Kemp elimination reactions

Scheme 2 Kemp elimination reaction of benzisoxazole with piperidine.

Acevedo, O. Role of water in the multifaceted catalytic antibody 4B2 for allylic isomerization and Kemp elimination reactions. J. Phys. Chem. B 2009,113,15372-81. 

The Kemp elimination is of special interest because it is known to be extraordinarily sensitive to the medium, and particularly well suited as a test reaction for potential enzyme mimics because it is a simple, one-step process. The joint conclusions from this work were that catalysis involves a combination of a number of different factors, even for this simple reaction by these simple catalysts. 

Figure 14 (a) Elimination reaction catalyzed by antibodies 43D4 and 3D12 raised against the quaternary ammonium 17 and (b) Kemp reaction catalyzed by antibody 34E4 raised against the amidinium 18. 

Kemp elimination was used as a probe of catalytic efficiency in antibodies, in non-specific catalysis by other proteins, and in catalysis by enzymes. Several simple reactions were found to be catalyzed by the serum albumins with Michaelis-Menten kinetics and could be shown to involve substrate binding and catalysis by local functional groups (Kirby, 2000). Known binding sites on the protein surface were found to be involved. In fact, formal general base catalysis seems to contribute only modestly to the efficiency of both the antibody and the non-specific albumin system, whereas antibody catalysis seems to be boosted by a non-specific medium effect. 

The data obtained by Kemp and Casey (1973) for the elimination reaction of substituted benzisoxazoles (22) which were interpreted as... 

The last design we present here is for a catalyst of the Kemp elimination, shown in Reaction 9.8. A hapten for this reaction, utilizing acetate as the base and acetic... 

Figure 2 Free-energy profile for the Kemp elimination of 5-nitro-benzisoxazole by antibody 4B2. The reaction coordinate for the proton transfer is r(0-H)-r(H-C) with r(0-H)+r(H-C)=2.85 A. Maximum free-energy values are truncated to 30 kcal/mol for clarity.

D Anna, E, La Marca, S., Noto, R. Kemp elimination A probe reaction to study ionic liquids... 

One model reaction that has proved a popular and appropriate probe for general base catalysis by potential binders of hydrophobic substrates is the Kemp elimination, the simple, single transition state ring-opening elimination of benzisoxazoles 4.19 (Scheme 2.39). 

Kemp elimination (unnatural reaction, for Catalytic promiscuity 95... 

Examples for a high degree of promiscuity obviously include nonenzymatic proteins such as serum albumins that exhibit promiscuous catalytic activities (Table 1, entry 14). Other cases may include catalysis of unnatural reactions, meaning reactions for which, to our knowledge, no natural enzyme has evolved (e.g., the Kemp elimination performed by serum albumin (Table 1, entry 14, or siloxane hydrolysis by lipase (Table 1, entry 7)). 

J. E. Kbjn, J. B. F. N. Engberts, Kemp elimination in membrane mimetic reaction media probing catalytic properties of catanionic vesicles formed from double-tailed amphiphiles, J. Am. Chem. Soc, 2003, 125, 1825-1833. 

Vesicles can be considered as minimal mimics of enzymes in terms of desolvation effects and entropy factors. If the general property of the vesicle membrane in promot-ing/accelerating chemical reactions is closely related to the one described above with micelles, it usually occurs with improved efficiency because of the higher structural organization of the bilayers. This was shown, for instance, in the study of the acceleration of the Kemp elimination in the presence of cationic micelles or cationic vesicles (Figure 17). ... 

Enzymes catalyze chemical reaction in aqueous media, but their active sites significantly differ in properties from water. In this chapter, the work on selected chemical reactions with important biological roles is reviewed to assess our current understanding of the effect of the environment that surrounds the reactive species. In particular, simple medium effects such as the ones provided by organic solvents, ionic liquids, and simple micelles are focused on. The findings that led to the computational design of enzymes that catalyze the Kemp elimination, a prototypical proton transfer reaction that has fascinated researchers for more than a century, are discussed. 

The base-catalyzed decomposition of benzisoxazoles to yield 2-cyanophenols (also called the Kemp ehmination. Figure 12) is a reaction that still fascinates researchers, even though it was first reported more than a century ago. The Kemp elimination (an E2 reaction) is not catalyzed by any known natural enzyme but it has been widely used for some time as a prototypical reaction for proton transfer from carbon, and very recently, has been one of the choices, and probably the most successful one (although far from perfect), for the de novo design of enzymes through the aid of computers.Its popularity is certainly facilitated by the ease of preparation of benzisoxazoles from salicylaldehydes, " and by the fact that the... 

Other simple systems are known to catalyze the Kemp elimination. These include amino-cyclodextrins, cationic micelles, vesicles, natural coals, ionic liquids, and methylated polyethyleneimine (syn-zymes) In all these systems, there was very htde contrihution from precise positioning of the catalytic base (if any), and electrostatic interactions with the transition state of the reaction were proposed to play a major role. 

D Anna F, La Marca S, Noto R. Kemp elimination a probe reaction to study ionic liquids properties. J Org Chem. 2008 73 3397-3403. 

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