The use of the novel glycosyl acceptor and supramer analysis in the synthesis of sialyl-α(2–3)-galactose building block

Abstract

A new glycosyl acceptor to be used in sialylation was designed as a 3-hydroxy derivative of 4-methoxyphenyl β-d-galactopyranoside with 2-O-acetyl group and O-4 and O-6 protected as benzylidene acetal. Two alternative syntheses of this compound were compared. Sialylation of 3-OH group of the glycosyl acceptor with O-chloroacetylated N-trifluoroacetylneuraminic acid phenyl thioglycoside (NIS, TfOH, MeCN, MS 3 Å, −40 °C) was studied in a wide concentration range (5–150 mmol L−1). The outcome of sialylation generally followed the predictions of supramer analysis of solutions of sialyl donor in MeCN, which was performed by polarimetry and static light scattering and revealed two concentration ranges differing in solution structure and the structures of supramers of glycosyl donor. The optimized conditions of sialylation (C = 50 mmol L−1) were used to synthesize protected Neu-α(2–3)-Gal disaccharide (78%, α:β = 13:1), which was then converted to sialyl-α(2–3)-galactose imidate building block useful for the synthesis of complex sialo-oligosaccharides.