Cellulose levulinate: a protecting group for cellulose that can be selectively removed in the presence of other ester groups

Levulinate is an important hydroxyl protecting group in carbohydrate chemistry but has not previously been so employed in cellulose chemistry, perhaps because of challenges involved in synthesis of cellulose levulinates. Herein we describe homogeneous acylation of cellulose in N,N-dimethylacetamide/LiCl using differently activated levulinic acid derivatives, including in situ activation with dicyclohexylcarbodiimide, p-toluenesulfonyl chloride, 1,1′-carbonyldiimidazole, or trifluoroacetic anhydride, providing and comparing several methods to access cellulose levulinates. Degree of substitution (DS) has been determined by 1H NMR spectroscopy using perpropionylated cellulose levulinates, showing that DS values as high as 2.42 are attainable. Cellulose levulinate esters were deacylated selectively by hydrazine without detectable loss of other alkanoate ester groups (acetate or propionate), indicating strong promise for levulinate as a useful protecting group for the synthesis of regioselectively substituted cellulose and other polysaccharide derivatives.