N-acetylneuraminic acid synthase

Synthetic studies for sialic acid and its modifications have extensively used the catabolic enzyme N-acetylneuraminic acid aldolase (NeuA E.C. 4.1.3.3), which catalyzes the reversible addition of pyruvate (70) to N-acetyl-D-mannosamine (ManNAc, 11) to form the parent sialic acid N-acetylneuraminic acid (NeuSNAc, 12 Scheme 2.2.5.23) [1, 2, 45]. In contrast, the N-acetylneuraminic acid synthase (NeuS E.C. 4.1.3.19) has practically been ignored, although it holds considerable synthetic potential in that the enzyme utilizes phosphoenolpyruvate (PEP, 71) as a preformed enol nucleophile from which release of inorganic phosphate during... 

Higher organisms and some bacteria utilize PEP-dependent N-acetylneuraminic acid synthase (NeuS EC 2.5.1.56) for the generation of sialic acids and related compounds (Scheme 17.3) [17, 21]. In mammaHan cells, NeuSAc is synthesized from the phosphorylated ManNAc-6-phosphate precursor by the PEP-dependent N-acetylneuraminic acid 9-phosphate synthase (Neu9PS EC 2.5.1.57). By simultaneous release of inorganic phosphate from the enol ester upon C-C bond formation, the additions are essentially irreversible. 

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