Synthesis of the tetrasaccharide Glc alpha (1 -> 3) Man alpha (1 -> 2) Man alpha (1 -> 2) Man alpha (OMe) as inhibitor of calnexin binding to GlcMan(9)GlcNAc(2)

Tetrasaccharide GlcMan(3) is an inhibitor of GlcMan(9)GlcNAc(2) binding to calnexin, a chaperone protein involved in CFTR-DeltaF 508 retention. A convergent route to its methyl glycoside, the title tetrasaccharide, was developed. The key building block Glc alpha (1-->3) Man 6 was stereoselectively obtained by condensation of a trichloroacetimidate glucosyl donor with an ethyl thiomannopyranoside acceptor. Di-mannose moiety 10 and final compound 12 resulted from thioglycoside activations.