A NEW LIGAND-FUNCTIONALIZED BETA-CYCLODEXTRIN AS A ESTEROLYTIC REAGENT AT NEUTRAL PH

The paper reports the synthesis of a beta-cyclodextrin (beta-CD) deriv ative (1) functionalized with a ligand subunit at the secondary-hydrox yl rim. The ligand subunit is 2-hydroxymethyl-6-thiomethyl pyridine co nnected to the macrocycle via a thioether bond. In the presence of Cu( II) ions 1 accelerates the cleavage of the p-nitrophenyl esters of pic olinic acid (PNPP), quinaldic acid (PNPQ) and its 6-phenyl derivative (PNPQPh) via the nucleophilic attack of the hydroxyl of the pyridine s ubunit. However, the beta-CD derivative is less effective than the lig an 2-hydroxymethyl-6-methylthiomethyl pyridine (2), indicating no coop eration between the hydrophobic and metal ion recognition sites. Howev er, in the case of PNPQPh, the observed rate constants in the presence of Cu(II) ions are close to that of model 2 and this suggests we are approaching a binding mode appropriate for taking advantage of the two binding sites of the metal receptor 1 . Cu(II). Interestingly, the mo st reactive derivative with native beta-CD is the p-nitrophenyl quinal date (PNPQ) in accord with its mode of complexation to the macrocycle and the location of the actual nucleophile (one of the secondary hydro xyls of beta-CD).