Methods for regioselective functionalization of one of the multiple hydroxy groups of carbohydrates have been poorly developed. Synthesis of complex glycoconjugates has usually been achieved by multi-step protection/deprotection procedures, which results in the long synthetic steps and low atom economy. For the progress of glycoscience, development of the methods for direct and regioselective functionalization of one of the multiple hydroxy groups is highly desired. We have developed catalysts for direct and regioselective functionalizations of carbohydrates. The acylation reaction of D-glucose derivatives with four hydroxy groups proceeded smoothly in the presence of catalyst 1 with perfect regioselectivity to give the 4-O-acylate exclusively. Investigation of mechanistic aspects for the regioselective acylation by 1 is expected to be benefickal to further development of catalysts for direct and regioselective functionalization of various carbohydrates. Choice of solvent is of critical importance for the regioselectivity. In polar solvents such as DMF and THF, the selectivity for the acylation of C(4)-OH of D-glucose derivatives was significantly diminished. On the other hand, in less polar solvents such as CHCl_3 and toluene, the C(4)-OH of glucose derivatives were preferentially acylated even in the presence of other sugar substrates. The lower temperature associated with high regioselectivity. All of these information indicate that multiple hydrogen bonding interactons between the catalyst and substrate are critical for the regioselective acylation with catalyst 1. The regioselective acylations is expected to proceed in an accelerative manner through the stabilization of transition state structure by these hydrogen bonding interactions. Improtantly, the accelerative acylation in the presence of catalyst 1 was observed specifically in D-glucose derivatives. In the poster session, we also would like to discuss further mechanistic details based on the structural analysis of the reactive intermediates.
