Synthesis of protected hexp-(1->4)-beta-D-GlcpNAc-(1->2)-alpha-D-Manp-(1->O)(CH2)(7)CH3 sequences (Hex equals beta-D-Glc, 4-deoxy-4-fluoro-beta-D-Gal, or 4-deoxy-beta-D-Gal) using a Glc-GlcNPhth donor, eventually fluorinated or deoxygenated at the oligosaccharide level

Three trisaccharide derivatives of the type beta-D-Hexp-(1 --> 4)-beta-D-GlcpNAc(1 --> 2) -alpha-D-Manp-(1 --> O)(CH2)(7)CH3 have been synthesized, with Hex being either glucose (15), 4-deoxy-4-fluorogalactose (20), or 4-deoxygalactose (27). These trisaccharides have been designed for the study of the acceptor specificity of glycosyltransferases involved in termination of N-acetyllactosamine-type N-glycans. Allyl (2-O-acetyl-3,6-di-O-benzyl-beta-D-glucopyranosyl)-(1--> 4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyrano side (10) was synthesized by condensation of 2,4,6-tri-O-acetyl-3-O-benzyl-alpha-D-glucosypanosyl trichloroacetimidate with allyl 3,6-di-O-benzyl-2- deoxy-2-phthalimido-beta-D-glucopyranoside, followed by 4',6'-de-O-acetylation, 4',6'-O-benzylidenation (8), and specific acetal ring opening. Acetylation or inverted fluorination of 10, followed by deallylation and imidation, gave suitable disaccharide donors which were each condensed with octyl 3,4,6-tri-O-benzyl-alpha-D-mannopyranoside (14) to afford the fully protected trisaccharides 15 and 20. Deallylation and imidation of 8, followed by coupling to 14 and subsequent specific acetal ring opening, triflation, halogenation, and reductive dehalogenation gave the protected 4'-deoxytrisaccharide.