Amine-catalyzed hydrolyses of cyclodextrin cinnamates.
Hydrolyses of beta-cyclodextrin cinnamate (betaCDC) and alpha-cyclodextrin cinnamate were catalyzed by amines such as 1,4-diazabicyclo(2.2.2)octane, triethylamine, quinuclidine, piperidine, diisobutylamine, and n-butylamine. The rate constant of hydrolyses of the betaCDC-amine complexes follows the order: 1,4-diazabicyclo(2.2.2)octane > n-butylamine > quinuclidine > piperidine > triethylamine >> diisobutylamine. The ratio of the catalytic rate constant for the betaCDC/1,4-diazabicyclo(2.2.2)octane complex to the spontaneous rate constant for betaCDC is about 6-fold and is almost independent of pH below pH 11.5; but, it then drastically increases with pH above pH 11.5, up to 57-fold at pH 13.6 which is much higher than previous attempts. The pH-rate constant profile and isotope effect with deuterium oxide solvent indicate that 1,4-diazabicyclo(2.2.2)octane, included in betaCDC, assists the catalytic nucleophilic attack by hydroxide ion toward the carbonyl carbon of betaCDC. Acceleration of deacylation of acyl-cyclodextrins, by amines, has made the cyclodextrin-catalyzed hydrolysis of esters an even better model of hydrolytic enzyme reactions than those developed previously.
Division of Biochemistry, Department of Chemistry, Northwestern University, Evanston, Illinois 60201.
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Bender