Benzylidene Acetal Protecting Group as Carboxylic Acid Surrogate: Synthesis of Functionalized Uronic Acids and Sugar Amino Acids

Abstract Direct oxidation of the 4,6‐ O ‐benzylidene acetal protecting group to C‐6 carboxylic acid has been developed that provides an easy access to a wide range of biologically important and synthetically challenging uronic acid and sugar amino acid derivatives in good yields. The RuCl 3 –NaIO 4 ‐mediated oxidative cleavage method eliminates protection and deprotection steps and the reaction takes place under mild conditions. The dual role of the benzylidene acetal, as a protecting group and source of carboxylic acid, was exploited in the efficient synthesis of six‐carbon sialic acid analogues and disaccharides bearing uronic acids, including glycosaminoglycan analogues.