Direct stereocontrolled synthesis of 3-amino-3-deoxy-beta-mannopyranosides: importance of the nitrogen protecting group on stereoselectivity.
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.
Crich
David
D
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, USA. dcrich@uic.edu
Xu
Huadong
H
D000080:Acetals / Q000737:chemistry; D000218:Adamantane / Q000737:chemistry; D000586:Amination; D005609:Free Radicals / Q000737:chemistry; D006027:Glycosides / Q000737:chemistry; D006031:Glycosylation; D008358:Mannose / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D013237:Stereoisomerism
D000080:Acetals; D005609:Free Radicals; D006027:Glycosides; D009584:Nitrogen; D008358:Mannose; D000218:Adamantane; D010100:Oxygen