Sulfoxide Reductases and Applications in Biocatalytic Preparation of Chiral Sulfoxides: A Mini-Review

Chiral sulfoxides are valuable organosulfur compounds that have been widely used in medicinal and organic synthesis. Biocatalytic approaches for preparing chiral sulfoxides were developed in the past few years, mainly through asymmetric oxidation of prochiral sulfides. Recently, the application of sulfoxide reductase to prepare chiral sulfoxides through kinetic resolution has emerged as a new method, exhibiting extraordinary catalytic properties. This article reviews the chemical and biological functions of these sulfoxide reductases and highlights their applications in chiral sulfoxide preparation.

Asymmetric sulfoxidation of thioether catalyzed by soybean pod peroxidase ：kinetic model

The asymmetric sulfoxidation catalyzed by soybean pod peroxidase (SPP) in water-in-oil microemulsions were carried out with the yield of 91.56% and e.e of 96.08% at the activity of SPP of 3200 U ml-1 and 50℃ for 5 h. The mechanism with a two-electron reduction of SPP-I is accompanied with a single-electron transfer to SPP-I and nonenzymatic reactions, indicating that three concomitant sub-mechanisms contribute to the asymmetric oxidation involving five enzymatic and two nonenzymatic reactions, which can represent the asymmetric sulfoxidation of organic sulfides to form enantiopure sulfoxides. With 5.44% of the average relative deviation, a kinetic model fitting experimental data was developed. The enzymatic reactions may follow ping-pong mechanism with substrate inhibition of H2O2 and product inhibition of esomeprazole, while nonenzymatic reactions, a power law. Those results indicate that SPP with a lower cost and higher thermal stability may be used as an effective substitute for Horseradish Peroxidase.

Asymmetric sulfoxidation of thioether catalyzed by soybean pod peroxidase to form enantiopure sulfoxide in water-in-oil microemulsions: kinetic model

The asymmetric sulfoxidation catalyzed by soybean pod peroxidase (SPP) in water-in-oil microemulsions were carried out with the yield of 91.56% and e.e of 96.08% at the activity of SPP of 3200 U ml-1 and 50℃ for 5 h. The mechanism with a two-electron reduction of SPP-I is accompanied with a single-electron transfer to SPP-I and nonenzymatic reactions, indicating that three concomitant sub-mechanisms contribute to the asymmetric oxidation involving five enzymatic and two nonenzymatic reactions, which can represent the asymmetric sulfoxidation of organic sulfides to form enantiopure sulfoxides. With 5.44% of the average relative deviation, a kinetic model fitting experimental data very well was developed. The enzymatic reactions may follow ping-pong mechanism with substrate inhibition of H2O2 and product inhibition of esomeprazole, while nonenzymatic reactions, a power law. Those results indicate that SPP with a lower cost and higher thermal stability may be used as an effective substitute for Horseradish Peroxidase.

Recent Application of Chiral Aryliodine Based on the 2-Iodo­resorcinol Core in Asymmetric Catalysis

Chiral iodoarenes have been steadily increasing in importance in recent years, especially in enantioselective synthesis and catalysis. Since the development of the concept of chiral iodine(I/III) catalysis, the use of various chiral aryliodine frameworks has been explored in this area. This short review gives an overview of the use of chiral hypervalent iodine(I/III) reagents based on the 2-iodoresorcinol core with two attached two lactic side chains bearing ester or amide groups for the catalytic enantioselective dearomatization of phenol compounds, asymmetric oxidation of alkenes, and enantioselective α-functionalization of carbonyl compounds highlighting the excellent reactivities in terms of yield and enantioselectivity.1 Introduction2 Enantioselective Dearomatization of Phenol Derivatives3 Asymmetric Oxidation of Alkenes4 Enantioselective α-Functionalization of Carbonyl Compounds5 Conclusion and Outlook

The Chiral 1:2 Adduct (S)S(S)C(−)589-Ethyl 2-Phenylbutyl Sulphide-Mercury (II) Chloride:(−)589[(S)S(S)C-Et(2-PhBu)S.(HgCl2)2]. Stereoselective Synthesis, Asymmetric Oxidation, Crystal and Molecular Structure and Circular Dichroism Spectra

Optically active (−)589ethyl (S)-2-phenylbutyl thioether, (−)(S)C-Et(PhBu)S (I), and its new diastereoisomeric mercury (II) chloride adduct, 1:2, (−)[(S)S(S)C-Et(PhBu)S.(HgCl2)2]2, (II) were stereoselectively synthesized; the absorbance (UV) and circular dichroism (CD) spectra were measured and the crystal and molecular structure of complex (II) was determined by single-crystal X-ray diffraction. Two different Hg centres are present whose coordination environments are built by two short bonds to chloride ligands in one case, and to one chloride and one sulphur in the other one. These originate digonal units. Electroneutrality is achieved by a further chlorine, which can be considered prevalently ionic and bonded to the two Hg centres, forming square bridging systems nearly perpendicular to the digonal molecules. The coordination polyhedra can be interpreted as 2 + 4 tetragonally-compressed octahedra with the four longer contacts lying in the equatorial plane. IR spectroscopic data are consistent with the presence of one bent and one linear Cl–Hg–Cl moiety. The absolute configurations at both stereogenic centres of the formed diastereoisomeric complex (II) are (S). The (S)S absolute configuration at the stereogenic sulphur atom bonded to the mercury(II) atom in complex (II) has been related with the negative Cotton effect assigned in its circular dichroism (CD) spectrum to a charge-transfer transition at ca. 230 nm. The stereoselective oxidation of (I) and (II) with hydrogen peroxide, induced by the stereogenic carbon atom (S)C of the enantiopure sulphide, gave (−)598ethyl (S)C-2-phenylbutyl(S)S-sulphoxide, (−)598[(S)S(S)C-Et(PhBu)SO], (III), having 18.1% de. Oxidations carried out in the presence of a 200 molar excess of mercury(II) chloride gave (−)598ethyl (S)C-2-phenylbutyl(R)S-sulphoxide, (−) 598[(R)S(S)C-Et(PhBu)SO], (IV) with 31% de, showing the cooperative influence of mercury(II) chloride on the selectivity of the oxidation reaction.