Title: Differential El Ion Fragmentation Pathways for Peracetylated C-Glycoside Ketals Authors
Submitted to: American Society for Mass Spectrometry
Publication Type: Abstract Only
Publication Acceptance Date: June 7, 2007
Publication Date: August 13, 2007
Citation: Adeuya, A., Momany, F.A., Price, N.P. 2007. Differential El Ion Fragmentation Pathways for Peracetylated C-Glycoside Ketals [abstract]. American Society for Mass Spectrometry. Paper No. TP200. 18:57S. Technical Abstract: Aqueous-based Knoevenagel condensation of sugars with beta-diketones is a useful method for preparing beta-C-glycoside ketones. A mechanism has been proposed in which C-C bond formation between the anomeric sugar carbon and the bridged methylene of the diketone is followed by beta-elimination of water. Given the propensity of ketones to form ketal rings it was surprising to us that there is comparatively little structural evidence for the bicyclic C-glycoside ketals. Several C-glycoside ketones and peracetylated C-glycoside ketones were prepared from aldose starting sugars, including various appropriately isotope-labeled aldohexoses ([1-13C]Glc, [U-13C]Glc, and [6,6’-2H2]Glc). The reaction products obtained by evaporation were analyzed by MALDI-TOF MS prior to pyridine-catalyzed peracetylation by reflux with acetic anhydride. The peracetylated products were analyzed by GC-MS and MALDI-TOF MS. The fragmentation pathways for the C-glycoside were deduced from mass spectra obtained following electron impact ionization of the peracetylated species. Following peracetylation, EI-MS fragmentations were used to define four different ion fragmentation pathways, for (i) aldopyranosyl; (ii) aldofuranosyl; (iii) 6-deoxypyranosyl; and (iv) 2-deoxyaldopyranosyl C-glycoside ketones. Pathways (i), (ii), and (iii) occur via gas phase furanoid intermediates, that are absent from pathway (iv). These findings support the conclusion that, except for the 2-deoxy analogs, the peracetylated C-glycoside ketones adopt a bicylic structure containing an intramolecular 2-ketal bond.