Analytical Chemistry and Spectroscopy
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The isobutane and methane direct chemical ionization (DCI) mass spectra of mono- and dianhydrosugars are substantially influenced by their stereochemistry at temperatures of 150-250°C. The best results are obtained under isobutane CI at 200 or 250°C. l,6:3,5-Dianhydrogulofuranose gives proton-bridge stabilized MH+ ions and fewer fragment ions compared with its ido epimer. The four diastereomeric 1,5-anhydropentofuranoses show increased MH+ and M2H+ abundances for the lyxo and ribo isomers with cis-1,2-diol sites capable of proton bridging. The xylo isomer gives a dominant [M — OH]+ ion. All isomers, but especially xylo and ribo, give abundant [C3H5O2]+ skeleton cleavage ions. They are attributed to an RDA fragmentation of pyranoglycosyl-type MH+ ions. The eight diastereomeric 1,6-anhydrohexofuranoses with endo/exo configured triol structures show very characteristic MH+ abundances (4-41% Σ). They parallel the amount of proton solvation in cis-diol sites of the isomers (gluco ≤ ido ≤ altro 〈 gulo 〈 galacto 〈 talo 〈 allo 〈 manno). The [M — OH]+ ion abundances (15-47% Σ) are also very characteristic (galacto ≤ talo 〈 manno 〈 altro ≪ atto 〈 gluco ≤ ido ≪ gulo). They reflect the possible H2O or C4H,OH loss from the MH+ and (M · C4H9]+ ions, respectively, with formation of protonated 1,6:3,5-and 1,6: 23-dianhydrehexofuranose species; the slightly flattened C(5) site of M might favour the departure of the 5-OH group. In addition, there are especially high abundances of skeleton fragment ions, 15% Σ [MH — HCOOH]+, 10% Σ [M — OH — H3O — CH3O]+ and 42% Σ [M — OH — C2H4O2)+, for the ido, galacto and gluco isomers, respectively.
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