Differentiation of anomeric unsaturated C‐glycosides by fast atom bombardment ionisation‐collision activated dissociation/mass‐analyzed ion kinetic energy analysis (original) (raw)
There has been growing interest in the synthesis of C-glycopyranosides in connection with the synthesis of chiral building blocks and naturally occuring products.1 In this field, we have shown that 2,3-unsaturated C-glycosides were conveniently prepared using palladium(0) as the catalyst.2 The structures of these anomeric unsaturated sugars were determined using N.M.R. spectroscopy. Sequential mass spectrometry with collision activated dissociation (CAD)3 has been applied to study the structures of polysaccharides and glycoconjugates and in some cases, the differentiation of stereoisomeric sugars was reported. Collision activation and chemical ionisation in massanalyzed ion kinetic energy spectra (MIKES) of permethylated disaccharides was used to discriminate among anomers in the complete set of glucose anomeric disaccharides.4 Fast atom bombardment (FAB), MIKE and CAD-MIKE technologies were also used for the differentiation of aldohexoses, anomeric methylglycosides of otherwise underivatized glucose and galactose, and stereoisomers of hexoses and 2-amino-2-deoxyhexoses.5-9 To our knowledge, no example of such differentiation was reported in the case of C-glycosides. However, at a given collision energy, C-glycosides which differ in one aspect of their stereochemical structures are expected to show A distinct and discriminating ion pattern, if the formation of these ions depends on the chemical stabilities of the parent compound. Therefore, it could be anticipated that configurations might be one of the largest factors in the inequalities of chemical free energy. The daughter ion mass spectra of two anomers would have an ion intensity "fingerprint" which would be characteristic of each anomer. The sequential dissociation of these daughter ions to grand daughter ions could also result in further characteristic "fingerprint" patterns which are unique to the molecular structure of the selected daughter ions. We describe in this communication our preliminary results concerning the differentiation of two sets of anomeric unsaturated C-glycosides 1 and 2 using positive favt atom bombardment-mass spectrometry (FAB-MS), mass analyzed ion kinetic energy (MIKE: spectra, and collision activated dissociation /mass analyzed ion kinetic energy (CAD-MIKE). In the positive ion FAB mass spectra of the two sets of anomers, using 3-nitrobenzyl alcohol as the mamx, the only clear and important finding was ihe presence of the
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