Aldehydes enzymatic reduction

Asymmetric reduction of ketones or aldehydes to chiral alcohols has received considerable attention. Methods to accomplish this include catalytic asymmetric hydrogenation, hydrosilylation, enzymatic reduction, reductions with biomimetic model systems, and chirally modified metal hydride and alkyl metal reagents. This chapter will be concerned with chiral aluminum-containing reducing re-... 

An EPR signal, characteristic for the superoxide radical, was observed by the rapid-freezing technique in the oxidation at pH 10 of xanthine by dioxygen catalysed by xanthine oxidase (EC 1,2.3.2) The enzymatic reduction of dioxygen by aldehyde oxidase (EC 1.2.3.1) produces also the superoxide radical. 

Reduction of Aldehydes. Stereospecificially labeled primary alcohols are useful in biochemical and physical organic studies. Such compounds may be prepared by enzymatic reduction of a labeled aldehyde using yeast. However, isolation of the product is often tedious. Alpine-Borane greatly simplifies the process and provides compounds of high enantiomeric purity. It is the most efficient reagent available for reduction of aldehydes. The limiting... 

Waxes mainly function as protective coatings, such as those found on leaf cuticles. They are mixtures of many constituents with high melting points, important members being esters of fatty acids with straight-chain saturated alcohols (fatty alcohols). The fatty acids and alcohols in these wax esters have similar chain lengths, mainly in the range C24 to C28. They have predominantly an even number of carbon atoms because the alcohols are biosynthesized from fatty acids by enzymatic reduction (Eqn 2.7). Lesser amounts of ketones, branched alkanes and aldehydes are present. 

Beer, on the other hand, is produced by more complex biochemical and technological processes, which all affect its flavor. Yeast amino acid metabolism, a key to the development of beer flavor as described earlier, is affected by process temperature and use of cell immobilization techniqnes. Therefore, technologies based on these features as well as other process conditions and strain selection have been developed to control beer flavor. The combination of immobilized yeast and low-temperature primary fermentation was found to produce beers with low diacetyl amounts, therefore indicating potential of low-cost industrial application since maturation is a high-energy-consuming process. Finally, Perpete and Collin showed that during alcohol-free beer production, the enzymatic reduction of worty flavor (caused by Strecker aldehydes) by brewer s yeast was improved by cold contact fermentation. 

Rauen s (1958) approach to the cleavage problem seems rather complicated. Pig liver homogenates or mitochondria-free preparations, in the presence of Ci donors and oxidizing agents, yielded a mbcture of iV -formyl-PGA and 2-NHr4-OH-pteridine-6-aldehyde. This apparently combines the enzymatic reduction of PGA to FH4 and formyl derivatives with their subsequent autoxidation and cleavage Rauen thinks that the process is nonenzymatic. 

The combination of a chemoselective enzymatic reduction step with another second enzymatic reaction is another opportunity to overcome limitations, for example, in the case of the enantiosdective reduction of prochiral unsaturated aldehydes by coupling a reduction step with an isolated ene reductase (OYE 2 or OYE3) together with an oxidation step with HLADH in a cascade system, which allowed both yields and enantioselectivities to be improved [136]. 

An intriguing finding was made while investigating ERED-catalyzed reductions of vinylnitro compounds 69 after successful hydride addition to the Michael acceptor, the resulting nitroalkane 70 was also prone to enzymatic reduction. Spontaneous protonation of the nitroso intermediate 71 and subsequent oxime 72 reduction leads to aldehyde 74 after hydrolysis of an intermediate imine 73, thus representing a biological equivalent of a catalyzed Nef reaction. 

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. 

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