4,6-O-benzylidene-directed beta-mannopyranosylation and alpha-glucopyranosylation: the 2-deoxy-2-fluoro and 3-deoxy-3-fluoro series of donors and the importance of the O2-C2-C3-O3 interaction.
A series of 4,6-O-benzylidene-protected 2-O-benzyl-3-deoxy-3-fluoro- and 3-O-benzyl-2-deoxy-2-fluorogluco- and mannopyranosyl thioglycosides were synthesized and their coupling reactions with a series of alcohols, on preactivation with 1-benzenesulfinylpiperidine and trifluoromethanesulfonic anhydride, investigated. In all cases, the selectivities were lower than those observed with the corresponding simple 4,6-O-benzylidene 2,3-di-O-benzylgluco- and mannopyranosyl thioglycosides. This leads to the conclusion that the high beta-selectivity observed with 4,6-O-benzylidene 2,3-di-O-benzylmannopyranosyl donors under the same conditions is in large part derived from the compression of the O2-C2-C3-O3 torsion angle on going from the intermediate covalent glycosyl triflate to the oxacarbenium ion, as compared to the relaxation of this torsion angle in the gluco series.
Crich
David
D
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607-7061, USA. dcrich@uic.edu
Li
Linfeng
L
D000438:Alcohols; D001597:Benzylidene Compounds / Q000138:chemical synthesis*; D003847:Deoxyglucose / Q000031:analogs & derivatives / Q000138:chemical synthesis; D006031:Glycosylation; D007202:Indicators and Reagents; D008358:Mannose / Q000737:chemistry; D013058:Mass Spectrometry; D008968:Molecular Conformation; D012210:Rhamnose / Q000031:analogs & derivatives / Q000138:chemical synthesis; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism
D000438:Alcohols; D001597:Benzylidene Compounds; D007202:Indicators and Reagents; C007253:3-deoxy-3-fluoro-D-glucose; C017190:2-deoxy-2-fluoromannose; D003847:Deoxyglucose; D008358:Mannose; D012210:Rhamnose