聚丁二烯链中孤立1,2-单元的两种构型

用¹³C-NMR波谱方法研究聚丁二烯的键接序列结构,在归属¹³C-NMR谱(脂碳谱)中各共振吸收峰时,使用经验方法无疑是十分有效的。然而作者仍然发现有两个小峰4'和8'(图1),它们的归属不能从经验方法得到令人满意的解释。最近一张新的聚丁二烯的¹³C-NMR谱图表明,在6峰的低场方向还有另一谱峰、6'峰存在(图2)。6'峰的出现同样不能通过运用经验方法处理聚丁二烯的键接序列结构得到理解。     

Comparison Study of Two Atmospheric Pressure Plasma Jet Configurations for Plasma-Catalyst Development

Plasma Chemistry and Plasma Processing - In this work, we have studied the influences of electrode geometrical shapes on the optical properties of two non-thermal atmospheric pressure plasma jets,...     

两种不同构型的吡唑啉酮衍生物的合成与结构

报道了PMBP-PCH(PCH为2-吡啶甲酰肼)和PMBP-INTH(INTH为异烟酰肼)2种化合物的合成与晶体结构分析,PMBP-PCH属三斜晶系,具有P空间群,a=7.783(2),b=10.993(3),c=12.621(3)?=92.96(2),=103.87(2),g=101.54(2),V=1021.5(5)3,Z=2,Dc=1.307g/cm3,m(MoK?=0.088mm-1,F(000)=421,R=0.0436,wR=0.0937.晶体结构表明,在此分子内形成了一个大的共轭体系,由于分子间氢键力的作用,使它们在晶体中以二聚体的形式存在.PMBP-INTH晶体属单斜晶系,具有P21/c空间群,a=14.083(4),b=13.865(3),c=10.609(2)?=101.66(2)o,V=2028.8(8)3,Z=4,Dc=1.301g/cm3,m(MoK?=0.087mm-1,F(000)=832,R=0.0473,wR=0.0898.此化合物在O(1)原子与邻近分子的N(1)原子之间存在较强的氢键,在结晶的过程中,通过分子间质子迁移,使该化合物形成了1个以N(2)为负电荷中心,N(1)为正电荷中心的两性离子结构,且分子通过此氢键形成了一维链状结构,并沿b轴呈层状堆积.     

A Rapid and Sensitive LC Method for Determination of Diastereomeric Purity of Tenofovir Alafenamide

A rapid and sensitive LC method was developed and validated for the determination of diastereomeric purity of tenofovir alafenamide (GS-7340). Baseline separation with resolution >2.8 was achieved within 17 min on a CHIRALPAK AD-3 (250 × 4.6 mm; particle size 3 μm) column using n-hexane:2-propanol (60:40 v/v) as the mobile phase at a flow rate of 1 mL min^?1. The analytes were detected by UV absorbance at 260 nm. The effects of ethanol, 2-propanol, and temperature on diastereomeric selectivity and resolution of diastereomerism were evaluated. The method was extensively validated and proved to be robust. The recoveries were between 98.17 and 102.84 % with <1.93 % relative standard deviation. The limit of detection and limit of quantitation for GS-7339 were 0.77 and 2.56 μg mL^?1 and for GS-7340 were 0.61 and 2.04 μg mL^?1, respectively. This method was extensively proved to be accurate, stable, rapid, and sensitive for the determination of diastereomeric purity of tenofovir alafenamide (GS-7340) in bulk samples.     

Diastereomeric recognition of chiral foldamer receptors for chiral glucoses

[reaction: see text] Three chiral aromatic hydrazide foldamers have been designed and synthesized, in which two R- or S-proline units were incorporated at the terminals of their backbones. The 1H NMR, circular dichroism (CD), and fluorescent experiments and molecular dynamics simulations revealed that the foldamers adopted a chiral helical conformation and complexed alkylated glucoses in chloroform with a good diastereomeric selectivity.     

圆二色谱研究两个新的呋喃雅槛蓝型倍半萜的绝对构型

前文我们从长梗千里光(Senecio Kaschkarovii)和森林千里光(Senecio Nernenrisis)中分离得到3个10位是羟基的9-氧-呋喃型倍半萜(Ⅰ—Ⅳ),其中Ⅰ和Ⅳ为首次发现的新化合物。这3种化合物A、B环是顺式连接,而6位取代基是β构型,这仅仅是通过它们的核磁共振氢谱与类似化合物对照及NOE差谱确定的。由于此类化合物10位缺少氢,使得用核磁共振氢谱确定A、B环的连接方式尚显论据不足。为进一步证明我们前文的推断的正确性,本文制备     

Unexpected Behavior of Diastereomeric Ions in the GasPhase: A Stimulus for Pondering on ee Measurements by ESI-MS

The most common protocols for the quantitative determination of the enantiomeric excess (ee) of raw mixtures by ESI-MS reveal inadequate in cases where the distribution of diastereomeric derivatives diverges from the ee of original solutions. This phenomenon is attributable to a matrix effect, i.e., to the stereospecific formation of high order noncovalent adducts in the ESI droplets, which alters the actual availability of the diastereomeric species under MS analysis. In this frame, the assumption of classic protocols that the ionization correction factor q is independent on the composition of the mixture submitted to analysis is questionable. An alternative methodology is presented in this paper, which is aimed at circumventing the problem by excluding any chemical derivatization of the original raw mixture. It is based on the measurement of the actual distribution of ESI-formed proton-bound diastereomeric complexes from the enantiomeric mixture through a careful analysis of their reaction kinetics with a suitable reactant.      

Enantioselective Syntheses and Absolute Configurations of Viridiene and Aucantene,Two Constitutents of Algae Pheromone Bouquets

Viridiene ((+)- 6 ; (+)-(3R,4S)-3-((1Z)-1,3-butadienyl)-4-vinylcyclopentene) and aucantene ((+)- 18 ; (+)-(4R,5R)-4-((1E)-1-propenyl)-5-vinylcyclohexene) are constituents of the pheromone bouquets of several brown algae species. Key synthons to the title compounds are optically active γ-lactones with known or experimentally determined absolute configurations. Horse liver alcohol dehydrogenase, which catalyses the oxidation of meso- and racemic non-meso diols to chiral lactones, and pig-liver esterase, which catalyzes the saponification of meso-diesters to chiral half-esters, were utilized for the asymmetric synthesis of such precursors. The racemic non-meso diol rac- 1 is converted to the two stereoisomeric γ-lactones (+)- 2 and (+)- 3 which are readily separated. meso-Diol 12 is oxidized to the chiral γ-lactone (?)- 11 . Its enantiomer (+)- 11 is obtained by enantioselective saponification of the meso-diester 9 with pig-liver esterase. Appropriately designed syntheses lead from these chiral intermediates to both enantiomers (+)- and (?)- 6 of viridiene and (+)- and (?)- 18 of aucantene. In addition, kinetically controlled reduction of the racemic aldehydes rac- 5a and rac- 15 with horse liver alcohol dehydrogenase offers a convenient alternative to the enantioselective preparation of the enantiomers of the two hydrocarbons 6 and 18 . Chromatography of 6 on triacetylated cellulose as a stationary chiral phase confirms the enantiospecificity of the synthetic routes designed.     

Leiocyclocin A and B, Two Cyclopeptides from Goniothalamus leiocarpus

Ongoing phytochemical studies on Goniothalamus species have led to the isolation of a number of annonaceous acetogenins and unusual new styryllactones which were found to possess significant cytotoxic activities against several hunan tumour cell lines1,2. Firstly, cyclopeptides were reported to be isolated from genus Goniothalamus in this paper.Goniothalamus leiocarpus is an evergreen tree which grows in the south of Yunnan, China. Four new anticancer styryllactones3,4 from the stem bark and…     

Configurations and calibration methods for passive sampling techniques

Passive sampling technology has developed very quickly in the past 15 years, and is widely used for the monitoring of pollutants in different environments. The design and quantification of passive sampling devices require an appropriate calibration method. Current calibration methods that exist for passive sampling, including equilibrium extraction, linear uptake, and kinetic calibration, are presented in this review. A number of state-of-the-art passive sampling devices that can be used for aqueous and air monitoring are introduced according to their calibration methods.     

Diastereomeric excess upon cleavage and reformation of diastereomeric alkoxyamines

The thermal reactions of several TEMPO and DEPN (N-(2-methylpropan-2-yl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-aminoxyl) based alkoxyamines were studied by means of (1)H and (31)P NMR spectroscopy aiming to distinguish the contributions of diastereoselective homolysis and coupling to the total equilibrium diastereomeric distribution. The TEMPO-based compounds reveal no diastereomeric excess while DEPN based compounds show a moderate excess both upon homolysis and coupling. The diastereomeric preference of homolysis for DEPN-(propionate-like) adducts does not depend on the ester group and it is mainly affected by the size of beta-substituents. The diastereoselective coupling is sensitive to the total recombination rate constant k(c) and diastereoselectivity increases with the decrease of k(c). Small diastereoselective coupling is found in the recombination of DEPN with sec-butyl isobutyrate radical, where no prochiral centers are formed upon cleavage of corresponding alkoxyamine.