Xylulose-5-phosphate, synthesis

This thermodynamic driving force is particularly useful tvith multienzyme equilibrium systems such as that used in the gram-scale synthesis of tv ro equivalents ofo-xylulose 5-phosphate (104) from (26) (Figure 10.38) [171,172]. Similarly, the corresponding 1-deoxy-D-xylulose 5-phosphate tvas efficiently produced from pyruvate and (34) by the catalytic action of the thiamine diphosphate-dependent 1-deoxy-D-xylulose 5-phosphate synthase (DXS) (EC 2.2.1.7) from E. coli [173]. 

Ribulose 5-phosphate is the substrate for two enzymes. Ribulose 5-phosphate 3-epimerase alters the configuration about carbon 3, forming another ketopentose, xylulose 5-phosphate. Ribose 5-phosphate ketoisom-erase converts ribulose 5-phosphate to the corresponding aldopentose, ribose 5-phosphate, which is the precursor of the ribose required for nucleotide and nucleic acid synthesis. Transketolase transfers the two-carbon... 

Sprenger, G.A. et al.. Identification of a thiamin-dependent synthase in Escherichia coli required for the formation of the 1-deoxy-D-xylulose 5-phosphate precursor to isoprenoids, thiamin, and pyridoxol, Proc. Natl. Acad Sci. USA 94, 12857, 1997. Lange, B.M. et al., A family of transketolases that directs isoprenoid biosynthesis via a mevalonate-independent pathway, Proc. Natl. Acad Sci. USA 95, 2100, 1998. Lois, L.M. et al., Cloning and characterization of a gene from Escherichia coli encoding a transketolase-like enzyme that catalyzes the synthesis of D-1- deoxyxylulose 5-phosphate, a common precursor for isoprenoid, thiamin, and pyridoxol biosynthesis, Proc. Natl. Acad. Sci. USA 95, 2105, 1998. 

Transketolase (TKase) [EC 2.2.1.1] essentially catalyzes the transfer of C-2 unit from D-xylulose-5-phosphate to ribose-5-phosphate to give D-sedoheptulose-7-phosphate, via a thiazolium intermediate as shown in Fig. 16. An important discovery was that hydroxypyruvate works as the donor substrate and the reaction proceeds irreversibly via a loss of carbon dioxide (Fig. 17). In this chapter, we put emphasis on the synthesis with hydroxypyruvate, as it is the typical TPP-mediated decarboxylation reaction of a-keto acid. ... 

Xylulose 5-phosphate (D-threo-2-pentulose 5-phosphate) is the best donor compound for TKT [6]. As its cost is, however, prohibitively high for routine assays (formerly available batches from commercial suppliers were sold at ca. 1000 per 100 mg), a multi-enzymatic synthesis and subsequent chromatographic purification were developed which allowed the gram-scale synthesis of xylulose 5-phos-phate with a 82% yield [13]. 

The ready availability of the transketolase (TK E.C. 2.2.1.1) from E. coli within the research collaboration in G. A. Sprenger s group suggested the joint development of an improved synthesis of D-xylulose 5-phosphate 19, which was expensive but required routinely for activity measurements [27]. In vivo, transketolase catalyzes the stereospecific transfer of a hydroxyacetyl nucleophile between various sugar phosphates in the presence of a thiamine diphosphate cofactor and divalent cations, and the C2 donor component 19 offers superior kinetic constants. For synthetic purposes, the enzyme is generally attractive for its high asymmetric induction at the newly formed chiral center and high kinetic enantioselectivity for 2-hydroxyaldehydes, as well as its broad substrate tolerance for aldehyde acceptors [28]. 

Scheme 2.2.5.S Multi-enzymatic route for the stereoselective synthesis of D-xylulose 5-phosphate 19 from commercial D-fructose 1,6-bisphosphate (abbreviations TPI, triose phosphate isomerase TK, transketolase).

The sugar metabolism is a source of many enzymes, the transketolase (TK) being one of them. TK transfers an a-hydroxy carbonyl fragment from D-xylu-lose-5-phosphate onto D-ribose-5-phosphate, forming D-sedoheptulose-7-phos-phate and D-glyceraldehyde-3-phosphate (Scheme 5.14). Since this reaction is an equilibrium reaction and starting materials and products are of similar stability, it is not very versatile for organic synthesis. Fortunately TK also accepts pyruvate instead of xylulose. Under these modified circumstances carbon dioxide... 

The dephosphorylation of 5-chloro and 5-bromo-D-xylulose-l-phosphate was carried out by the addition of acid phosphatase. After purification, 5-chloro-D-xylu-lose and 5-bromo-D-xylulose were recovered as pure compounds in 47 and 12% yields, respectively, from DHAP. In this study, we have shown that DHAP generated from glycidol 7 can be used in situ as a donor substrate of FruA in the presence of 2-halo-acetaldehydes 20 as acceptor substrates for the synthesis of 5-halo-D-xylulose 19. Given that DHAP aldolases display a broad specificity towards acceptor substrates, this strategy can be applied generally to the synthesis of various analogs of monosaccharides. 

In the third reaction, transketolase catalyzes the synthesis offructose 6-phosphate and glyceraldehyde 3-phosphate from erythrose 4-phosphate and xylulose 5-phosphate. 

Fosmidomycin is an antimicrobial drug that acts by inhibiting 1-deoxy-D-xylulose 5-phosphate reductoisomerase, a key enzjme of the non-mevalonate pathway of isopre-noid biosynthesis. It inhibits the synthesis of isoprenoids by Plasmodium falciparum and suppresses the growth of multidrug-resistant strains in vitro. 

Glucuronic acid pathway. The first part consists of synthesis of UDP-glucuronic acid and release of free D-glucuronic acid. The second part is the metabolism of D-glucuronic acid. D-Glucuronic acid is written as both the cyclic hemiacetal and the open-chain aldohexose and two orientations of L-gulonic acid and D-xylulose are shown. P = phosphate. 

The thiamin biosynthetic pathway is outlined in Fig. 22 [88]. Overall the pathway involves the separate synthesis of the thiazole 111 and the pyrimidine 114 which are then coupled. l-Deoxy-D-xylulose-5-phosphate (see sections 11 and 12 of this review) is the precursor to the five carbon unit of the thiazole [89], cysteine is the sulfur source [90, 91], and the C2-N3 atoms of the thiazole are derived from the a-carbon and the amino group of tyrosine [92-94]. The pyrimidine is derived from 5-aminoimidazole riboside (AIRs), an intermediate on the purine biosynthetic pathway. This reaction involves a complex rearrangement in which the C4 carbon of AIRs is inserted into the C4-C5 imidazole double bond, converting the imidazole to a pyrimidine, and the C2 carbon of AIRs is used to methylate the C2 position of the imidazole [95-98]. 

Synthesis.—Comprehensive reviews on glycosyl esters of nucleoside pyrc>-phosphates and teichoic acids have appeared in the past year as have details of the preparation of xylulose-5-phosphate using transketolase. Phosphorylation of glucose by inorganic phosphate in the presence of histidine occurs under simulated primitive earth conditions and the reactive species is probably an iST-phosphorylated histidine. Phosphorylation of sugars by heating them with 100% phosphoric acid in vacuo is a novel experimental... 

S ATP + 4-methyl-5-(2-hydroxyethyl)thiazole <1, 2> (<1> enzyme involved in biosynthesis of thiamine [1] <1> the bifunctioinal enzyme hydroxyethylthiazole kinase/thiamine-phosphate pyrophosphorylase catalyzes two sequential steps in the synthesis of thiamin monophosphate from hydroxyethylthiazole [2] <2> the enzyme is a salvage enzyme in the thiamin biosynthetic pathway and enables the cell to use recycled 4-methyl-5-j8-hydroxyethylthiazole as an alternative to its synthesis from 1-deoxy-o-xylulose-5-phosphate, cysteine, and tyrosine [3]) (Reversibility <1, 2> [1,2,3]) [1,2, 3]... 

Schiirmann M, Schiirmann M, Sprenger GA (2002) Fructose 6-phosphate aldolase and 1-deoxy-D-xylulose 5-phosphate synthase from Escherichia coli as tools in enzymatic synthesis of 1-deoxysugars. J Mol Catal B Enzym 19 247-252 Shelton CM, Toone EJ (1995) Differential dye-ligand chromatography as a general purification protocol for 2-keto-3-deoxy-6-phosphogluconate aldolases. Tetrahed Asymm 6 207-211 Silvestri MG, Desantis G, Mitchell M et al. (2003) Asymmetric aldol reactions using aldolases. Top Stereochem 23 267-342... 

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