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

Abstract

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 degrees 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 NaB(2)H(4) 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 alpha- and beta-Glcp, HO-2>HO-4>HO-3>HO-6, Me alpha- and beta-Galp, HO-3>HO-2>HO-4>HO-6, Me alpha-Manp, HO-3>HO-2>HO-4>HO-6, Me beta-Manp, HO-3>HO-4HO-6>HO-2, Me alpha-Rhap, OH-3>OH-2>OH-4; Me alphabeta-Fucp, OH-2>OH-3>OH-4, and Me alphabeta-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.