title: Synthesis of C-5-thioglycopyranosides and their sulfonium derivatives from 1-C-(2'-oxoalkyl)-5-S-acetylglycofuranosides.
abstract: 1-C-(2'-oxoalkyl)-5-S-acetylglycofuranosides of L-arabinose, D-ribose, and D-xylose were converted to 1-C-(2'-oxoalkyl)-5-thioglycopyranosides by base treatment. The transformation was achieved through beta-elimination to an acyclic alpha,beta-conjugated aldehyde (ketone or ester), followed by an intramolecular hetero-Michael addition by the 5-thiol group. The cycloaddition was highly stereoselective in favor of an equatorial 1-C-substitution. The resultant C-5-thioglycopyranosides were further converted to the sulfonium salts by treatment with cyclic sulfate and methyl iodide. Two sulfonium isomers were obtained due to the presence of both S-axial and S-equatorial substitutions. We observed that the chemical shifts of both C-1 and C-5 in the S-axial substituted sulfonium sugars are always shifted up-field (5-10 ppm) in comparison to those in the S-equatorial substitutions (deltaC 49-53 ppm vs 42-45 ppm at C-1 and 37-42 ppm vs 32-35 ppm at C-5), which provides an easy way for determination of the stereochemistry.
authors.affiliation: Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario, K1A 0R6, Canada.
authors.forename: Tian
authors.initials: T
authors.lastname: Yi
authors.forename: Shih-Hsiung
authors.initials: SH
authors.lastname: Wu
authors.forename: Wei
authors.initials: W
authors.lastname: Zou
mesh_terms: D005663:Furans / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011714:Pyrans / Q000737:chemistry*; D013452:Sulfonium Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D013865:Thioglycosides / Q000138:chemical synthesis* / Q000737:chemistry*
chemical_list: D005663:Furans; D011714:Pyrans; D013452:Sulfonium Compounds; D013865:Thioglycosides