Alkaline biocatalysis for the direct synthesis of N-acetyl-D-neuraminic acid (Neu5Ac) from N-acetyl-D-glucosamine (GlcNAc)

Integration between the alkaline epimerization of N-acetyl-D-glucosamine (GlcNAc) to N-Acetyl-D-mannosamine (ManNAc) and the N-acetyl-D-neuraminic acid (Neu5Ac) aldolase-catalyzed biotransformation has been assessed experimentally. GlcNAc epimerization took place above pH 9.0, and the initial rate of ManNAc formation increased exponentially to 10.37 mmol/L per hour at pH 12. However, above this pH, severe degradation of pyruvate occurred. A value of 31.3% molar conversion on Pyr was achieved in an integrated biotransformation. The "pseudo"-steady state at the end of the reaction was comparable to the equilibrium achieved with a combination of an epimerase and aldolase enzymes. The integrated reaction proved feasible, but at the expense of pyruvate and Neu5Ac aldolase degradation.