Glycan ester deacylation by TBAOH or TBAF: regioselectivity vs. polysaccharide structure.

Tetrabutylammonium fluoride (TBAF) and tetrabutylammonium hydroxide (TBAOH) have been found to mediate regioselective deacylation of cellulose esters, with unexpected selectivity for removal of acyl groups at the more hindered secondary O-2/3 positions. This simple, efficient, one-step process triggers our investigation of TBAF/TBAOH deacylation on other glycan (amylose, curdlan, dextran, pullulan and glucomannan) esters to examine the generality of this reaction and the impact of glucan and glucomannan structure on deacylation regioselectivity. Remarkably regioselective O-2/3 deacylation was observed with amylose triesters, while moderately regioselective O-2/4 deacylation of curdlan triester occurred. No regioselectivity was observed with dextran triester, as predicted due to the lack of primary OH groups. We observed deacylation of pullulan and glucomannan triesters, but due to the complexity of the partially substituted products have not yet been able to determine the deacylation regioselectivity for these glycan esters.