Aldolase catalyzed aldol addition

Aldolase-catalyzed Aldol Additions of DHAP to JV-Cbz-Amino Aldehydes... 

Figure 19.3 DHAP-aldolase catalyzed aldol addition of DHAP to N-Cbz-aminoaldehydes. Reaction conversion to aldol adduct in gel emulsion (black bars) and dimethylformamide/ water 1 4 system (gray bars) for reactions catalyzed by (a) RAMA, (b) RhuA and (c) FucA.

As pointed out before, the mechanism of aldolase-catalyzed aldol addition is different for class I and class II enzymes. 

Calveras 1, Bujons J, PareUa T et al. (2006) Influence of iV-amino protecting group on aldolase-catalyzed aldol additions of dihydroxyacetone phosphate to amino aldehydes. Tetrahedron 62 2648-2656... 

The influence of N-protecting groups on the conversion and stereoselectivity of aldolase-catalyzed aldol addition of dihydroxyacetone phosphate to N-protected-3-aminopropanal has been examined. ... 

Scheme 16.1 Chemo-enzymatic synthesis of iminocyclitols. (a) Aldolase-catalyzed aldol addition, (b) Liberation of the amino group and reductive amination. (N) Synthetic...

Scheme 16.2 Preparation of diverse pyrrolidine-type iminocyclitols by DHAP-dependent aldolase-catalyzed aldol addition of DHAP to a structural variety of N-Cbz-aminoaldehydes (1). (a) DHAP-dependent...

DHAP-Dependent Aldolases Catalyzed Aldol Addition of Dihydroxyacetone Phosphate to Cbz (or similar) Deriv ives of Amino or Azido Aldehydes... 

Two-step chemo-enzymatic synthesis of iminocyclitols (a) aldolase-catalyzed aldol addition and phosphate hydrolysis and (b) one-pot Cbz removal and reductive amination. 

There are two distinct groups of aldolases. Type I aldolases, found in higher plants and animals, require no metal cofactor and catalyze aldol addition via Schiff base formation between the lysiae S-amino group of the enzyme and a carbonyl group of the substrate. Class II aldolases are found primarily ia microorganisms and utilize a divalent ziac to activate the electrophilic component of the reaction. The most studied aldolases are fmctose-1,6-diphosphate (FDP) enzymes from rabbit muscle, rabbit muscle adolase (RAMA), and a Zn " -containing aldolase from E. coli. In vivo these enzymes catalyze the reversible reaction of D-glyceraldehyde-3-phosphate [591-57-1] (G-3-P) and dihydroxyacetone phosphate [57-04-5] (DHAP). 

Aldol reactions occur in many biological pathways, but are particularly important in carbohydrate metabolism, where enzymes called aldolases catalyze the addition of a ketone enolate ion to an aldehvde. Aldolases occur in all organisms and are of two types. Type 1 aldolases occur primarily in animals and higher plants type II aldolases occur primarily in fungi and bacteria. Both types catalyze the same kind of reaction, but type 1 aldolases operate place through an enamine, while type II aldolases require a metal ion (usually 7n2+) as Lewis acid and operate through an enolate ion. 

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). 

Pig. 6.5.13 d-Fructose-6-phosphate aldolase (FSA) catalyzed aldol additions of DHA to a number of aldehyde acceptors... 

Highly intriguing accounts on enzymatic DCL generation applied to a carbohydrate-binding protein have also been reported [50, 51]. Using the N-acetyl-neuraminic acid aldolase (sialic acid aldolase), reversible aldol addition of three or four different carbohydrates to pyruvate was catalyzed, yielding small DCLs of... 

The FDP-aldolase catalyzed DHAP-addition to glyoxylic acid, examined in detail by Wandrey and Bossow-Berke under continuous flow reaction conditions [18], required the determination of the relative and absolute configuration. Employing the SAMP-/RAMP-hydrazone method, the aldol reaction of 1 with benzyl glyoxylate afforded a doubly protected adduct, which was deprotected with trifluoroacetic acid anhydride (TFAA) and subsequent debenzylation with H2/ Pd-C to give the final product, identical with the enzyme product. The independent chemical synthesis and the enzymatic route are compared in scheme 4. It... 

Other syntheses of natural products have capitalized on the 38C2-catalyzed aldol addition of hydroxyacetone to install 1,2-syn-diol functionality. Aldolase antibody 38C2 was also used for synthesis of brevicomins 59-61 (Scheme 6.7) [23] and 1-deoxy-L-xylulose (62) (Scheme 6.8) [24]. Antibody 38C2-catalyzed kinetic resolution of a tertiary aldol was used for the synthesis of (+)-frontalin (63) (Scheme 6.9) [10]. 

Consecutive aldol additions by combination of RibA and other aldolases such as FruA (Scheme 10.10) or NeuA (Scheme 10.11) have also been studied for the synthesis of nonnatural sugars [169,170]. In all these reactions, the main driving force is the formation of a stable hemiketal of the target product. In the combination of RibA and FruA from rabbit muscle (RAMA), the aldehyde formed after the first RibA catalyzed aldol addition reaction underwent a second... 

Recent advances in enzyme-catalyzed aldol addition reactions for biocatalytic carbon-carbon bond formation by means of aldolases are described. They offer an exceptionally stereoselective and green tool for asymmetric framework construction and preparation of innovative molecules with engineered enz5unes. 

This cleavage is a retro aldol reaction It is the reverse of the process by which d fruc tose 1 6 diphosphate would be formed by aldol addition of the enolate of dihydroxy acetone phosphate to d glyceraldehyde 3 phosphate The enzyme aldolase catalyzes both the aldol addition of the two components and m glycolysis the retro aldol cleavage of D fructose 1 6 diphosphate... 

Table 4. IV-Acetylneuraminic Acid Aldolase Catalyzed Preparative Aldol Additions with Pyruvate...

Deoxy-D- /rce/ o-D- a/ac7i7-nonulosonie Acid (KDN) V-Acetylneuraminic Acid Aldolase Catalyzed Preparative Aldol Additions with Pyruvate Typical Procedure27 ... 

Espelt, L., Parella, T., Bujons, J., Solans, C., Joglar, J., Delgado, A. and, Clapes, P., Stereoselective aldol additions catalyzed hy dihydroxyacetone phosphate-dependent aldolases in emulsion systems preparation and structural characterization of linear and cyclic iminopolyols from aminoaldehydes. Chem. Eur. J., 2003, 9, 4887. 

Aldolases are part of a large group of enzymes called lyases and are present in all organisms. They usually catalyze the reversible stereo-specific aldol addition of a donor ketone to an acceptor aldehyde. Mechanistically, two classes of aldolases can be recognized [4] (i) type I aldolases form a Schiff-base intermediate between the donor substrate and a highly conserved lysine residue in the active site of the enzyme, and (ii) type II aldolases are dependent of a metal cation as cofactor, mainly Zn, which acts as a Lewis acid in the activation of the donor substrate (Scheme 4.1). 

Here, we will focus on the enzymatic routes since enzymatic preparation of DHAP is usually coupled with the aldol addition catalyzed by the aldolase representing genuine multi-enzyme systems. 

Rare or unnatural monosaccharides have many useful applications as nonnutritive sweeteners, glycosidase inhibitors and so on. For example, L-glucose and L-fructose are known to be low-calorie sweeteners. In addition, rare or unnatural monosaccharides are potentially useful as chiral building blocks for the synthesis of biologically active compounds. Therefore, these compounds have been important targets for the development of enzymatic synthesis based in the use of DHAP-dependent aldolases alone or in combination with isomerases. Fessner et al. showed that rare ketose-1-phosphates could be reached not only by aldol addition catalyzed by DHAP-dependent aldolases, but by enzymatic isomerization/ phosphorylation of aldoses [35]. Thus, for example, L-fructose can be prepared... 

DHAP-dependent aldolases have also been used as key step in the synthesis of several complex natural products starting from achiral precursors. Thus, the sex pheromone (+)-exo-brevicomin can be synthesized in a multi-step route starting with the stereospecific aldol addition between DHAP and 5-oxohexanal or its 5-dithiane-protected analog catalyzed by FBPA from rabbit muscle ( RAMA ) as the key step by which the absolute configuration of the target is estabUshed (Scheme 4.16) [40]. 

Asymmetric C-C bond formation is the most important and most challenging problem in synthetic organic chemistry. In Nature, such reactions are facilitated by lyases, which catalyze the addition of carbonucleophiles to C=0 double bonds in a manner that is classified mechanistically as an aldol addition [1]. Most enzymes that have been investigated lately for synthetic applications include aldolases from carbohydrate, amino acid, or sialic acid metabolism [1, 2]. Because enzymes are active on unprotected substrates under very mild conditions and with high chemo-, regio-, and stereoselectivity, aldolases and related enzymes hold particularly high potential for the synthesis of polyfunctionalized products that are otherwise difficult to prepare and to handle by conventional chemical methods. 

Another promising route was reported in patent and open hterature by both DSM and Diversa [13, 14]. This route employs a 2-deoxy-D-ribose 5-phosphate aldolase (DERA) that catalyzes a tandem aldol addition in which two equivalents of acetaldehyde (AA) are added in sequence to chloroacetaldehyde (CIAA) to produce a lactol derivative that is similar to the 3,5-dihydoxy side chain of synthetic statins (Figure 6.2e). Diversa screened environmental libraries for novel wild-type DERAs and identified an enzyme that was both tolerant to increased substrate concentrations and more active than DERA from E. coli in the target reaction [13]. 

Scheme 1 Reversible aldol addition reaction catalyzed by fructose diphosphate aldolase.

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