Mass spectrometric stereoisomeric differentiation between α‐ and β‐ascorbic acid 2‐ O ‐glucosides. Experimental and density functional theory study

L‐Ascorbic acid and two distinct anomers, namely the α‐D‐glucopyranosyl and β‐D‐glucopyranosyl‐(1→2)‐L‐ascorbic acid (stereoisomers), were studied within the scope of collision‐induced dissociation (CID) experiments, performed by linear ion acceleration and collision with argon atoms inside a hexapole quadrupole hexapole ion beam guide, which is coupled to an ion cyclotron resonance (ICR) cell with a 12 Tesla magnet for high‐resolution measurements. Loss of C 2 H 4 O 2 neutral from the [M–H] − anion of L‐ascorbic acid was observed. Density functional theory (DFT) calculations on the 6‐311+G(2d,p)//6‐31+G(d) level of theory reveal a new concerted mechanism for an intramolecular gas‐phase rearrangement, through which the observed ejected neutral C 2 H 4 O 2 can take place. A similar rearrangement also occurs in the case of α‐ and β‐D‐glucopyranosyl‐(1→2)‐L‐ascorbic acid. For the α isomer, only homolytic glycoside fragmentation was observed. For the β isomer, both homolytic and heterolytic glycoside cleavages were possible. The mechanisms behind all observed fragmentation pathways were fully understood by the implementation of accurate DFT calculations. Stereoisomeric differentiation between α and β isomers of the L‐ascorbic acid‐2‐ O ‐glucoside could be revealed by tandem mass spectrometry (MS/MS) experiments and were explained theoretically. Copyright © 2011 John Wiley & Sons, Ltd.