Analysis of linkage positions in 2-acetamido-2-deoxy- d-glucopyranosyl residues by the reductive-cleavage method

Abstract

The fate of methylated 2-acetamido-2-deoxy- d-glucopyranosyl residues under reductive-cleavage conditions was investigated by using methyl 2-(acetylmethylamino)-2-deoxy-3,4,6-tri- O-methyl-β- d-glucopyranoside ( 1), its α anomer ( 8), and fully methylated lacto- N-tetraitol as test compounds. Treatment of 1 with triethylsilane and trimethylsilyl trifluoromethanesulfonate in dichloromethane gave rise to (1,2-dideoxy-3,4,6-tri- O-methyl-α- d-glucopyrano)-2,3-dimethyl[2,1- d]-2-oxazolinium trifluoromethanesulfonate. Quenching of the reaction by addition of aqueous sodium hydrogencarbonate resulted in hydrolysis of the oxazolinium salt. Compound 8 was fully stable to reductive-cleavage conditions. Thus, participation by the 2-acetamido group is necessary for glycosidic carbon-oxygen bond-cleavage to occur. Treatment of methyl 2-deoxy-2-(ethylmethylamino)-3,4,6-tri- O-methyl-α-β- d-glycopyranoside under reductive-cleavage conditions resulted in some anomerization, but neither hydrolysis nor reductive cleavage of the glycosidic carbon-oxygen bond was observed, as expected. Reductive cleavage of fully methylated lacto- N-tetraitol gave the products predicted on the basis of these and prior model studies, including 3- O-acetyl-2-(acetylmethylamino)-2-deoxy-4,6-di- O-methyl- d-glucopyranose derived from the 3-linked 2-acetamido-2-deoxy-β- d-glucopyranosyl residue