双标记~(13)C,~(15)N_3-呋喃妥因的制备

以双标记13 C,15 N3-氨基脲为原料,先与苯甲醛缩合,继而与氯乙酸乙酯取代、环化,再经盐酸水解反应后与5-硝基糠醛二乙酯反应,最终制得双标记13 C,15 N3-呋喃妥因.产物经红外光谱、高效液相色谱及质谱表征.结果表明,所选用的合成路线反应条件温和,产物总收率高于60%,且同位素丰度不下降;目标产物的化学纯度>99.0%,13 C同位素丰度>98%,15 N同位素丰度>99%.     

Synthesis of 6-15N and 1-15N labeled adenosine monophosphates

A chemical synthesis of 6-¹⁵N and 1-¹⁵N AMPs from 5'-O-acety1-2',3'-O-isopropylideneinosine is reported.     

13C/15N distance determination by CPMAS NMR in uniformly 13C labeled molecules

The REDOR and CPMAS techniques are applied for measuring 13C-15N dipolar coupling constants in glycine. It is shown that the selective CP or SPECIFIC CP technique removes the coherent evolution of the spin system under homonuclear 13C-13C J couplings. While the large coupling constant (approximately 900 Hz) is readily determined because of the presence of large oscillations in the CPMAS dynamics, their absence precludes the measurement of the small coupling constant (approximately 200 Hz). The experimental results and numerical simulations demonstrate that the determination of 13C-15N coupling constants of medium size (<1 kHz) by the CPMAS technique is mainly limited by the strength of the 1H decoupling field and the size of the 13C and 15N chemical shift anisotropies.     

Diode laser spectroscopy of the fundamental bands of 12C14N, 13C14N, 12C15N, 13C15N free radicals in the ground 2 Sigma+ electronic state

Rotationally resolved spectra of the fundamental band of the CN free radical in four isotopic forms have been measured using tunable diode laser absorption spectroscopy. The source of the radical was a microwave discharge in a mixture of isotopically selected methane and nitrogen diluted with argon. The lines were measured to an accuracy of 5 x 10(-4) cm(-1) and fitted to the formula for the vibration rotation spectrum of a diatomic molecule, including quartic distortion constants. The band origins of each of the isotopomers from the five parameter fits were found to be 12C14N: 2042.42115(38) cm(-1), 13C14N: 2000.08479(23) cm(-1), 12C15N: 2011.25594(25) cm(-1), 13C15N: 1968.22093(33) cm(-1) with one standard deviation from the fit given in parenthesis. Some of the lines showed a resolved splitting due to the spin rotation interaction. This was averaged for fitting purposes. The average equilibrium internuclear distance derived from the upsilon = 0 and 1 rotational constants of the four isotopomers is 1.171800(6) A which is in good agreement with the value determined from microwave spectroscopy.     

Nitrogen-15 n.m.r. studies of 13C, 15N labeled arginine

¹⁵N n.m.r. spectra of [¹³C-2, 3-¹⁵N₂-guanidino]arginine and [¹³C, ¹⁵N₂] urea were obtained in D₂O and H₂O at a variety of pH values both with and without proton decoupling. The effects of the proton exchange rate are readily observable in the proton coupled ¹⁵N spectra. When the guanidino group is deprotonated (pK = 12.5), the terminal nitrogens give a single resonance 6.6 ppm downfield of the protonated species, indicating a rapid tautomeric exchange. The observed NH and CN couplings are compared with calculated values, and good agreement is found for ¹J(CN) using a Blizzard–Santry type calculation. The ramifications of the proton exchange on ¹⁵N n.m.r. spectra of amino acids and peptides are discussed.     

13C, 14N, 15N and 17O NMR spectra of nitropyrroles and nitroimidazoles

Carbon, nitrogen and oxygen NMR spectra of some nitro derivatives of pyrrole and imidazole have been investigated. The ¹³C chemical shifts of para-carbons and the ¹⁷O chemical shifts of the nitro group correlate qualitatively with the electron densities on these carbon and oxygen atoms, which in turn depend upon the degree of conjugation of the nitro groups with the heterocyclic ring. Conjugation of several nitro groups with the benzene ring is in most cases not impaired by mutual interactions and the ¹³C shifts show good additivity. Such additivity is much worse in pyrrole and imidazole derivatives. Taken together with the diamagnetic nature of these deviations from additivity, this leads to a possible conclusion about the less pronounced conjugation of the nitro groups with the heterocyclic ring in heterocyclic dinitro derivatives.     

Investigation of the alkylation of nitroazoles with α-haloketones by13C,15N,and14N NMR

General methods have been worked out for the alkylation of nitroazoles with bromoacetone, bromoacetophenone, and diazoacetone in homogeneous media and by phase-transfer catalysis. The structures of the N-acetonylazoles were established by¹³C,¹⁵N, and¹⁴N high-resolution NMR spectroscopy.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1827–1837, August, 1990.     

Synthesis of doubly labeled polyacrylic acid with14C and3H

Polyacrylic hydrogels were¹⁴C- and³H-labeled in three main steps. In the first one, the monomer as sodium salt was¹⁴C-labeled at the carboxyl group via the carbonation of vinylmagnesium bromide and [1-¹⁴C]acrylic acid was obtained, followed by labeling with tritium via isotopic exchange in heterogeneous catalysis. The monomer was purified and its radiochemical purity was analyzed using TLC. In the last step, the hydrogel was obtained through radiopolymerization of the doubly labeled monomer using a⁶⁰Co source. The oligomers and unpolymerized monomers were eliminated from the hydrogel by swelling in water followed by dehydration with methanol.     

15N NMR spectroscopy of labeled alkoxyamines. 15N-labeled model compounds for nitroxide-trapping studies in free-radical (Co)polymerization

Eight (15)N-labeled derivatives of 1-ethoxy-2,2,6,6-tetramethylpiperidine were synthesized in order to investigate the effects of their structural units on (15)N NMR spectra. A single peak is found for each alkoxyamine. The chemical shift depends extensively on the nature of the alpha carbon atom of the alkoxy group. The remote functional group attached to position 4 of the piperidine ring has a smaller but still significant effect. The results of the (15)N NMR measurements are supported by the detection of the N-H and N-C spin-spin coupling from the (1)H and (13)C NMR. The investigated alkoxyamines are model compounds for the radical-trapping products of styryl, methyl methacryloyl, alpha-methylstyryl, and methyl acryloyl radicals by (15)N-labeled nitroxides. The potential of (15)N NMR spectroscopy to analyze such products is discussed. In addition, it is shown that the (13)C chemical shifts of the alpha carbon atom of the alkoxy group fall in an empty part of the (13)C NMR spectrum, which allows the identification of trapped (macro)radicals via natural abundance (13)C NMR.     

Antiviral drug Triazavirin,selectively labeled with 2H, 13C,and 15N stable isotopes. Synthesis and properties

Chemistry of Heterocyclic Compounds - Isotope-labeled antiviral drug Triazavirin containing 2H, 13C, and 15N atoms in its structure has been synthesized. 13C2H3I and KS13CN served as donors of 13C...     

15N13C coupling constants in 15N labelled azaadamantane

The ¹⁵N¹³C coupling constants in ¹⁵N labelled azaadamantane have been measured and interpreted in terms of their conformational dependence as compared with ¹⁵N-quinuclidine.     

Biosynthesis and mass spectral fragmentation pathways of 13C and 15N labeled cytochalasin D produced by Xylaria arbuscula

The fungus Xylaria arbuscula was isolated as an endophyte from Cupressus lusitanica and has shown to be a prominent producer of cytochalasins, mainly cytochalasins C, D and Q. Cytochalasins comprise an important class of fungal secondary metabolites that have aroused attention due to their uncommon molecular structures and pronounced biological activities. Due to the few published studies on the ESI‐MS/MS fragmentation of this important class of secondary metabolites, in the first part of our work, we studied the cytochalasin D fragmentation pathways by using an ESI‐Q‐ToF mass spectrometer coupled with liquid chromatography. We verified that the main fragmentation routes were generated by hydrogen and McLafferty rearrangements which provided more ions than just the ones related to the losses of H₂O and CO as reported in previous studies. We also confirmed the diagnostic ions at m /z 146 and 120 as direct precursor derived from phenylalanine. The present work also aimed the production of structurally diverse cytochalasins by varying the culture conditions used to grow the fungus X. arbuscula and further insights into the biosynthesis of cytochalasins. HPLC‐MS analysis revealed no significant changes in the metabolic profile of the microorganism with the supplementation of different nitrogen sources but indicated the ability of X. arbuscula to have access to inorganic and organic nitrogen, such as nitrate, ammonium and amino acids as a primary source of nitrogen. The administration of 2‐¹³C‐glycine showed the direct correlation of this amino acid catabolism and the biosynthesis of cytochalasin D by X. arbuscula , due to the incorporation of three labeled carbons in cytochalasin chemical structure. Copyright © 2017 John Wiley & Sons, Ltd.     

Probing platinum azido complexes by 14N and 15N NMR spectroscopy

Metal azido complexes are of general interest due to their high energetic properties, and platinum azido complexes in particular because of their potential as photoactivatable anticancer prodrugs. However, azido ligands are difficult to probe by NMR spectroscopy due to the quadrupolar nature of (14)N and the lack of scalar (1)H coupling to enhance the sensitivity of the less abundant (15)N by using polarisation transfer. In this work, we report (14)N and (15)N NMR spectroscopic studies of cis,trans,cis-[Pt(N(3))(2)(OH)(2)(NH(3))] (1) and trans,trans,trans-[Pt(N(3))(2)(OH)(2)(X)(Y)], where X=Y=NH(3) (2); X=NH(3), Y=py (3) (py=pyridine); X=Y=py (4); and selected Pt(II) precursors. These studies provide the first (15)N NMR data for azido groups in coordination complexes. We discuss one- and three-bond J((15)N,(195)Pt) couplings for azido and am(m)ine ligands. The (14)N(α) (coordinated azido nitrogen) signal in the Pt(IV) azido complexes is extremely broad (W(1/2)≈2124 Hz for 4) in comparison to other metal azido complexes, attributable to a highly asymmetrical electric field gradient at the (14)N(α) atom. Through the use of anti-ringing pulse sequences, the (14)N NMR spectra, which show resolution of the broad (14)N(α) peak, were obtained rapidly (e.g., 1.5 h for 10 mM 4). The linewidths of the (14)N(α) signals correlate with the viscosity of the solvent. For (15) N-enriched samples, it is possible to detect azido (15)N resonances directly, which will allow photoreactions to be followed by 1D (15)N NMR spectroscopy. The T(1) relaxation times for 3 and 4 were in the range 5.7-120 s for (15)N, and 0.9-11.3 ms for (14)N. Analysis of the (1)J((15)N,(195)Pt) coupling constants suggests that an azido ligand has a moderately strong trans influence in octahedral Pt(IV) complexes, within the series 2-pic相似文献   

14N and15N NMR spectra of 2-substituted 5-nitrofurans

The¹⁴N and¹⁵N NMR spectra of a number of 2-substituted 5-nitrofurans were studied. On the basis of experimental data it was concluded that there is considerable π-electron density on the nitrogen atom of the nitro group. A linear relationship between the chemical shifts in the¹⁴N NMR spectra and the frequencies of the asymmetrical deformation vibrations of the nitro group in the IR spectra was found for the series of investigated 5-nitrofurans. The observed¹⁵N-H spin-spin coupling constants showed that in the 5-nitrofuran molecule transmission of spin information through the ring oxygen atom to the H₂ nucleus is appreciably greater than through the carbon atom to the H₄ nucleus. It was established by measurement of the¹⁵N NMR spectra that the crude adduct formed in the nitration of furfural diacetate with acetyl nitrate is a mixture of trans and cis isomers of 5-nitro-2-acetoxy-2,5-dihydrofurfural diacetate in a ratio of 7∶1. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 741–743, June, 1980.     

High-yield synthesis of 14C labeled alicyclic amino acids with high specific radioactivity using potassium (14C) cyanide

In order to study the tumor specificity of synthetic nonmetabolizing amino acids, 10 different 14C labeled alicyclic amino acids (3a-3j) were synthesized in high yield and with high specific radioactivity. Carbon-14 labeled alicyclic hydantoins (2a-2j) were synthesized from a small amount of radioactive potassium [14C] cyanide and corresponding ketones (1a-1j). Th 14C hydantoins (2a-2j) thus obtained were hydrolyzed without isolation to give 14C labeled alicyclic amino acids (3a-3j). The overall radiochemical yields of the amino acids (3a-3j) from potassium [14C] cyanide were 55.6-93.2% with radiochemical purity more than 99%. Specific activities of these 14C labeled compounds (3a-3j) were 209- 250 MBq/mmol (5.66-6.75 mCi/mmol). When non-radioactive potassium cyanide was not added as a carrier, 1-aminocyclopentane[14C]-carboxylic acid (3b) and 1-aminocyclooctane[14C]carboxylic acid (3e) were synthesized in the yield of 64.9 and 19.0% respectively with the specific activity exceed more than 1.85 GBq/mmol (50mCi/mmol).