Chemo-enzymatic oxidation

A similar oxidative protocol has been used for the oxidation of (fluoroalkyl)alkanols, Rf(CH2) CH20H, to the respective aldehydes [146], in the one-pot selective oxidation/olefination of primary alcohols using the PhI(OAc)2-TEMPO system and stabilized phosphorus ylides [147] and in the chemo-enzymatic oxidation-hydrocyanation of 7,8-unsaturated alcohols [148]. Other [bis(acyloxy)iodo]arenes can be used instead of PhI(OAc)2 in the TEMPO-catalyzed oxidations, in particular the recyclable monomeric and the polymer-supported hypervalent iodine reagents (Chapter 5). Further modifications of this method include the use of polymer-supported TEMPO [151], fluorous-tagged TEMPO [152,153], ion-supported TEMPO [154] and TEMPO immobilized on silica [148],... 

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. 

Rather less attention has been paid to enzymatic oxidations in ionic liquids. Chloroperoxidase (CPO) catalyzed the chemo- and enantioselective sulfoxidation of thioanisole (Figure 10.21) in aqueous mixtures containing up to 50% [HOEtMe3N] [citrate] or [MMIm][Me2P04] [145]. 

In the same contribution, the authors also introduce a very interesting chemo-enzymatic initiation system based on alcohol oxidase in combination with iron salts. Here, H202 originating for example, from the oxidation of methanol to formaldehyde undergoes Fenton-formation [73] of hydroxyl radicals to initiate polymerization (Figure 6.16). 

Mikrfajczyk M, Luczak J, Kielbasinski P, Colonna S (2009) Biocatalytic oxidation of thiophosphoryl compounds a new chemo-enzymatic approach to enantiomeric insecticidal thionophosphates and their oxons. Tetrahedron Asymmetry 20 1948-1951... 

Starting from UDP-Glc/UDP-GlcNAc biocatalytic epimerization and oxidation were combined with chemical hydrazone formation. These simultaneously occurring steps may be also classified as chemo-enzymatic one-pot cascade reaction. 

Mischitz, M. and Faber, K. (1996) Chemo-enzymatic s5mthesis of (2R,5S)- and (2R,5R)-5-(1-hydroxy-1-methylethyl)-2-vinyl-tetrahydrofuran ("linalool oxide") preparative application of a highly selective bacterial epoxide hydrolase. Synlett, 978-980. 

Karmee SK, Roosen C, Kohlmann C, Lutz S, Greiner L, Leitner W. Chemo-enzymatic cascade oxidation in supercritical carbon dioxide/water biphasic media. Green Chem. 2009 11 1052-1055. 

Some companies are successfully integrating chemo- and biocatalytic transformations in multi-step syntheses. An elegant example is the Lonza nicotinamide process mentioned earlier (.see Fig. 2.34). The raw material, 2-methylpentane-1,5-diamine, is produced by hydrogenation of 2-methylglutaronitrile, a byproduct of the manufacture of nylon-6,6 intermediates by hydrocyanation of butadiene. The process involves a zeolite-catalysed cyciization in the vapour phase, followed by palladium-catalysed dehydrogenation, vapour-pha.se ammoxidation with NH3/O2 over an oxide catalyst, and, finally, enzymatic hydrolysis of a nitrile to an amide. 

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