Submitted to: Journal of Mass Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 5, 2007
Publication Date: August 13, 2007
Citation: Price, N.P., Momany, F.A., Adeuya, A. 2007. Differential EI fragmentation pathways for peracetylated C-glycoside ketones as a consequence of bicyclic ketal ring structures. Journal of Mass Spectrometry. 43:53-62. Interpretive Summary: Carbohydrates called "C-glycosides" are commercially valuable but currently difficult to produce. A novel method was used to generate a variety of these compounds from thirteen common sugars. Analysis showed that the C-glycosides retained the desirable characteristics of the parent sugars. Results will be valuable to researchers in the field and the pharmaceutical industry.
Technical Abstract: Several C-glycoside ketones and peracetylated C-glycoside ketones have been synthesized from 13 structurally-diverse aldoses sugars (including isotope labeled [1-**13C]Glc, [U-**13C]Glc, and [6,6’-**2H2]Glc) via an aqueous-based Knoevanagel condensation with aliphatic 1,3-diketones. Sodium adduct molecular ions observed by MALDI-TOF MS confirmed that the reactions are essentially quantitative, and that the acetylation products are the expected peracetylated C-glycoside ketones, rather than cyclized ketofurans. Analysis of the peracetylated C-glycoside ketones by gas chromatography-EI-MS show characteristic fragment ions that have been assigned to four distinct fragmentation pathways. Peracetylated aldohexose-, aldopentose-, and 6-deoxyaldohexose-C-glycoside ketones fragment via gas phase furanoid intermediates. These data, and DFT calculations, indicate that the furanoid intermediates arise because the peracetylated C-glycoside ketones adopt a bicyclic structure containing a 5-member ketal ring. This ketal ring is the precursor of the furanoid rings in the gas phase. The 2-deoxyhexose-C-glycoside ketones are unable to form an intramolecular 2-ketal bond, and therefore undergo ion fragmentations via non-furanoid pathways.