Accession Number:

ADA218444

Title:

Rapid Transacylations of Activated Ester Substrates Bound to the Primary Side Beta-Cyclodextrin-Cyclen Conjugate and its M(2+) Complexes

Descriptive Note:

Technical rept.

Corporate Author:

OHIO STATE UNIV COLUMBUS DEPT OF CHEMISTRY

Report Date:

1990-02-20

Pagination or Media Count:

16.0

Abstract:

The ability of cyclodextrins to affect rapid transacylations of bound substrates has been well studied. One important difference between cyclodextrin and enzyme-mediated transacylation is the pH required. The hydrolytic cleavage of phenyl esters promoted by cyclodextrin has been extensively investigated and the mechanism of the catalyzed reaction clearly established to involve nucleophilic attack by a deprotonated secondary-side hydroxyl group on the carbonyl carbon of the bound substrate. As a result, transacylations are accelerated in the presence of cyclodextrin under basic conditions pH 10.5. Several derivatives of cyclodextrin have been prepared in efforts to provide a nucleophilic group near neutral pH. Pendant groups that have been used successfully in this regard include imidazole, N-methylhydroxamic acid, and histamine. Of particular pertinence to this manuscript are those cyclodextrins that have been substituted with metal ion complexes. Metal ions have long been recognized to afford accelerations in ester, amide, and phosphate hydrolyses, due in part to their ability to form metal-bound hydroxide under conditions that are not strongly basic. The first such artificial metalloenzyme 1 was described by Breslow in 1970, in which a Beta Cyclodextrin NiII complex demonstrated accelerated transacylation of bound p-nitrophenyl acetate at pH 5. 2. Subsequent descriptions of cyclodextrin-based artificial metalloenzymes have been reported. aw

Subject Categories:

  • Organic Chemistry

Distribution Statement:

APPROVED FOR PUBLIC RELEASE