Abstract
A concise and practical synthesis of the antigenic globotriose, α- d-Gal-(1→4)-β- d-Gal-(1→4)-β- d-Glc ( 13), was achieved by coupling of a monosaccharide donor, 3- O-allyl-2- O-benzoyl-4,6- O-benzylidene-α- d-galactopyranosyl trichloroacetimidate ( 4) with a disaccharide acceptor, p-methoxyphenyl 2,3,6-tri- O-benzoyl-β- d-galactopyranosyl-(1→4)-2,3,6-tri- O-benzoyl-β- d-glucopyranoside ( 8), followed by deprotection. In spite of the existence of a C-2-ester substituent capable of neighboring-group participation in the donor, the coupling gave exclusively the α-linkage in satisfactory yield. The acceptor 8 was readily obtained from selective 3- O-benzoylation of the galactosyl ring of p-methoxyphenyl 2,6-di- O-benzoyl-β- d-galactopyranosyl-(1→4)-2,3,6-tri- O-benzoyl-β- d-glucopyranoside ( 7), which was prepared from p-methoxyphenyl β- d-lactoside ( 5) via isopropylidenation, benzoylation, and deisopropylidenation. Donor 4 was obtained from p-methoxylphenyl 3- O-allyl-2,4,6-tri- O-benzoyl-β- d-galactopyranoside ( 1) via selective 4,6-di-O-debenzoylation, oxidative removal of 1- O-MP, benzylidenation, and trichloroacetimidate formation.
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