Deconjugation efficiency

Monch, S., and Rychlik, M., 2012. Improved Folate Extraction and Tracing Deconjugation Efficiency by Dual Label Isotope Dilution Assays in Foods. Journal of Agricultural and Food Chemistry. 60 1363-1372. 

Deconjugation of oL, -enones. The photochemical deconjugation of a,P-unsat-urated acids and esters via a dienol is often a useful preparative route to the P,y-unsaturated isomers. The corresponding reaction with a,p-enones is erratic it can result in reversion to the original enone or the trans-isomer. Irradiation in the presence of a mild base such as pyridine (or imidazole) can promote conversion of a,P-enones to p,7-enones. A stronger base such as triethylamine catalyzes reconjugation of the intermediate dienol. Base-catalyzed deconjugation is more efficient in polar solvents (DMF, CH,CN, CH,OH) than in ether or hydrocarbon solvents. Thus under proper conditions several a,p-enones previously considered inert to irradiation can be isomerized to the p,y-isomers. 

Hammond, G.B., and deMendonca, D.J.. An efficient synthesis of (Zl-y-fluoroallylphosphonates using a base-promoted deconjugation of (Ej-y-fluorovinylphosphonates, and its utility as fluoroolefin-containing building block, J. Fluorine Chem.. 102. 189, 2000. 

Around one-quarter of the bile acid conjugates reaching the ileum have the amino acid moiety removed by the action of bacterial enzymes. A decon-jugating enzyme, choloylglycine hydrolase (EC 3.5.1.24) has been isolated from clostridial bacteria (Nl) and is used in methods for the analysis of bile acids. The majority of deconjugated bile acids are reabsorbed and return to the liver, where they are efficiently reconjugated with glycine or taurine (V7). 

When bile salts are deconjugated by abnormal bacterial proliferation in the small bowel (40), yielding free or unconjugated bile salts with a pK of 4-6, they are quickly absorbed by nonionic diffusion in the jejunum so that intraluminal bile salt concentration may be insufficient for efficient fat absorption and steatorrhea may result (41). 

In this chapter, asymmetric organocatalyzed umpolung conjugate additions are considered. Particular emphasis on deconjugative Michael additions with a,a-dicyanoalkenes, the intramolecular Rauhut-Currier reaction, and the Stetter reaction is placed. These are very efficient transformations in the synthetic chemist s arsenal, but they are also challenging to control. 

The photo-Fries rearrangement has been used in various synthetic reactions. A recent application concerned the synthesis of the mitomycin precursor (148) in high yield from the lactone (147). Finally, reference is made to the efficient photochemical deconjugation of piperidine esters (149) to the endocyclic isomers (150), presumably by a photoenolization reaction. ... 

Obviously, the reaction of deconjugation is also highly sensitive to the substitution of the substrates, especially on the y-position. With substrates without substituents at this site, the reaction is not synthetically efficient, and starting materials are recovered almost quantitatively even after prolonged irradiation. ... 

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