scholarly journals Electrophilic Sulfur Reagent Design Enables Catalytic syn-Carbosulfenylation of Unactivated Alkenes

Author(s):  
Zi-Qi Li ◽  
Yilin Cao ◽  
Taeho Kang ◽  
Keary Engle

A multi-component approach to structurally complex organosulfur products is described via the nickel-catalyzed 1,2-carbosulfenylation of unactivated alkenes with organoboron nucleophiles and tailored organosulfur electrophiles. Key to the development of this transformation is the identification of a modular N-alkyl-N-(arylsulfenyl)arenesulfonamide family of sulfur electrophiles. Tuning the electronic and steric properties of the leaving group in these reagents controls pathway selectivity, favoring three-component coupling and suppressing side reactions, as examined via computational studies. The unique syn-stereoselectivity differs from traditional electrophilic sulfenyl transfer processes involving a thiiranium ion intermediate and arises from the directed arylnickel(I) migratory insertion mechanism, as elucidated through reaction kinetics and control experiments. Reactivity and regioselectivity are facilitated by a collection of monodentate, weakly coordinating native directing groups, including sulfonamides, alcohols, amines, amides, and azaheterocycles.

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Siddarth Chandrasekaran ◽  
Connor M. Schneps ◽  
Robert Dunleavy ◽  
Changfan Lin ◽  
Cristina C. DeOliveira ◽  
...  

AbstractLight-induction of an anionic semiquinone (SQ) flavin radical in Drosophila cryptochrome (dCRY) alters the dCRY conformation to promote binding and degradation of the circadian clock protein Timeless (TIM). Specific peptide ligation with sortase A attaches a nitroxide spin-probe to the dCRY C-terminal tail (CTT) while avoiding deleterious side reactions. Pulse dipolar electron-spin resonance spectroscopy from the CTT nitroxide to the SQ shows that flavin photoreduction shifts the CTT ~1 nm and increases its motion, without causing full displacement from the protein. dCRY engineered to form the neutral SQ serves as a dark-state proxy to reveal that the CTT remains docked when the flavin ring is reduced but uncharged. Substitutions of flavin-proximal His378 promote CTT undocking in the dark or diminish undocking in the light, consistent with molecular dynamics simulations and TIM degradation activity. The His378 variants inform on recognition motifs for dCRY cellular turnover and strategies for developing optogenetic tools.


Synthesis ◽  
2021 ◽  
Author(s):  
Zheng-Yang Gu ◽  
Yang Wu ◽  
Feng Jin ◽  
Bao Xiaoguang ◽  
Ji-Bao Xia

An atom- and step-economic intermolecular multi-component palladium-catalyzed C–H amidation of alkenes with carbon monoxide and organic azides has been developed for the synthesis of alkenyl amides. The reaction proceeds efficiently without an ortho-directing group on the alkene substrates. Nontoxic dinitrogen is generated as the sole by-product. Computational studies and control experiments have revealed that the reaction takes place via an unexpected mechanism by tandem palladium catalysis.


2015 ◽  
Vol 727-728 ◽  
pp. 56-60
Author(s):  
Min Li ◽  
Liu Meng Chen ◽  
Bo Quan Jiang

Collagen, as an important biomedical material, has been widely used in medical industry. Fish waste (scales, skins, bones, fins and swim bladders) is a kind of newly developed alternative collagen raw material.This paper uesd papain as enzyme and local bighead fish scales as raw material to extract collagen. More attention was paid to the study on enzymatic reaction kinetics of papain-extracted collagen. The results showed that two kinds of kinetic models(Michaelis-Menten equations and exponential type dynamic equations) at 20, 25 and 28°C were established, respectively and experimentally proved to be basically in agreement with the actual values. These models have a great significance to predict, adjust and control the reaction rate and production output under different conditions.


1990 ◽  
Vol 3 (5) ◽  
pp. 480-486 ◽  
Author(s):  
M.K. Bologa ◽  
A.B. Berkov ◽  
V.L. Solomyanchuk

1999 ◽  
Vol 121-122 ◽  
pp. 665
Author(s):  
S. Ido ◽  
M. Kashiwagi ◽  
M. Takahashi ◽  
T. Yoshida

Author(s):  
Kamel S. Saidi ◽  
Jongwon Seo ◽  
S. V. Sreenivasan ◽  
Carl T. Haas ◽  
Alfred E. Traver

Abstract The design of a novel tele-operated robotic device for clearing undesirable residues (known as clinkers) from the bottom of boiler hoppers in electric power plants is presented in this article. A key aspect of the problem that drives the design process is the fact that the environment inside the hopper is harsh and unstructured. The part of the device that goes into the boiler through a hatch door must be able to handle high temperatures, highly corrosive ash, and the possibility of large residues falling on the device which could lead to serious structural damage to the device. This has led to a new robot design which has all its sophisticated mechanical and control hardware located outside the boiler hopper access port. The only component that goes into the boiler is an inexpensive pole which is expendable and easily replaceable. Also, it can be pulled out from the hopper even if it is seriously damaged. A special insertion mechanism serves as a prismatic joint for inserting and extracting the pole. Forward (sensing) and inverse (control) kinematics problems that are unique to this new design are also presented. Finally, a discussion of the results from preliminary experimental testing in a laboratory setting is included. An important component of the process of designing the robot was the inclusion of ideas from the currently practiced manual clinker clearing process. This was accomplished via periodic discussions with the plant workers who perform the manual process.


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