Synthesis of β-D-Galp-(1→4)-β-D-GlcpNAc-(1→2)-α-D-Manp(1→O)(CH2)7CH3 mimics to explore the substrate specificity of sialyltransferases and trans-sialidases

Eleven trisaccharide octyl glycosides related to the N-glycan sequence beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->O)-(CH2)(7)CH3 (1) designed for detailed exploration of the acceptor specificity of alpha-2,3- and alpha-2,6-sialyltransferases as well as trans-sialidases, have been synthesised: beta-D-Galp-(1-->4)-beta-D-GlcpNPr-(1-->2)-alpha-D-Manp-(1-->O)(CH2)(7)CH3 (2), beta-D-Fucp-(1-->4)-O-D-GlcpNR-(1-->2)-alpha-D-Manp-(1-->O)-(CH2)(7)CH3 (3, R = Ac; 4, R = Pr), 6-amino-6-deoxy-beta-D-Galp(1-->4)-beta-D-GlcpNR-(1--> 2)-alpha-D-Manp-(1-->O)(CH2)(7)CH3 (5, R = Ac; 6, R = Pr), 2-deoxy-beta-D-Galp-(1-->4)-beta-D-GlcpNR-(1-->2)-alpha-D-Manp-(1-->O)(CH2)(7)CH3 (7, R = Ac; 8, R = Pr), beta-D-GalpNR(1)-(1-->4)-beta-D-GlcpNR-(1-->2)-alpha-D-Manp-(1-->O)- (CH2)(7)CH3 (9, R R-1 = Ac; 10, R = R-1 = Pr; 11, R = Ac, R-1 = Pr; 12, R = Pr, R1 Ac). All trisaccharides were obtained by condensation of suitably modified glycosyl donors based on imidates or thioglycosides with the single disaccharide acceptor octyl (3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1-->2)-3,4,6-tri-O-benzyl-alpha-D-manno-pyranoside, followed by deprotection. For the trisaccharides containing an N-acylated glucosamine as well as an N-acylated galactosamine unit, use was made of a combination of N-phthaloyl and N-dimethylmaleoyl protection. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.