Michael reaction, aldolase antibody

On the basis of encouraging work in the development of L-proline-DMSO and L-proline-ionic liquid systems for practical asymmetric aldol reactions, an aldolase antibody 38C2 was evaluated in the ionic liquid [BMIM]PF6 as a reusable aldolase-ionic liquid catalytic system for the aldol synthesis of oc-chloro- 3-hydroxy compounds (288). The biocatalytic process was followed by chemical catalysis using Et3N in the ionic liquid [BMIM]TfO at room temperature, which transformed the oc-chloro-(3-hydroxy compounds to the optically active (70% ee) oc, (3-epoxy carbonyl compounds. The aldolase antibody 38C2-ionic liquid system was also shown to be reusable for Michael additions and the reaction of fluoromethylated imines. 

We routinely use these substrates for kinetic characterizations of new aldolase catalysts. However, they are not suitable for cell-based screenings because both substrate and product are readily cell permeable. The solution to this problem came when we discovered that our aldolase antibodies catalyze the -elimination (or r ro-Michael reactions) of (3-hetero substituted ketones 37 [Scheme 8 (1)]. 

A proposed mechanism for the Michael addition reaction is shown in Scheme 10.7. Note that enamine, generated from the reaction of hydroxyacetone and aldolase antibody 38C2, reacts with the activated methylene group in 2-(phenyl)ethyl-2-(tri-fluoromethyl)acrylate. 

Because aldolase antibodies operate by an enamine mechanism, they also catalyze other reactions that proceed by a similar mechanism. For example, as described in the section on prodrug activation reactions, antibodies 38C2 and 33F12 catalyze / -elimination (retro-Michael) reactions (Section 6.3.6). These antibodies also catalyze decarboxylation of j5-keto acids (Scheme 6.12)... 

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