577-71-9Relevant articles and documents
Biochemical identification of the catalytic residues of a glycoside hydrolase family 120 β-xylosidase, involved in xylooligosaccharide metabolisation by gut bacteria
Cecchini, Davide A.,Faur, Rgis,Laville, Elisabeth,Potocki-Veronese, Gabrielle
, p. 3098 - 3106 (2015/10/19)
The β-xylosidase B from Bifidobacterium adolescentis ATCC15703 belongs to the newly characterized family 120 of glycoside hydrolases. In order to investigate its catalytic mechanism, an extensive kinetic study of the wild-type enzyme and mutants targeting the three highly conserved residues Asp393, Glu416 and Glu364 was performed. NMR analysis of the xyloside hydrolysis products, the change of the reaction rate-limiting step for the Glu416 mutants, the pH dependency of E416A activity and its chemical rescue allowed to demonstrate that this GH120 enzyme uses a retaining mechanism of glycoside hydrolysis, Glu416 playing the role of acid/base catalyst and Asp393 that of nucleophile.
Leaving-group substituent controls reactivity and reaction mechanism in aminolysis of phenyl y-substituted-phenyl carbonates
Kang, Ji-Sun,Song, Yoon-Ju,Um, Ik-Hwan
, p. 2023 - 2028 (2013/09/02)
A kinetic study is reported for the nucleophilic substitution reactions of phenyl Y-substituted-phenyl carbonates (5a-5k) with piperidine in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The plots of k obsd vs. [piperidine] for the reactions of substrates possessing a strong electron-withdrawing group (EWG) in the leaving group (i.e., 5a-5i) are linear and pass through the origin. In contrast, the plots for the reactions of substrates bearing a weak EWG or no substituent (i.e., 5j or 5k) curve upward, indicating that the electronic nature of the substituent Y in the leaving group governs the reaction mechanism. Thus, it has been suggested that the reactions of 5a-5i proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate (i.e., T±) while those of 5j and 5k proceed through a stepwise mechanism with two intermediates (i.e., T± and its deprotonated form T-). The slope of the Bronsted-type plot for the second-order rate constants (i.e., kN or Kk2) changes from -0.41 to -1.89 as the leaving-group basicity increases, indicating that a change in the rate-determining step (RDS) occurs. The reactions of 5a-5k with piperidine result in larger k1 values than the corresponding reactions with ethylamine. Copyright
Chemoselective amide formation using O-(4-nitrophenyl)hydroxylamines and pyruvic acid derivatives
Kumar, Sonali,Sharma, Rashi,Garcia, Megan,Kamel, Joseph,McCarthy, Caroline,Muth, Aaron,Phanstiel, Otto
, p. 10835 - 10845 (2013/02/23)
A series of O-(4-nitrophenyl)hydroxylamines were synthesized from their respective oximes using a pulsed addition of excess NaBH3CN at pH 3 in 65a-75% yield. Steric hindrance near the oxime functional group played a key role in both the ease by which the oxime could be reduced and the subsequent reactivity of the respective hydroxylamine. Reaction of the respective hydroxylamines with pyruvic acid derivatives generated the desired amides in good yields. A comparison of phenethylamine systems bearing different leaving groups revealed significant differences in the rates of these systems and suggested that the leaving group ability of the Na-OR substituent plays an important role in determining their reactivity with pyruvic acid. Competition experiments (in 68% DMSO/phosphate buffered saline) using 1 equiv of N-phenethyl-O-(4-nitrophenyl)hydroxylamine and 2 equiv of pyruvic acid in the presence of other nucleophiles such as glycine, cysteine, phenol, hexanoic acid, and lysine demonstrated that significant chemoselectivity is present in this reaction. The results suggest that this chemoselective reaction can occur in the presence of excess α-amino acids, phenols, acids, thiols, and amines.
