Relationship between effective nucleophilic catalysis in the hydrolysis of esters with poor leaving groups and the lifetime of the tetrahedral intermediate

1984 ◽  
Vol 106 (12) ◽  
pp. 3687-3688 ◽  
Author(s):  
Jik Chin ◽  
Xiang Zou
Keyword(s):  
Nucleophilic Catalysis ◽  
Tetrahedral Intermediate ◽  
Leaving Groups ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

Synthesis, structure, and hydrolysis of esters of strained and unstrained N-phosphonylureas

1987 ◽  
Vol 65 (8) ◽  
pp. 1838-1844 ◽  
Author(s):  
Ronald Kluger ◽  
Gregory R. J. Thatcher ◽  
William C. Stallings
Keyword(s):  
Membered Ring ◽  
Equatorial Position ◽  
Alkyl Esters ◽  
Aqueous Acetonitrile ◽  
Phenoxy Group ◽  
X Ray Crystallography ◽  
Urea Group ◽  
Leaving Groups ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

Compounds 1–5 were prepared to compare reactivity patterns of cyclic and acyclic phosphonylurea esters. The rates and products of reactions of phosphonylurea esters (1–3) with hydroxide in aqueous acetonitrile were analyzed. In these compounds the phosphonate moiety is in a strained five-membered ring, which also contains the ureido group. Structural determination of 1 by X-ray crystallography indicates that the five-membered ring is planar and the internal ring angle at phosphorus is 93.1°. The endocyclic N—C—N angle of the ureido group is 111°. The compounds undergo hydrolysis in alkaline aqueous acetonitrile at 35 °C with a rate about 106 times that of analogues (4, 5) in which the phosphonate group is exocyclic to the ureido ring. Compound 1 undergoes alkaline hydrolysis (k = 9.0 × 103 M−1 s−1) to release the phenoxy group to give 6. The hydrolysis of alkyl esters 2 (k = 2.4 × 104 M−1 s−1)and 3(k = 1.3 × 103 M−1 s−1) leads to cleavage of the endocyclic P—N bond, producing 7 and 8 respectively. The exocyclic alkyl esters (4 and 5) also cleave at the P—N bond with respective rate constants of 6.5 × 10−3 M−1 s−1 and 4.4 × 10−2 M−1 s−1. The data are consistent with a mechanism in which hydroxide adds to 1 to form a pentacoordinate phosphorus intermediate with the phenoxy group in an equatorial position and the ureido ring in apical and equatorial positions (with nitrogen apical). The departure of the urea group is slower than pseudorotation of the intermediate and expulsion of phenoxide. In the isomerized intermediate, phenoxy is apical but the methylene group of the ring, which has low apicophilicity, must also be apical. Reactions of 2 and 3, which have more basic oxygen leaving groups, occur with P—N cleavage because expulsion from the isomerized intermediate in those cases is not sufficiently fast. These results fit reaction patterns at phosphorus that are determined by ring strain and electronegativity of ligands. Contributions from effects due to antiperiplanar interactions between bonding and nonbonding electrons are not detected.

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 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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