Synthesis of p-nitrophenyl 2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl- β-d-glucopyranoside, and p-nitrophenyl 6-O-(2-acetamido-2-deoxy-3-O- and -4-O-β-d-galactopyranosyl- β-d-glucopyranosyl)-α-d-mannopyranoside

A facile synthesis of p-nitrophenyl 2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl- β-d-glucopyranoside was accomplished by saponification of the product obtained by reaction of 2-acetamido-3,6-di-O-acetyl-2-deoxy-4-O-(2,3,4,6-tetra-O-acetyl- β-d-galactopyranosyl)-α-d-glucopyranosyl chloride and Amberlyst A-26 p-nitrophenoxide. The reaction of p-nitrophenyl 2,3-O-isopropylidene-α-d-mannopyranoside (7) with the easily accessible 2-methyl-[4,6-di-O-acetyl-2-deoxy-3-O-(2,3,4,6-tetra-O- acetyl-β-d-galactopyranosyl)-α-d-glucopyrano]-[2,1-d]-2-oxazoline proceeded readily, to give the protected trisaccharide derivative which, on deacetonation, followed by O-deacetylation, produced one of the title trisaccharides, namely, p-nitrophenyl 6-O-(2-acetamido-2-deoxy-3-O-β-d-galactopyranosyl-β-d-glucopyranosyl)-α-d-mannopyranoside. Synthesis of the other trisaccharide, p-nitrophenyl 6-O-(2-acetamido- 2-deoxy-4-O-β-d-galactopyranosyl-β-d-glucopyranosyl)-α-d-mannopyranoside was accomplished by a similar reaction-sequence when the corresponding 2-methyl-[3,6- di-O-acetyl-2-deoxy-4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-glucopyrano]- [2,1-d]-2-oxazoline (19) reacted with 7. Preparation of oxazoline 19 was achieved via acetolysis of methyl 2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl-α-d-glucopyranoside. The structures assigned to the final saccharides were supported by ¹H- and ¹³C-n.m.r.-spectral data.