. "The method of claim 1, wherein the sialic acid precursor has the structure wherein: A is CH2 or NH; B, C, D and E are each independently selected from the group consisting of: H, OH, X, O???CO???X or O???X, wherein X is a substituted or unsubstituted alkyl or alkenyl, X being selected independently for each group B, C and D; G is H, OH, Y or O???Y, wherein Y is a substituted or unsubstituted alkyl" . . .