Model studies on methyl amyloses: correlation between reaction conditions and primary structure

Methyl amyloses have been prepared under various conditions and studied as model compounds for the determination of the substitution pattern in the polymer chain. After permethylation with iodomethane-d3 the glucosidic linkages were statistically cleaved by partial methanolysis or reductive cleavage. The distribution of substituents in the dimer-, trimer-, and tetramer fraction was determined by FAB-MS and MALDI-TOF-MS and compared with that calculated from the monomer composition. While a homogeneous methylation in water gave the expected random distribution, a reaction in Me2SO solution with sodium hydroxide and iodomethane yielded a methyl amylose with a surprising bimodal substitution pattern. A third example indicates a ds gradient in the sample as a result of topochemical reaction control.