Aldolase catalyzed

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... 

Further steps m glycolysis use the d glyceraldehyde 3 phosphate formed m the aldolase catalyzed cleavage reaction as a substrate Its coproduct dihydroxyacetone phosphate is not wasted however The enzyme triose phosphate isomerase converts dihydroxyacetone phosphate to d glyceraldehyde 3 phosphate which enters the glycol ysis pathway for further transformations... 

Fig. 6. FDP-aldolase-catalyzed addition of electrophiles (94) with DHAP (139—146). Representative R groups ia (94) are given as (a—j) (a) methyl, CH (b)...

FIGURE 14.2 The breakdown of glucose by glycolysis provides a prime example of a metabolic pathway. Ten enzymes mediate the reactions of glycolysis. Enzyme A, fructose 1,6, hiphos-phate aldolase, catalyzes the C—C bondbreaking reaction in this pathway. 

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. 

Table t. Products from Complementary Aldolase Catalyzed Additions of Dihydroxyacetone Phosphate to Simple Aldehydes... 

Tabic 2. Fructose 1,6-Bisphosphate Aldolase Catalyzed Additions of Dihy-droxyacelone Phosphate to Sugar Phosphates... 

Table 3. Selection of Products Derived from Fructose 1,6-Bisphosphatc Aldolase Catalyzed Additions of Dihydroxyacetonc Phosphate to Respective Aldehydes...

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 ... 

R)-2-Hydroxy-3-thiopropanal (Table 5), which could not be isolated from the reaction mixture, can be directly converted into 6-thio-D-wnimo-2-hexulose (7%) and 6-thio-L-xylo-2-hexulose (93 %) via rabbit muscle aldolase catalyzed condensation with dihydroxyacetonephos-phate28. 

Figure 10.21 Aldolase-catalyzed asymmetric synthesis of uncommon L-configured sugars (a), and selected examples of carbohydrate-related product structures that are accessible by enzymatic aldolization (b).

Such aldolase-catalyzed bidirectional chain elongation ( tandem aldolization) of simple, readily available dialdehydes has been developed into an efficient method for the generation of higher carbon sugars (e.g. (87)/(89)) by simple one-pot operations (Figure 10.32) [126,156]. The choice offuranoid (87) or pyranoid (89) nature of the products can be determined by a suitable hydroxyl substitution pattern in a corresponding cycloolefinic precursor (86) versus (88)). The overall specific substitution... 

Whereas SHMT in vivo has a biosynthetic function, threonine aldolase catalyzes the degradation of threonine both l- and D-spedfic ThrA enzymes are known [16,192]. Typically, ThrA enzymes show complete enantiopreference for their natural a-D- or a-t-amino configuration but, with few exceptions, have only low specificity for the relative threo/erythro-configuration (e.g. (122)/(123)) [193]. Likewise, SHMT is highly selective for the L-configuration, but has poor threo/erythro selectivity [194]. For biocatalytic applications, the knovm SHMT, d- and t-ThrA show broad substrate tolerance for various acceptor aldehydes, notably induding aromatic aldehydes [193-196] however, a,P-unsaturated aldehydes are not accepted [197]. For preparative reactions, excess of (120) must compensate for the unfavorable equilibrium constant [34] to achieve economical yields. 

Aldolases catalyze asymmetric aldol reactions via either Schiff base formation (type I aldolase) or activation by Zn2+ (type II aldolase) (Figure 1.16). The most common natural donors of aldoalses are dihydroxyacetone phosphate (DHAP), pyruvate/phosphoenolpyruvate (PEP), acetaldehyde and glycine (Figure 1.17) [71], When acetaldehyde is used as the donor, 2-deoxyribose-5-phosphate aldolases (DERAs) are able to catalyze a sequential aldol reaction to form 2,4-didexoyhexoses [72,73]. Aldolases have been used to synthesize a variety of carbohydrates and derivatives, such as azasugars, cyclitols and densely functionalized chiral linear or cyclic molecules [74,75]. 

Dean, S.M., Greenberg, W.A. and Wong, C.-H. (2007) Recent advances in aldolase-catalyzed asymmetric synthesis. Advanced Synthesis Catalysis, 349, 1308-1320. 

Greenberg, W.A., Varvak, A., Hanson, S.R. el ai (2005) Development of an efficient, scalable, aldolase-catalyzed process for enantioselective synthesis of statin intermediates. Proceedings of the National Academy of Sciences of the United States of America, 101, 5788-5793. 

Steinreiber, J., Schurmann, M., Wolberg, M. et al. (2007) Overcoming thermodynamic and kinetic limitations of aldolase-catalyzed reactions by applying multienzymatic dynamic kinetic asymmetric transformations. Ange-wandte Chemie International Edition. 46, 1624-1626. 

Sugiyama, M., Hong, Z.Y., Liang, RH. et al. (2007) D-Fructose-6-phosphate aldolase-catalyzed one-pot synthesis of iminocyclitols. Journal of the American Chemical Society, 129, 14811-14817. 

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. 

Jack-bean aldolase and liver aldolase catalyze the conversion of one mole of D-fructose 1-phosphate into one mole each of dihydroxyacetone phosphate and D-glycerose, and the reaction is reversible.73-77... 

Scheme 11. Aldolase-catalyzed synthesis of statin drugs via the megagenonuc approach...

Development of an efficient, scalable, aldolase-catalyzed process for enantioselective synthesis of statin intermediates. Proc Natl Acad Sci USA 101 5788-5793... 

Liu, J. and Wong C.-H., Aldolase-catalyzed asymmetric synthesis of novel pyranose syn-thons as a new entry to heterocycles and epothilones. Angew. Chem. Int. Ed., 2002, 41, 1404-1407. 

N-Acetvlneuraminic Acid Aldolase. A new procedure has also been developed for the synthesis of 9-0-acetyl-N-acetylneuraminic acid using the aldolase catalyzed reaction methodology. This compound is an unusual sialic acid found in a number of tumor cells and influenza virus C glycoproteins (4 ). The aldol acceptor, 6-0-acetyl-D-mannosamine was prepared in 70% isolated yield from isopropenyl acetate and N-acetyl-D-mannosamine catalyzed by protease N from Bacillus subtilis (from Amano). The 6-0-acetyl hexose was previously prepared by a complicated chemical procedure (42.) The target molecule was obtained in 90% yield via the condensation of the 6-0-acetyl sugar and pyruvate catalyzed by NANA aldolase (Figure 6). With similar procedures applied to KDO, 2-deoxy-NANA and 2-deoxy-2-fluoro-NANA were prepared from NANA. 

This enzyme [EC 4.1.3.6] (also known as citrate (pro-35)-lyase, citrase, citratase, citritase, citridesmolase, and citrate aldolase) catalyzes the conversion of citrate to acetate and oxaloacetate. Citrate lyase can be dissociated into subunits, two components of which are identical with citrate CoA-transferase [EC 2.8.3.10] and citryl-CoA lyase [EC 4.1.3.34]. 

This enzyme [EC 4.1.3.16], also known as 2-keto-4-hy-droxyglutarate aldolase and 2-oxo-4-hydroxyglutarate aldolase, catalyzes the reversible conversion of 4-hy-droxy-2-oxoglutarate to pyruvate and glyoxylate. Interestingly, the enzyme is reported to be able to act on both stereoisomers. 

This enzyme [EC 4.1.2.21], also referred to as 6-phospho-2-dehydro-3-deoxygalactonate aldolase, catalyzes the reversible conversion of 2-dehydro-3-deoxy-o-galactonate 6-phosphate to pyruvate and o-glyceraldehyde 3-phos-phate. 

Researchers at the University of Graz, in collaboration with scientists from DSM, have developed an elegant and novel approach to the synthesis of P-amino alcohols using two different enzymes in one pot (Scheme 2.35). For example, a threonine aldolase-catalyzed reaction was initially used, under reversible conditions, to prepare L-70 from glycine 69 and benzaldehyde 68. L-70 was then converted to (R)-71 by an irreversible decarboxylation catalyzed by L-tyrosine decarboxylase. In a second example, D/L-syn-70 was converted to (R)-71 using the two enzymes shown combined with a D-threonine aldolase in greater than 99% e. e. and 67% yield ]37, 38]. 

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. 

Scheme 4.5 Enzymatic routes to DHAP based in the use of glycerophosphate oxidase (GPO) coupled with the aldolase-catalyzed reaction and with dephosphorylation of the aldol adduct.

Azido aldehydes and a-protected amino aldehydes have been used to incorporate the nitrogen in the aldolase-catalyzed reaction (for an extensive review on aldolase-mediated synthesis of iminocyclitols, see [28] and references therein). The steri-cally unhindered azido and N-formylamino aldehydes display a marked kinetic advantage over analogs having larger and/or poor water-soluble N-protecting groups [29]. 

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