SYNTHESIS OF SULFUR ANALOGS OF METHYL AND ALLYL KOJIBIOSIDES AND METHYL ISOMALTOSIDE AND CONFORMATIONAL-ANALYSIS OF THE KOJIBIOSIDES

The synthesis of methyl and allyl 5'-thio-alpha-D-kojibiosides and methyl 5'-thio-alpha-D-isomaltoside is described. The phenylselenoglycoside and trichloroacetimidate of 2,3,4,6-tetra-O-acetyl-5-thioglucose have been employed as glycosyl donors to glycosylate glucopyranosyl accepters with 2-OH and 6-OH positions free. The disaccharides thus obtained are potential glucosidase inhibitors. The conformational preferences of allyl 5'-thiokojibioside (34) were studied by comparison of experimental NOE curves with the theoretical counterparts for the corresponding methyl glycoside 25, derived from a Boltzmann-averaged grid search using the program PIMM91. Very goad agreement of experimental NOE curves derived from selective NOE measurements with the theoretical curves is found. The data are consistent with the population of a global minimum structure Phi=-43, Psi-39 degrees) to the extent of 90%, and a second local minimum (Phi=-36, Psi=-173 degrees) to the extent of 6%. An X-ray crystal structure of 34 at 190 K (R=4.2%) indicates a conformation (Phi=-46, Psi=-23 degrees) that is similar to that of the global minimum.