Ketones enzymatic oxidation

Enzymatic oxidations have been reported. Bacilus stearothermophilus, for example, oxidizes secondary alcohols to the ketone. 

Fig. 5 Enzymatic oxidation of highly hydrolysed PVA proceeds in two steps 1,3-diol elements in PVA are oxidised via the [l-OH-ketone to form a diketone moiety. Three enzyme systems using different electron acceptors as cofactors/cosubstrates are shown...

An enzyme reactor with immobilized 3 -hydroxysteroid dehydrogenase has been successfully used for the analysis of residues of 17 -methyltestosterone in trout by high-performance liquid chromatography (HPLC) (269). Following their separation by reversed-phase chromatography, the major tissue metabolites of 17 -methyltestosterone, namely 5 -androstane-17 -methyl-3, 17 -diol, and 5 -androstane-17 -methyl-3, 17 -diol, were enzymatically modified in the presence of a coreactant, nicotinamide-adenine dinucleotide (NAD), to the corresponding ketone. The position at 3 was enzymatically oxidized, and NADH, the reduced form of NAD, was produced as a coproduct and subjected to fluorescence detection. Reoxidation of NADH to NAD provides the possibility for electrochemical detection. 

N-oxide groups can undergo enzymatic demethy-lation thiol and catchol groups that can undergo methylation some methyl (CH3) and methylene (CH2) groups can be enzymatically oxidized to produce aldehyde and ketone groups, respectively (-2H-1-0=-1-14 Da). 

Mention should also be made here of the extensive use of poly(vinyl alcohol) in potentially biodegradable applications. At appropriate hydroxyl contents these polymers will dissolve in water (see Chapter 14) and can apparently be conveniently washed away after use as a water-soluble packaging. Biodegradation does, however, appear to be slow and first requires an oxidative step involving enzymatic attack to a ketone such as polyenolketone, which then biodegrades more rapidly. 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can be reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. Monosaccharides can also be chain-lengthened by the multistep Kiliani-Fischer synthesis and can be chain-shortened by the Wohl degradation. 

After the first hydrolytic step, secondary alcohols seem to continue biodegradation through ketone, hydroxyketone, and diketone. Diketones then produce a fatty acid and a linear aldehyde which is further oxidized to fatty acid. Finally, these two fatty acids continue biodegradation by enzymatic 3 oxidation [410],... 

During the past few years, increasing numbers of reports have been published on the subject of domino reactions initiated by oxidation or reduction processes. This was in stark contrast to the period before our first comprehensive review of this topic was published in 1993 [1], when the use of this type of transformation was indeed rare. The benefits of employing oxidation or reduction processes in domino sequences are clear, as they offer easy access to reactive functionalities such as nucleophiles (e. g., alcohols and amines) or electrophiles (e. g., aldehydes or ketones), with their ability to participate in further reactions. For that reason, apart from combinations with photochemically induced, transition metal-catalyzed and enzymatically induced processes, all other possible constellations have been embedded in the concept of domino synthesis. 

Preparation and phytochemical reduction of 2,2 -thenoin and 2,2 -thenil have been studied in the authors laboratory (20a). It has been shown that 2,2 -thenoin gives a color reaction similar to that shown by benzoin and other acyloin condensation products in- the presence of alcoholic alkali. The hydroxy ketone may be oxidized by iodine in the presence of sodium methoxide to give the diketone, 2,2 -thenil, in excellent yields. Phytochemical reduction was shown also to be applicable to both compounds. It is significant that thenoin differs from benzoin, since reduction products were not obtained enzymatically from the latter. 

A comparable metabolic fate is documented for the hydraulic fluid tributyl phosphate. Following administration to rats, the Bu groups were oxidized to alcoholic, ketonic, and acidic metabolites. The oxidized Bu groups were then cleaved by enzymatic hydrolysis [103], With 2-ethylhexyl diphenyl phosphate (9.48), an interesting case of regioselectivity was noted during its in vivo metabolism in rats. Indeed, this flame retardant and plasticizer was... 

All evidence presented here indicates that the methoxime-to-ketone reaction is enzymatic, but the nature of the reaction is unclear. Hydrolysis by an uncharacterized hydrolase, as postulated by the authors, is a valid assumption. However, one should not dismiss another possibility, namely oxidative O-demethylation to the oxime, followed by spontaneous oxime-to-ketone hydrolysis, and stereospecific reduction, as explained above. 

Adlerol, i.e. l-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxyphenoxy)propan-l-ol, is a well-established dimeric model compound of lignin and, as such, its oxidation to the ketone-derivative Adlerone, i.e. l-(3,4-dimethoxyphenyl)-3-hydroxy-2-(2-methoxyphen-oxy)propan-l-one, has been taken as a benchmark reaction (Scheme 20) to evaluate the efficiency of several chemo-enzymatic procedures. 

Chain degradation proceeds at the oxidised sites, where two different routes can be discerned. One way uses the p-hydroxy ketone functionalities introduced by the initial enzymatic attack as direct substrates in an aldolase-like scission reaction. The other way proceeds via further oxidation of this structure to a 1,3-diketone, which serves as a target structure for a hydrolase-type splitting enzyme. 

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