The Importance of Conformation of the Tetrahedral Intermediate in the Hydrolysis of Esters. Selective Cleavage of the Tetrahedral Intermediate Controlled by Orbital Orientation

1972 ◽  
Vol 50 (20) ◽  
pp. 3405-3408 ◽  
Author(s):  
Pierre Deslongchamps ◽  
Paul Atlani ◽  
Daniel Fréhel ◽  
Alain Malaval
Keyword(s):  
Lone Pair ◽  
Tetrahedral Intermediate ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of ◽  
Orbital Orientation ◽  
Oxygen Atoms

The hydrolysis or the transesterification of esters proceeds via a hemi-orthoester tetrahedral intermediate. There are nine different gauche conformers possible for such a tetrahedral intermediate and it is proposed that each of them should decompose in a highly selective manner. It is further proposed that the lone pair orbitals of the oxygen atoms control this selective decomposition.

The Importance of Conformation of the Tetrahedral Intermediate in the Hydrolysis of Amides. Selective Cleavage of the Tetrahedral Intermediate Controlled by Orbital Orientation

1973 ◽  
Vol 51 (10) ◽  
pp. 1665-1669 ◽  
Author(s):  
Pierre Deslongchamps ◽  
Claude Lebreux ◽  
Roland Taillefer
Keyword(s):  
Experimental Evidence ◽  
Lone Pair ◽  
Tetrahedral Intermediate ◽  
Basic Hydrolysis ◽  
Hydrolysis Of ◽  
Orbital Orientation

The basic hydrolysis of N-disubstituted imidate salts proceeds via a hemi-orthoamide tetrahedral intermediate which can in principle give amide–alcohol or ester–amine products. Experimental evidence has been obtained which shows that the specific conformation of the tetrahedral intermediate determines products formation and it is further suggested that the orientation of the lone pair orbitals of the heteroatoms governs this remarkable selective decomposition.

The Hydrolysis of Imidate Salts. Stereoelectronic Control in the Cleavage of the Hemiorthoamide Tetrahedral Intermediate

1975 ◽  
Vol 53 (18) ◽  
pp. 2791-2807 ◽  
Author(s):  
Pierre Deslongchamps ◽  
Serge Dubé ◽  
Claude Lebreux ◽  
Dennis R. Patterson ◽  
Roland J. Taillefer
Keyword(s):  
Alkyl Group ◽  
Lone Pair ◽  
The Other ◽  
Tetrahedral Intermediate ◽  
Hydrolysis Products ◽  
Anti Conformation ◽  
Stereoelectronic Control ◽  
Basic Hydrolysis ◽  
Hydrolysis Of ◽  
Nitrogen Bond

A new stereoelectronic theory for the cleavage of the tetrahedral intermediate (hemiorthoamide) in the hydrolysis of amides is presented. In this new theory, the precise conformation of the tetrahedral intermediate controls the nature of the hydrolysis products. It is postulated that the breakdown of the tetrahedral intermediate depends upon the orientation of the lone pair orbitals of the heteroatoms. Specific cleavage of a carbon–oxygen or a carbon–nitrogen bond in any conformer is allowed only if the other heteroatoms (oxygen and nitrogen) each have an orbital oriented antiperiplanar to the leaving O-alkyl or N-alkyl group. Experimentally, a study of the basic hydrolysis of a variety of N,N-dialkylated imidate salts having either a syn or an anti conformation demonstrates clearly that there is a stereoelectronic control in the cleavage of the hemiorthoamide.

The Effects of Amines on the Esterase Activities of Thrombin and Thrombokinase and on Several Clotting Tests

1974 ◽  
Vol 31 (02) ◽  
pp. 309-318
Author(s):  
Phyllis S Roberts ◽  
Raphael M Ottenbrite ◽  
Patricia B Fleming ◽  
James Wigand
Keyword(s):  
Choline Chloride ◽  
Polymerization Process ◽  
Ammonium Bromide ◽  
Bovine Thrombin ◽  
One Stage ◽  
Human Proteins ◽  
Rate Of Hydrolysis ◽  
The One ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

Summary1. Choline chloride, 0.1 M (in 0.25 M Tris. HCl buffer, pH 7.4 or 8.0, 37°), doubles the rate of hydrolysis of TAME by bovine thrombokinase but has no effect on the hydrolysis of this ester by either human or bovine thrombin. Only when 1.0 M or more choline chloride is present is the hydrolysis of BAME by thrombokinase or thrombin weakly inhibited. Evidence is presented that shows that these effects are due to the quaternary amine group.2. Tetramethyl ammonium bromide or chloride has about the same effects on the hydrolysis of esters by these enzymes as does choline chloride but tetra-ethyl, -n.propyl and -n.butyl ammonium bromides (0.1 M) are stronger accelerators of the thrombokinase-TAME reaction and they also accelerate, but to a lesser degree, the thrombin-TAME reaction. In addition, they inhibit the hydrolysis of BAME by both enzymes. Their effects on these reactions, however, do not follow any regular order. The tetraethyl compound is the strongest accelerator of the thrombokinase-TAME reaction but the tetra-ethyl and -butyl compounds are the strongest accelerators of the thrombin-TAME reaction. The ethyl and propyl compounds are the best (although weak) inhibitors of the thrombokinase-BAME and the propyl compound of the thrombin-BAME reactions.3. Tetra-methyl, -ethyl, -n.propyl and -n.butyl ammonium bromides (0.01 M) inhibit the clotting of fibrinogen by thrombin (bovine and human proteins) at pH 7.4, imidazole or pH 6.1, phosphate buffers and they also inhibit, but to a lesser degree, a modified one-stage prothrombin test. In all cases the inhibition increases regularly as the size of the alkyl group increases from methyl to butyl. Only the ethyl com pound (0.025 M but not 0.01 M), however, significantly inhibits the polymerization of bovine fibrin monomers. It was concluded that inhibition of the fibrinogen-thrombin and the one-stage tests by the quaternary amines is not due to any effect of the com pounds on the polymerization process but probably due to inhibition of thrombin’s action on fibrinogen by the quaternary amines.

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