SPECIFIC FEATURES OF THE BEHAVIOR OF ALPHA-GLYCOSYLFLUORIDE AND BETA-GLYCOSYLFLUORIDE TETRAACETATES DURING CHEMICAL-IONIZATION IN ISOBUTANEAND TETRAMETHYLSILANE

Reactions of alpha- and beta-glycosylfluoride tetraacetates with trime thylsilicenium ion in the gas phase during chemical ionization have be en studied. The [M+SiMe(3)](+) ions formed from the glycosylfluorides are more stable than the corresponding [M+H](+) ions. The cleavage of the weakest glycosidic bond leading to the generation of glycosidic io ns is not dominant for the trimethylsilylated ions, as it has been obs erved in the corresponding protolytic reactions. The ratio of the inte nsities of the [M+SiMe(3)](+) and [M-F](+) ions characterizes the prob ability of the initial localization of the trimethylsilyl ion at the g lycosidic center; the equatorial orientation of fluorine at C(1) makes it possible for the electrophile to bond with this substituent. Gener ation of the glycosidic ions is rather weakly affected by increasing t emperature, whereas [M-AcO](+) formation is significantly intensified.