Preparation of C-Glycoside Pendant β2- and β2,2-Amino Acids

Abstract

Abstract Facile preparations of C-glycosyl β2- and β2,2-amino acids are described. Selective formation of a β-C-glycoside linkage was achieved by the reaction of a 2,3,4,6-tetra-O-acetyl-α-d-gluco/galactopyranosyl bromide (α-acetobromoglucose/galactose) with the carbanion of a cyanoacetate ester. Crystallization selectively afforded one of two diastereomers with respect to the chiral center at the α-carbon of the side chain (C-2), however, this compound was found to epimerize during the following nitrile reduction. Separation of the diastereomers was achieved via the Fmoc derivatives. Diastereomerically pure C-glycosyl β2,2-amino acids were prepared by diastereoselective alkylation of C-glycosylated enolate, followed by nitrile hydrogenation. The present procedure serves as an efficient route to C-glycosylated β-amino acids containing a non-biodegradable linkage.