Amine-catalyzed hydrolyses of cyclodextrin cinnamates
1Division of Biochemistry, Department of Chemistry, Northwestern University, Evanston, Illinois 60201.
Summary
Amines catalyze the hydrolysis of beta-cyclodextrin cinnamate, with 1,4-diazabicyclo(2.2.2)octane showing significant catalytic activity. This cyclodextrin-amine complex serves as an improved model for enzyme-like ester hydrolysis reactions.
Area of Science:
- Supramolecular Chemistry
- Catalysis
- Biomimetic Chemistry
Background:
- Cyclodextrins are cyclic oligosaccharides with a hydrophobic cavity capable of host-guest complexation.
- Acyl-cyclodextrins, like beta-cyclodextrin cinnamate (betaCDC), undergo hydrolysis reactions.
- Amine catalysts can accelerate the deacylation of acyl-cyclodextrins.
Purpose of the Study:
- To investigate the catalytic hydrolysis of beta-cyclodextrin cinnamate (betaCDC) and alpha-cyclodextrin cinnamate using various amines.
- To determine the catalytic efficiency and mechanism of amine-catalyzed hydrolysis.
- To evaluate the potential of these systems as models for hydrolytic enzyme reactions.
Main Methods:
- Kinetic studies of betaCDC and alpha-cyclodextrin cinnamate hydrolysis in the presence of different amines.
- Determination of rate constants and catalytic rate constants.
- pH-rate profile analysis and deuterium oxide solvent isotope effect studies.
- Characterization of betaCDC-amine complexes.
Main Results:
- The catalytic activity of amines in betaCDC hydrolysis followed the order: 1,4-diazabicyclo(2.2.2)octane > n-butylamine > quinuclidine > piperidine > triethylamine >> diisobutylamine.
- The betaCDC/1,4-diazabicyclo(2.2.2)octane complex showed a 6-fold increase in catalytic rate constant compared to spontaneous hydrolysis, increasing to 57-fold at pH 13.6.
- Mechanistic studies suggest 1,4-diazabicyclo(2.2.2)octane assists hydroxide ion attack on the carbonyl carbon of betaCDC.
Conclusions:
- Amine catalysis significantly accelerates the hydrolysis of beta-cyclodextrin cinnamate.
- The 1,4-diazabicyclo(2.2.2)octane/betaCDC system demonstrates a highly efficient catalytic mechanism, particularly at high pH.
- These findings establish cyclodextrin-amine complexes as superior models for enzyme-catalyzed ester hydrolysis.
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