQC are demonstrated in this article through the acquisition of (31)P/S through-space two-dimensional correlation NMR spectra providing unreported structural information on (i) a sodium alumino-silicate glass doped with only 3% of P(2)O(5), (ii) a potassium boro-phosphate glass containing BO(3) and BO(4) groups and (iii) a crystalline zirconium vanado-phosphate. All these systems, representative of the most important mixed phosphate network materials, cannot be correctly investigated with the conventional CP-HETCOR NMR technique.

Investigation of wheat straw biodegradation by Phanerochaete chrysosporium

Production of renewable fuels and chemicals from biomass requires an efficient pretreatment technology, which further depends on better understanding of biodegradation process of such lignocellulosic biomass. The biodegradation of wheat straw by Phanerochaete chrysosporium was investigated in this study. The fungal secretomes and compositional, functional groups and structural changes of the fungal spent wheat straw lignin were determined. The result showed ∼ 30% loss of total lignin within three weeks of biopretreatment by P. chrysosporium. Detailed structural analysis through two dimentional heteronuclear multiple quantum coherence nuclear magnatic resonance (2D HMQC NMR) of the pretreated lignin (acetylated) revealed low abundance of substructures D (dibenzodioxacin) and E (cinnamyl alcohol). Further, analysis of lignin by Fourier Transmission Infrared (FTIR) and Pyrolysis Gas Chromatography/Mass Spectrometry (Py-GC/MS) demonstrated the significant decrease of guaiacyl (G) units. The results support the previous findings in the biodegradation of wheat straw analyzed by 13C cross polarization magic angle spinning (CPMAS). Revealing the characteristic behavior of P. chrysosporium mediated biomass degradation, the information presented in this paper offers new insights for understanding the biological lignin degradation of wheat straw by P. chrysosporium.

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).

SEQUENCE AND STRUCTURAL ANALYSIS OF κ-CARRAGEENAN-DERIVED OLIGOSACCHARIDES BY TWO-DIMENSIONAL NUCLEAR MAGNETIC RESONANCE1

κ-Carrageenan was hydrolyzed with mild hydrochloric acid and separated into a series of oligosaccharides, the sequences and structures of which were investigated by double-quantum filtered correlation spectroscopy (DQF-COSY), total correlation spectroscopy (TOCSY), heteronuclear multiple-quantum coherence (HMQC), and heteronuclear multiple-bond correlation (HMBC) techniques, respectively. The chemical structures and conformations of the individual sugar residues were identified, as well as the sequential connectivity of the oligosaccharides. The interresidue nuclear Overhauser effects (NOEs)/rotating frame Overhauser effects (ROEs) revealed an ordered helical structure of the carrageenan oligosaccharide chains. Therefore, a general two-dimensional (2-D) NMR methodology for the unambiguous sequence and structure analysis of κ-carrageenan-derived oligosaccharides was established in this study.