脯氨酸类N-酰胺衍生物的核磁共振研究

脯氨酸类衍生物结构独特,鲜有报道利用核磁共振（nuclear magnetic resonance,NMR）技术对氨基酸的手性进行鉴别.利用多种NMR技术:1H NMR、1H-1H同核位移相关谱（1H-1H COSY）、1H-1H质子全相关谱（1H-1H TOCSY）、1H-1H核Overhauser效应谱（1H-1H NOESY）、13C NMR、无畸变的极化转移增强法（DEPT135°）、1H-13C检出1H的异核单量子相干（1H-13C HSQC）和1H-13C检出1H的异核多键相关（1H-13C HMBC）,对脯氨酸类N-酰胺衍生物两种构象异构体的1H和13C NMR进行了全归属,确定了室温下在二甲基亚砜（DMSO）中L型和D型的顺反异构体以相同的比例同时存在.     

Geminally activated β-nitrostyrenes in reactions with cyclic β-diketones

The interaction of gem-benzoylnitroethenes and gem-alkoxycarbonylnitroethenes with cyclic β-diketones (dihydroresorcinol and dimedone) occurs as a one-pot process via sequential Ad_N and S_N steps followed by denitration to give functionally substituted hexahydrobenzofurans. The intermediate products of the nucleophilic addition have been isolated in the reactions of gem-acetylnitroethenes with dihydroresorcinol. The structures of the synthesized compounds have been confirmed by IR, ¹H, and ¹³C-{¹H} spectroscopy including the heteronuclear correlation experiments (¹H-¹³C HMQC and ¹H-¹³C HMBC).     

Simulation of 2D H homo- and H-C heteronuclear NMR spectra of organic molecules by DFT calculations of spin-spin coupling constants and H and C-chemical shifts

Simulation of 2D ¹H homo- and ¹H-¹³C heteronuclear NMR spectra of organic molecules are here suggested as a tool in the structure elucidation of organic compounds. DFT calculations of ¹H and ¹³C chemical shifts are performed on a sample compound, the ethyl ester of the exo-2-norbornanecarbamic acid, with the mPW1PW91 method using the 6-31G(d) basis set, following a full optimization of the geometry. Homo and heteronuclear spin-spin coupling constants are also calculated, providing full prediction of the common 2D ¹H-¹H COSY, 2D ¹H-¹³C HSQC, and 2D ¹H-¹³C HMBC.     

Synthesis and 1H, 13C and 15N NMR characterisation of substituted Pyrazolo[4,3-c]quinolines and related compounds

A wide range of novel and known alkyl substituted pyrazolo[4,3-c]quinolines and related compounds were synthesized. Some of these compounds can undergo tautomerism and differences have been noted in the structural assignments already published. For each of these compounds, a complete assignment was made using ¹H, ¹³C and ¹⁵N one- and two-dimensional NMR measurements, including NOESY, COSY, ¹H-¹³C HSQC and ¹H-¹³C HMBC. ¹H-¹⁵N HMBC NMR has proved crucial in determining the relevant tautomeric and protonated state of the compounds.     

Synthesis and structure of β-aryl-α-nitroacrylates

The method for preparation of ethyl α-nitrocinnamates by nitroacetic acid ester alkenylation with aromatic aldehydes in the presence of acetic acid and β-alanine has been modified. Structures of the prepared compounds have been proved by electronic, IR, ¹H, and ¹³C-{¹H} NMR spectroscopy (including heteronuclear correlation experiments ¹H-¹³C HMQC and ¹H-¹³C HMBC). In solution these compounds exist in the form of Z-isomer; the Z?E isomerization is observed in the case of the compound containing strong electron-donor group [N(CH₃)₂] at benzene ring.     

Quantification of multiple compounds containing heterogeneous elements in the mixture by one‐dimensional nuclear magnetic resonance spectroscopy of different nuclei using a single universal concentration reference

One‐dimensional (1D) quantitative NMR (qNMR) is a useful tool for concentration determination due to its experimental simplicity and the direct proportionality of the integrated signal area to the number of nuclei spin. For complex mixtures, however, signal overlapping often in one‐dimensional quantitative ¹H NMR (1D ¹H qNMR) spectrum limits the accurate quantification of individual compound. Here, we introduced employing joint 1D qNMR methods of different nuclei, such as ¹H and ³¹P (or/and ¹⁹F), to quantify multiple compounds in a complex mixture using a single universal concentration reference. When the concentration ratio of several compounds containing different elements in a complex mixture is of interest, the result calculated from measured intensities from 1D qNMR of different nuclei is independent of the gravimetric error from the reference. In this case, the common reference also serves as a ‘quantitative bridge’ among these 1D qNMR of different nuclei. Quantitative analysis of choline, phosphocholine, and glycerophosphocholine mixture is given as an example using trimethylphosphine oxide ((CH₃)₃P(O)) as concentration reference. Compounds containing multiple elements, such as tetramethylammonium hexafluorophosphate (N⁺(CH₃)₄PF₆^?), are proposed as the common concentration reference for ¹H, ¹³C, ¹⁵N, ³¹P, and ¹⁹F qNMR for the quantitative analysis of complex mixture containing these different elements. We anticipate that the proposed joint 1D qNMR approach using a universal concentration reference will be a valuable alternative for simultaneous quantification of multiple compounds in a complex mixture due to its accuracy and single and simple sample preparation. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of 13c-labelled [s]-proline and its conformational analysis by nuclear magnetic resonance

In order to analyze completely the ring conformation of [S]-Proline (l-thiazolidine-4-carboxylic acid) this compound has been synthesized with its C_δ atom enriched at 90% in ¹³C. The ¹H-¹H, ¹³C-¹H, ¹³C-¹³C vicinal coupling constants measured at several pH values describe well the geometry of the thiazolidine ring. The results suggest that the ring has an average planar conformation only in a narrow range of pH close to the pK of the amine group. Above and below this pH the ring tends to adopt preferentially the S_γendo and S_γexo puckered conformations respectively. It is concluded that a good correlation exists between the value of the dihedral angle ø and the character S_γendo or S_γexo of the ring.     

2D NMR characterization of poly(ethylene-co-5-vinyl-2-norbornene)

Unsaturated poly(ethylene-co-5-vinyl-2-norbornene) was synthetized using the [Ph₂C(Flu)(Cp)]ZrCl₂ metallocene/methylaluminoxane (MAO) catalyst system. ¹H and ¹³C NMR spectra of the copolymer were assigned by means of DEPT, homonuclear 2D ¹H-¹H COSY, and heteronuclear 2D ¹H-¹³C correlation NMR experiments. The used catalyst system produces mainly isolated 5-vinyl-2-norbornene (VNB) sequences. VNB is incorporated selectively via the cyclic double bond. The unreacted double bond of the copolymer exists in the 5-endo: 5-exo positions (3 : 1). Both isomers of VNB are polymerized with the same propability.     

Design and synthesis of self-included pillar[5]arene-based bis-[1]rotaxanes

Two strategies for the design of new pillar[5]arene-based mechanically self-interlocked molecules (MSMs) are reported here. The first strategy is based on the construction of an intermediate pseudo[1]rotaxane followed by the desired bis-[1]rotaxane. The other one is based on the construction of the desired bis-[1]-rotaxane directly via a condensation reaction through host-guest interactions between a mono-functionalized pillar[5]arene and the axle. This compound has interesting self-assembly properties in methanol and some extended applications of this compound will be reported in the near future.     

盐酸莫西沙星的结构分析研究

报道了盐酸莫西沙星的元素分析、红外光谱(IR) 、紫外光谱(UV) 、质谱(MS) 、氢-氢相关谱(1H-1HCOSY) 、碳谱(DEPT-45、DEPT-90、DEPT-135) 、多键碳氢相关谱(HMBC)等波谱数据,并对特征数据进行了化合物的结构解析。对所有的1H-NMR、13C-NMR谱的信号进行了归属。     

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.     

Precise molecular weight determination and structure characterization of end-functionalized polymers: An NMR approach <Emphasis Type="Italic">via</Emphasis> combination of one-dimensional and two-dimensional techniques

We present here the application of one-dimensional and two-dimensional NMR techniques to characterize the structure of methoxyl end-functionalized polystyrenes (PS). The peaks in ¹H-NMR spectra corresponding to main-chain, side-chain and chain-end groups are assigned by ¹H-¹H gCOSY, ¹H-¹³C gHSQC and gHMBC spectra. For the first time, the spin-lattice relaxation time (T ₁) of protons of the chain-ends is revealed to be affected more by polymer molecular weight (MW) than by the protons of the main-chains and the side-chains (almost independent from MW). As a result, a much higher delay time (d1) for chain-ends (d1 > 20T ₁) is needed for quantitative NMR measurement when using end-group estimation method to obtain the MW of PS, which is in accordance with the value estimated by GPC. An improved method for the polymer MW determination is established, by combination of different NMR techniques to distinguish the peaks, and a large d1 setting to achieve quantitative NMR analysis.     

Triterpene Glycosides of Astragalus and Their Genins. LXVIII. Cycloorbigenin C, a New Cycloartane Genin

The new triterpenoid cycloartane cycloorbigenin C, the structure of which is 23ξ,24ξ-cycloartan-3β,6α,16β,23,24,25-hexaol, was obtained from the aerial part of Astragalus orbiculatus Ledeb. (Leguminosae). The structure of cycloorbigenin C was proved using chemical transformations, IR spectroscopy, electron-impact mass spectrometry, and PMR and ¹³C NMR spectra interpreted using J-modulation and the 2D NMR spectroscopies: ¹H-¹H COSY, TOCSY, ROESY, HSQC, and HMBC.     

Observation of 2izsz order in NMR relaxation studies for measuring cross-correlation of chemical shift anisotropy and dipolar interactions

The cross-correlation spectral density of chemical shift anisotropy and dipolar interactions in isotropic solution of methyl formate is measured using a novel NMR technique designed to monitor the appearance of longitudinal two-spin order 2I_zS_z during inversion recovery. The result is tentatively interpreted in terms of the orientation of the ¹³C-¹H internuclear vector with respect to the principal axes of the ¹³C chemical shift anisotropy tensor of the carboxyl group.     

Assignment of the relative and absolute configurations of acyclic secondary 1,2-diols

The NMR profiles (¹³C-δ, ¹H-δ, ¹H(OH)-δ, and ³J_H,H) of syn- and anti-diols—3a,b in achiral solvents were found to be very similar to each other. Contrarily, their Δδ (Δδ=δ_(R,R)-2−δ_(S,S)-2) behaviors in chiral bidentate NMR solvent (R,R)- and (S,S)-BMBA-p-Me (2) were found to be significantly different. On the basis of this NMR characteristic, a method has been developed to predict both the relative and absolute configurations of acyclic secondary 1,2-diols.     

New C2-symmetric chiral phosphinite ligands based on amino alcohol scaffolds and their use in the ruthenium-catalysed asymmetric transfer hydrogenation of aromatic ketones

Asymmetric transfer hydrogenation processes of ketones with chiral molecular catalysts are attracting increasing interest from synthetic chemists due to their operational simplicity. C₂-symmetric catalysts have also received much attention and been used in many reactions. A series of new chiral C₂-symmetric bis(phosphinite) ligands has been prepared from corresponding amino acid derivated amino alcohols or (R)-2-amino-1-butanol through a three- or four-step procedure. Their structures have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis. ¹H-³¹P NMR, DEPT, ¹H-¹³C HETCOR or ¹H-¹H COSY correlation experiments were used to confirm the spectral assignments. In situ prepared ruthenium catalytic systems were successfully applied to ruthenium-catalyzed asymmetric transfer hydrogenation of acetophenone derivatives by iso-PrOH. Under optimized conditions, these chiral ruthenium catalyst systems serve as catalyst precursors for the asymmetric transfer hydrogenation of acetophenone derivatives in iso-PrOH and act as good catalysts, giving the corresponding optical secondary alcohols in 99% yield and up to 79% ee.     

Studies on the configuration of nitrogenous stereogenic centres in adducts of rhodium(II) tetraacylates with chiral amines: the application of 1H and 13C NMR spectroscopy

The ¹H and ¹³C NMR spectra of enantiomerically pure amines (S)-N,N-dimethyl-1-phenylethylamine, (S)-N-methyl-1-phenylethylamine, (S)-N-ethyl-1-phenylethylamine and (S)-N-ethyl-N-methyl-1-phenylethylamine in the presence of a twofold molar excess of dirhodium(II) tetratrifluoroacetate and dirhodium(II) Mosher’s acid derivatives [(4S) and (4R)] were measured in CDCl₃ as a solvent. The amines having various substituents at the nitrogen atom (H, CH₃ and CH₂CH₃) formed in such conditions as an equilibrium mixture of C_SN_R and C_SN_S 1:1 adducts. The signals of both diastereoisomers were observed in NMR spectra at either room temperature (303 K) or moderately decreased temperatures (263–273 K). The rates of mutual diastereoisomer conversion were estimated by selective inversion recovery experiments and varied from less than 0.1 to ca. 10 s^?1, depending on the ligand and temperature. Analysis of ¹³C NMR data and NOE experimental data resulted in the unambiguous determination of the configuration at the nitrogen atom with respect to the carbon stereogenic centre.Modelling of adduct structures and calculations of molecular energy and NMR parameters (GIAO) using Density Functional Theory (DFT) were performed in order to support the experimental findings. The calculations were carried out using 3-21G//B3LYP (structure optimizing) and 311G(2d,p)/LanL2DZ//B3LYP theory levels (molecular energy and NMR shielding).     

Light-driven interconversion of Pd2L4 cage and mononuclear PdL2 mediated by the isomerization of azobenzene ligand

The lantern-shaped cage Pd₂L₄ and tweezer-like PdL₂ can be synthesized from the trans- and cis-isomer of an azobenzene-containing ligand, respectively, which were characterized by ¹H, ¹³C, ¹H-¹H COSY, DOSY NMR spectroscopies, high-resolution ESI-MS and density function theory (DFT) calculations. The interconversion of Pd₂L₄ and PdL₂ can be achieved via the cis-trans isomerization of the azobenzene unit on the ligand upon alternative irradiation of light 365 nm or 420 nm.     

Triterpene glycosides ofAstragalus and their genins. XLVIII. The structures of cycloalpigenin B and cycloalpioside B

The structures of the new cycloartane methylsteroid cycloalpigenin B and its glycoside cycloalpioside B, isolated fromAstragalus alopecurus Pall. (Leguminosae) have been determined on the basis of chemical transformations with the assistance of¹H and¹³C NMR spectroscopy and 2D NMR¹H-¹H and¹H-¹³C correlations of chemical signals and IR, CD, and electron-impact mass spectrometry. Cycloalpigenin B is 20R,24S-epoxycycloartane-3β,12α,16β,25-tetraol. A transition from cycloalpigenin B to cycloalpigenin A has been achieved. Cycloalpioside B is 20R,24S-epoxycycloartane-3β,12α,16β,25-tetraol 3-O-β-D-xylopyranoside.     

Aldingenin A, new brominated sesquiterpene from red algae Laurencia aldingensis

A new brominated bisabolene derivative, aldingenin A, was isolated from red alga Laurencia aldingensis Saito et Womersley (Ceramiales, Rodophyta). Its structure was determined by analysis of spectroscopic data (¹H and ¹³C NMR, IR, MS), including bidimensional NMR (¹H-¹H COSY, HMQC, HMBC and NOESY) and biogenetic considerations.