Rate and equilibrium studies of the reaction of oxyanions with 2-phenyloxazol-5(4H)-one
作者:Edwin Chrystiuk、Adelina Jusoh、Dino Santafianos、Andrew Williams
DOI:10.1039/p29860000163
日期:——
Equilibrium constants for the reaction of phenoxide ions with 2-phenyloxazol-5(4H)-one at 25 °C and 1 M ionic strength obey a Brønsted relationship (log kOH/kArO= log K′=–1.73pKArOH– 15.81) and are not subject to steric effects from ortho-substituents. Both forward and reverse rate parameters exhibit steric effects, and the Brønsted equations for meta- and para-substituted species are log kOH=–0.81
在25°C和1 M离子强度下,酚盐离子与2-苯基恶唑-5(4 H)-one反应的平衡常数服从布朗斯台德关系(log k OH / k ArO = log K '= –1.73p K ArOH – 15.81),并且不受邻位取代基的空间位阻的影响。正向和反向速率参数均显示出空间效应,间位和对位取代物种的Brønsted方程为log k OH = –0.81 p K ArOH + 9.75,log k ArO = 0.95p KArOH – 6.40。在p K ArOH 5-11的区域内,Brønsted线没有中断,这与一个过渡态一致。低碱度的氧阴离子存在向上偏差(p K XOH <5);这些氧阴离子之一,甜菜碱,由于其与恶唑酮的反应大于2,具有溶剂性氘氧化同位素作用,这与攻击这些物质的一般基本机理相符。酚酸根阴离子的亲核攻击结果与羰基的协同位移一致。
The mechanism of hydrolysis and ethylaminolysis of N-benzoylglycine and N-benzoylsarcosine esters
作者:Charles R. Farrar、Andrew Williams
DOI:10.1039/p29800000181
日期:——
The hydrolysis and ethylaminolysis of N-benzoylglycine and N-benzoylsarcosineesters have been studied for a range of leaving hydroxy-functions with pKa from 5.45 to 15.5. Ethylaminolysis of N-benzoylglycinate esters involves kinetic terms in [EtNH2] and [EtNH2][OH–]. The mechanism of ethylaminolysis of the glycinates does not involve the oxazolinone intermediate as a major contributor to the reaction
Neue Methoden zur Herstellung von Carbonsäure-arylestern. Über aktivierte Ester VIII
作者:B. Iselin、W. Rittel、P. Sieber、R. Schwyzer
DOI:10.1002/hlca.19570400216
日期:——
Two new methods for preparing carboxylic acid aryl esters are presented. They consist in reacting the carboxylic acid with (a) aryl sulfites or (b) aryl phosphites in the presence of pyridine. A possible mechanism of the sulfite method is discussed.
Chemoselective Ligation of Peptide Phenyl Esters with N-Terminal Cysteines
作者:Ge-Min Fang、Hong-Kui Cui、Ji-Shen Zheng、Lei Liu
DOI:10.1002/cbic.201000165
日期:——
Simple phenyl esters of peptides were found to undergo native chemical ligation with cysteine smoothly under the promotion of imidazole. This new ligation proceeded rapidly at both stericallyunhindered and hindered C‐terminal sites (e.g., Val, Ile, Pro) to form the desired product in good to excellent yields.
Substrate Mimetics and Freezing Strategy: A Useful Combination That Broadens the Scope of Proteases for Synthesis
作者:Nicole Wehofsky、Sebastian W. Kirbach、Marion Haensler、Johannes-Dieter Wissmann、Frank Bordusa
DOI:10.1021/ol005867g
日期:2000.7.1
[reaction: see text] We present an irreversible and efficient protease-based method for peptidesynthesis which occurs independently of the primary specificity of proteases and also without proteolytic side reactions. The key feature of this approach is the combination of the substratemimeticsstrategy with frozen state enzymology. Model reactions catalyzed by several proteases qualify this approach