Rapid synthesis of partially O-methylated alditol acetate standards for GC–MS: some relative activities of hydroxyl groups of methyl glycopyranosides on Purdie methylation Original Research Article

Mixtures containing the majority of partially O-methylated alditol acetates (PMAAs), necessary for the GC–MS based identification of glycosidic linkages in oligo- and polymeric structures were prepared. Rha, Fuc, Rib, Ara, Xyl, Man, Gal, and Glc were converted to their Me glycosides, and the products were progressively O-methylated using the Purdie reagent at 25 °C. Resulting PMGs were assayed by TLC and at times that were optimum for formation of mono-O-methyl derivatives and later for higher degrees of methylation; they were converted to PMAAs, in a process incorporating NaB2H4 reduction. The majority of these can be used as standards for simultaneous identification of pyranosides and some furanosyl units particularly in heteropolysaccharides. The relative reactivities of OH-groups were determined by GC–MS as: Me α- and β-Glcp, HO-2 > HO-4 > HO-3 > HO-6, Me α- and β-Galp, HO-3 > HO-2 > HO-4 > HO-6, Me α-Manp, HO-3 > HO-2 > HO-4 > HO-6, Me β-Manp, HO-3 > HO-4 ⩾ HO-6 > HO-2, Me α-Rhap, OH-3 > OH-2 > OH-4; Me αβ-Fucp, OH-2 > OH-3 > OH-4, and Me αβ-Xylp, OH-2 > OH-4 > OH-3. The results differ from those obtained with Haworth, Hakomori, and Ciucanu methylation techniques, although some similarities occurred with the more rapid Kuhn method.