Enzymatic transformations reductions

Zhu, D., Ankati, H., Mukheijee, C. et al. (2007) Asymmetric reduction of /3-ketonitriles with a recombinant carbonyl reductase and enzymatic transformation to optically pure /3-hydroxy carboxylic acids. Organic Letters, 9 (13), 2561-2563. 

In MET, a low-molecular-weight, redox-active species, referred to as a mediator, is introduced to shuttle electrons between the enzyme active site and the electrode.In this case, the enzyme catalyzes the oxidation or reduction of the redox mediator. The reverse transformation (regeneration) of the mediator occurs on the electrode surface. The major characteristics of mediator-assisted electron transfer are that (i) the mediator acts as a cosubstrate for the enzymatic reaction and (ii) the electrochemical transformation of the mediator on the electrode has to be reversible. In these systems, the catalytic process involves enzymatic transformations of both the first substrate (fuel or oxidant) and the second substrate (mediator). The mediator is regenerated at the electrode surface, preferably at low overvoltage. The enzymatic reaction and the electrode reaction can be considered as separate yet coupled. 

A high-yielding, all-aqueous process for the manufacture of ceftibuten 69 from fermented CPC broth has also been described via enzymatic transformations and electrochemical reduction without isolation of any precursors <20020PD152, 20020PD158, 20020PD169>. 

There are many reactions in soil-water systems pertaining to nutrient availability, contaminant release, and nutrient or contaminant transformations. Two processes regulating these reactions are chemical equilibria (Chapter 2) and kinetics. The specific kinetic processes that environmental scientists are concerned with include mineral dissolution, exchange reactions, reductive or oxidative dissolution, reductive or oxidative precipitation, and enzymatic transformation. This chapter provides a quantitative description of reaction kinetics and outlines their importance in soil-water systems. 

A multifunctional biosynthetic machinery mediates the synthesis of these complex natural products from acetyl- and propionyl-coenzyme A [3). In the case of type I polyketide-synthases, the )8-oxo-esters made by polycondcnsa-tion steps are modified for example by reduction or dehydration after the chain elongation. Additional specific enzymatic transformations, e.g. oxidations and glycosylations, usually take place after the decoupling at the completed macrocyclic ring framework [1,3],... 

Reduction Phase I can also be accomplished by means of reductions. The reductive enzymes are localized both in the micro-somes and the cytosol. They trigger the enzymatic transformation of ketones, aldehydes, sulphoxides, nitro- and azo-linkages, etc. The intestinal flora also contributes to the reductive metabolism of foreign substances. 

Enzymes are an increasingly available and important tool in the arsenal of the synthetic chemist. Enzymatic reductions are often straightforward and highly stereoselective. There are now many enzymatic transformations that are compatible with the use of organic solvents.6l5 Other solvents can be used as well, illustrated by the enzyme alcohol dehydrogenase from Geotrichum candidum, which is active in supercritical carbon dioxide.6i6 Prelog studied the reduction of ketones with several enzymatic systems. Reduction of... 

Many substances, both natural (e.g steroid hormones) and foreign (e.g. drugs) are transformed or degraded in the L. and transported to the kidneys in the blood, in the form of glucuronides or sulfates, where they are excreted in the urine. Insulin is inactivated in the L. by reduction. Vitamin D3 (cholecalci-ferol) is enzymatically transformed into 25-hydroxy-... 

In addition, metal-catalyzed carbon-carbon bond formation and subsequent enzymatic transformations turned out to be compatible. This has been demonstrated by the Groger and Hummel groups [59], combining the Suzuki reaction as an example for a paUadium-catalyzed cross<oupling reaction with an asymmetric ADH-catalyzed ketone reduction in an aqueous reaction medium (Scheme 19.24). In such a one-pot process, the amount of boronic acid turned out to be critical because of strong inhibition of the enzyme. Thus, a two-step one-pot strategy was developed which was based on the use of 1 equiv of boronic acid in the Suzuki reaction, and addition of the enzyme directly to the reaction mixture after consumption... 

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