General Base and General Acid Catalyzed Intramolecular Aminolysis of Esters. Cyclization of Esters of 2-Aminomethylbenzoic Acid to Phthalimidine

2000 ◽  
Vol 65 (12) ◽  
pp. 3579-3586 ◽  
Author(s):  
Thomas H. Fife ◽  
L. Chauffe
Keyword(s):  
General Base ◽  
General Acid ◽  
Acid Catalyzed

Deuterium exchange of C-methyl protons in lumazine derivatives

1970 ◽  
Vol 48 (2) ◽  
pp. 263-270 ◽  
Author(s):  
J. M. McAndless ◽  
Ross Stewart
Keyword(s):  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Acid Catalysis ◽  
Deuterium Exchange ◽  
Base Catalysis ◽  
Resonance Spectroscopy ◽  
Methyl Group ◽  
General Base ◽  
General Acid ◽  
Acid Catalyzed

Proton magnetic resonance spectroscopy has been used to examine the deuterium exchange of the methyl protons in two lumazine derivatives. The exchange occurs at the C-7 methyl group in 6,7,8-trimethyllumazine (2) and at the C-6 methyl group in 1,7-dihydro-6,7,8-trimethyllumazine (3). The former reaction is subject to both general acid- and general base-catalysis but the latter only to general acid-catalysis. Plausible mechanisms for the reactions of both compounds are advanced, involving in the case of 3, acid-catalyzed addition of water across the C6—N5 double bond.

The proton activating factor and its application to acid and base catalysis of aldehyde hydration

1984 ◽  
Vol 62 (5) ◽  
pp. 907-910 ◽  
Author(s):  
Ross Stewart
Keyword(s):  
Nucleophilic Addition ◽  
Base Catalysis ◽  
General Base ◽  
Uncatalyzed Reaction ◽  
General Acid ◽  
Acid And Base ◽  
Alternative Means ◽  
Acid Catalyzed ◽  
Substituted Benzaldehydes ◽  
Class E

The data of McClelland and Coe for the general acid and general base catalyzed hydration of a series of substituted benzaldehydes has been analyzed in terms of the proton activating factor, paf, and concepts related thereto. Although the latter were derived for use with prototropic systems, the present work shows that they have application to nucleophilic addition as well. Three conclusions emerge from the analysis. 1. Alternative means of calculating paf from buffer catalytic data that were previously derived on theoretical grounds can be used in practice to give essentially the same results. 2. The mechanism of the general acid catalyzed pathway for aldehyde hydration is that favoured by McClelland and Coe and by Jencks, to wit the class (e) mechanism, rather than the class (n) mechanism. 3. Electron-withdrawing groups in the benzaldehyde ring cause the disparity between the contributions of alternative, kinetically equivalent, pathways for the uncatalyzed reaction to become greater.

Intramolecular nucleophilic participation by the thiol group during amide hydrolysis. Part 2. The imidazole catalysis dilemma

1992 ◽  
Vol 70 (1) ◽  
pp. 62-67 ◽  
Author(s):  
Robert S. McDonald ◽  
Patricia Patterson ◽  
June Rodwell ◽  
Ann Whalley
Keyword(s):  
Aqueous Solution ◽  
Thiol Group ◽  
Tetrahedral Intermediate ◽  
General Base ◽  
General Acid ◽  
Amide Hydrolysis ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Imidazole Catalysis

Catalysis by imidazole and N-methylimidazole buffers of the intramolecular thiolysis of N-n-propyl 2-mercaptomethylbenzamide (forming 2-thiophthalide) has been studied in aqueous solution at 40.0 °C, μ = 1.0. Unlike other buffers previously studied, imidazole and N-methylimidazole are able to catalyze, by a general base route, formation of neutral tetrahedral intermediate; this pathway is rate limiting at pH ≤ 7.5. At higher pH, the previously reported general acid-catalyzed breakdown of this intermediate is rate limiting. The relevance of these observations to the currently accepted pathway for the acylation of papain by amide substrates is discussed. Keywords: amide hydrolysis, intramolecular, thiol participation, imidazole, papain model.

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

The nature of the steric effect in the general-acid-catalyzed hydrolyses of benzaldehyde acetals

1983 ◽  
Vol 48 (23) ◽  
pp. 4175-4179 ◽  
Author(s):  
James L. Jensen ◽  
Anna B. Martinez ◽  
Cheryl L. Shimazu
Keyword(s):  
Steric Effect ◽  
General Acid ◽  
Acid Catalyzed

DNA and RNA enzymes with peroxidase activity — An investigation into the mechanism of action

2006 ◽  
Vol 84 (4) ◽  
pp. 613-619 ◽  
Author(s):  
Paola Travascio ◽  
Dipankar Sen ◽  
Andrew J Bennet
Keyword(s):  
Nucleic Acid ◽  
Hydrophobic Interactions ◽  
Basic Component ◽  
Axial Position ◽  
General Base ◽  
Dna And Rna ◽  
Polar Environment ◽  
Guanine Quadruplex ◽  
Acid Catalyzed ◽  
Catalyzed Reactions

A DNA–hemin complex (PS2.M–hemin), and its RNA counterpart (rPS2.M–hemin), have previously been reported, in the presence of nitrogenous buffers such as HEPES, to show enhanced peroxidative activity relative to both uncomplexed hemin and a control DNA–hemin complex (Chem. Biol. 5, 505, 1998). A kinetic analysis of these two hemin-utilizing nucleic acid enzymes provides key insights into the mechanisms for their catalyzed peroxidation reactions. First, control experiments indicate that charge on the added detergent, required for solubility reasons, has little effect on the efficiency of the nucleic-acid-catalyzed reactions. Second, the key functional impact of the two nucleic acid frameworks, either DNA or RNA, appears to be a reduction in the acidity of a water molecule coordinated to the iron atom of the hemin that is bound to the ribozyme and DNAzyme scaffolds. This effect could result from a polar environment and possibly hydrogen bond(s) at the axial position of the hemin, along with favourable hydrophobic interactions for the periphery of the porphyrin ring. Third, the basic component of the buffer enhances the activities; this likely results from a general-base-catalyzed process. Cumulatively, these data supply important clues as to how biopolymers other than a protein can complex with hemin to form productive peroxidase enzymes.Key words: ribozyme, DNAzyme, hemin, peroxidase, mechanism, guanine quadruplex.

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