Aldol condensation aldolase catalysis

Very recently the group of Resmini described the development of imprinted microgels mimicking a class I aldolase in the catalysis of the aldol condensation between 4-nitrobenzaldehyde and acetone [79]. They prepared highly crosslinked microgels (80 mol%) based on /V,/V -methyIenebisaery 1 amide as the crosslinker and containing as catalytically active monomer a proline derivative (Fig. 5). 

Primary amine catalysis (usually involving a lysine residue) has been recognised to play an important role in various enzyme-catalysed reactions. Examples are the conversion of acetoacetate to acetone catalysed by acetoacetate decarboxylase, the condensation of two molecules of S-aminolevulinic acid catalysed by -aminolevulinic deshydratase during the biosynthesis of porphyrins, and the reversible aldol condensation of dihydroxy-acetone phosphate with glyceraldehyde which in the presence of aldolase yields fructose-1-phosphate (64) (For reviews see, for example, Snell and Di Mari,... 

The role of metal ions in catalysis is well documented. Matsui etal. [115] used a co-ordinating Co2+ ion in a transition state analogue imprinting procedure to prepare synthetic class II aldolase mimics as catalysts of the aldol condensation (Figure 6.30). 

Cyclodextrins with two imidazole groups on the primary hydroxyl side can enhance the enolate formation [86] of a simple bound ketone by bifunctional acid-base catalysis and accelerating the intramolecular aldol condensation of bound ketoaldehyde and dialdehyde. The aldolase mimics which catalyzed crossed aldol condensations were obtained by the assembly of (i-CD and various amino moieties as Schiff base [87]. 

Glucose-6-P is then isomerized by phosphohexose isomerase to fructose-6-P (making up 30% of the equilibrium mixture). Another kinase phosphorylates the 1-position and the resulting fructose diphosphate is cleaved in an equilibrium reaction to two trioses, namely dihydroxyacetone phosphate (C-1 to C-3) and glyceral-dehyde phosphate (C-4 to C-6). The equilibrium mixture is composed of 89% hexose and 11% triose (under the conditions of Meyerhof s measurements) condensation, therefore, is the preferred (= exergonic) reaction. The reaction is analogous to the aldol condensation described in organic chemistry (Chapt. 1-2, XV-5). Catalysis of the reverse reaction by the enzyme aldolase is explained by the fact that enzymes always catalyze up to the equilibrium. ... 

Antibody Catalysis. Recent advances in biocatalysis have led to the generation of catalytic antibodies exhibiting aldolase activity by Lemer and Barbas. The antibody-catalyzed aldol addition reactions display remarkable enantioselectivity and substrate scope [18]. The requisite antibodies were produced through the process of reactive immunization wherein antibodies were raised against a [Tdiketone hapten. During the selection process, the presence of a suitably oriented lysine leads to the condensation of the -amine with the hapten. The formation of enaminone at the active site results in a molecular imprint that leads to the production of antibodies that function as aldol catalysts via a lysine-dependent class I aldolase mechanism (Eq. 8B2.12). 

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