Synthesis of Sialic Acids, Their Derivatives, and Analogs by Using a Whole-Cell Catalyst.

Sialic acids (Sias) are important constituents of cell surface glycans. Ready access to Sias in large quantities would facilitate the development of carbohydrate-based vaccines and small-molecule drugs. We now present a facile method for synthesizing various natural forms and non-natural derivatives or analogs of Sias by using a whole-cell catalyst, which is constructed by adding a plasmid containing necessary enzyme genes into a metabolically engineered strain of Escherichia coli. The flexible substrate tolerance of incorporated enzymes (N-acetylglucosamine 2-epimerase and N-acetylneuraminic acid aldolase) allows the cellular catalyst to convert a wide range of simple and inexpensive sugars into various Sia-related compounds through an easily scalable fermentation process. Further, syntheses using this whole-cell biotransformation in combination with three conventional enzymatic reactions provide a series of complex Sia-containing glycans (sialyloligosaccharides) and their derivatives bearing different substituents. The processes described herein should permit the large-scale and economical production of both Sias and sialyloligosaccharides, and may complement existing chemical and enzymatic strategies.