A simultaneous stereoselective 2-O-deacetylation and 4-amination reaction of peracetylated Neu5Ac 1
has been established with cyclic secondary amines, such as 1-N-Boc-piperazine. Four C2-symmetric and
two asymmetric sialic acid dimers with (4/4)-piperazine derivatives linked were synthesized. They
may serve as precursors of unnatural polysialic acids.