Chiral sulfoxides monooxygenases

Oxidations catalyzed by monooxygenases Oxygenations of C-H and C=C bonds forming alcohols, epoxides enantioselective Baeyer-Villiger oxidations of ketones to chiral lactones and of sulfides to chiral sulfoxides nuclear and side-chain hydroxylation of aromatic compounds. 

Other oxidoreduction examples of inversion are the sulfoxide/sulfide and N-oxide/tertiary amine equihbria. Chiral sulfoxides (e.g., sulindac, flosequinan, pantoprazole) that contain tricoordinated sulfur atoms or tertiary amine N-oxides are first reduced by reductases to the corresponding achiral sulfides or tertiary amines, respectively. The reduced metabohtes are nthen reoxygenated by monooxygenases back to the parent compound, which can result in an altered ratio of the two enantiomers or epimers. 

Walsh and coworkers oxidized ethyl p-tolyl sulfide on an analytical scale to the S-sulfoxide of 64% enantiomeric purity using a bacterial flavoenzyme cyclohexanone monooxygenase derived from Adnetobacter . Using a flavin adenine dinucleotide containing monooxygenase purified from hog liver microsomes yielded the R-sulfoxide of 90% enantiomeric purity. HPLC on a column containing a 3,5-dinitrobenzoyl-D-phenylglycine chiral stationary phase was used to determine the optical purity of the sulfoxides. 

Light DR, Waxman DJ, Walsh C. 1982. Studies on the chirality of sulfoxidation catalyzed by bacterial flavoenzyme cyclohexanone monooxygenase and hog liver flavin adenine dinucleotide containing monooxygenase. Biochemistry 21 2490-2498. 

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