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3.5.2.3.2 Oxidation in the Presence of Bovine Serum Albumin

DOI: 10.1055/sos-SD-216-00175

Grogan, G.Science of Synthesis: Biocatalysis in Organic Synthesis, (20153307.

Bovine serum albumin (BSA) has proved to be an effective chiral environment for oxidation of sulfides effected by common oxidants such as sodium metaperiodate and hydrogen peroxide. It has been demonstrated that either of these reagents is capable of catalyzing the asymmetric oxidation of alkyl aryl sulfides, but that the level of asymmetric induction is greatly dependent upon the concentration of bovine serum albumin and the pH of the reaction.[‌111‌] Oxidation at pH 9.2 gives the best results, with isopropyl phenyl sulfide being converted into the corresponding (R)-sulfoxide 51 (Ar1 = Ph; R1 = iPr) in 78% yield and with 81% ee (Scheme 28). The substrate range has been extended to include alkoxycarbonyl aryl sulfides[‌112‌] and other alkyl aryl and heterocyclic sulfides,[‌113‌] and (+)-1-phenyl-2-(phenylsulfinyl)ethan-1-ol is also obtained with 80% ee, albeit with only 20% yield. This extension in scope indicates no dependence of enantioselectivity on pH, but reactions are routinely performed using a lower concentration of bovine serum albumin (0.05 equivalents) than the previous work. It has subsequently been demonstrated that dioxiranes such as dimethyl dioxirane, generated in situ from the reaction of ketones and Oxone (potassium peroxomonosulfate), are also suitable oxidants, and that the enantioselectivity of oxidation could depend upon the dioxirane structure.[‌114‌,‌115‌] For example, isopropyl phenyl sulfide undergoes oxidation with methyl(trifluoromethyl)dioxirane to give the corresponding (R)-sulfoxide 51 (Ar1 = Ph; R1 = iPr) with 89% ee compared to 16% ee for the dioxirane derived from cyclohexanone (Scheme 28).

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