Identification of methyl (methylO-acetyl-O-methylhexopyranosid)uronates by mass spectrometry

Fragmentation of methyl (methylO-acetyl-O-methyl-α-d-gluco- and -galactopyranosid, uronates has been studied at 70 and 12 eV. At 12 eV, the production of ions resulting from secondary and further processes is greatly diminished and the spectra are simpler and easier to interpret. The energy required for the elimination of acetic acid and ketene has been calculated from the ion-appearance potentials. The number and location of methyl groups in methyl (methylO-acetyl-O-methyl-hexopyranosid)uronates can be determined. The procedure is particularly suitable for g.l.c.-m.s. of the uronic acid portion of methanolysates of methylated biopolymers and other substances containing uronic acids. From the presence or absence of peaks for molecular ions in the 12-eV spectra,gluco andgalacto isomers which do not contain a methoxyl group at C-4 can be distinguished. The synthesis of methyl (methyl 2,3-di-O-methyl-α-d-galactopyranosid)uronate is also described.