title: Studies on the stereoselective synthesis of a protected α-D-Gal-(1→2)-D-Glc fragment.
abstract: A novel 1,2-cis stereoselective synthesis of protected α-D-Gal-(1→2)-D-Glc fragments was developed. Methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-D-galactopyranosyl-(1→2)-3-O-benzoyl-4,6-O-benzylidene-α-D-glucopyranoside (13), methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-D-galactopyranosyl-(1→2)-3,4,6-tri-O-benzoyl-α-D-glucopyranoside (15), methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-D-galactopyranosyl-(1→2)-3-O-benzoyl-4,6-O-benzylidene-β-D-glucopyranoside (17), and methyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-α-D-galactopyranosyl-(1→2)-3,4,6-tri-O-benzoyl-β-D-glucopyranoside (19) were favorably obtained by coupling a new donor, isopropyl 2-O-acetyl-3-O-allyl-4,6-O-benzylidene-1-thio-β-D-galactopyranoside (2), with acceptors, methyl 3-O-benzoyl-4,6-O-benzylidene-α-D-glucopyranoside (4), methyl 3,4,6-tri-O-benzoyl-α-D-glucopyranoside (5), methyl 3-O-benzoyl-4,6-O-benzylidene-β-D-glucopyranoside (8), and methyl 3,4,6-tri-O-benzoyl-β-D-glucopyranoside (12), respectively. By virtue of the concerted 1,2-cis α-directing action induced by the 3-O-allyl and 4,6-O-benzylidene groups in donor 2 with a C-2 acetyl group capable of neighboring-group participation, the couplings were achieved with a high degree of α selectivity. In particular, higher α/β stereoselective galactosylation (5.0:1.0) was noted in the case of the coupling of donor 2 with acceptor 12 having a β-CH(3) at C-1 and benzoyl groups at C-4 and C-6.
authors.affiliation: College of Chemistry, Key Laboratory of Environmentally Friendly Chemistry and Application of Ministry of Education, Xiangtan University, Xiangtan, Hunan Province 411105, PR China. chengood2003@263.net
authors.forename: Langqiu
authors.initials: L
authors.lastname: Chen
authors.forename: Shen-De
authors.initials: SD
authors.lastname: Shi
authors.forename: Yong-Qing
authors.initials: YQ
authors.lastname: Liu
authors.forename: Qing-Jiao
authors.initials: QJ
authors.lastname: Gao
authors.forename: Xing
authors.initials: X
authors.lastname: Yi
authors.forename: Kai-Ke
authors.initials: KK
authors.lastname: Liu
authors.forename: Hao
authors.initials: H
authors.lastname: Liu
mesh_terms: D000107:Acetylation; D002236:Carbohydrate Conformation; D004187:Disaccharides / Q000138:chemical synthesis* / Q000737:chemistry; D005690:Galactose / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry; D006027:Glycosides / Q000138:chemical synthesis* / Q000737:chemistry; D006031:Glycosylation; D008956:Models, Chemical; D013237:Stereoisomerism
chemical_list: D004187:Disaccharides; D006027:Glycosides; D005690:Galactose