Enzymatic synthesis pyruvate aldolases

CMP-N-acetylneuraminic acid (CMP-NeuAc). CMP-N-acetylneuraminic acid has been prepared enzymatically on small scales (> 0.5 mmol) from CTP and NeuAc, under catalysis by CMP-NeuAc synthetase (EC 2.7.7.43) [131l An improvement in this procedure, involving in situ production of CTP from CMP under adenylate kinase and pyruvate kinase catalysis, is suitable for multigram-scale synthesis11321. Adenylate kinase catalyzes the equilibration of CTP and CMP to CDP, which is subsequently phosphorylated by pyruvate kinase to provide CTP. A one-pot synthesis of CMP-NeuAc based on this procedure involves the in situ synthesis of NeuAc from N-acetylmannosamine and pyruvate, catalyzed by sialic acid aldolase (Fig. 11.3-12)[10S1. Chemical syntheses of CMP-NeuAc have also been reported11421. 

N-Acetylneuraminic acid aldolase catalyzes the reversible aldol condensation of pyruvate (23) and N-acetylmannosamine (22 ManNAc) to form N-acetylneuraminic acid (24 NeuAc N-acetyl-5-amino-3,5-dideoxy-D-glycerogalacto-2-nonulopyronic acid Scheme 6).80-83 In vivo the enzyme has a catabolic function and the equilibrium for this reaction is near unity the presence of excess pyruvate can shift this equilibrium. NeuAc and other derivatives of neuraminic acid are termed sialic acids. These compounds are found at the termini of mammalian glycoconjugates and play an important role in cellular recognition.84-89 The production of analogs of NeuAc is a point of great interest to synthetic and medicinal chemists. The enzymatic approach has not been fully explored but it may be a practical alternative to the chemical synthesis of certain sialic acids.89... 

The monosaccharide sialic acid remains relatively costly for preparative-scale synthesis. Although it has been demonstrated that NeuAc can be generated in situ by reaction of ManNAc with pyruvate, catalyzed by NeuAc aldolase [27], ManNAc is also relatively expensive and difficult to prepare. Therefore, a method for the generation of NeuAc from the inexpensive monosaccharide GlcNAc in a two-enzyme system might also prove useful in regeneration schemes. It has been shown that GlcNAc can be converted to ManNAc chemically [28], or enzymatically by the... 

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