A practical synthesis of α-d-Manp-(1→3)-α-d-Manp-(1→2)-[α-d-Glcp-(1→3)]-α-d-Manp-(1→2)-α-d-Manp-(1→2)-α-d-Manp, an O-specific heterohexasaccharide fragment of Citrobacter braakii O7a, 3b, 1c Original Research Article

An O-specific heterohexasaccharide fragment of Citrobacter braakii O7a, 3b, 1c, α-d-Manp-(1→3)-α-d-Manp-(1→2)-[α-d-Glcp-(1→3)]-α-d-Manp-(1→2)-α-d-Manp-(1→2)-α-d-Manp was synthesized as its methyl glycoside. Acetylation of allyl 4,6-O-benzylidene-α-d-mannopyranoside, followed by debenzylidenization and benzoylation gave allyl 2,3-di-O-acetyl-4,6-di-O-benzoyl-α-d-mannopyranoside (3), and subsequent deacetylation of 3 with CH3COCl–MeOH gave the monosaccharide acceptor 4. Condensation of isopropyl 2,3,4,6-tetra-O-benzyl-1-thio-β-d-glucopyranoside (6) with 4 selectively afforded the α-(1→3)-linked disaccharide 7. Condensation of 7 with the (1→3)-linked disaccharide donor 9, followed by deallylation and trichloroacetimidation, afforded the tetrasaccharide donor 12. Coupling of 12 with disaccharide acceptor 13, followed by debenzylation and deacylation, furnished the target heterohexasaccharide 16.