致癌性胺离子反应过程中电荷和化学位移的计算

应用原子-键电负性均衡方法中的σπ模型(ABEEMσπ)计算了由致癌性胺离子所参与的反应过程中的电荷分布,所计算出的电荷分布可以和从头算很好的相关联,并且所需要的时间也大大的缩短;同时应用从头计算程序计算致癌性胺离子反应过程中的NMR化学位移.结果表明,在反应过程中电荷的变化和NMR化学位移的变化有很好的对应关系.     

新型松香基酰基亚胺噻唑烷衍生物的合成

以脱氢枞酸或二氢枞酸为起始原料经酰卤化、硫氰酸根加成、有机胺加成异构、浓盐酸催化脱水成环合成了两个新型的松香基酰基亚胺噻唑烷衍生物,产率分别为29％和41.8％,其结构经1H NMR,13C NMR和IR表征.     

线性标度方法计算几个藜芦生物碱的13C NMR化学位移

本文采用几种密度泛函方法计算了环杷明(cyclopamine)的~(13)C NMR化学位移。与实验值比较发现采用B97-2/pcSseg-1的气相优化结构结合SMD溶剂化模型计算获得的~(13)C NMR化学位移最合适。在此基础上,对藜芦中的五种典型生物碱结构(环杷明、介芬胺、藜芦胺、计明胺和棋盘花胺)进行了相应的~(13)C NMR化学位移计算。通过与实验值进行拟合,得到线性标度公式σ=(184.4-σ_(cal))/1.0261。其相关系数R~2=0.9976。此外,理论计算也可以解决化合物中的相似碳的~(13)C NMR化学位移归属困难的问题。线性标度方法获得化学位移对建立天然产物的NMR数据库、匹配结构和解析实验测试数据提供了一种快捷可靠的解决方案。     

锆氢化反应研究III.从亚胺制备N-酰基仲胺

不含α-H的亚胺Ar-CH=N-R可以发生锆氢化还原,当R为正构烷基时,生成中间体ArCH~2N(R)ZrCp~2Cl.后者用酰基化试剂分解,可得到酰基仲胺,其结构已通过化学和物理方法得到证明.     

锆氢化反应研究——Ⅲ.从亚胺制备N-酰基仲胺

不含α-H的亚胺Ar-CH-N-R可以发生锆氢化还原,当R为正构烷基时,生成中间体ArCH_2N(R)ZrCp_2Cl。后者用酰基化试剂分解,可得到酰基仲胺,其结构已通过化学和物理方法得到证明。     

红紫素-18酰亚胺衍生物的合成及其可见光谱的研究

选择脱镁叶绿酸 a甲酯为原料进行 3 位化学修饰和E环改造 .经 3 乙烯基的溴化氢加成和与联苯酚的亲核取代反应 ,完成了 3 位联苯氧基的引入 ;在碱性条件下 ,通过空气氧化将E环转变为环己二羧酸酐形成红紫素 18甲酯衍生物 ;所得氧化产物进而和盐酸羟胺反应 ,经胺解开环和再缩合成环构成N 羟基红紫素 18酰亚胺衍生物 ;对其羟基进行烷基化和酰基化 ,合成出N 取代红紫素 18酰亚胺衍生物 .同时讨论了化学结构变化对分子可见光谱的影响 .所合成新化合物的结构均经UV ,IR ,1 HNMR光谱和元素分析予以确认     

α-苯亚甲氨基苯甲基膦酸酯的1,3-偶极及其负离子的环加成反应

用α-苯亚甲氨基苯甲基膦酸酯与几种亲偶极物进行热及碱催化反应得到含磷酰基与不含磷酰基的加成产物,描述了产品的合成方法和立体化学测定,根据立体化学分析结果,可以认为反应是通过环加成的途径进行的.     

有机和生物晶体固态核磁共振参数的准确预测

理论计算有助于复杂的有机和生物系统光谱的鉴定.对于核磁共振光谱,固体结晶中的化学位移和四极耦合常数(QCC)受到邻近的分子和晶格的氢键和范德华作用较大的影响,从而显示出与气态单体分子不同的NMR参数.因此,在固体晶体NMR参数的理论计算中有必要将氢键和范德华作用这两个因素考虑进来.基于周期性方法,本文采用L-Ala-Gly二肽和硝基苯晶体作为模型体系来考察该方法计算NMR参数的精度.研究结果显示周期结构模型能够将分子间的氢键和范德华作用考虑进来,得到的化学位移和QCC值明显优于传统的单分子模型和超分子模型得到的结果,采用该方法计算的结果能够重现NMR实验结果.     

[60]富勒烯与1,1′-联茚的Diels-Alder加成物的合成与结构表征

通过Diels-Alder环加成反应,发现可控制反应条件,使1,1′-联茚与C60反应,并高产率地得到具有新颖结构的单加成物.用HPLC,FT-IR,FD-MS及1H NMR,13C NMR,HMQC,HMBC等多种波谱技术对其结构进行表征,测得它的两个sp3杂化的桥头碳的化学位移为δC:70.91,证明生成的衍生物为[6,6]闭式环加成.13C NMR谱共给出38个信号,表明C601,1′-联茚衍生物分子具有Cs对称性;此外,还发现单加成衍生物C601,1′-联茚热稳定性好,在四氢呋喃、丙酮等极性溶剂中溶解性好,很适合于在LB膜及光限幅性能方面的研究.     

水辅助的氢转移对一种特殊的亚胺加成物生成过程的重要影响

在笔者实验室发表于J.Org.Chem.的论文(本文参考文献[12])中提出的芳香胺离子与腺苷反应所得到非常特殊的亚胺加成物的生成机理指出,腺嘌呤对4-联苯胺离子中对位碳原子初始进攻是得到非常特殊的亚胺加成物的最可行生成路径,而腺嘌呤对4-联苯胺离子中邻位碳原子初始进攻的其它3个反应路径,由于涉及几个氢转移过程的反应的能垒较高,所以,理论上讲,它们是不能发生的.但是,研究发现,如果在这些氢转移过程中有水作为媒介,它们的能垒会大大的降低,从而可能使腺嘌呤对4-联苯胺离子中邻位碳原子初始进攻的3个反应路径成为对对位碳原子初始进攻路径的竞争性反应路径.     

Theoretical and experimental study of imine-enamine tautomerism of condensation products of propanal with 4-aminobenzoic acid in ethanol

The tautomerism of the reaction products of propanal with 4-aminobenzoic acid in ethanol was studied by J-modulated spin-echo (JMOD) ¹³C NMR spectroscopy and gradient-enhanced heteronuclear (ge-2D) ¹H–¹³C HSQC spectroscopy. The existence of imine and enamine tautomeric forms of the reduced compounds in solution was established. The tautomeric equilibrium of the condensation product of propanal with 4-aminobenzoic acid in ethanol was found to be shifted toward the imine form. Quantum chemical calculations by the density functional theory (DFT) method demonstrated that the 4-(N-propylidene)aminobenzoic acid molecule forms a stronger hydrogen bond with an ethanol solvent molecule compared to the enamine molecule, resulting in a higher stability of the ethanol adduct of azomethine compared to the adduct of enamine.     

Modeling mechanisms of unusual benzene imine n6 adduct formation in carcinogenic reactions of arylnitrenium ions with adenosine

Reaction mechanisms of the unusual benzene imine N6 adduct formation in carcinogenic reactions of arylnitrenium ions with adenosine have been investigated with density functional theory (DFT) and high-level ab initio methods. The DFT calculations indicate that the reaction pathways initiated by attack of adenine at the ortho C site of 4-biphenylylnitrenium ion are favored. However, high-level MP2 and QCISD calculations provide a contrary conclusion, that is the reaction pathways initiated by attack of adenine at the para C site of 4-biphenylylnitrenium ion are more feasible. Comparing with experimental results, the conclusion from high-level ab initio calculations is ultimately supported. The present study makes a theoretical prediction on the final products in the studied reaction, which is in agreement with experimental observations. In addition, this study provides some inspirations to the attacks of arylnitrenium ions at amino group of purines and pyrimidines in similar carcinogenic reactions.     

Ab initio/GIAO-CCSD(T) study of structures, energies, and 13C NMR chemical shifts of C4H7(+) and C5H9(+) ions: relative stability and dynamic aspects of the cyclopropylcarbinyl vs bicyclobutonium ions

The structures and energies of the carbocations C 4H 7 (+) and C 5H 9 (+) were calculated using the ab initio method. The (13)C NMR chemical shifts of the carbocations were calculated using the GIAO-CCSD(T) method. The pisigma-delocalized bisected cyclopropylcarbinyl cation, 1 and nonclassical bicyclobutonium ion, 2 were found to be the minima for C 4H 7 (+) at the MP2/cc-pVTZ level. At the MP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ + ZPE level the structure 2 is 0.4 kcal/mol more stable than the structure 1. The (13)C NMR chemical shifts of 1 and 2 were calculated by the GIAO-CCSD(T) method. Based on relative energies and (13)C NMR chemical shift calculations, an equilibrium involving the 1 and 2 in superacid solutions is most likely responsible for the experimentally observed (13)C NMR chemical shifts, with the latter as the predominant equilibrating species. The alpha-methylcyclopropylcarbinyl cation, 4, and nonclassical bicyclobutonium ion, 5, were found to be the minima for C 5H 9 (+) at the MP2/cc-pVTZ level. At the MP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ + ZPE level ion 5 is 5.9 kcal/mol more stable than the structure 4. The calculated (13)C NMR chemical shifts of 5 agree rather well with the experimental values of C 5H 9 (+).     

Crown Ethers Analogues and their Complexes with NaSCN: Stoichiometry and Stability Constants Determined by 13C NMR Spectroscopy

¹³C NMR spectroscopy was used to study thecomplexation reaction between sodium ion and12-crown-4, 15-crown-5, methylurazolyl-12-crown-4 andmethylurazolyl-15-crown-5 in CD₃OD solutions. Thetype of complexes, the stability constants and therelative chemical shifts have been established byfitting experimental titration curves with theoreticalfunctions of the observed chemical shifts. Thesingle-crystal X-ray diffraction measurements for anew crystalline complex confirmed the stoichiometry ofthe complex.     

Theoretical and experimental 15N NMR study of enamine–imine tautomerism of 4‐trifluoromethyl[b]benzo‐1,4‐diazepine system

The tautomeric structure of 4‐trifluoromethyl[b]benzo‐1,4‐diazepine system in solution has been evaluated by means of the calculation of ¹⁵N NMR chemical shifts of individual tautomers in comparison with the averaged experimental shifts to show that the enamine–imine equilibrium is entirely shifted toward the imine form. The adequacy of the theoretical level used for the computation of ¹⁵N NMR chemical shifts in this case has been verified based on the benchmark calculations in the series of the push–pull and captodative enamines together with related azomethynes, which demonstrated a good to excellent agreement with experiment. Copyright © 2015 John Wiley & Sons, Ltd.     

Carbazolyl nitrenium ion: electron configuration and antiaromaticity assessed by laser flash photolysis, trapping rate constants, product analysis, and computational studies

Laser flash photolysis of 1-(carbazol-9-yl)-2,4,6-trimethylpyridinium tetrafluoroborate generates the carbazolyl nitrenium ion (tau = 333 ns, kobs = 3.0 x 106 M-1s-1) having absorption bands at 570 and 620 nm in CH3CN. The nitrenium ion is found to have reactivity comparable to structurally similar closed-shell diarylnitrenium ions, but spectroscopic evidence favors an open-shell singlet diradical assignment for the observed nitrenium ion. The carbazolyl nitrenium ion is also more reactive than diarylnitrenium ions as a likely result of antiaromatic character. Ab initio and hybrid DFT calculations were performed to address the degree of antiaromaticity in this and similar nitrenium ions through analysis of optimized geometries, nucleus independent chemical shifts, and isodesmic reactions.     

Control of stepwise radial complexation in dendritic polyphenylazomethines

The fourth generation of a dendritic polyphenylazomethine (DPA G4) has 2, 4, 8, and 16 imine groups in the first, second, third, and fourth shells, respectively (total, 30 imine groups). DPA G4 can trap 30 equiv of SnCl(2) molecules, because the imine group is complexed with SnCl(2) at a ratio of 1:1. During addition of 30 equiv of SnCl(2) to DPA G4, four shifts in the isosbestic point were observed in the UV-vis spectra, and the amount of SnCl(2) added in each step is in agreement with the number of imine groups in each shell of DPA G4. This result shows that the complexation of the imine groups in DPA G4 with SnCl(2) occurs stepwise in the order of the first, second, third, and fourth shells. The unique stepwise complexation was also observed in DPA G2 and G3 as two and three shifts of the isosbestic point, respectively. The stepwise complexation was supported by TEM, NMR, and a novel shell-selective reduction (SSR) method for imines. An expansion in the molecular size of DPA G4 by the complexation was revealed by molecular modeling and TEM measurements. The stepwise complexation is caused by the different basicity of the imine groups between the shells, which was supported by the chemical shifts of the peaks attributed to the imine carbons in the (13)C NMR spectra. The gradients in the basicity were controlled by the introduction of electron-withdrawing or -releasing groups to the core of the dendrimers; the core imines were complexed last in DPAs having a 2,3,5,6-tetrafluoro or 2,5-dichlorophenyl core due to the low basicity of the core imines. The different complexation pattern was also clearly confirmed by the SSR method.     

Chemical ionization mass spectrometric characteristics of morphine alkaloids

The ion-molecular reaction behavior of ten morphine alkaloids with several commonly used reagent gases are studied under chemical ionization mass spectrometry conditions. These studies emphasize the correlation of the structural characteristics of the 10 alkaloids with the following four mass spectrometric parameters: (i) mass shifts of the protonated ion as a result of replacing ammonia with deuterated ammonia as the reagent gas, (ii) relative tendencies of the adduct ion and the protonated ion to lose molecules of water, (iii) relative intensity ratio of the adduct ion and the protonated ion and (iv) tendency of a compound to undergo a reduction reaction.     

Effects of formation of an adduct of trialkylpyrazole with CdBr2 in15N NMR

The¹⁵N NMR chemical shifts for the analogous diamagnetic adduct of 3,5-dipropyl-4-ethylpyrazole with cadmium dibromide were measured to obtain reference data for estimating the isotropic paramagnetic NMR shifts of nitrogen in paramagnetic adducts of alkylpyrazoles with transition metal salts. The¹³C and¹H NMR spectra were obtained for the same adduct in conditions of frozen protometallotropic rearrangement of the hydrogen in the NH group and the temperature-dependent NMR spectra of isotopes of Cd were made.A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, Moscow 117813. N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 756–761, June, 1998.     

Experimental and theoretical NMR and IR studies of the side-chain orientation effects on the backbone conformation of dehydrophenylalanine residue

Conformation of N-acetyl-(E)-dehydrophenylalanine N', N'-dimethylamide (Ac-(E)-ΔPhe-NMe(2)) in solution, a member of (E)-α, β-dehydroamino acids, was studied by NMR and infrared spectroscopy and the results were compared with those obtained for (Z) isomer. To support the spectroscopic interpretation, the Φ, Ψ potential energy surfaces were calculated at the MP2/6-31 + G(d,p) level of theory in chloroform solution modeled by the self-consistent reaction field-polarizable continuum model method. All minima were fully optimized by the MP2 method and their relative stabilities were analyzed in terms of π-conjugation, internal H-bonds and dipole interactions between carbonyl groups. The obtained NMR spectral features were compared with theoretical nuclear magnetic shieldings, calculated using Gauge Independent Atomic Orbitals (GIAO) approach and rescaled to theoretical chemical shifts using benzene as reference. The calculated indirect nuclear spin-spin coupling constants were compared with available experimental parameters.