Partial methylation of methyl 4,6-dideoxy-α- and β-L-ribo-hexopyranosides

Abstract

Anomeric methyl 4,6-dideoxy-L-ribo-hexopyranosides I and V, prepared from aldose IX, were etherified with methyl iodide in acetonitrile in the presence of sodium hydroxide. From the products of partial methylation methyl 4,6-dideoxy-2-O-methyl-α-L-ribo-hexopyranoside (II) and methyl 4,6-dideoxy-2,3-di-O-methyl-α-L-ribo-hexopyranoside (IV), or methyl 4,6-dideoxy-2-O-methyl-β-D-ribo-hexopyranoside (VI) and methyl 4,6-dideoxy-2,3-O-methyl-β-L-ribo-hexopyranoside (VIII), respectively, were isolated. The substances were identified by 1H NMR, mass and IR spectra and comparison with standards. The course of etherification of glycosides I and V was checked by gas chromatography and the reactivity of the hydroxyl groups was evaluated by determining the rate constants or their ratios. The observed values were compared with analogous data for other isomers of methyl 4,6-dideoxyhexopyranosides and discussed from the view-point of sterical and polar influence on the reactivity of both their hydroxylic groups.