冬凌草甲素和冬凌草乙素与谷胱苷肽的迈克尔加成反应

采用紫外光谱动力学方法测定了抗肿瘤对映贝壳杉烯二萜冬凌草甲素和冬凌草乙素与谷胱苷肽迈克尔加成反应的级数、速率常数和平衡常数.结果表明,冬凌草甲素和冬凌草乙素与与谷胱苷肽迈克尔加成反应符合二级动力学方程,25℃下的速率常数分别为16.196 0L·(mol·s)-1和7.480 5L·(mol·s)-1,平衡常数分别为177.98L/mol和85.60L/mol.冬凌草甲素与谷胱苷肽迈克尔加成反应速率和反应程度均比冬凌草乙素的大得多,反应活性更好.对映贝壳杉烯二萜通过与机体发生迈克尔加成反应而产生抗肿瘤作用;因此,冬凌草甲素可能比冬凌草乙素具有更好的抗肿瘤活性.     

冬凌草甲素的结构修饰与生物活性研究进展

冬凌草甲素为对映贝壳杉烷类二萜化合物,主要分布在中草药冬凌草及相关植物中,具有多种生物活性如抗肿瘤、抗菌、抗炎等.主要综述了2000年以来冬凌草甲素的多功能结构修饰,表明冬凌草甲素结构修饰是提高冬凌草甲素药理活性的一种有效途径.     

2D NMR方法研究抗癌药物冬凌草乙素的结构与谱线归属

用异核化学位移相关谱、远程异核化学位移相关谱和同核化学位移相关谱等现代核磁共振技术对抗癌中草药冬凌草中分离出的抗癌、抗菌有效成分冬凌草乙素分子的~(13)C和~1H化学位移进行了完全归属,为冬凌草乙素分子溶液中的三维空间结构研究提供了可靠的结构参数。     

冬凌草甲素葡萄糖苷的合成

为研究冬凌草甲素的构效关系,合成生物活性更高的化合物,以冬凌草甲素为先导化合物,通过对其进行选择性保护,再进行糖苷化,最后脱保护,经五步反应,以23.0%的总收率,合成了冬凌草甲素-6-O-β-D-葡萄糖苷,并得到一系列冬凌草甲素衍生物,它们的结构经IR,1H NMR,MS和元素分析确证.     

关于冬凌草甲素晶体结构的讨论

通过对《结构化学》，第１１卷，第６期，第４７１－４７５页报道的冬凌草甲素结构参数的分析，提出与原文不同的结论，即：冬凌草甲素晶体结构不对称单元中的两个冬凌草甲素分子的绝对构型相同。     

冬凌草甲素的电化学性质及电分析方法研究

研究了抗癌药物冬凌草甲素在悬汞电极上的电化学行为。在NaAc-NaOH(pH 7.8)的缓冲溶液中,冬凌草甲素有一受吸附控制的还原峰,峰电位为-1.150 V,峰电流与冬凌草甲素浓度在7.25×10-7~1.01×10-5mol/L范围内有良好的线性关系,检出限为1.45×10-7mol/L(S/N=3)。对冬凌草片剂实际样品中冬凌草甲素含量测定,结果满意。     

贵州冬凌草的对映－贝壳杉烷二萜化合物

从贵州产冬凌草[Isodon rubescens (Hemsl.) Hera]中分离得到12个6，7－断 裂－7，20－内酯－对映－贝壳杉烷二萜化合物，经波谱分析鉴定了它们的结构， 其中有7个新化合物，分别命名为贵州冬凌草乙素～辛素（guidongnins B～H, 1～ 7)，以及卢氏冬凌草甲素（8）、卢氏冬凌草乙素（9）、贵州冬凌草素（10）、狭 叶香茶菜素(angustifolin, 11)和6－表香茶菜素（6-epiangustifolin, 12)等5个 已知化合物。另外，将作者原命名的贵州冬凌草素（guidongnin, 10）更名为贵州 冬凌草甲素(guidongnin A, 10)，并利用二维核磁区振波谱技术修订了卢氏冬凌草 乙素的结构。     

贵州冬凌草的对映－贝壳杉烷二萜化合物

从贵州产冬凌草[Isodon rubescens (Hemsl.) Hera]中分离得到12个6，7－断 裂－7，20－内酯－对映－贝壳杉烷二萜化合物，经波谱分析鉴定了它们的结构， 其中有7个新化合物，分别命名为贵州冬凌草乙素～辛素（guidongnins B～H, 1～ 7)，以及卢氏冬凌草甲素（8）、卢氏冬凌草乙素（9）、贵州冬凌草素（10）、狭 叶香茶菜素(angustifolin, 11)和6－表香茶菜素（6-epiangustifolin, 12)等5个 已知化合物。另外，将作者原命名的贵州冬凌草素（guidongnin, 10）更名为贵州 冬凌草甲素(guidongnin A, 10)，并利用二维核磁区振波谱技术修订了卢氏冬凌草 乙素的结构。     

高效液相色谱法测定血液中冬凌草甲素的含量

冬凌草甲素(Rubescensin A,以下简称甲素),是从植物冬凌草中经提取分离出的一种抗癌有效成分。它具有多方面的药理作用,目前临床上用于治疗食管癌、肝癌和胰腺癌等。为给临床合理用药提供理论依据,研究甲素的动力学特性,准确测出服药后血液中甲素浓度随时间变化的规律显得十分重要。对药物和生理体液中微量成分的分离和测定,目前大部分都采用高效液相色谱法。但血液中甲素的高效液相色谱测定,国     

鄂西香茶菜甲素立体、区域和化学选择性转变成冬凌草甲素

本文报道首次将鄂西香茶菜甲素(3)用立体、区域和化学选择性的反应转变成冬凌草甲素(oridonin,1),7步反应总产率为9％.     

J-coupling constants for a trialanine peptide as a function of dihedral angles calculated by density functional theory over the full Ramachandran space

We present 13 (3)J, seven (2)J and four (1)J coupling constants (24 in all) calculated using B3LYP/D95** as a function of the φ and ψ Ramachandran dihedral angles of the acetyl(Ala)(3)NH(2) capped trialanine peptide over the entire Ramachandran space. With the exception of three of these J couplings, all show significant dependence upon both dihedral angles. For each J coupling considered, a two dimensional grid with respect to φ and ψ angles can be used to interpolate the values for any pair of φ and ψ values. Such simple interpolation is shown to be very accurate. Most of these calculated J couplings should prove useful for improving the accuracy of the determination of peptide and protein structures from NMR measurements in solution over that provided by the common procedure of treating the J couplings as functions of a single dihedral angle by means of Karplus-type fittings.     

Force-field parametrization of retro-inverso modified residues: Development of torsional and electrostatic parameters

Summary Torsional and the electrostatic parameters for molecular mechanics studies of retro-inverso modified peptides have been developed using quantum mechanical calculations. The resulting parameters have been compared with those calculated for conventional peptides. Rotational profiles, which were obtained spanning the corresponding dihedral angle, were corrected by removing the energy contributions associated to changes in interactions different from torsion under study. For this purpose, the torsional energy associated to each point of the profiles was estimated as the corresponding quantum mechanical energy minus the bonding and nonbonding energy contributions produced by the perturbations that the variation of the spanned dihedral angle causes in the bond distances, bond angles and the other dihedral angles. These energies were calculated using force-field expressions. The corrected profiles were fitted to a three-term Fourier expansion to derive the torsional parameters. Atomic charges for retro-inverso modified residues were derived from the rigorously calculated quantum mechanical electrostatic potential. Furthermore, the reliability of electrostatic models based on geometry-dependent charges and fixed charges has been examined.     

NMR spectra and structures of oridonin derivatives complexes with β‐cyclodextrin

Complexations between three oridonin derivatives and β‐cyclodextrin (βCD) were studied by nuclear magnetic resonance (NMR) method. Job's plots for complexes were depicted by ¹H NMR spectra chemical shifts, which proved the 1:1 stoichiometry inclusion complex formation between each derivative and βCD. Two‐dimensional rotating frame overhauser effect spectroscopy (2D ROESY) support the above conclusion and also proved that ring A of each oridonin derivative deeply enters into hydrophobic cavity from the wider rim and the other parts are outside the cavity. Apparent formation constants (K_a) of complexes between three oridonin derivatives and two CDs are calculated according to Scott's equation. Copyright © 2011 John Wiley & Sons, Ltd.     

Etude de la conformation des n-aryl azoles par la methode e.h.t. (extended hückel theory)

E.H.T. calculations of total energy as a function of dihedral angle are presented for 8 N-aryl azoles, six with dihedral angle α and two with dihedral angles α and β. The rotational barriers to the planar and to the orthogonal geometries are discussed. The dihedral angles α or β corresponding to the minimum of the calculated potential curve or surface are important; a uniform correction of these values is necessary to find the experimental values.     

Amide I vibrational circular dichroism of dipeptide: Conformation dependence and fragment analysis

The amide I vibrational circular dichroic response of alanine dipeptide analog (ADA) was theoretically investigated and the density functional theory calculation and fragment analysis results are presented. A variety of vibrational spectroscopic properties, local and normal mode frequencies, coupling constant, dipole, and rotational strengths, are calculated by varying two dihedral angles determining the three-dimensional ADA conformation. Considering two monopeptide fragments separately, we show that the amide I vibrational circular dichroism of the ADA can be quantitatively predicted. For several representative conformations of the model ADA, vibrational circular dichroism spectra are calculated by using both the density functional theory calculation and fragment analysis methods.     

Structure of molecular nanoparticles of petroleum asphaltenes

Ab initio RHF/3-21G** and MM+ molecular mechanics method are employed to calculate the structural chemical parameters of molecular nanoparticles of petroleum asphaltenes. It is found that naphtheno-aromatic rings have a non-planar cup-like character. The values of dihedral angles α ₁ between the planes of aromatic and naphthene rings, which are calculated by the RHF/3-21G** method, are within 156–163°. The values of dihedral angles α₂, which were calculated by the molecular mechanics method, are within 156–164°.     

2D-NMR测定人参皂苷Rb~1溶液中的三维空间结构

本文用一维和二维NMR归属了人参皂苷Rb~1的质子化学位移, 测定了质子偶合常数, 并用相敏NOESY谱测定了分子中质子间的距离。以所测定的化学位移, 偶合常数和质子间距等NMR结构参数为初始数据, 用自编和改进的分子结构计算程序计算出人参皂苷Rb~1在溶液中的三维空间结构。     

Verification of the correlation between geometric parameters of molecules and the parameters of their 1H NMR spectra

The dihedral and bond direction angles between all pairs of vicinal protons of the arabinofuranose residue were calculated from the coordinatees of the hydrogen atoms found by an X-ray study of 3-O-acetyl-β-L -arabinofuranose 1,2,5-orthobenzoate. The values found were compared with those calculated with the help of correlation equations previously proposed by Karplus and recently by the authors, linking the values of those angles with the spin-spin coupling constants of vicinal protons [³J(H,H′)]. It has been found that the best agreement between the angles found crystallographically and calculated from the ¹H NMR data can be achieved using the equation which includes bond direction angles and the sum of the chemical shifts of the protons involved.     

Topological steric effect index and its application

This paper proposed a Topological Steric Effect Index (TSEI) of a group based on the relative specific volume of the reaction center screened by the atoms of the substituents. Investigated results show good correlations between the parameter TSEI and the dihedral angles between both phenyl rings determined by photoelectron spectroscopy for 7 alkylbiphenyl compounds and calculated by a molecular mechanics force field for 78 alkylbiphenyl compounds, whose correlation coefficients are 0.9912 and 0.9845, respectively. The TSEI value of the group is easily calculated and has a clear physical meaning. In addition, it is correlated well to dihedral angles of the 1,2-disubstituted benzene compounds, stereoselectivity of organomagnesium compounds addition to some cyclohexanones and cyclopentanones, and the relative rates of some SN2 reactions.     

The conformations of bicyclo[3.1.0]hexane derivatives by 1H and 13C NMR

The ¹H and ¹³C spectra of bicyclo[3.1.0]hexanes and thujanes have been recorded and assigned. Application of the Karplus equation has yielded dihedral angles, and a computer calculation of the angle of ring buckle as a function of the main dihedral angles has been carried out. The calculated angles of ring buckle agree well with known values in the bicyclo[3.1.0]hexanes, but for 1-methylbicyclo[3.1.0]hexanes and thujanes the results are not self consistent. It is suggested that the bridgehead substituent causes the boat to twist, although the twist can be reduced by an axial methyl substituent on C-4.