Un nouvel agent de glycosylation: l'anhydride trifluorométhanesulfonique. Synthèse des α et β O-glycosyl-L-sérine, -L-thréonine et -L-hydroxyproline

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Abstract
When 2,3,4,6-tetra-O-benzyl-D-glucopyranose, -D-galactopyranose and 2,3,4-tri-O-benzyl-D-xylopyranose were allowed to react in the cold in dichloromethane or acetonitrile as solvent in the presence of trifluoromethanesulfonic (triflic) anhydride, with methyl or benzyl esters of the N-(benzyloxycarbonyl)-L-serine, -L-threonine, and -L-hydroxyproline, an anomeric mixture of the corresponding O-glycosylaminoacids was obtained (55 to 90% overall yield), with the α-anomer being predominant. The same experimental procedure was successfully applied to the condensation of the benzyl ester of the N-(benzyloxycarbonyl)-L-hydroxyproline with 2,3,4-tri-O-benzyl-L-arabinopyranose and 2,3,5-tri-O-benzyl-L-arabinofuranose affording the corresponding condensation products with similar yield. Pure α and β anomers were obtained after column chromatography or crystallization with 30 to 65% yield. Hydrogenolysis of benzyl derivatives afforded the unprotected compounds. Optical rotation, 1H and 13C nmr were the main methods used to assess structure and stereochemistry.