Cooperative Conformational Regulation in N-Heterocyclic Fluorohydrins

2015 ◽  
Vol 68 (1) ◽  
pp. 50 ◽  
Author(s):  
Alpesh Ramanlal Patel ◽  
Fei Liu
Keyword(s):  
Prior Work ◽  
Conformational Control ◽  
Relative Configuration ◽  
Ring Structures ◽  
Conformational Regulation ◽  
Flexible Ring ◽  
Major Conformation

Seven-membered N-heterocycles are flexible ring structures, and their conformational control is important to their bioactivity. Our prior work shows that stereoselective monofluorination, if installed diastereoselectively, can bias a seven-membered, substituted azepane ring to one major conformation. However, multiple fluorination may not provide as much conformational bias due to conflicting effects. Here we show in our model azepane system that fluorohydrins can confer strong conformational bias if the relative configuration of the fluorine and hydroxy substitutent is appropriate to enable cooperative conformational control.

In-Plane Flexible Ring Tire Model—Part 1: Modeling and Parameter Identification

2018 ◽  
Vol 46 (3) ◽  
pp. 174-219 ◽  
Author(s):  
Bin Li ◽  
Xiaobo Yang ◽  
James Yang ◽  
Yunqing Zhang ◽  
Zeyu Ma
Keyword(s):  
Static Load ◽  
Model Parameters ◽  
Tire Model ◽  
Test Results ◽  
Lumped Mass ◽  
Virtual Test ◽  
Proposed Model ◽  
Particle Swarm Method ◽  
Vehicle Dynamic Simulation ◽  
Flexible Ring

ABSTRACT The tire model is essential for accurate and efficient vehicle dynamic simulation. In this article, an in-plane flexible ring tire model is proposed, in which the tire is composed of a rigid rim, a number of discretized lumped mass belt points, and numerous massless tread blocks attached on the belt. One set of tire model parameters is identified by approaching the predicted results with ADAMS® FTire virtual test results for one particular cleat test through the particle swarm method using MATLAB®. Based on the identified parameters, the tire model is further validated by comparing the predicted results with FTire for the static load-deflection tests and other cleat tests. Finally, several important aspects regarding the proposed model are discussed.

Kinetic Solvent Effects in Organic Reactions

2017 ◽  
Author(s):  
Belinda Slakman ◽  
Richard West
Keyword(s):  
Solvent Effect ◽  
Reaction Kinetics ◽  
Computational Methods ◽  
High Throughput ◽  
Kinetic Modeling ◽  
Solvent Effects ◽  
Reaction Rates ◽  
Prior Work ◽  
Solvent Phase ◽  
High Throughput Manner

<div> <div> <div> <p>This article reviews prior work studying reaction kinetics in solution, with the goal of using this information to improve detailed kinetic modeling in the solvent phase. Both experimental and computational methods for calculating reaction rates in liquids are reviewed. Previous studies, which used such methods to determine solvent effects, are then analyzed based on reaction family. Many of these studies correlate kinetic solvent effect with one or more solvent parameters or properties of reacting species, but it is not always possible, and investigations are usually done on too few reactions and solvents to truly generalize. From these studies, we present suggestions on how best to use data to generalize solvent effects for many different reaction types in a high throughput manner. </p> </div> </div> </div>

Diastereoselective Reduction of Selected α-substituted β-keto Esters and the Assignment of the Relative Configuration by 1H-NMR Spectroscopy

2020 ◽  
Vol 07 ◽  
Author(s):  
Christian Trapp ◽  
Corinna Schuster ◽  
Chris Drewniok ◽  
Dieter Greif ◽  
Martin Hofrichter
Keyword(s):  
Nmr Spectroscopy ◽  
1H Nmr ◽  
1H Nmr Spectroscopy ◽  
Selective Reduction ◽  
Reducing Agents ◽  
Relative Configuration ◽  
Curtius Rearrangement ◽  
Keto Esters ◽  
Hydroxy Esters ◽  
Diastereoselective Reduction

Background:: Chiral β-hydroxy esters and α-substituted β-hydroxy esters represent versatile building blocks for pheromones, β-lactam antibiotics and 1,2- or 1,3-aminoalcohols. Objective:: Synthesis of versatile α-substituted β-keto esters and their diastereoselective reduction to the corresponding syn- or anti-α-substituted β-hydroxy esters. Assignment of the relative configuration by NMR-spectroscopy after a CURTIUS rearrangement of α-substituted β-keto esters to 4-substituted 5-methyloxazolidin-2-ones. Method:: Diastereoselective reduction was achieved by using different LEWIS acids (zinc, titanium and cerium) in combination with complex borohydrides as reducing agents. Assignment of the relative configuration was verified by 1H-NMR spectroscopy after CURTIUS-rearrangement of α-substituted β-hydroxy esters to 4-substituted 5-methyloxazolidin-2-ones. Results:: For the syn-selective reduction, titanium tetrachloride (TiCl4) in combination with a pyridine-borane complex (py BH3) led to diastereoselectivities up to 99% dr. High anti-selective reduction was achieved by using cerium trichloride (CeCl3) and steric hindered reducing agents such as lithium triethylborohydride (LiEt3BH). After CURTIUS-rearrangement of each α-substituted β-hydroxy ester to the corresponding 4-substituted 5-methyloxazolidin-2-one, the relative configuration was confirmed by 1H NMR-spectroscopy. Conclusion:: We have expanded the procedure of LEWIS acid-mediated diastereoselective reduction to bulky α-substituents such as the isopropyl group and the electron withdrawing phenyl ring.

Auditor Industry Specialization and Earnings Quality

2003 ◽  
Vol 22 (2) ◽  
pp. 71-97 ◽  
Author(s):  
Steven Balsam ◽  
Jagan Krishnan ◽  
Joon S. Yang
Keyword(s):  
Audit Quality ◽  
Earnings Quality ◽  
Discretionary Accruals ◽  
Prior Work ◽  
Brand Name ◽  
Absolute Level ◽  
Industry Specialization ◽  
Earnings Response Coefficients ◽  
Auditor Industry Specialization ◽  
Earnings Response

This study examines the association between measures of earnings quality and auditor industry specialization. Prior work has examined the association between auditor brand name and earnings quality, using auditor brand name to proxy for audit quality. Recent work has hypothesized that auditor industry specialization also contributes to audit quality. Extending this literature, we compare the absolute level of discretionary accruals (DAC) and earnings response coefficients (ERC) of firms audited by industry specialists with those of firms not audited by industry specialists. We restrict our study to clients of Big 6 (and later Big 5) auditors to control for brand name. Because industry specialization is unobservable, we use multiple proxies for it. After controlling for variables established in prior work to be related to DAC and the ERC, we find clients of industry specialist auditors have lower DAC and higher ERC than clients of nonspecialist auditors. This finding is consistent with clients of industry specialists having higher earnings quality than clients of nonspecialists.

Sterically Crowded Heterocycles. VI. Relative Configuration of Diastereoisomeric (Z)-1,3-Diphenyl-3-(5-methyl-2-phenylimidazo[1,2-a]pyridin-3-yl)prop-2-en-1-ols

1996 ◽  
Vol 61 (9) ◽  
pp. 1380-1385 ◽  
Author(s):  
Jan Čejka ◽  
Richard Kubík ◽  
Bohumil Kratochvíl ◽  
Josef Kuthan
Keyword(s):  
Preparative Separation ◽  
Orthorhombic Space Group ◽  
Relative Configuration ◽  
Space Group ◽  
X Ray

Relative configuration of the titled racemic compounds 1a and 1b has been elucidated on the basis of a complete X-ray structure determined for the higher melting diastereoisomer. The compound 1a crystallizes in the orthorhombic space group P21212, a = 15.610(3) Å, b = 18.634(4) Å, c = 7.5672(7) Å, V = 2201.1(6) Å3, Z = 4. Preparative separation of both diastereoisomers is reported.

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