Nucleophilic replacement reactions of sulphonates. Part III. The synthesis of derivatives of 2,3,4,6-tetra-amino-2,3,4,6-tetradeoxy-D-galactose and -D-idose

Abstract

Methyl 2,3,4,6-tetra-amino-2,3,4,6-tetradeoxy-α-D-galactopyranoside has been synthesised from a 2-acetamido-2-deoxy-allopyranoside by the stepwise introduction of azide groups into the molecule by the nucleophilic displacement of sulphonyloxy-groups. These displacement reactions are greatly facilitated by the use of hexamethylphosphoric triamide as reaction solvent, which is superior to NN-dimethylformamide for this purpose because the reactions can be carried out at a lower temperature at which little or no decomposition of the sulphonate ester occurs. The corresponding idopyranoside has been prepared in a similar fashion from methyl 3-acetamido-2-azido-4,6-O-benzylidene-2,3-dideoxy-α-D-altropyranoside. Steric and electronic factors affecting the displacement reactions of sulphonate esters are discussed.