Distribution of substituents in 2-hydroxypropyl ethers of cyclomaltoheptaose

The distribution of substituents in 2-hydroxypropyl ethers of cyclomaltoheptaose, prepared by alkylation of the carbohydrate with propylene oxide in aqueous sodium hydroxide, was investigated. The samples were fully methylated and hydrolyzed, and the resulting mixture of alkylated sugars analyzed as their alditol acetates by g.l.c.-m.s. High and low alkali concentration favored the formation of 2-hydroxypropyl ethers at O-6 and O-2, respectively; substitution at O-2 increased the reactivity of O-3. The overall extent of substitution had only secondary effects on the relative reactivities of O-6 and O-2, and the 2-hydroxypropyl groups remained unevenly distributed among the glucose residues, even when the overall substitution increased. Only small proportions of the isomeric 2-(1-hydroxypropyl) ethers were formed, and the percentage of oligopropylene glycol ethers was also low.