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Enantioselective ester hydrolysis catalyzed by imprinted polymers.
B Sellergren1, R N Karmalkar, K J Shea
1Department of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg University, Mainz, Duesbergweg 10-14, D-55099, Mainz, Germany.
The Journal of Organic Chemistry
|June 24, 2000
Summary
Molecularly imprinted polymers catalyzed enantioselective hydrolysis of BOC-Phe-ONP. These polymers mimic chymotrypsin active sites, showing selective hydrolysis of specific BOC-Phe-ONP enantiomers.
Area of Science:
- Polymer Chemistry
- Catalysis
- Biomimetic Chemistry
Background:
- Molecular imprinting creates polymers with specific binding sites.
- Mimicking enzyme active sites in synthetic polymers is a key goal in catalysis.
- Chymotrypsin's catalytic mechanism involves specific amino acid residues.
Purpose of the Study:
- To prepare highly cross-linked polymers using molecular imprinting.
- To incorporate chymotrypsin-like catalytic elements into polymer active sites.
- To evaluate the enantioselective hydrolysis of N-tert-butoxycarbonyl phenylalanine-p-nitrophenyl ester (BOCPheONP).
Main Methods:
- Free radical copolymerization of template molecules with methacrylic acid (MAA) and ethylene glycol dimethacrylate (EDMA).
- Template removal by hydrolysis to generate catalytic sites.
- Enantioselective hydrolysis assays using BOCPheONP and phenylalanine ethyl esters.
Main Results:
- Polymers exhibited enantioselective hydrolysis of BOCPheONP, with D-selectivity (kD/kL = 1.9) for series A and L-selectivity (kL/kD = 1.2) for series B.
- Maximum rate enhancement of 10-fold compared to solution-phase imidazole.
- Catalytic activity increased after nucleophilic treatment due to higher site density and flexibility.
- Polymers discriminated between transition state and ground state structures in transesterification.
- Catalysis observed only at acidic pH; inhibition at basic pH.
- Rate enhancement of up to 3-fold for nonactivated phenylalanine ethyl esters, with D-templated polymers showing preferential hydrolysis of D-ethyl ester and saturation kinetics.
Conclusions:
- Molecularly imprinted polymers can effectively mimic enzyme active sites for enantioselective catalysis.
- The polymer structure and template design influence catalytic activity and selectivity.
- These synthetic catalysts show potential for applications in chiral synthesis and resolution.