Direct stereocontrolled synthesis of 3-amino-3-deoxy-beta-mannopyranosides: importance of the nitrogen protecting group on stereoselectivity.

ABSTRACT: The highly stereocontrolled synthesis of the 3-amino-3-deoxy-beta-mannopyranosides is achieved by means of thioglycoside donors protected with a 4,6-O-benzylidene or alkylidene acetal and a benzylidene imine group. Among the various nitrogen protecting groups investigated only the Schiff's base was found to give high beta-selectivity. N-Phthalimido and N-acetamido protected donors were found to be highly alpha-selective, whereas 3-azido-3-deoxy glycosyl donors gave intermediate selectivity. The reasons for the protecting group dependency are discussed in terms of the change in the O2-C2-C3-N3 torsional interaction on conversion of the covalent glycosyl triflates to the transient oxacarbenium ions.

SUBMITTER: Crich D 

PROVIDER: S-EPMC2621320 | biostudies-literature | 2007 Jul

REPOSITORIES: biostudies-literature