Synthesis of N-acetylneuraminic acid

Thus, an alkene can be considered as a masked ketone that can be unmasked by ozonolysis. This is illustrated by the synthesis of N-acetylneuraminic acid via the ozonolysis of the precursor acrylic acid in THF/aqueous media (Eq. 3.22). The use of aqueous media facilitated the solubility of the polyhydroxyacids.92... 

An aldehyde with a-ether functionality was used in the synthesis of N-acetylneuraminic acid by Danishefsky (equation 37). A series of cis- and trans-alkenes with a-oxygen functionality were synthesized by Cinquinin and coworkers. Of the examples generated, the HWE reaction proceeded in the expected ( )-selective manner (164), while the trifluoroethyl phosphonate was used to form the (Z)-al-kenes (163) selectively (Scheme 26). Interestingly, 18-crown-6 was not used for (Z)-alkene formation. 

Both of the N-acylated neuraminic acids mentioned have been synthesized. Comforth, Daines, and Gottschalk192 made the first synthesis of N-acetylneuraminic acid. They condensed 2-acetamido-2-deoxy-D-glucose with oxalacetic acid at pH 11, and obtained a low yield (about 2%). Carroll and Comforth193 obtained a higher yield from 2-acetamido-2-deoxy-D-mannose and oxalacetic acid. 

In the following discussion the method of reactor optimization will be demonstrated using two enzyme systems introduced earlier, namely the enzymatic synthesis of N-acetylneuraminic acid and the enzymatic synthesis of cyanohydrins using oxynitrilase. 

N-Acetyl-D-mannosamine serves as the in situ generated substrate for the synthesis of N-acetylneuraminic acid. Since N-acetyl-D-mannosamine is quite expensive it is synthesized from N-acetyl-D-glucosamine by epimerization at C2. This biotransformation is integrated into the production of N-acetylneuraminic acid (Neu5Ac). 

Sialic Acid - Figure 16.14 depicts the synthesis of N-acetylneuraminic acid (sialic acid) from UDP-N-acetylglucosamine. Sialic acid is an important constituent of glycoproteins. Activated sialic acid is made by linking, not to a nucleoside diphosphate (as in other sugar derivative activations), but to a nucleoside monophosphate, CMP, in the following reaction ... 

R. Csuk, M. Hugener, and A. Vasella, A new synthesis of N-acetylneuraminic acid, Helv. Chim. Acta 77 609 (1988). 

Subsequently, the enzyme from E. coli has been overexpressed in an inducible system at very high expression levels, and homogenized bacterial cells were directly used to immobilize the enz3une from crude extracts onto Eupergit C beads without any clarification, and the immobilized enzyme was used for the synthesis of N-acetylneuraminic acid 117 at 155 g/1 concentration. At the manufacturing scale, the same batch of enzymes was reused in >2000 cycles in batch column reactors, without any significant loss of activity, to produce multi-tonne quantities of N-acetylneuraminic acid [152],... 

Malapelle, A Coslovi, A., Doisneau, G and Beau, (.-M. (2007) An expeditious synthesis of N-acetylneuraminic acid a-C-glycosyl derivatives ( a-C-glycosides from the anomeric acetates. Eur. J. Org. Chem., 3145-3157. 

Comb, D. G., and Roseman, S., 1958, Composition and enzymatic synthesis of N-acetylneuraminic acid (sialic acid),/. Am. Chem. Soc. 80 497. 

In spite of the fact that the reaction equilibrium is greatly in favor of breakdown, it was felt that the NAN-aldolase was responsible for the synthesis of N-acetylneuraminic acid by coupling to the next enzyme in the pathway (Figure 2 CMP-sialic acid synthetase). That notion was partially dispelled by the inability to detect this enzyme in mucin-producing tissues (tissues extremely rich in secreted sialic acid) (Bru-netti et aL, 1962) and by the abundance of this enzyme in the bacteria V. cholerae and C. perfingens, which totally lack sialic acid. Thus it was felt this enzyme may primarily be a degradative enzyme, and the search continued for a second synthetic (anabolic) pathway. 

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