Synthesis of two isomeric pentasaccharides, the possible repeating unit of the β-glucan from the micro fungus Epicoccum nigrum Ehrenb. ex Schlecht Original Research Article

Two isomeric pentasaccharides, β-d-Glcp-(1→3)-[β-d-Glcp-(1→6)]-β-d-Glcp-(1→3)-[β-d-Glcp-(1→6)]-β-d-Glcp (I) and β-d-Glcp-(1→6)-β-d-Glcp-(1→3)-[β-d-Glcp-(1→3)-β-d-Glcp-(1→6)]-β-d-Glcp (II), the possible repeating unit of the β-glucan from the micro fungus Epicoccum nigrum Ehrenb. ex Schlecht, were synthesized as their 4-methoxyphenyl glycosides in a regio- and stereoselective manner. The pentasaccharide I was obtained from 3-O-selective glycosylation of 4-methoxyphenyl 4,6-O-benzylidene-β-d-glucopyranoside (12) with 2,3,4,6-tetra-O-benzoyl-β-d-glucopyranosyl-(1→3)-[2,3,4,6-tetra-O-benzoyl-β-d-glucopyranosyl-(1→6)]-2,4-di-O-acetyl-α-d-glucopyranosyl trichloroacetimidate (6) followed by acetylation, debenzylidenation, and 6-O-selective glucosylation with 2,3,4,6-tetra-O-benzoyl-β-d-glucopyranosyl trichloroacetimidate (1), and then by deprotection. The pentasaccharide II was obtained from 3-O-selective coupling of 12 with 2,3,4,6-tetra-O-benzoyl-β-d-glucopyranosyl-(1→6)-2,4-di-O-acetyl-3-O-allyl-α-d-glucopyranosyl trichloroacetimidate (10) followed by acetylation, debenzylidenation, and 6-O-selective glycosylation with 2,3,4,6-tetra-O-benzoyl-β-d-glucopyranosyl-(1→3)-2,4,6-tri-O-acetyl-α-d-glucopyranosyl trichloroacetimidate (11), and finally by deprotection.