Enzymatic sulfoxidation

Recent Developments in Flavin-Based Catalysis Enzymatic Sulfoxidation... 

Mechanism of the enzymatic sulfoxidation of prochiral sulfides catalyzed by flavoprotein monooxygenases. 

Enzymatic Sulfoxidations Catalyzed by Flavin-Containing Monooxygenases... 

Very recently, CPO was assessed in an enantioselective cascade oxidation using a biphasic media composed of supercritical carbon dioxide/water." Herein, the enzymatic sulfoxidation was carried out by generating hydrogen peroxide via Pd(0)-catalyzed formation from hydrogen and oxygen (in SCCO2) (Scheme 36.30). Overall, this example represents an outstanding case on how biocatalysis can be applied under different nonconventional reaction media, as... 

Soluble organic solvents have often been used as cosolvents to solubilize miscible organic substrates. Since organic compounds including solvents are possibly incorporated inside of the enzyme, they may affect the stereoselectivity of enzymatic reactions. For example, dimethyl sulfoxide (DMSO) (10%) enhance not only chemical yield but also enantioselectivity of yeast reduction. Thus, the poor yield of 23% with 80% ee was increased to 65% yield with >99% ee (Figure 8.20) [17]. 

The enzymatic oxygenation process is of particular value as there is a significant difference in the formation rates of sulfoxides and sulfones. The initial conversion of sulfide to the optically active sulfoxide by an MO is usually very fast compared to the subsequent oxidation step to sulfone, upon which chirality is lost (Scheme 9.26). In many cases, over-oxidation to sulfone is not observed at all when employing MOs. 

An attempt at the enzymatic hydrolysis of racemic a-acetoxymethyl sulfoxides rac-25 gave the recovered esters in yields up to 40% and with ees up to 95%. The hydrolysis products, a-hydroxymethyl sulfoxides 26, underwent decomposition like in the case of analogous hydroxy sulfides (Equation 1) and hydroxy... 

FIGURE 7. The enzymatic reduction of N-acetyl-L-methionine sulfoxide. 

Oxime carbamates are not directly amenable to gas chromatography (GC) because of their high thermal instability, which often leads to their breakdown at the injection port or in the column during analysis. Analysis of oxime carbamates by GC with sulfur detection or flame photometric detection involves oxidation of the intact insecticides or alkaline hydrolysis to form the more volatile but stable oxime compound. Enzymatic techniques have been reported for the analysis of these compounds. Enzyme-linked immunosorbent assay (ELISA) has been used to determine aldicarb and its sulfone and sulfoxide metabolites and methomyl in water, soil, and sediment samples. 

In contrast to the situation with the Baeyer-Villiger oxidation, synthetic chemists have a choice of both enzymatic or non-enzymatic methods for the oxidation of sulfides to optically active sulfoxides with good to excellent yields and enantiomeric excesses. 

Disulfoton causes neurological effects in humans and animals. The mechanism of action on the nervous system depends on the metabolism of disulfoton to active metabolites. The liver is the major site of metabolic oxidation of disulfoton to disulfoton sulfoxide, disulfoton sulfone, demeton S-sulfoxide and demeton S-sulfone, which inhibit acetylcholinesterase in nervous tissue. These four active metabolites are more potent inhibitors of acetylcholinesterase than disulfoton. Cytochrome P-450 monooxygenase and flavin adenine dinucleotide monooxygenase are involved in this metabolic activation. The active metabolites ultimately undergo nonenzymatic and/or enzymatic hydrolysis to more polar metabolites that are not toxic and are excreted in the urine. 

Sulfoxidation reactions are characterized by enzymatic conversion of a divalent compound to sulfoxide (Fig. 15.7) or, in some cases, to sulfone (S SO O ). The degradation also may be catalyzed by minerals, converting organic sulfides (thioesters) and sulfites to the corresponding sulfoxides and sulfates. Because it is difficult to determine if the reaction is chemically or biologically induced, microbially mediated sulfoxidation in the subsurface environment can be established only when a biocatalyst is found. 

In this enzymatic transformation, three optically active compounds were prepared in one step. Besides the enantiomerically enriched hydroperoxide (5)-16/17a, also the opposite enantiomer of the corresponding alcohol (/f)-19/18a and enantiomerically enriched (S)-sulfoxide 23 could be isolated (equation 13). 

Enantiopure (5)-fluoroalanine has been prepared by an enzymatic path starting from 3-fluoropyruvate in the presence of alanine dehydrogenase, and also by chemical synthesis from (5)-p-tolyl methyl sulfoxide (Figure 5.1) or from the L-serine. The analogue labeled with F has been prepared for use in positron emission tomography (PET) used in cancer diagnosis. ... 

Scheme 7.3 Enzymatic production of sulfur-containing flavour compounds in Allium species from amino acid flavour precursors, a S-Alk(en)yl cysteine sulfoxides and b (+)-S-l-propenyl cysteine sulfoxide (isoalliin) P-5 -Ppyridoxal-5 -phosphate...

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