Aldolase dihydroxyacetone-dependent

Scheme 2.192 Aldol reaction catalyzed by dihydroxyacetone-dependent fhictose-6-phosphate aldolase...

The equilibrium constant of the aldolase reaction depends greatly on temperature. At low temperatures the condensation is more favored, whereas the amount of triose at equilibrium increases with rising temperatures. The equilibrium constant is evaluated as (dihydroxyacetone phosphate) (phosphoglyceraldehyde)/(HDP) = IT, = 6 X 10 at 28 C. At first glance it appears that this implies that very little triose exists at equilibrium at this temperature. This is an example of reactions in which one compound is converted to two, and closer examination shows that the percentage conversion in such cases is a function of the absolute concentration. Thus, with 1 M HDP, only a fraction of 1 per cent is split at equilibrium, whereas at 10 M, approximately half is converted to triose phosphates. The equilibrium constant is markedly affected by temperature. Lower temperatures favor the condensation to HDP, while higher temperatures cause the reaction to shift toward increased formation of triose phosphates. 

Garrabou, X., Joglar, J., Parella, T., Bujons, J., and Clapes, R, Redesign of the phosphate binding site of L-rhamnulose-1-phosphate aldolase towards a dihydroxyacetone dependent aldolase. Adv. Synth. Catal. 2011,353 (1), 89-99. 

Figure 12 Aldol reactions catalyzed in vivo by the four stereocomplementary dihydroxyacetone-dependent aldolases.

Dihydroxyacetone Phosphate-Dependent Aldolases in the Core of Multi-Step Processes... 

The main group of aldolases from the biocatalytic point of view is, arguably, the one that uses dihydroxyacetone phosphate (DHAP) as donor. Here, we will concentrate on that appHcations in which DHAP-dependent aldolase are part of a multi-enzyme system or, alternatively, on those in which the aldolase-catalyzed reaction is key in a multi-step synthetic pathway. 

Efforts to overcome the Dff AP dependence of aldolases have involved the in situ formation of arsenate [9] or borate [10] complexes with dihydroxyacetone (DHA), which could mimic a phosphate ester (Scheme 4.3). 

With respect to practical applications in asymmetric synthesis, the four stereo-chemically distinct dihydroxyacetone phosphate (DHAP, 1)-dependent enzymes had been particularly appealing to us because these enzymes control the creation of two new asymmetric centers at the termini of a newly formed C-C bond, thus allowing an effective stereocombinatorial synthesis of stereoisomers (Scheme 2.2.5.1) [1, 3]. The individual aldolases are involved in the reversible cleavage of... 

While the lyases that transfer a pyruvate unit form only a single stereogenic center, the group of dihydroxyacetone-phosphate-(DHAP, 41)-dependent aldolases create two new asymmetric centers, one each at the termini of the new C-C bond. A particular advantage for synthetic endeavors is the fact that Nature has evolved a full set of four stereochemically-complementary aldolases [189] (Scheme 6) for the retro-aldol cleavage of diastereoisomeric ketose 1-phosphates— D-fructose 1,6-bisphosphate (42 FruA), D-tagatose 1,6-bisphosphate (43 TagA), L-fuculose 1-phosphate (44 FucA), and L-rhamnulose 1-phosphate (45) aldolase (RhuA). In the direction of synthesis this formally allows the... 

Scheme 6. Stereochemically complementary set of dihydroxyacetone-phosphate-dependent aldolases...

In nature, most aldolases are rooted in the sugar metabolic cycle and accept highly functionalized substrates for the aldol reaction. Nevertheless, the scope of enzymatic aldol reactions is limited, since aldolases strictly distinguish between the acceptor and the donor, yielding almost exclusively one product, and is furthermore restricted to only a few different possible natural donors. According to the donor molecules, aldolases are grouped in dihydroxyacetone phosphate-, phosphoenolpyruvate- or pyruvate-, acetaldehyde-, and glycine-dependent aldolases [41]. 

Fructose 1,6-biphosphate aldolase from rabbit muscle in nature reversibly catalyzes the addition of dihydroxyacetone phosphate (DHAP) to D-glyceraldehyde 3-phosphate. The tolerance of this DHAP-dependent enzyme towards various aldehyde acceptors made it a versatile tool in the synthesis of monosaccharides and sugar analogs [188], but also of alkaloids [189] and other natural products. For example, the enzyme-mediated aldol reaction of DHAP and an aldehyde is a key step in the total synthesis of the microbial elicitor (—)-syringolide 2 (Fig. 35a) [190]. 

It was reported by Horecker and coworkers that one class of aldolases (called Class I to distinguish it from the Class II aldolase that is metal ion-dependent) could be inhibited by the addition of borohydride reducing agent to reaction mixtures containing both enzyme and substrate129,130. It was then shown for the fructose- 1,6-bis-phosphate aldolase that the inhibition resulted from reduction of the Schiff base formed between the dihydroxyacetone phosphate substrate and the -amino group of a lysine side chain, thereby compromising the ability of the lysine to participate in subsequent turnover. 

Dihydroxyacetone phosphate (DHAP) is the donor ketone that is utilized by the DHAP-dependent aldolases. These aldolases come under the class of lyases, just like the hydroxynitrile lyases (see Section 5.2.1.1). As for the HNLs, no cofactor... 

A significant drawback of the DHAP-dependent aldolases is that DHAP cannot be replaced by dihydroxyacetone. DHAP is expensive and it is labile at neutral and basic pH values. It can be synthesized chemically, however the procedures are not very atom efficient. Therefore alternative enzyme-catalyzed approaches have been developed. A variety of them can be performed in the... 

The first group is the dihydroxyacetone phosphate (DHAP)-dependent aldolases, which use DHAP as the donor to produce 2-keto-l, 3, 4-trihydroxy motifs. The second group, the pyruvate- or phosphoenol pyruvate (PEP)-dependent aldolases, uses pyruvate to form 4-hydroxy-2-ketoacids. The third... 

Scheme 5.2. The four main groups of aldolase reactions classified by their donor substrate (1) Dihydroxyacetone phosphate (DHAP)- dependent aldolases, (2) phosphoenol pyruvate (PEP)-and pyruvate-dependent aldolases, (3) 2-deoxyribose-5-phosphate aldolase (DERA), a member of the acetaldehyde-dependent aldolases, and (4) glycine-dependent aldolases (GDA).

In vivo, six known DHAP-dependent aldolases are known to catalyze the reversible enanotioselective aldol addition of dihydroxyacetone phosphate to an acceptor aldehyde. The group is comprised of fructose 1,6-diphosphate (FDP) aldolase (EC 4.1.2.13), L-fuculose 1-phosphate (Fuc 1-P) aldolase (EC 4.1.2.17), tagatose 1,6-diphosphate (TDP) aldolase (EC 4.1.2.2), ketotetrose phosphate aldolase (EC 4.1.2.2), L-rhamnulose 1-phosphate (Rha 1-P) aldolase (EC 4.1.2.19), and phospho-5-keto-2-deoxygluconate aldolase (EC 4.1.2.29). The in vivo catalyzed reactions of this group are shown in Scheme 5.3. 

Scheme 5.3. Dihydroxyacetone phosphate (DHAP) dependent aldolases, their natural substrates and products. P = PO32. ...

In this sense, enzymatic catalysis is especially attractive for syntheses demanding highly regio- and stereoselectivity. Particularly dihydroxyacetone phosphate (DHAP) dependent aldolases are among the most suitable biocatalyst for imino-sugar synthesis due to their high stereoselectivity and chiral induction capacity [10, 12, 13]. The aldol addition of DHAP (1) to a synthetic equivalent of an... 

In vertebrate liver, the enzyme fructokinase phosphorylates fructose to fructose- 1-phosphate (FIP). FIP is then cleaved by a specific enzyme, aldolase B to dihydroxyacetone phosphate (DHAP), a glycolytic intermediate, and D-glyceraldehyde (see below). The latter is then phosphorylated in an ATP-dependent reaction to give the glycolytic intermediate glyceraldehyde-3-phosphate. 

The four enzymes of the family of dihydroxyacetone phosphate (DHAP)-dependent aldolases fructose-1,6-bisphosphate aldolase (FruA, EC 4.1.2.13), fuculose-1-phosphate aldolase (FucA, EC 4.1.2.17), rhamnulose-1-phosphate aldolase (RhuA, EC 4.1.2.19) and tagatose-1,6-bisphosphate aldolase (TagA, EC 4.1.2.40), catalyze in vivo the reversible asymmetric addition of DHAP to d-glyceraldehyde-3-phosphate (G3P) or L-lactaldehyde, leading to four complementary diastereomers. DHAP-dependent aldolases create two new stereogenic centers, with excellent enantio and diastereoselectivity in many cases. These enzymes are quite specific for the donor substrate DHAP, but accept a wide range of aldehydes as acceptor substrates. There are only two fructose-6-phosphate aldolase isoenzymes reported to be able to use dihydroxyacetone (DHA) as donor substrate (Schiirmann and Sprenger 2001). 

Dihydroxyacetone phosphate-dependent aldolases (DHAP-aldolases) have been used widely for preparative synthesis of monosaccharides and sugar analogs (Fessner and Walter 1997 Wymer and Toone 2000 Silvestri et al. 2003). Among them, RAMA RhuA and FucA from E. coli are the most available aldolases, especially the former which was one of the first to be commercialized (Fessner and Walter 1997 Takayama et al. 1997). In many of the chemo-enzymatic strategies they are involved, the biocatalytic aldol addition to the configuration of the newly stereogenic centers is fixed by the enzyme. However, pertinent examples have been reported in which... 

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