De novo chemoenzymatic synthesis of sialic acid

A chemoenzymatic synthesis of sialic acid from inexpensive N -acetyl- D -glucosamine is described. In a three-step Wittig-protection-ozonolysis strategy manno -configured aldehydes are obtained. Treatment with oxaloacetate in the presence of macrophomate synthase affords the signature α-keto-γ-hydroxy acid moiety with high diastereoselectivity.