Synthesis and NMR assignments of galactosylgloboside and its β-d-GalNAc-(1→4)-α-d-Gal-linked positional isomer in a conjugatable form

Two pentasaccharides suitable for conjugation, namely 3-aminopropyl glactosylgloboside and its β-d-GalNAc-(1→4)-α-d-Gal-linked positional isomer, were synthesized from 3III,4III-di-O-unprotected globotrioside and the trichloroacetimidate of β-d-Gal-(1→3)-β-d-GalNPhth derivative. Glycosylation at both positions led to the formation of β-d-GalNPhth-(1→4)-α-d-Gal and β-d-GalNPhth-(1→3)-α-d-Gal-linked products in a ratio of 1:1 without selectivity. Complete NMR spectral assignments are also described.