Aldolase organic synthesis

TKsubstrate pNZYTffiS IN ORGANIC SYNTHESIS] (Vol 9) D-Glyceraldehyde-3-phosphate[591-57-l]aldolase-cataly zed additions... 

The charged group introduced into products by the aldol donors (phosphate, carboxylate) facilitates product isolation and purification by salt precipitation and ion exchange techniques. Although many aldehydic substrates of interest for organic synthesis have low water solubility, at present only limited data is available on the stability of aldolases in organic cosolvents, thus in individual cases the optimal conditions must be chosen carefully. 

Like many other antibodies, the activity of antibody 14D9 is sufficient for preparative application, yet it remains modest when compared to that of enzymes. The protein is relatively difficult to produce, although a recombinant format as a fusion vdth the NusA protein was found to provide the antibody in soluble form with good activity [20]. It should be mentioned that aldolase catalytic antibodies operating by an enamine mechanism, obtained by the principle of reactive immunization mentioned above [15], represent another example of enantioselective antibodies, which have proven to be preparatively useful in organic synthesis [21]. One such aldolase antibody, antibody 38C2, is commercially available and provides a useful alternative to natural aldolases to prepare a variety of enantiomerically pure aldol products, which are otherwise difficult to prepare, allovdng applications in natural product synthesis [22]. 

A number of mechanistically distinct enzymes can likewise be employed for the synthesis of product structures identical to those accessible from aldolase catalysis. Such alternative cofactor-dependent enzymes (e.g. transketolase) are emerging as useful catalysts in organic synthesis. As these operations often extend and/or... 

Expanding the Scope of Aldolases as Tools for Organic Synthesis 111... 

Castillo, J.A., Calveras, J., Casas, J. et al. (2006) Fructose-6-phosphate aldolase in organic synthesis preparation of D-fagomine, /V-alkylated derivatives, and preliminary biological assays. Organic Letters, 8, 6067-6070. 

Yu, H. and Chen, X. (2006) Aldolase-catalyzed synthesis of beta-D-Gal-(l-9)-D-KDN a novel acceptor for sialyltransferases. Organic Letters, 8, 2393-2396. 

In contrast to the above two examples, for which applications were developed long before the responsible biocatalyst was discovered, aldolase applications are more recently developed. Indeed, aldolases and their natural function were extensively studied between the end of the 1960s and the beginning of the 1970s. The first patents about their applications in organic synthesis appear in the 1990s [67-69] and the first ton-scale applications were reported in 1997... 

Figure 2.20 The two mechanisms of aldolases. Group 1 enzymes from animals and higher plants use an amino group in the enzyme to form a Schiff s base intermediate to activate the aldol donors. Group II enzymes from lower organisms, use a metal ion, usually Zn " in the active site to form an enolate intermediate. The two mechanisms are examplified by fiuctose-1,6-diphosphate aldolase, a very important aldolase in synthesis and breakdown of sugars.

S. David, A. Malleron, and B. Cavayd, Aldolases in organic synthesis Acylneuraminate-pyiuvaie lyase accepts furanoses as substrates, New J. Chem. 76 751 (1972). 

The difference between then and now can be attributed in major part to the advent of enzymes in organic synthesis. Aldolases are nature s catalysts for the poor man s chemical aldol reaction. These remarkable enzymes can produce rare and important deoxyulosonic acids such as sialic acid and KDO on a small or large scale. 

In addition to the larger families of preparatively useful aldolases, some less common aldolases have been evaluated lately for preparative use. A range of mechanistically distinct enzymes, which are actually categorized as transferases but which also catalyze aldol-related additions through the aid of cofactors such as pyridoxal 5-phosphate (PLP), thiamine pyrophosphate (TPP), tetrahydro-folate (THF), or coenzyme A (CoA), are becoming more frequently applied in organic synthesis. Because of their emerging importance and/or commercial availability, a selection of these enzymes and examples of their synthetic utility will be included in further separate chapters. 

Fessner W-D (1992) A Building Block Strategy for Asymmetric Synthesis The DHAP Aldolases. In Servi S (ed) Microbial Reagents in Organic Synthesis. Kluwer Academic, Dordrecht, vol. 381, p 43... 

To date, 2-deoxy-D-ribose 5-phosphate aldolase (DERA) is the only acetaldehyde-dependent aldolase being applied in organic synthesis. Thus the stereoselectivity of DERA is significant, all known enzymes from different organisms showing the same preferences, limiting the field of application to syntheses in which specifically the DERA-catalyzed enantiomer is needed. 

The availability of 38C2 as a broad scope, enantioselective, efficient aldolase enzyme has had a significant impact on organic synthesis. Some of the molecules we have synthesized with 38C2 include the natural products ( + ) —frontalin [( + )— 27] (List et al., 1999), some brevicomins [( —) —28 and (—) —29] (List etal., 1998a), epothilones A (30) and C (31) (Sinha et al., 1998), and the Wieland-Miescher ketone [( ) — ( + )—32] (Hoffmann et al., 1998 Zhong et al., 1997). The brevicomin examples represent the first use of a catalytic antibody to decrease the total number of synthetic steps and increase the enantioselectivity of natural product syntheses. 

Aldolases are enzymes that form aldol products, most commonly in the metabolism of carbohydrates or sugars. In contrast to the chemical reaction, aldolases generate just one product stereospecifically. Hence, they are sometimes used in organic synthesis for key transformations. 

Although TA from yeast is commercially available, it has rarely been used in organic synthesis applications, and no detailed study of substrate specificity has yet been performed. This is presumably due to high enzyme cost and also since the reaction equilibrium is near unity, resulting in the formation of a 50 50 mixture of products. In addition the stereochemistry accessible by TA catalysis matches that of FruA DHAP-dependent aldolase and the latter is a more convenient system to work with. In one application, TA was used in the synthesis D-fructose from starch.113 The aldol moiety was transferred from Fru 6-P to D-glyceraldehyde in the final step of this multi-enzyme synthesis of D-fructose (Scheme 5.60). This process was developed because the authors could not identify a phosphatase that was specific for fructose 6-phosphate and TA offered an elegant method to bypass the need for phosphatase treatment. 

The use of aldolases and transketolase has opened the way to many highly multifunctional organic compounds [1]. In organic synthesis, the most widely used dihydroxyacetonephosphate (DHAP) aldolase is the commercially available fruc-tose-1,6-bisphosphate aldolase from rabbit muscle (FruA). This enzyme is a key enzyme of the glycolytic pathway, reversibly catalyzing the cleavage of fructose-... 

Whalem LJ, Wong C-H. Enzymes in organic synthesis aldolase-mediated synthesis of iminocyclitols and novel heterocycles. Aldrichimica Acta 2006 39 63-71. 

C. Aug6, C. Gautheron, S. David, A. Malleron, B. Cavayd, and B. Bouxom, Sialyl aldolase in organic synthesis From the trout egg acid, 3-deoxy-D-g7ycero-D-ga/acto-2-nonulosonic acid (KDN), to branched-chain higher ketoses as possible new chitons, Tetrahedron 46 201 (1990)... 

Aldolases hold potential for convergent synthesis of fluorocarbohydrates. There have been more than 20 aldolases isolated, eight of which have been explored for organic synthesis. This presentation describes the application of fructose-1,6-diphosphate aldolase, 2-deoxynbose-5-phosphate aldolase and sialic acid aldolase to the synthesis of fluorosugars. 

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