Differential EI fragmentation pathways for peracetylated C-glycoside ketones as a consequence of bicyclic ketal ring structures

✍ Scribed by Neil P. J. Price; Frank A. Momany; Anthony Adeuya

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 375 KB
• Volume: 43
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.1269

✦ Synopsis

Abstract

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. Published in 2007 by John Wiley & Sons, Ltd.