Highly diastereoselective alpha-mannopyranosylation in the absence of participating protecting groups.
S-Phenyl 2,6-di-O-benzyl-3,4-O-(2',3'-dimethoxybutane-2', 3'-diyl)-1-thia-alpha-D-mannopyranoside and its sulfoxide, following activation at -78 degrees C with benzenesulfenyl triflate or triflic anhydride, respectively, provide the corresponding alpha-mannosyl triflate as demonstrated by NMR spectroscopy. On addition of an acceptor alcohol alpha-mannosides are then formed. Similarly, S-phenyl 2,3-O-carbonyl-4, 6-O-benzylidene-1-thia-alpha-D-mannopyranoside and ethyl 3-O-benzoyl-4, 6-O-benzylidene-2-O-(tert-butyldimethylsilyl)-1-thia-alpha-D-mannopyr anoside both provide alpha-mannosides on activation with benzenesulfenyl triflate followed by addition of an alcohol. These results stand in direct contrast to the highly beta-selective couplings of comparable glycosylations with 2,3-di-O-benzyl-4, 6-O-benzylidene protected mannosyl donors and draw attention to the subtle interplay of reactivity and structure in carbohydrate chemistry.
Crich
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Department of Chemistry, University of Illinois at Chicago, 60607-7061, USA.
Cai
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Dai
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D000080:Acetals / Q000378:metabolism; D002236:Carbohydrate Conformation; D006031:Glycosylation; D009682:Magnetic Resonance Spectroscopy; D008358:Mannose / Q000737:chemistry / Q000378:metabolism*; D008362:Mannosides / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D013237:Stereoisomerism
D000080:Acetals; D008362:Mannosides; D008358:Mannose