Kinetics of ultrasound-assisted lipase-catalyzed glycerolysis of olive oil in solvent-free system

This work reports experimental kinetic data of solvent-free glycerolysis of olive oil using a commercial immobilized lipase (Novozym 435) under the influence of ultrasound irradiation. The experiments were performed in a mechanically stirred reactor under ultrasound irradiation, evaluating the effects of temperature (50-70 °C), enzyme concentration (2.5-10 wt%) and glycerol to oil molar ratio (0.8:1-3:1). Results show that ultrasound-assisted lipase-catalyzed glycerolysis might be a potential alternative route to conventional methods, as high contents of reaction products, especially monoglycerides, were achieved at mild irradiation power supply (∼130 W) and temperature, in a relatively short reaction time (2 h) and low enzyme content (7.5 wt%). To completeness, two simplified kinetic modeling approaches, based on the ordered-sequential bi bi mechanism and reaction stoichiometry, were employed to represent the experimental data, thus allowing a better understanding of the reaction kinetics.     

溶剂调控布洛芬乙烯酯酶促水解的立体选择性的热力学研究

采用高效液相色谱研究了不同溶剂体系中褶皱假丝酵母菌脂肪酶（CRL）催化布洛芬乙烯酯水解反应的立体选择性.研究发现,在单一溶剂体系中Eyring曲线呈线性,在10~50 ℃的实验温度内均呈S选择性;在混合溶剂体系中Eyring曲线呈非线性,且观察到不同的转变温度（T_inv）.研究还发现：在亲水性有机溶剂二氧六环/水均相混合溶剂体系中,Eyring曲线的T_inv处立体选择性E 值为极小值,在疏水性有机溶剂异辛烷/水两相混合溶剂体系中,T_inv处E 值为极大值,而在氯仿/水两相混合溶剂体系中,随着温度的变化,立体选择性发生了反转.     

Giant Fullerene Polyelectrolytes Composed of C60 Building Blocks with an Octahedral Addition Pattern and Discovery of a New Cyclopropanation Reaction Involving Dibromomalonates

We report here on the facile synthetic access of a new family of bis‐, tetra‐, hexa‐, and heptafullerenes (prototypes I–IV), which can be easily converted into very water soluble polyelectrolytes with up to 60 charges located on their periphery. Their very regioselective formation is based on the use of C_2v‐symmetrical pentakisadducts 3 and hexakisadducts 2 as key intermediates. All fullerene moieties incorporated in these macromolecular structures involve a complete or partial octahedral addition pattern. Tripod‐shaped tetrafullerenes 9 a , b (type II), which can accumulate up to thirty positive or negative charges, are very soluble in acidic or basic water, respectively. Hexafullerenes 13 a , b (type III) were synthesized via isoxazolinofullerenes 10 followed by photolytic cleavage of the isoxazoline group. The giant heptafullerene 1 b (type IV) representing the anionic counterpart of the previously synthesized polyelectrolyte 1 a can store up to 60 negative charges on its periphery within a defined three‐dimensional structure. We also discovered a new cyclopropanation reaction of C₆₀ involving dibromomalonates and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU). This reaction allows even for the highly regioselective formation of hexakisadducts with an octahedral addition pattern without requiring activation with reversibly binding addends such as 9,10‐dimethylanthracene (DMA).     

Mechanism of Copper(I)‐Catalyzed Allylic Alkylation of Phosphorothioate Esters: Influence of the Leaving Group on α Regioselectivity

The mechanism of Cu^I‐catalyzed allylic alkylation and the influence of the leaving groups (OPiv, SPiv, Cl, SPO(OiPr)₂; Piv: pivavloyl) on the regioselectivity of the reaction have been explored by using density functional theory (DFT). A comprehensive comparison of many possible reaction pathways shows that [(iPr)₂Cu]^? prefers to bind first oxidatively to the double bond of the allylic substrate at the anti position with respect to the leaving group, and this is followed by dissociation of the leaving group. If the leaving group is not taken into account, the reaction then undergoes an isomerization and a reductive elimination process to give the α‐ or γ‐selective product. If OPiv, SPiv, Cl, or SPO(OiPr)₂ groups are present, the optimal route for the formation of both α‐ and γ‐substituted products changes from the stepwise elimination to the direct process, in which the leaving group plays a stabilizing role for the reactant and destabilizes the transition state. The differences to the energy barrier for the α‐ and γ‐substituted products are 2.75 kcal mol^?1 with SPO(OiPr)₂, 2.44 kcal mol^?1 with SPiv, 2.33 kcal mol^?1 with OPiv, and 1.98 kcal mol^?1 with Cl, respectively; these values show that α regioselectivity in the allylic alkylation follows a SPO(OiPr)₂>SPiv>OPiv>Cl trend, which is in satisfactory agreement with the experimental findings. This trend mainly originates in the differences between the attractive electrostatic forces and the repelling steric interactions of the SPO(OiPr)₂, SPiv, OPiv, and Cl groups on the Cu group.     

A General and Highly Selective Palladium‐Catalyzed Hydroamidation of 1,3‐Diynes

A chemo‐, regio‐, and stereoselective mono‐hydroamidation of (un)symmetrical 1,3‐diynes is described. Key for the success of this novel transformation is the utilization of an advanced palladium catalyst system with the specific ligand Neolephos. The synthetic value of this general approach to synthetically useful α‐alkynyl‐α, β‐unsaturated amides is showcased by diversification of several structurally complex molecules and marketed drugs. Control experiments and density‐functional theory (M06L‐SMD) computations also suggest the crucial role of the substrate in controlling the regioselectivity of unsymmetrical 1,3‐diynes.     

Screening,isolation and selection of a potent lipase producing microorganism and its use in the kinetic resolution of drug intermediates

Lipases are ubiquitous enzymes that belong to family of serine hydolases with a wide variety of industrial applications. This study reports isolation, screening and identification of enantioselctive lipase producing microorganism for kinetic resolution of racemic alcohols. For this, we collected soil samples from different oil rich environments and we performed primary screening that was by carried out by using MSM-tributryin clear zone assay. The selected samples from first screen were subjected to secondary screening to distinguish lipase producing strains from esterase producing strains using p-nitrophenyl palmitate lipase assay. In tertiary screening, 16 lipase producing strains that were identified in secondary screening were employed for resolution of 5 different (RS)-alcohols. Out of all 16 lipase producing strains, only one strain selectively converted 3 racemic alcohols. Based on morphological, biochemical and physiological characteristics, and 16S rRNA gene sequencing, the strain was identified as Pseudomonas beteli. The strain was found to be S-selective and there been no reports on use of Pseudomonas beteli lipase for kinetic resolution of alcohols. The lipase activity was further increased by media optimization and by improving growth conditions, and production of lipase in shake flask study as well as in laboratory scale fermenter. The optimum time for enzyme production by Pseudomonas beteli was 96 ​h whereas cell mass growth was highest at 72 ​h. Optimum temperature and pH were 30 ​°C and 6, respectively. Beef extract (5 ​g/L), peptone (5 ​g/L), sodium chloride (5 ​g/L), yeast extract (1 ​g/L) and glucose (5 ​g/L) were found as optimum nutrition sources for the cell mass growth and lipase production by Pseudomonas sp. Overall, 3.4 times higher enzyme activity and 2.75 times higher cell mass growth were achieved in bioreactor in comparison to the shake flask study. Lipase having high titer was employed successfully for the kinetic resolution of several drug intermediates.     

Synthesis of Site‐Specifically Phosphate‐Caged siRNAs and Evaluation of Their RNAi Activity and Stability

A complete set of new photolabile nucleoside phosphoramidites were synthesized, then site‐specifically incorporated into sense or antisense strands of siRNA for phosphate caging. Single caging modification was made along siRNA strands and their photomodulation of gene silencing were examined by using the firefly luciferase reporter gene. Several key phosphate positions were then identified. Furthermore, multiple caging modifications at these key positions led to significantly enhanced photomodulation of gene silencing activity, suggesting a synergistic effect. The caging group on both the terminally phosphate‐caged siRNA and the single‐stranded caged RNA has comparatively high stability, whereas hydrolysis of the caged group from the internally caged siRNA was observed, irrespective of the presence of Mg²⁺. Molecular dynamic simulations demonstrated that enhanced hydrolysis of the caging group on internally phosphate‐caged siRNAs was due to easy fragmentation of the caging group upon formation of the pentavalent intermediate of the phosphotriester with attack by water. The caging group in the terminally phosphate‐caged siRNA or single‐stranded caged RNA prefers to form π–π stacks with nearby nucleobases. In addition to providing explanations for previous observations, this study sheds further light on the design of caged oligonucleotides and indicates the direction of future development of nucleic acid drugs with phosphate modifications.     

Mechanistic Study of Unprecedented Highly Regioselective Hydrocyanation of Terminal Alkynes: Insight into the Origins of the Regioselectivity and Ligand Effects

Density functional theory (DFT) calculations were performed to gain insight into the mechanism of the nickel-catalyzed hydrocyanation of terminal alkynes with Zn(CN)₂ and water to exclusively generate the branched nitrile with excellent Markovnikov selectivity. After precatalyst activation to give the LNi(0) active species, the transformation proceeds via the following steps: (1) oxidative addition of H₂O to the LNi(0) provides the intermediate LNi(II)H(OH); (2) ligand exchange of LNi(II)H(OH) with Zn(CN)₂ gives the intermediate LNi(II)H(CN); (3) alkyne insertion to the LNi(II)H(CN) forms the alkenyl nickel complex, followed by the reductive elimination step reaching the final product. This mechanism is kinetically and thermodynamically more favorable than that of the experimental proposed ones. On the basis of the experimental observations, more water molecules cannot further improve the reaction as it has also been rationalized. Furthermore, the origin of the high regioselectivity of the product, the variable effectiveness of the metal mediator as function of ligands, as well as the high yield of the alkyl-substituted alkynes substrates, is analyzed in detail. © 2019 Wiley Periodicals, Inc.     

Stereo‐ and Regioselective Synthesis of Tricyclic Spirolactones by Diastereoisomeric Differentiation of a Collective Key Precursor

A general, parallel, and collective synthesis of 5/5/5‐ and 5/5/6‐ring fusion topologies of tricyclic spiranoid lactones through the controlled cyclizations of easily accessible, common key precursors is described. The rapid composition of key cycloalkyl methylene precursors yielded an assembly of bicyclic diastereoisomeric iodolactones, which were individually converted into a wide range of tricyclic, angularly fused spiranoid lactones in a regioselective and stereodirected fashion through the diastereoisomeric differentiation of a collective key precursor. The critical stereochemical assignment of the bicyclic starting materials, as well as the tricyclic targets, was confirmed by X‐ray crystal structure determination.