Stereoselective beta-Hydrogen Elimination from Nickel(II)-N-Glycoside Complexes

Octahedral nickel(II)-N-glycoside complexes of glucose, galactose, mannose, and talose were synthesized and analyzed by electrospray ionization (ESI). A resulting tricoordinate species generated from the octahedral complex was subjected to collision-induced dissociation. A highly stereoselective dissociation pathway involving beta-hydrogen elimination and cross-ring cleavages was observed in complexes possessing equatorial C-2 substituents. (2)H- and (13)C-labeling experiments indicate that the hydrogen on C-2 and a labile proton are involved in the beta-hydrogen elimination. Additionally, C-4, C-5, and C-6 are shown to be lost from the monosaccharide as a result of the cross-ring cleavages. A mechanism is postulated to explain the stereoselectivity of this dissociation.