Stereospecific generation and analysis of α- and β-hemiacetals of monosaccharides in gas phase

• The stereospecific generation of sugar hemiacetals was first achieved in gas phase.
• Boc-protected 4-aminobutyl glycosides are useful precursors of hemiacetals.
• All the sugar hemiacetals were distinguishable by energy-resolved mass spectrometry.
• The order of affinity of sodium to anomers of monosaccharides was obtained.

A series of Boc-protected 4-aminobutyl α- and β-glycosides of commonly found neutral monosaccharides were synthesized. The sodium adducted ions of these individual molecules were used in producing corresponding α- and β-anomers of hemiacetal species under collision-induced dissociation (CID) conditions. The Boc group was successfully removed under CID conditions producing 4-aminobutyl glycosides, which were then used as the precursors. An intramolecular attack of the aglyconic nitrogen atom onto C-1 position of aglycon assisted to leave hemiacetal ion species without affecting anomeric configurations. In this manner, stereospecific syntheses of sugar hemiacetals were first achieved in gas phase. The dissociation of sodium cation from a series of these hemiacetals was further studied according to energy-resolved mass spectrometry. In this study, it was found that all the sugar hemiacetals could be distinguished even if they have same m/z values. Furthermore, the order of affinity of Na+ toward the hemiacetals was determined.

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