Rapid Transformation of D-Mannose into Orthogonally Protected D-Glucosamine and D-Galactosamine Thioglycosides

An expedient protocol for synthesis of orthogonally protected 2-azido-2-deoxy-D-glucosamine and 2-azido-2-deoxy-D-galactosamine donors from D-mannose is described. Readily available phenyl,beta-D-thiomannoside is rapidly transformed into D-GlcN(3) thioglycosides via a highly regioselective 3-O-acylation followed by 4,6-O-benzylidenation and azide displacement of C-2-OTf, which is further converted into D-GalN(3) thioglycosides through Lattrell-Dax inversion of the C4 hydroxy group and its Boc protection. The reaction sequence may be completed in 2 days and involves simple workups and minimal column chromatography.