Mass‐analysed ion kinetic energy spectra and collisional activation spectra of cluster ions of methly 2,3,4,6‐tetra‐o‐methly‐d‐hexopyranosides with ammonia and methylamine

Per-O-methylated saccharides (M) react with protonated ammonia and protonated amines (RH +), respectively, under the conditions of chemical ionization mainly by the formation of cluster ions [M + RH'].' In addition, cluster ions consisting of fragment ions formed by loss of the glycosidic group (so called type A+ ions') and the base R are observed. A Fouriertransform ion cyclotron resonance (FT-ICR) study has shown3 that these latter cluster ions are also formed by a reaction of ions A' with NH, . In the case of ions A , + formed from methyl 2,3,4,6-tetra-0-methyl-~-hexopyranosides by loss of the glycosidic C H 3 0 group the rate for the formation of the adduct ions [A,' + NH,] is rather small, but depends on the stereochemistry of the monosaccharide. Additional information about the structure and reactivity of both types of cluster ions can be gained by mass-analysed ion kinetic energy (MIKE) spectra and collisional activation (CA) spectra. In this letter, the results of a corresponding study of the [M + RH'] and [ A , + + R] (R = (NH,, CH,NH,) of stereoisomeric per-O-methylated-o-hexopyranosides are discussed. Methyl 2,3,4,6-tetra-0-methyl-~-~-glucopyranos~de (l), methyl 2,3,4,6-tetra-O-methyI-,f-~-galactopyranoside (2), and methyl 2,3,4,6-tetra-O-methyl-~-mannopyranoside (3) were used as model compounds. 1-3 were introduced into a modified chemical ionization (CI) ion source of a VG ZAB-2F mass spectrometer by a heated direct inlet system with a leak valve until the pressure reading at the ion gauge of the ion-source housing was 10-6-10-5 mbar. Then, the reagent gas (NH, or CH,NH,) was introduced by the usual CI-gas inlet line until a sufficient intensity of the adduct ions was obtained, using 70 eV electron impact ionization and an ion-source temperature of about 190°C. The ions under study were focused magneti-