Analysis of neutral isomeric low molecular weight carbohydrates using ferrocenyl boronate derivatization and tandem electrospray mass spectrometry

A new analytical technique for small carbohydrates utilizing the cyclic ferrocenyl boronic esters (FcBors) of several neutral mono- and disaccharides is demonstrated. Distinction between the diastereomers of mono- and disaccharides is obtained. Analysis is by tandem electrospray-mass spectrometry (ES-MS) using a modified ion-source that promotes the preformation of ions. Selection of the molecular ion produced during single-electron oxidation of the ferrocene moiety of a specific population of saccharide isomers permits a variety of collisionally induced dissociation (CID) experiments. The resultant MS2/MS3 spectra reflect the ensemble of possible cyclic esters in equilibrium. An array of stable cross pyranose ring fragment ions representing sequential carbon loss as 30 u is observed. Consequently, the system provides an information-rich set of MSn spectra containing large amounts of structural information. Identification of D-glucose (D-Glc), its two commonly found epimers (D-mannose and D-galactose), and the two major L-diastereomers of 6-dideoxymonosaccharides, L-fucose (L-Fuc) and L-rhamnose (L-Rhm), are demonstrated. Selected pairs of disaccharides can be distinguished in terms of their anomeric linkage by reference to their MS3 spectra.