A novel, readily accessible lactosaminyl donor: N-Trichloroethoxycarbonyl-hexa-O-benzoyl-β-D-lactosaminyl fluoride

Article abstract of DOI:10.1246/bcsj.68.1172

A simple, preparatively satisfactory 10-step sequence is described for converting lactose into a novel, suitably blocked lactosaminyl donor: N-Trichloroethoxycarbonyl-β-D-lactosaminyl fluoride (5). The key intermediate in this conversion is the particularly well-accessible oxime of lactosulosyl bromide (52% for the 6 steps from lactose), which on α-glycosidation with p-methoxybenzyl alcohol, oxime reduction, N-protection by Troc chloride, and the anomeric fluorination yields 5 (37% for the 4 steps). The utility of 5 as an effective donor was proved by the β-selective glycosylation of the primary 6-OH of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (14) and the 3-OH of methyl 2,4,6-tri-O-benzyl-β-D-galactopyranoside (16), both affording the respective trisaccharides 15 and 18 in high yields. The latter, when subjected to N-deprotection, N-acetylation, and de-O-acylation gave, in 42% yield based on donor 5, β-D-Gal-(1 → 4)-β-D-GlcNAc-(1 → 3)-β-D-Gal-(1 → Me), a core trisaccharide unit of immunologically important carbohydrate antigens.