R. Fornasier et al., A NEW LIGAND-FUNCTIONALIZED BETA-CYCLODEXTRIN AS A ESTEROLYTIC REAGENT AT NEUTRAL PH, Journal of inclusion phenomena and molecular recognition in chemistry, 14(3-4), 1993, pp. 205-215
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).