Biotransformation pathways reduction

Surh YJ, Lee SS. (1992). Enzymatic reduction of shogaol a novel biotransformation pathway for the alpha, beta-unsaturated ketone system. Biochem Int. 27(1) 179-87. 

Two general biotransformation pathways have been observed for nitroaromatics, including TNT (1) sequential nitro-to-amino reduction, and (2) elimination of the nitro group to form nitrite. By far, the most commonly reported reactions involve the nitro-to-amino reduction in which the nitro groups are utilized as electron acceptors or cometabolites. 

In addition to the physicochemical factors that affect xenobiotic metabolism, stereochemical factors play an important role in the biotransformation of drugs. This involvement is not unexpected, because the xenobiotic-metabolizing enzymes also are the same enzymes that metabolize certain endogenous substrates, which for the most part are chiral molecules. Most of these enzymes show stereoselectivity but not stereospecificity in other words, one stereoisomer enters into biotransformation pathways preferentially but not exclusively. Metabolic stereochemical reactions can be categorized as follows substrate stereoselectivity, in which two enantiomers of a chiral substrate are metabolized at different rates product stereoselectivity, in which a new chiral center is created in a symmetric molecule and one enantiomer is metabolized preferentially and substrate-product stereoelectivity, in which a new chiral center of a chiral molecule is metabolized preferentially to one of two possible diastereomers (87). An example of substrate stereoselectivity is the preferred decarboxylation of S-a-methyIdopa to S-a-methyIdopamine, with almost no reaction for R-a-methyIdopa. The reduction of ketones to stereoisomeric... 

Experimental evidence implies that the electrons from the cathodic electrode are transported into cells with different unclear electron transfer routes, and then elevate the intracellular reducing equivalents ie., NADHVNAD ), which forces the CO2 reduction to more complicated organics through different metabolic pathways. Although several inwards electron transfer pathways and CO2 biotransformation pathways have been proposed,the detailed mechanisms are still ambiguous and more efforts should be made at understanding them. ... 

Absorption - Diethylpropion is rapidly absorbed from the Gl tract after oral administration and is extensively metabolized through a complex pathway of biotransformation involving N-dealkylation and reduction. Many of these metabolites are biologically active and may participate in the therapeutic action of diethylpropion. 

Two types of enzymatic pathways, the so-called phase I and phase II pathways, are generally implicated in drug biotransformation. Phase I pathways correspond to functionalization processes, whereas phase II correspond to biosynthetic or conjugative processes. Phase I functionalization processes include oxidation, reduction, hydrolysis, hydration, and isomerization reactions. 

Fig. 3.5 Metabolism of 2 furnishes 118 metabolites via 25 different pathways ofwhich those are depicted in this scheme that are gluthatione (GSH) dependent. From the exemplary biotransformation of 2 can be inferred that besides stereoselective reduction there exist competing pathways in S. cerevisiae as a result of xenobiotic cell stress (/) stereoselective reduction,...

As described in Chapter Ih drug metabolism is composed of two distinct pathways of biochemical processing/ Phase I and Phase II. Phase I is a chemical modification (typically oxidatioiy hydrolysis/ or reduction reactions) performed primarily by members of the CYP enzyme family (49). Phase II metabolism consists of the biotransformation... 

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