The Formation of Alkenes by the Thermal Elimination Reaction of N-Methyl-4-alkoxypyridinium Iodides. II. An Investigation of the Mechanism

1972 ◽  
Vol 50 (8) ◽  
pp. 1188-1191
Author(s):  
George H. Schmid ◽  
Aaron W. Wolkoff
Keyword(s):  
Elimination Reaction ◽  
Product Composition ◽  
Thermal Elimination ◽  
Leaving Group ◽  
Elimination Reactions ◽  
Leaving Groups

A comparison of the products from elimination reactions of a number of compounds containing various leaving groups with those containing the N-methyl oxypyridinium leaving group suggests that the elimination is not occurring by means of a simple E1 mechanism. Changing the anion of the salt from iodide to methyl-sulphate and tetrafluoroborate affects the product composition indicating that the anion is taking part in the reaction. The mechanism of this reaction appears to be on the E1-E2 borderline.

scholarly journals Nucleophilic re-activation of the PC1 β-lactamase of Staphylococcus aureus and of the dd-peptidase of Streptomyces R61 after their inactivation by cephalosporins and cephamycins

1987 ◽  
Vol 246 (3) ◽  
pp. 651-658 ◽  
Author(s):  
W S Faraci ◽  
R F Pratt
Keyword(s):  
Staphylococcus Aureus ◽  
Strong Support ◽  
Model Systems ◽  
Elimination Reaction ◽  
Beta Lactam ◽  
Beta Lactamases ◽  
Processing Enzymes ◽  
Leaving Group ◽  
Leaving Groups ◽  
Kinetics Of

It has been shown previously [Faraci & Pratt (1985) Biochemistry 24, 903-910; (1986) Biochemistry 25, 2934-2941; (1986) Biochem. J. 238, 309-312] that certain beta-lactam-processing enzymes form inert acyl-enzymes with cephems that possess good leaving groups at the C-3′ position. These inert species arise by elimination of the leaving group from the initially formed and more rapidly hydrolysing acyl-enzyme, which has the ‘normal’ cephalosporoate structure. The present paper shows that a strong nucleophile, thiophenoxide, can catalyse the re-activation of three examples of these inert acyl-enzymes, generated on reaction of cephalothin and cefoxitin with the PC1 beta-lactamase of Staphylococcus aureus and of cephalothin with D-alanyl-D-alanine transpeptidase/carboxypeptidase of Streptomyces R61. In view of the reversibility of the elimination reaction, demonstrated in model systems [Pratt & Faraci (1986) J. Am. Chem. Soc. 108, 5328-5333], this catalysis is proposed to arise through nucleophilic addition to the exo-methylene carbon atom of the inert acyl-enzyme to regenerate a more rapidly hydrolysing normal cephalosporoate. Strong support for this scenario was obtained through comparison of the kinetics of the catalysed re-activation reaction with those of turnover of the relevant 3′-thiophenoxycephems, thiophenoxycephalothin and thiophenoxycefoxitin. The enzymes appear to stabilize the products of the elimination reaction with respect to the normal cephalosporoate, but more strongly to destabilize the transition states. The effects of other nucleophiles, including cysteine, glycine amide and imidazole, on the above enzymes and on other beta-lactamases can be understood in terms of the model reaction kinetics and thermodynamics.

The effect of steric size of leaving group on rates of the competing syn- and anti-pathways in biomolecular elimination

1980 ◽  
Vol 45 (8) ◽  
pp. 2171-2178
Author(s):  
Jiří Závada ◽  
Magdalena Pánková
Keyword(s):  
Comparative Analysis ◽  
Homologous Series ◽  
Leaving Group ◽  
Leaving Groups

Approximate rates of the competing syn- and anti-pathways have been determined in t-C4H9OK-t-C4H9OH promoted elimination from two homologous series of tosylates: I-OTs trans-III (R = H, CH3, C2H5, n-C3H7, i-C3H7, t-C4H9) and II-OTs trans-IV (R = CH3, C2H5, n-C3H7, i-C3H7, t-C4H9). A comparison has been made with rates of the same processes in the (+) elimination of the corresponding trimethylammonium salts I-N(CH3)3 trans-III and (+) II-N(CH3)3 trans-IV. The title effect is demonstrated by a comparative analysis of the rate patterns obtained for the two leaving groups.

Copper(II) complexes with tridentate halogen‐substituted Schiff base ligands: synthesis, crystal structures and investigating the effect of halogenation, leaving group and ligand flexibility on antiproliferative activities

2021 ◽  
Author(s):  
Nazanin Kordestani ◽  
Hadi Amiri Rudbari ◽  
Alexandra R Fernandes ◽  
Luís R Raposo ◽  
André Luz ◽  
...  
Keyword(s):  
Schiff Base ◽  
Anticancer Activity ◽  
Crystal Structures ◽  
Copper Complexes ◽  
Schiff Base Ligands ◽  
Leaving Group ◽  
Leaving Groups ◽  
Tridentate Schiff Base ◽  
Antiproliferative Activities

To investigate the effect of different halogen substituents, leaving groups and the flexibility of ligand on the anticancer activity of copper complexes, sixteen copper(II) complexes with eight different tridentate Schiff-base...

DENSITY FUNCTIONAL STUDY OF SELECTED MONO-ZINC AND GEM-DIZINC RADICAL CARBENOID CYCLOPROPANATION REACTIONS: OBSERVATION OF AN EFFICIENT RADICAL ZINC CARBENOID CYCLOPROPANATION REACTION AND THE INFLUENCE OF THE LEAVING GROUP ON RING CLOSURE

2003 ◽  
Vol 02 (03) ◽  
pp. 357-369 ◽  
Author(s):  
CUNYUAN ZHAO ◽  
DONG-QI WANG ◽  
DAVID LEE PHILLIPS
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Radical Reaction ◽  
Ring Closure ◽  
Functional Study ◽  
Reaction Step ◽  
Leaving Group ◽  
Reaction Barriers ◽  
Leaving Groups ◽  
Zinc Carbenoid

We report a theoretical study of the cyclopropanation reactions of EtZnCHI, (EtZn)2CH EtZnCHZnI, and EtZnCIZnI radicals with ethylene. The mono-zinc and gem-dizinc radical carbenoids can undergo cyclopropanation reactions with ethylene via a two-step reaction mechanism similar to that previously reported for the CH2I and IZnCH2 radicals. The barrier for the second reaction step (ring closure) was found to be highly dependent on the leaving group of the cyclopropanation reaction. In some cases, the (di)zinc carbenoid radical undergoes cyclopropanation via a low barrier of about 5–7 kcal/mol on the second reaction step and this is lower than the CH2I radical reaction which has a barrier of about 13.5 kcal/mol for the second reaction step. Our results suggest that in some cases, zinc radical carbenoid species have cyclopropanation reaction barriers that can be competitive with their related molecular Simmons-Smith carbenoid species reactions and produce somewhat different cyclopropanated products and leaving groups.

Unimolecular HBr and HF Elimination Reactions of Vibrationally Excited C2H5CH2Br and C2D5CHFBr: Identification of the 1,1-HBr Elimination Reaction from C2D5CHFBr and Search for the C2D5(F)C:HBr Adduct

2019 ◽  
Vol 123 (41) ◽  
pp. 8776-8786
Author(s):  
Timothy M. Brown ◽  
Blanton R. Gillespie ◽  
Mallory M. Rothrock ◽  
Anthony J. Ranieri ◽  
Melinda K. Schueneman ◽  
...  
Keyword(s):  
Elimination Reaction ◽  
Vibrationally Excited ◽  
Elimination Reactions

scholarly journals Improvement in hydrolytic antibody activity by change in haptenic structure from phosphate to phosphonate with retention of a common leaving-group determinant: evidence for the ‘flexibility’ hypothesis

2003 ◽  
Vol 376 (3) ◽  
pp. 813-821 ◽  
Author(s):  
Sheraz GUL ◽  
Sanjiv SONKARIA ◽  
Surapong PINITGLANG ◽  
José FLOREZ-ALVAREZ ◽  
Syeed HUSSAIN ◽  
...  
Keyword(s):  
Structural Motif ◽  
Catalytic Antibody ◽  
Antibody Activity ◽  
Reaction Centre ◽  
Binding Characteristics ◽  
Leaving Group ◽  
Catalytic Mechanisms ◽  
Leaving Groups ◽  
Antibody Preparations ◽  
Ester Substrate

To investigate the hypothesis that decreased hapten flexibility may lead to increased catalytic antibody activity, we used two closely related immunogens differing only in the flexibility of the atomic framework around the structural motif of the haptens, analogous to the reaction centre of the corresponding substrates. Identical leaving-group determinants in the haptens and identical leaving groups in the substrates removed the ambiguity inherent in some data reported in the literature. Anti-phosphate and anti-phosphonate kinetically homogeneous polyclonal catalytic antibody preparations were compared by using carbonate and ester substrates respectively, each containing a 4-nitrophenolate leaving group. Synthetic routes to a new phosphonate hapten and new ester substrate were developed. The kinetic advantage of the more rigid anti-phosphonate/ester system was demonstrated at pH 8.0 by a 13-fold advantage in kcat/knon-cat and a 100-fold advantage in the proficiency constant, kcat/knon-cat·Km. Despite these differences, the pH-dependences of the kinetic and binding characteristics and the results of chemical modification studies suggest closely similar catalytic mechanisms. The possible origin of the kinetic advantage of the more rigid hapten/substrate system is discussed.

scholarly journals Isoxazole Formation by Thermal Elimination Reaction of 5-Substituted Isoxazolines

1972 ◽  
Vol 30 (10) ◽  
pp. 894-896 ◽  
Author(s):  
Yoshio IWAKURA ◽  
Keikichi UNO ◽  
Shinsaku SHIRAISHI ◽  
Masahiro YUYAMA ◽  
Yoshinori KIHARA
Keyword(s):  
Elimination Reaction ◽  
Thermal Elimination
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