Differential EI fragmentation pathways for peracetylated C-glycoside ketones as a consequence of bicyclic ketal ring structures.
Several C-glycoside ketones and peracetylated C-glycoside ketones have been synthesized from 13 structurally-diverse aldoses sugars (including isotope labeled [1-(13)C]Glc, [U-(13)C]Glc, and [6, 6'-(2)H(2)]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 nonfuranoid pathways.
Price
Neil P J
NP
USDA-ARS-NCAUR, Bioproducts and Biocatalysis Research Unit, 1815 North University Street, Peoria, IL 61604, USA. neil.price@ars.usda.gov
Momany
Frank A
FA
Adeuya
Anthony
A
D000107:Acetylation; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006027:Glycosides; D007659:Ketones / Q000737:chemistry*; D009005:Monosaccharides / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
C438934:C-glycoside; D006027:Glycosides; D007659:Ketones; D009005:Monosaccharides