N-Glycosidation of d-arabino-hex-2-ulosonic acid

Two approaches to N-functionalized d-arabino-hex-2-ulosonic acid derivatives were established by nucleophilic substitution of methyl (3,4,5-tri-O-acetyl-β-d-arabino-hex-2-ulopyranosyl)onate bromide (1). Reaction of 1 with amino compounds in the presence of mercury(II) cyanide led to the 2,3-cis configured β-d-arabino N-glycosides. On the other hand, the reaction of bromide 1 with azide, followed by catalytic hydrogenation led to 2,3-trans α-d-arabino glycosyl amine methyl 3,4,5-tri-O-acetyl-2-amino-α-d-arabino-hex-2-ulopyranosonate, which was easily rearranged to the thermodynamically more stable β-d-arabino N-acetyl derivative methyl 4,5-di-O-acetyl-2-acetylamino-3-hydroxy-β-d-arabino-hex-2-ulopyranosonate. The assignment of configuration of the tertiary anomeric centre and conformation of all products was based on 1H NMR H,H coupling constants and NOE difference experiments.