Noncatalytic reaction of isonitriles and carboxylic acids en route to amide-type linkages

This protocol describes the preparation of an N-methyl-asparagine-linked glycosyl amino acid, on the basis of a reaction between carboxylic acids and isonitriles. Under microwave/thermolysis, carboxylic acids can couple with isonitriles without an external catalyst to form N-formyl-amides, which may be further advanced to the corresponding amides, N-methyl amide and N-methyloyl amide. The example reaction of beta-galactopyranosyl isonitrile (7) with a protected aspartic acid under microwave condition in 30 min stereoselectively leads to a beta-galactopyranosyl-N-formyl-asparagine (9). Further chemical transformations readily convert 9 into beta-galactopyranosyl-N-methyl-asparagine (11).