Facile Resolution of Racemic 4-Phenyl-2-hydroxy Butyrate via Enzymatic Esterification and Transesterification

The optically active R-4-phenyl-2-hydroxy butyrates were prepared by esterification of the racemic acid or transesterification of the racemic ester catalyzed by lipase from Candida cyclindra (CCL) in organic media.     

Nickel-Catalyzed Kinetic Resolution of Racemic Unactivated Alkenes via Enantio-, Diastereo-, and Regioselective Hydroamination

Kinetic resolution is a powerful strategy for the isolation of enantioenriched compounds from racemic mixtures, and the development of selective catalytic processes is an active area of research. Here, we present a nickel-catalyzed kinetic resolution of racemic α-substituted unconjugated carbonyl alkenes via the enantio-, diastereo-, and regioselective hydroamination. This protocol affords both chiral α-substituted butenamides and syn-β^2,3-amino acid derivatives with high enantiomeric purity (up to 99 % ee) and selectivity factor up to >684. The key to the excellent kinetic resolution efficiency is the distinctive architecture of the chiral nickel complex, which enables successful resolution and enantioselective C−N bond construction. Mechanistic investigations reveal that the unique structure of the chiral ligand facilitates a rapid migratory insertion step with one enantiomer. This strategy provides a practical and versatile approach to prepare a wide range of chiral compounds.     

激光诱导游离色氨酸对血红蛋白反应动力学影响及机理

血红蛋白活性中心铁卟啉具有环状共轭结构,类似于叶绿素,可以吸收特定波长光,光会诱导铁卟啉发生氧化还原反应。研究中发现,紫外区波长光照射血红蛋白的氧化还原反应情况优于铁卟啉特征吸收波长(406 nm)光照射情况。无游离色氨酸(Trp)时,266 nm激光激发后高铁血红蛋白(metHb)、脱氧血红蛋白(deoxy Hb)、氧合血红蛋白(HbO_2)和碳氧血红蛋白(HbCO)均被激发至各自相应的激发态,其Soret带谱峰衰减至基态的时间大致相同;加入游离Trp后,激发态Trp会转移能量到铁卟啉,在直接和间接光能量双重作用叠加下,激发态铁卟啉衰减时间发生变化。metHb、deoxy Hb和HbCO衰减时间明显延长,但对HbO_2影响相对较小。根据瞬态吸收光谱、动力学曲线和紫外-可见吸收光谱综合分析可知,在加入游离Trp前后,4种形态血红蛋白在被入射光激发后,铁卟啉均反应至具有(或近似具有)一空位的铁六配位平面卟啉结构状态。     

激光诱导游离半胱氨酸对血红蛋白反应动力学的影响及机理

血红蛋白(hemoglobin,Hb)是具有环状共轭结构的呼吸蛋白,可以吸收特定波长的光,通过血红素辅基的结构变化,进而影响血红蛋白生物功能的表达。研究中发现,紫外区波长光照射血红蛋白能够引起其结构发生一定的变化,光照实验中加入游离半胱氨酸有助于高铁血红蛋白(methemoglobin,metHb)结构的稳定。266nm光照后高铁血红蛋白、去氧血红蛋白(deoxyhemoglobin,deoxyHb)、氧合血红蛋白(oxyhemoglobin,HbO2)和碳氧血红蛋白(carboxyhemoglobin,HbCO)均被激发至各自相应激发态,其Soret带谱峰衰减至基态的时间大致相同;加入游离半胱氨酸后,半胱氨酸与各激发态铁卟啉发生电子传递,在直接和间接地进行了电子传递后,激发态铁卟啉衰减时间发生变化,metHb、HbO2和HbCO衰减时间明显延长,但deoxyHb变化相对较小。对瞬态吸收光谱、动力学曲线和紫外-可见吸收光谱综合分析可知,4种形态血红蛋白被光激发至各自激发态后,铁卟啉均反应形成具有一空位的六配位平面结构状态。     

激光诱导游离色氨酸对血红蛋白反应动力学影响及机理

血红蛋白活性中心铁卟啉具有环状共轭结构,类似于叶绿素,可以吸收特定波长光,光会诱导铁卟啉发生氧化还原反应。研究中发现,紫外区波长光照射血红蛋白的氧化还原反应情况优于铁卟啉特征吸收波长(406 nm)光照射情况。无游离色氨酸(Trp)时,266 nm激光激发后高铁血红蛋白(metHb)、脱氧血红蛋白(deoxyHb)、氧合血红蛋白(HbO₂)和碳氧血红蛋白(HbCO)均被激发至各自相应的激发态,其Soret带谱峰衰减至基态的时间大致相同;加入游离Trp后,激发态Trp会转移能量到铁卟啉,在直接和间接光能量双重作用叠加下,激发态铁卟啉衰减时间发生变化。metHb、deoxyHb、和HbCO衰减时间明显延长,但对HbO₂影响相对较小。根据瞬态吸收光谱、动力学曲线和紫外-可见吸收光谱综合分析可知,在加入游离Trp前后,4种形态血红蛋白在被入射光激发后,铁卟啉均反应至具有(或近似具有)一空位的铁六配位平面卟啉结构状态。     

Biocatalytic Synthesis of Optically Active Hydroxyesters via Lipase-Catalyzed Decarboxylative Aldol Reaction and Kinetic Resolution

A two-step sequential biocatalytic process for the synthesis of chiral hydroxyesters that combines a lipase-catalyzed decarboxylative aldol reaction followed by kinetic resolution has been developed. The excellent combination of conventional and unconventional functions provides an attractive route for expanding the applications of biocatalysis.     

The Kinetics and Mechanism of the Reaction of Onium Cyclopentadienylides with Tetrahalo-p-Benzoquinones

Abstract

The reaction of triphenylphosphonium cyclopentadienylide (1) with halogen-substituted p-benzoquinones (4) is shown to give a new class of dipolar (zwitterionic) dyes (5) containing phosphorus. The general structure of these molecules has been investigated by a combination of mass spectrometry and multinuclear (¹H, ^l3C and 3l^P) nmr using the specialist techniques of DEPT spectroscopy, homonuclear (COSY) and heteronuclear, 2-D nmr. In addition, stopped-flow (uv/vis) techniques have been used to study the kinetics of the reactions and hence demonsrate that the rate-limiting step is nucleophilic addition of the ylid to the quinone, followed by a rapid loss of halide ion. The mechanism follows the classical pattern associated with nucleophilic aromatic substitution in activated aryl halides.     

邻氨基酚萃取催化光度法测定痕量钒及其催化反应机理

研究了在ｐＨ３．５的弱酸性介质中，痕量钒（Ｖ）能催化溴酸钾氧化邻氨基酚的指示反应，用萃取平衡控制反应时间和水相中邻氨基酚的浓度及反应程度，通过测量４２４ｎｍ下有机相的吸光度，建立了萃取催化光度法测定钒的新方法，方法的线性范围为０．００１０～０．３０ｍｇ／Ｌ检出限为１．０×１０＾－６ｇ／Ｌ用于人发，煤和岩石中痕量钒的测定，结果满意，此外，还探讨了反应机理，建立了动力方程。     

The Kinetics and Mechanism of the Reversible Chain Reaction of Quinone Imine with Hydroquinone

The kinetics of the reaction of N-phenyl-1,4-benzoquinone monoimine with 2,5-di-tert-butyl-1,4-hydroquinone in chlorobenzene was studied at 298.2 and 340 K. The previously proposed chain mechanism was confirmed and discussed. The rate constants and Arrhenius parameters of all elementary steps were determined or reliably estimated. Data on the possibility of radical formation by a termolecular reaction of quinone imine with two 4-hydroxydiphenylamine molecules were obtained, and the rate constant of this reaction was evaluated: k= 0.22 l²mol^–2s^–1at 298 K. The reversibility of all of the most important steps of this chain reaction (chain initiation, propagation, and termination) was demonstrated.     

Kinetic Resolution of the Racemic 2‐Hydroxyalkanoates Using the Enantioselective Mixed‐Anhydride Method with Pivalic Anhydride and a Chiral Acyl‐Transfer Catalyst

A variety of optically active 2‐hydroxyalkanoates and the corresponding 2‐acyloxyalkanoates are produced by the kinetic resolution of racemic 2‐hydroxyalkanoates by using achiral 2,2‐diarylacetic acid with hindered carboxylic anhydrides as the coupling reagents. The combined use of diphenylacetic acid, pivalic anhydride, and (+)‐(R)‐benzotetramisole ((R)‐BTM) effectively produces (S)‐2‐hydroxyalkanoates and (R)‐2‐acyloxyalkanoates from the racemic 2‐hydroxyalkanoates (s‐values=47–202). This protocol directly provides the desired chiral 2‐hydroxyalkanoate derivatives from achiral diarylacetic acid and racemic secondary alcohols that do not include the sec‐phenethyl alcohol moiety by using the transacylation process to generate the mixed anhydrides from the acid components with bulky carboxylic anhydrides under the influence of the chiral acyl‐transfer catalyst. The transition state that provides the desired (R)‐2‐acyloxyalkanoate from (R)‐2‐hydroxyalkanoate included in the racemic mixture is disclosed by DFT calculations, and the structural features of the transition form are also discussed.     

多元曲线分辨等方法和红外光谱用于二硝基五亚甲基四胺的合成反应机理研究

通过红外光谱在线监测强酸催化下硝酰胺、甲醛和氨水合成二硝基五亚甲基四胺(DPT)的反应过程, 利用渐进因子分析(EFA)、直观推导式演进特征投影法(HELP)和多元曲线分辨-交替最小二乘法(MCR-ALS)等化学计量学方法对反应过程获得的红外光谱信息进行解析, 得到了各组分纯物质的浓度变化曲线和对应的红外光谱, 并把多元曲线分辨-交替最小二乘法与直观推导式演进特征投影法的分析结果进行比较, 得出可相互验证的一致结论, 以此推测出该反应合理的反应机理. 化学计量学方法对在线红外光谱信息的分辨可以快速有效地反映DPT合成过程中各组分的浓度和红外光谱变化情况, 对其反应机理研究具有重要指导意义.     

Enhanced Detection of Sulphur and Phospho-rous Containing Compounds in HPLC-Induc-tively Coupled Plasma Mass Spectrometry Using Chemical Resolution via Hexapole-Based Reaction with Oxygen

The sensitive detection of sulphur and phosphorous-containing compounds using HPLC-ICPMS is difficult due to the high background caused by polyatomic interferences. One potential solution to the problem of polyatomic interferences for S and P is to react the latter with oxygen in the collision hexapole to separate them from interferences eg; (O₂ on S and NOH on P). This has the effect of moving the detection mass from 31 and 32 to 47 and 48 m/z for P and S respectively. This region is clear from interferences thereby providing an increase in the sensitivity of detection for the analytes of approximately 50–100 fold. For omeprazole, a model S containing compound, a limit of detection (LOD) of 800 pg on column was achieved, an increase of ca. 100 fold in sensitivity. Similarly in the case of ZD6126 a phosphorous-containing pro-drug, an increase in sensitivity of 50 times was observed with an LOD of 1 ng on column.     

The Kinetics and Mechanism of the Reaction between Barbituric Acid and Glycidol,Part I: The Products Analysis

The hydroxyalkyl derivatives of barbituric acid (BA) were formed in the reaction between BA and glycidol (GL). The reaction was performed at BA:GL 1:1, 1:2, and 1:4 molar ratios in DMF or without solvent. The progress of reaction was monitored by determination of the epoxide number and IR and NMR spectroscopy. It was found that primary reactive site of BA was C5 and further nitrogen ring atoms. BA was always involved in keto‐enol equilibrium, the latter form being less reactive. The isolated hydroxyalkyl derivatives are useful precursors of oligoetherols with the pyrimidine ring.     

Systematic Investigation of the Kinetic Resolution of 3-Hydroxy Fatty Acid Esters Using Candida antarctica Lipase B (CALB) and the Influence of Competing Oligomerization on the Enantiomeric Ratios

The kinetic resolution of 3-hydroxy fatty acid esters C8:0 to C16:0 with Candida antarctica lipase B shows common plots of the enantiomeric excesses of the product and substrate, respectively, versus the conversion and an enantiomeric ratio E of 27 calculated from ee(p). Differences in E, either calculated from the products or the substrates, could be explained by competing oligomerization as a second substrate-consuming process. This reaction is slow compared to acylation, and the remaining enantiomer was oligomerized.     

The Reaction Mechanism and Kinetics of the Zn2.5VMoO8 Phase Synthesis in the Solid State

Studies on the reaction kinetics and mechanism of the synthesis of the Zn_2.5VMoO₈ compound in the solid state have been carried out in situ in a high-temperature X-ray diffraction attachment. The apparent activation energy, 212±26 kJ mol^-1 was calculated by using the diffusion controlled Ginstling-Brounstein model. There was also determined a temperature dependence of unit cell parameters for Zn₃V₂O₈ and Zn_2.5VMoO₈. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mechanism of Enzymatic Hydrolysis of Poly(butylene succinate) and Poly(butylene succinate‐co‐L‐lactate) with a Lipase from Pseudomonas cepacia

Enzymatic hydrolysis of poly(butylene succinate) (PBS) and poly(butylene succinate‐co‐L ‐lactate) (PBSL) has been studied by using a lipase originated from Pseudomonas cepacia. It has been found that the drawn fibers of PBSL are readily hydrolyzed by the action of the lipase, while those of PBS undergo little enzymatic hydrolysis. Since the polymer films of PBS and PBSL are readily hydrolyzed under the same conditions, the enzymatic hydrolysis should depend not only on the crystallinity but also on the molecular orientation. The molecular weight of the samples gradually decreases with incubation time, because nonspecific hydrolysis occurs on the main chains of both PBS and PBSL even in the absence of lipase. The enzymatic hydrolysis of PBS and PBSL gives 4‐hydroxybutyl succinate (HBS) as the main product with traces of succinic acid and butane‐1,4‐diol together with L ‐lactic acid in the case of PBSL. In addition, the hydrolysis rate of the carboxyl end‐capped PBS is much slower than that of the original or hydroxyl end‐capped PBS. These results imply a hydrolysis mechanism involving the preferential exo‐type chain scission from the carboxyl terminals.

Mass remaining of various PBS and PBSL samples as a function of time.     

The Growth of Phosphonium Gold Nanoparticles in Alkaline Media: Kinetics and Mechanism of the Process

Colloid Journal - It has been found that the addition of ammonia water to a gold sol obtained by the Duff method induces the growth of the gold particles. The growth kinetics of such particles in...     

The Influence of Amines Basicity,Carbonyl and Hydrophosphoryl Compounds Structure on Kinetics and Mechanism of the Kabachnic-Fields Reaction

Abstract

On the basis of kinetic and preparative investigation of the Kabachnic-Fields reaction in the series of substituted benzaldehydes. amines and hydrophosphoryl compounds the united mechanism of the reaction has been suggested, including its both cciminic)) and uhydroxyphosphonatic)) variants, considered previously as strictly alternative