Neuraminic acid synthase

The NeuS from N. meningitidis is Mn dependent and active in the pH range 7.0-9.0as adimerof38 kDa subunits [22]. First preparative studies have shown that the enzyme exhibits a broad substrate tolerance with complete stereocontrol [22]. Most remarkably, the enzyme is highly tolerant to structural modifications of the 

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A -acetyl-D-neuraminic acid is biosynthesized from A -acetyl-D-mannosamine and phosphoenol pyruvate, catalyzed by N-acetyl-D-neuraminic acid synthase. The first step involves the addition of an electron pair from the double bond of the phosphoenol pyruvate to the aldehyde group to give an aldol-type condensation (see Fig. 10.8A). The product is the nine-carbon sugar acid, A -acetyl-D-neuraminic acid [23]. In some instances the enzyme requires A-acetyl-D-mannosamine-6-phosphate as the substrate and forms A-acetyl-D-neuraminic acid-9-phosphate. Various hydroxyl groups on C-4, -7, -8, and -9 can be acetylated by specific acetyl transferases using acetyl CoAas the donor. KDO (2-keto-3-deoxy-D-mannooctulosonic acid) is biosynthesized by a very similar condensation between D-arabinose-5-phosphate and pyruvic acid, catalyzed by KDO synthase (see Fig. 10.8B) [24]. 

Glycogen synthase kinase 3 inhibitor 288 N-Glycolyl neuraminic acid 772, 811, 849 Glycosylation 678... 

A short review (11 pages, 14 references) on the synthesis and evaluation of mechanism-based inhibitors of Kdo8P synthase has appeared. " A review on the alkaline biocatalysis for the direct biosynthesis of iV-acetyl-D-neuraminic acid (NeuSAc) from iV-acetyl-D-glucosamine has also been written. The syntheses of furanose derivatives of 3-deoxy-D-cryt/iro-2-hexulosonic acid and their 3-bromo and 3-deuterio analogues have been reported. 3-Deoxyoctulosonic acid 16 has been prepared by use of E. coli heptulosonate synthase (Scheme 6). ... 

CMP-NeuAc. Derivatives of neuraminic acid frequently terminate mammalian glycoconjugates. Activated NeuAc is therefore an especially important target for enzyme-based synthesis. NeuAc is synthesized in vivo by an NeuAc aldolase-catalyzed condensation of N-acetylmannosamine and pyruvate (Scheme 11 above). NeuAc is then coupled directly to CTP by CMP-NeuAc synthase (E.C. 2.7.7.43). We have recently published a multigram preparation of CMP-NeuAc which makes use of both NeuAc aldolase and CMP-NeuAc synthase (Scheme 19) (47). NeuAc aldolase has been cloned and overexpressed, and is commercially available. The final enzyme required, CMP-NeuAc synthase, was isolated from calf brain. 

This conception works out as shown in Scheme 10 CTP 23 formed by the above described sequence is directly consumed by -acetyl neuraminic acid 26 under the catalytic influence of cytidine-5 -monophosphosialate synthase (E.C. 2.7.7.43). This enzyme is isolated from calf brain by ammonium sulfate precipitation (2 5) and subsequent affinity chromatography. The stationary phase consists of CNBr-activated Sepharose 4B reacted with p-[3-(2-amino ethylthio)propyl]-iV-acetyl neuraminic acid 27, which is synthesized by radiating a mixture of the allyl glycoside and cysteamine to achieve radical C-S bond formation (24), The behavior of methyl p-N-acetyl-neuraminic acid as an inhibitor is in accordance with Zbiral s findings (25), where the methyl a-glycoside has been shown to compete with the native substrate for the enzyme, and thus 27 is recommended to be an ideally suited ligand (Scheme 9). A typical analytical run is shown in Scheme 9. Due to elution of the protein fraction by a salt gradient, the transfer to a preparative scale is rather difEcult denaturation occurs and thus a drop in activity down to 6% is observed. 

The a- and P-glycopyranosyl phosphates of 3-deoxy-D-ma no-2-octulosonic acid have been prepared from Kdo as inhibitors of 3-deoxy-D-/nowio-2-octuloso-nate-8-phosphate synthase, which occurs in Gram-negative bacteria. iV-Acetyl-neuraminic add has been 0-alkylated at C-4 by selective alkylation of an 8,9-0-isopropylidene derivative, and treatment of the a-benzyl glycoside of N-acetylneuraminic acid with iluoroacetyl imidazole has afforded a mixture of 4,5-and 4,9-di-0-(fluoroacetyl) derivatives. A 4-acetamido-4-deoxy-4-epi-derivative of -acetylneuraminic acid has been prepared using standard techniques. ... 

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