Transesterification inhibitors

Transesterification of PET/PC blends can lead to copious gas evolution (carbon dioxide). To suppress transesterification of binary polyesters, inhibitors such as inorganic phosphates can be added. 

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We succeeded in showing that recycling of the enzyme was indeed possible in our IL solvent system, though the reaction rate gradually dropped with repetition of the reaction process. Since vinyl acetate was used as acyl donor, acetaldehyde was produced hy the hpase-catalyzed transesterification. It is well known that acetaldehyde acts as an inhibitor of enzymes because it forms a Schiff base with amino residue in the enzyme. However, due to the very volatile nature of acetaldehyde, it easily escapes from the reaction mixture and therefore has no inhibitory action on the lipase. However, this drop in reactivity was assumed to be caused by the inhibitory action of acetaldehyde oligomer which had accumulated in the [bmim][PFg] solvent system. In fact, it was confirmed that the reaction was inhibited by addition of acetaldehyde trimer. =... 

The transesterification of cocaine to cocaethylene is an enzymatic reaction catalyzed by microsomal carboxylesterases and blocked by inhibitors of serine hydrolases [124][125], In Chapt. 3, we have discussed the mechanism of serine hydrolases, showing how a H20 molecule enters the catalytic cycle to hydrolyze the acylated serine residue in the active site of the enzyme. In the case of cocaine, the acyl group is the benzoylecgoninyl moiety (Fig. 7.9,d ), which undergoes esterification with ethanol according to Steps e and/ (Fig. 7.9). 

In animals pretreated with ethanol, metabolism of cocaine to norcocaine and benzoylnorecgonine increased, as reflected by higher tissue AUCs, as compared with those receiving water. Ethanol pretreatment also resulted in measurable levels of norcocaethylene in liver and lung. These observations are consistent with the increased hepatotoxicity (presumably due to enhanced N-oxidative metabolism) observed when mice were exposed to cocaine or cocaethylene and the esterase inhibitor diazinon (Roberts et al. 1992 Thompson et al. 1979). This shift toward N-oxidative metabolism provides a mechanism to explain potentiation of cocaine hepatotoxicity by ethanol (lover et al. 1991). Detection of norcocaethylene in ethanol- pretreated rats is consistent with norcocaethylene detected in the hair of heavy cocaine users, suggesting common pathways including hydrolysis, transesterification, and N-demethylation (figure 1) (Cone etal. 1991). 

The same transesterification approach was used for the synthesis of synthetic phostone analogue 75 of phosphoamidone, which is a natural selective inhibitor of thermolisine and endoteline produced by Actinomices. (Scheme 42) [94],... 

Moniruzzaman, M. Kamiya, N. Goto, M. (2010). Activation and stabilization of enzymes in ionic liquids. Org, Biomol. Chem., 8,13, 2887-2899 Nagaoka, T. Banskota, A.H. Tezuka, Y. Midorikawa, K. Matsushige, K. Kadota, S. (2003). Caffeic acid phenethyl ester (cape) analogues Potent nitric oxide inhibitors from the netherlands propolis. Biol Pharm. Bull, 26,4,487-491 Nara, S.J. Harjani, J.R. Salunkhe, M.M. (2002). Lipase-catalysed transesterification in ionic liquids and organic solvents A comparative study. Tetrahedron Lett., 43, 16, 2979-2982... 

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