Direct amidation of aldoses and decarboxylative amidation of alpha-keto acids: an efficient conjugation method for unprotected carbohydrate molecules.

With use of iodine as an appropriate oxidant, unprotected and unmodified aldoses undergo oxidative amidation with a variety of functionalized amines, alpha-amino esters, and peptides, whereas KDO, sialic acid, and other alpha-keto acids proceed with oxidative decarboxylation followed by in situ amidation. Glycoside bond and many other functional groups are inert under such mild reaction conditions. This reaction protocol for direct ligation of carbohydrate molecules looks promising in the development of a general and efficient synthesis of glycoconjugates.