Preparation of 6-O-Acyl Amylose Derivatives

Abstract

ABSTRACTTwo new direct approaches for selective 6-O-acylation of amylose under homogeneous conditions were investigated. In the first method, amylose was initially brominated at C-6 using Nbromosuccinimide and triphenylphosphine in N,N-dimethyfformamide containing lithium bromide. The procedure was found to be highly selective and proceeded with no detectable reaction at the secondary positions. Several 6-bromo-6-deoxyamylose derivatives were prepared with different degrees of substitution by changing the molar equivalence of the reactants. In the second stage these were converted into 6-laurate esters by treatment with cesium laurate in dimethylsulfoxide, which proceeded rapidly under mild conditions. In the second method, the feasibility of 6-O-benzoylation in one step using the Mitsunobu reaction was evaluated. Amylose was treated with diethylazodicarboxylate in the presence of triphenylphosphine and benzoic acid in dimethysulfoxide under ambient conditions. While exclusively 6-O-benzoylation resulted up to degree of substitutions of ca. 0.5, at higher values a small amount of esterification at secondary hydroxyl groups also occurred. Products were characterized by 13C NMR, FTIR and elemental analyses.