title: Preparation of alpha and beta anomers of 1,2,3,6-tetra-O-acetyl-4-chloro-4-deoxy-D-galactopyranose based upon anomerization and kinetic acetylation.
abstract: 4-Chloro-4-deoxy-alpha-d-galactopyranose, 1,2,3,6-tetra-O-acetyl-4-chloro-4-deoxy-alpha-d-galactopyranose and 1,2,3,6-tetra-O-acetyl-4-chloro-4-deoxy-beta-d-galactopyranose were readily prepared from 1,4:3,6-dianhydro-beta-d-fructofuranosyl 4-chloro-4-deoxy-alpha-d-galactopyranoside. In the study, we found an interesting anomerization phenomenon of 4-chloro-4-deoxy-d-galactose. The molar ratio of alpha and beta anomers in solution is about 1:2 when the anomerization reaches a dynamic equilibrium, and the beta anomer could completely convert to the alpha anomer in the process of crystallization and precipitation. The acetylation of 4-chloro-4-deoxy-d-galactopyranose is kinetically controlled, and the configuration of the starting galactose determines the configuration of the resulting acetates. The influence of the chloro group at C-4 and the O-acetyl group at the anomeric carbon on the galactopyranose ring conformations is discussed, based upon the crystallographic data for the alpha and beta anomers of 1,2,3,6-tetra-O-acetyl-4-chloro-4-deoxy-d-galactopyranose.
authors.affiliation: Department of Chemistry, Zhengzhou University, Zhengzhou 450052, PR China.
authors.forename: Feng-Wu
authors.initials: FW
authors.lastname: Liu
authors.forename: Yan-Bing
authors.initials: YB
authors.lastname: Zhang
authors.forename: Hong-Min
authors.initials: HM
authors.lastname: Liu
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Song
mesh_terms: D000107:Acetylation; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D011232:Chemical Precipitation; D003460:Crystallization; D018360:Crystallography, X-Ray; D005643:Fucose / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D006860:Hydrogen Bonding; D007536:Isomerism; D007700:Kinetics; D008969:Molecular Sequence Data; D015394:Molecular Structure
chemical_list: C503196:1,2,3,6-tetra-O-acetyl-4-chloro-4-deoxygalactopyranose; C411482:4-chloro-4-deoxygalactose; D005643:Fucose