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Tyrosinase catalyzes asymmetric sulfoxidation
Roberta Pievo1, Michele Gullotti, Enrico Monzani
1Dipartimento di Chimica Inorganica, Metallorganica e Analitica - Università di Milano, Istituto ISTM-CNR 20133 Milano, Italy.
Biochemistry
|February 26, 2008
Summary
Mushroom tyrosinase oxidizes organic sulfides to sulfoxides using a catechol cosubstrate. This novel reaction, achieving high enantioselectivity, demonstrates oxygen transfer from the enzyme to the sulfide.
Area of Science:
- Biocatalysis
- Enzymology
- Organic Chemistry
Background:
- Mushroom tyrosinase typically catalyzes diphenol oxidation.
- Organic sulfides are important chemical intermediates.
- Sulfoxidation reactions are crucial in synthetic chemistry.
Purpose of the Study:
- To investigate the novel catalytic activity of mushroom tyrosinase in sulfoxidation.
- To explore the mechanism and optimize conditions for enzyme-catalyzed sulfoxidation.
- To achieve enantioselective synthesis of sulfoxides using mushroom tyrosinase.
Main Methods:
- Enzymatic oxidation of thioanisole using mushroom tyrosinase.
- Employing l-3,4-dihydroxyphenylalanine (L-dopa) as a cosubstrate.
- Utilizing ascorbic acid to enhance enzyme stability and reaction yield.
- Employing (18)O2 isotopic labeling to confirm oxygen transfer.
Main Results:
- Mushroom tyrosinase catalyzed the oxidation of thioanisole to methyl phenyl sulfoxide.
- The reaction proceeded with moderate yields (approx. 20%) and high enantioselectivity (approx. 85% e.e.), favoring the (S)-enantiomer.
- Enantioselectivity exceeded 90% e.e. with added ascorbic acid.
- (18)O2 labeling confirmed direct oxygen transfer from the enzyme to the sulfide.
Conclusions:
- Mushroom tyrosinase exhibits unprecedented monooxygenase-like activity in catalyzing sulfoxidation.
- The reaction mechanism involves oxygen transfer from the oxy-tyrosinase form.
- This biocatalytic approach offers a promising route for enantioselective sulfoxide synthesis.
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