5-azido derivatives of neuraminic acid - Synthesis and structure

Benzyl sialoside 1 was transformed into the corresponding 5-azido derivativ e 4 by N-nitrosation of the fi-acetylamino group and treatment with base fo llowed by hydrazoic acid or, alternatively, by N,O-deacetylation followed b y diazo group transfer to the amino moiety by means of TfN3. Regioselective 4-O-acetylation and introduction of the MPM group at 9-O afforded glycosyl acceptor 11. N,O-Deacetylation of ethyl 2-thiosialoside 13 afforded 14 whi ch, after diazo group transfer to the amino group, furnished 5-azido deriva tive 16, which can serve as a sialyl donor. Activation of the ethylthio lea ving group in the absence of an acceptor afforded 2,3-dehydro derivative 17 . Regioselective 4-O-acetylation and 9-O-benzylation furnished glycosyl acc eptor 22, An X-ray analysis was obtained from crystals of the 7,8,9-O-unpro tected intermediate 21.