Structure of Galactomannans from <Emphasis Type="Italic">Gleditsia delavayi</Emphasis> and <Emphasis Type="Italic">G. aquatica</Emphasis> by <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR Spectroscopy

The structure of galactomannans isolated from seeds of G. delavayi and G. aquatica was studied by ¹H and ¹³C NMR spectroscopy. It was found that the galactomannans consisted mainly of β-1-4-bound mannopyranoses, a part of which was substituted on the C-6 hydroxyl by terminal units of α-galactopyranose.__________Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 12–13, January–February, 2005.     

Stereochemicai study of 7-aryl-1,7,8,8a-tetrahydro-3(2H)indolizinones by1H and13C NMR

Stereochemistry of 7-aryl-1,7,8,8a-tetrahydro-3(2H)-indolizinones was studied by¹H and¹³C NMR. Complete assignment of¹H NMR signals and analysis of¹H-¹H coupling constants were performed using the iterative PANIC program. Values of³ J _6,7,³ J _7,8endo, and⁴ J _5,7 allow one to unambiguously identify the correspondingexo- andendo-stereoisomers. For stereoisomers with exo-orientation of H(7), complete assignment of¹³C NMR signals was performed on the basis of analysis of the¹³C-¹H coupling constants using two dimensional heteronuclear shift-correlating spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 591–593, March, 1996.     

Structure Solution of Nano-Crystalline Small Molecules Using MicroED and Solid-State NMR Dipolar-Based Experiments

Three-dimensional electron diffraction crystallography (microED) can solve structures of sub-micrometer crystals, which are too small for single crystal X-ray crystallography. However, R factors for the microED-based structures are generally high because of dynamic scattering. That means R factor may not be reliable provided that kinetic analysis is used. Consequently, there remains ambiguity to locate hydrogens and to assign nuclei with close atomic numbers, like carbon, nitrogen, and oxygen. Herein, we employed microED and ssNMR dipolar-based experiments together with spin dynamics numerical simulations. The NMR dipolar-based experiments were ¹H-¹⁴N phase-modulated rotational-echo saturation-pulse double-resonance (PM-S-RESPDOR) and ¹H-¹H selective recoupling of proton (SERP) experiments. The former examined the dephasing effect of a specific ¹H resonance under multiple ¹H-¹⁴N dipolar couplings. The latter examined the selective polarization transfer between a ¹H-¹H pair. The structure was solved by microED and then validated by evaluating the agreement between experimental and calculated dipolar-based NMR results. As the measurements were performed on ¹H and ¹⁴N, the method can be employed for natural abundance samples. Furthermore, the whole validation procedure was conducted at 293 K unlike widely used chemical shift calculation at 0 K using the GIPAW method. This combined method was demonstrated on monoclinic l-histidine.     

Structural Refinement of Carbimazole by NMR Crystallography

The characterization of the three-dimensional structure of solids is of major importance, especially in the pharmaceutical field. In the present work, NMR crystallography methods are applied with the aim to refine the crystal structure of carbimazole, an active pharmaceutical ingredient used for the treatment of hyperthyroidism and Grave’s disease. Starting from previously reported X-ray diffraction data, two refined structures were obtained by geometry optimization methods. Experimental ¹H and ¹³C isotropic chemical shift measured by the suitable ¹H and ¹³C high-resolution solid state NMR techniques were compared with DFT-GIPAW calculated values, allowing the quality of the obtained structure to be experimentally checked. The refined structure was further validated through the analysis of ¹H-¹H and ¹H-¹³C 2D NMR correlation experiments. The final structure differs from that previously obtained from X-ray diffraction data mostly for the position of hydrogen atoms.     

Triterpene Glycosides and Their Genins from Astragalus. LXIX. Orbigenin, the First Lanostanoid from Astragalus Plants

The new lanostane methylsteroid orbigenin, the structure of which is 23,24-lanost-9(11)-en-3,7,16,19,23,24,25-heptaol, was isolated from Astragalus orbiculatus Ledeb. (Leguminosae). The structure of the new triterpenoid, the first lanostanoid from plants of the Astragalus genus, was determined using electron-impact mass spectrometry and PMR and ¹³C NMR spectroscopies interpreted using J-modulation, DEPT, and the 2D NMR methods: ¹H-¹H COSY, HSQC, and HMBC.     

Structural Studies and Biological Activity of Plant Triterpenoids from the <Emphasis Type="Italic">Thalictrum</Emphasis> Genus

Structures and chemical and spectral properties of triterpenoids isolated from plants of the Thalictrum genus were systematized for the first time. Features of ¹³C NMR spectra of cycloartane triterpenoids were discussed. Data for the biological activities of certain cycloartane and oleanane triterpenoids were given.__________Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 97–114, March–April, 2005.     

Fabrication of a novel Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MoO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> film modified electrode and its application as an electrochemical sensor of iodate

A novel organic gel film modified electrode was simply and conveniently fabricated by casting Li_xMoO_y and polypropylene carbonate (PPC) onto the surface of a gold electrode. The cyclic voltammetry and amperometry studies demonstrated that the Li_xMoO_y film modified electrode has a high stability and a good electrocatalytic activity for the reduction of iodate. In amperometry, a good linear relationship between the steady current and the concentration of iodate was obtained in the range from 3×10^–7 to 1×10^–4 mol L^–1 with a correlation coefficient of 0.9997 and a detection limit of 1×10^–7 mol L^–1.     

Configurational and conformational preferences in stereoselective acylations of <Emphasis Type="Italic">N</Emphasis>-methyl-1,3-diaminopropane with acyl chlorides

Evidence for a stereoinduction profile of the reaction of N-methyl-1,3-diaminopropane with acyl chlorides has been provided. A possibility to engage in intramolecular CH₂⋯HN and Cl⋯H-N interactions and the proton migration process to the methylamino group leads to the E secondary amides carrying the N⋯H⁺⋯N or N-H⋯N bridges, that show unusual spectroscopic images. Empirical relations between the Δδ _C chemical shift differences, the polarizability of the CO(S) groups and hydrogen bonding strength have been found. Both ¹H-¹⁵N-GHSQC and GHMBC experiments provide insight into the nature of hydrogen bonding and confirm the cyclic array of atoms.     

Triterpene Glycosides of Astragalus and Their Genins. LXX. Orbicoside, the First Lanostane Glycoside from Astragalus Plants

Orbicoside, a new lanostane glycoside and the first from plants of the Astragalus genus, was isolated from the aerial organs of Astragalus orbiculatus Ledeb. (Leguminosae). It has the structure 23,24-lanost-9(11)-en- 3,7,16,19,23,24,25-heptaol 3-O--D-xylopyranoside. The structure of orbicoside was established using PMR and ¹³C NMR, which were interpreted using DEPT and 2D NMR spectroscopies ¹H-¹H COSY, HSQC, and HMBC.     

Rapid and novel discrimination and quantification of oleanolic and ursolic acids in complex plant extracts using two-dimensional nuclear magnetic resonance spectroscopy—Comparison with HPLC methods

A novel strategy for NMR analysis of mixtures of oleanolic and ursolic acids that occur in natural products is described. These important phytochemicals have similar structure and their discrimination and quantification is rather difficult. We report herein the combined use of proton-carbon heteronuclear single-quantum coherence (¹H-¹³C HSQC) and proton-carbon heteronuclear multiple-bond correlation (¹H-¹³C HMBC) NMR spectroscopy, in the identification and quantitation of oleanolic acid (OA) and ursolic acid (UA)in plant extracts of the Lamiaceae and Oleaceae family. The combination of ¹H-¹³C HSQC and ¹H-¹³C HMBC techniques allows the connection of the proton and carbon-13 spins across the molecular backbone resulting in the identification and, thus, discrimination of oleanolic and ursolic acid without resorting to physicochemical separation of the components. The quantitative results provided by 2D ¹H-¹³C HSQC NMR data were obtained within a short period of time (∼14 min) and are in excellent agreement with those obtained by HPLC, which support the efficiency of the suggested methodology.     

Cribrarione A, a new antimicrobial naphthoquinone pigment from a myxomycete Cribraria purpurea

Cribrarione A (1), a new dihydrofuranonaphthoquinone pigment with antimicrobial activity against Bacillus subtilis has been isolated from a myxomycete Cribraria purpurea and its structure was elucidated by spectral data. The ¹H-¹³C long-range couplings through an intramolecular hydrogen bond were clearly observed in the HMBC spectrum of 1.     

Terpenes,Coumarins, and Flavones from <Emphasis Type="Italic">Acacia pennatula</Emphasis>

The chemical analysis of the acetone extract of the dried leaves from Acacia pennatula yielded triacontanol, β-sitosterol palmitate, β-sitosterol, squalene, nonaprenol, norphytane, lupenone, lupeol, daphnetin and catechin, while from the methanol extract were isolated catechin, epigallocatechin, eriodictyol, β-sitosteryl-β-D-glucopyranoside, and stigmasteryl-β-D-glucopyranoside. The structures of all these natural products were established based on their IR, ¹H, and ¹³C NMR and MS data.__________Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 240–241, May–June, 2005.     

2D-NMR of natural products,part V Structure elucidation and complete1H- and13C-assignment of resin acid derivatives

Application of 2D-NMR-techniques including heteronuclear 2D-J-resolved spectroscopy and¹H-¹³C-2 D-shift correlation is used to assign the¹H- and¹³C-resonances of resin acid derivatives.

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2D-NMR von Naturprodukten, 5. Mitt.: Strukturaufklärung und komplette ^1H-und ^13C-Zuordnung von Harzsäure-Derivaten

Zusammenfassung 2D-NMR-Methoden (2D-J-resolved-Spektren,¹H-¹³C-Shiftkorrelations-spektren) erlauben die Zuordnung der¹H- und¹³C-Signale von Harzsäurederivaten.

     

Synthesis,structural and conformational study of selected <Emphasis Type="Italic">N</Emphasis>-substituted phthalimides

This paper synthesizes N-substituted phthalimides derived from nitrogen heterocycles as potential 5-HT₄ ligands by using the Mitsunobu reaction. Conformational studies of some of the new compounds have been conducted using ¹H and ¹³C-NMR spectroscopy. Proton and carbon resonances were achieved through the application of one-dimensional selective NOE, two-dimensional NMR techniques-homonuclear COSY-45, NOESY and heteronuclear ¹H-¹³C HMQC correlated spectroscopy- and double resonance experiments. The crystal structure of compound 1 was determined by X-ray diffraction.     

2D-NMR: Part VI. 2D-INADEQUATE spectral analysis and crystal structure of tricyclo[7.3.1.02,7]tridecane

2-Hydroxy-13-oxo-tricyclo[7.3.1.0^2,7]tridecane derivatives can be obtained by reaction of cyclohexanone with alcohols under alkaline conditions. The unambiguous assignment of all signals of the¹H-NMR- and¹³C-NMR-spectrum is possible by 2D-¹H-¹³C-shift correlation and 2D-INADEQUATE. Compound1 crystallizes in space group P2₁/n witha=8.518 (1),b=14.789 (2),c=19.321 (2) Å, =94.91 (1)°,Z=8,D _c =1.22 Mg cm^–3. The structure refined toR=0.100 andR _w =0.097 for 1719 observed reflections. Two independent molecules form centrosymmetric hydrogen-bonded dimers.Part V:Haslinger E.,Kalchhau-ser H.,Robien W.,Steindl H., Monatsh. Chem.115, 597 (1984).     

Caffeic Acid Decyl Ester: An Antioxidant Principle from <Emphasis Type="Italic">Phleum pratense</Emphasis>

The isolation, comprehensive structure elucidation, and assessment of the free radical scavenging activity of caffeic acid decyl ester (1) from the seeds of Phleum pratense have been described. The RC₅₀ value of this compound in the DPPH assay was found to be 3.60 × 10⁻³ mg/mL, whereas that of positive control, trolox, was 3.07 × 10⁻³ mg/mL.__________Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 237–239, May–June, 2005.     

Chemiluminescence detection of superoxide anion release and superoxide dismutase activity: modulation effect of<Emphasis Type="Italic"> Pulsatilla chinensis</Emphasis>

A novel flow-injection chemiluminescence-based method has been developed for determination of superoxide dismutase (SOD) activity. An in-vitro superoxide anion generation xanthine/xanthine oxidase stable source was established on line with FIA/CL-detection apparatus, for measuring SOD activity. This method can detect SOD in the linear range of 0.002–2.00 U mL^–1 with a detection limit of 0.001 U mL^–1. Another method for detection of superoxide anion is based on the luminol–FeCl₃ chemiluminescence (CL) reaction. This method was used to evaluate superoxide release and SOD activity in rats treated with the traditional Chinese herb Pulsatilla chinensis, which resulted in high clearance of hepatitis B virus (HBV) after treatment of a hepatitis B patient. Interestingly, we found that treatment with Pulsatilla chinensis can specifically increase superoxide release by liver tissues and, at the same time, slightly increase extracellular SOD (ECSOD) activity in plasma; in particular it can markedly increase MnSOD activity in mitochondria in liver tissue. This work revealed a possible mechanism whereby Pulsatilla chinensis prevents possible infection (for example HBV) by specifically increasing superoxide release in the liver and increasing MnSOD activity to minimize superoxide-mediated toxicity.     

Chemical Constituents of Brown Rice Grain (<Emphasis Type="Italic">Oryza sativa</Emphasis>)

One new compound 3,7,11,15,19-pentamethyl-9α,10α,11α,17α,18α-pentahydroxy-n-tetracosan-1-oxy-p-hydroxycaffeoate (oryzaterpenyl caffeoate) (1), together with three known fatty acids linoleic acid, stearic acid and myristic acid were isolated and identified from the rice grain of Oryza sativa. The structure of the new compound was elucidated by 1D and 2D NMR spectroscopic techniques (¹H-¹HCOSY, ¹H-¹³C HETCOR) aided by EI-MS, and IR spectra. __________ Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 535–537, November–December, 2005.     

Use of ICP and XAS to determine the enhancement of gold phytoextraction by <Emphasis Type="Italic">Chilopsis linearis</Emphasis> using thiocyanate as a complexing agent

Under natural conditions gold has low solubility that reduces its bioavailability, a critical factor for phytoextraction. Researchers have found that phytoextraction can be improved by using synthetic chelating agents. Preliminary studies have shown that desert willow (Chilopsis linearis), a common inhabitant of the Chihuahuan Desert, is able to extract gold from a gold-enriched medium. The objective of the present study was to determine the ability of thiocyanate to enhance the gold-uptake capacity of C. linearis. Seedlings of this plant were exposed to the following hydroponics treatment: (1) 5 mg Au L^–1 (2.5×10^–5 mol L^–1), (2) 5 mg Au L^–1+10^–5 mol L^–1 NH₄SCN, (3) 5 mg Au L^–1+5×10^–5 mol L^–1 NH₄SCN, and (4) 5 mg Au L^–1+10^–4 mol L^–1 NH₄SCN. Each treatment had its respective control. After 2 weeks we determined the effect of the treatment on plant growth and gold content by inductively coupled plasma–optical emission spectroscopy (ICP–OES). No signs of shoot-growth inhibition were observed at any NH₄SCN treatment level. The ICP–OES analysis showed that addition of 10^–4 mol L^–1 NH₄SCN increased the concentration of gold by about 595, 396, and 467% in roots, stems, and leaves, respectively. X-ray absorption spectroscopy (XAS) studies showed that the oxidation state of gold was Au(0) and that gold nanoparticles were formed inside the plants.