Synthesis of seven penta- N,O-acetyl-pseudo-2-amino-2-deoxy- dl-hexopyranoses

Abstract

The 1,5-dialdehyde generated through periodate oxidation of 4,7- O-isopropylidene-pseudo-α- dl-galactopyranose ( 3) undergoes base-catalysed cyclisation with nitromethane to give three crystalline pseudo-2-deoxy-2-nitro- dl-hexopyranose derivatives with the β- galacto ( 10), β- gulo ( 11), and α- galacto configurations ( 12) in the ratios of 9:1:2 in 86% combined yield. Hydrogenation of the nitro group with Raney nickel gave, in high yields, the respective pseudo-2-amino-2-deoxy- dl-hexose derivatives 13, 17, and 19, which were characterised as the penta- N,O-acetyl derivatives 16, 18, and 20. In addition, treatment of the 1,3-dimesylate of 13 with anhydrous sodium acetate in 2-methoxyethanol resulted in inversion of the configurations at C-1 and C-3 to give, after acetylation, the pseudo-2-acetamido-2-deoxy-α- dl-gulopyranose derivative 21, which was converted into the penta- N,O-acetyl derivative 22. Likewise, the 4,7- O-benzylidene derivative of pseudo-β- dl-glucopyranose ( 2) was subjected to the sequence of periodate oxidation, nitro-methane cyclisation, and neutralisation, giving two pseudo-deoxynitrohexopyranose derivatives with β- gluco ( 24, 42%) and β- allo configurations ( 25, 19%), which were converted by two steps into the penta- N,O-acetyl derivatives 29 and 33, respectively. The stereoisomer 35 with the α- allo configuration was prepared via the dimesylate obtained from 4,7- O-benzylidene-pseudo-2-acetamido-2-deoxy-β- dl-glucopyranose ( 26). Elucidation of the structures and configurations was mainly based on the 1H-n.m.r. data.