"Super armed" glycosyl donors: conformational arming of thioglycosides by silylation.
Glycosyl donors protected with bulky silyl protective groups (tert-butyldimethylsilyl, TBS), on the 2-, 3-, and 4-OH groups were found to have superior reactivity compared with benzylated thioglucosides. The enhanced reactivity is explained by the stereoelectronic effects associated with the conformational change induced by the silylation. A TBS silylated thioglucoside donor has axial OR groups, whereas a benzylated thioglucoside has equatorial OR groups, leading to much more favorable charge-dipole interactions in the transition state. This concept could be used to create "super armed" glucosyl, mannosyl, rhamnosyl, and galactosyl donors, which could cross-couple with the armed acceptors, phenyl 2,3,4-tri-O-benzyl-beta-D-thioglucoside or phenyl 2,3,6-tri-O-benzyl-beta-D-thioglucoside, to give the corresponding armed disaccharides in good to excellent yields.
Pedersen
Christian Marcus
CM
Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark.
Nordstrøm
Lars Ulrik
LU
Bols
Mikael
M
D001593:Benzyl Compounds / Q000737:chemistry; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D012821:Silanes / Q000138:chemical synthesis / Q000737:chemistry*; D013865:Thioglycosides / Q000138:chemical synthesis / Q000737:chemistry*
D001593:Benzyl Compounds; D007202:Indicators and Reagents; D012821:Silanes; D013865:Thioglycosides