1,3-Di-peptido-conjugates of calix[4]arene and its di-OCH₃ derivatives: synthesis, characterization and phosphate recognition

Abstract

Novel double-armed peptido-conjugates of calix[4]arene have been developed on the lower rim of the macrocycle. The functional group pendants exhibit conformational bend through the involvement of 11-atom N-H···O hydrogen bond inscribed in a 14-atom O-H···O interaction. As a result, only the terminal -COOR and -COOH groups are exposed to the environment, but not the amide moiety. The cone-conformation of the calix[4]arene is further stabilized through the O-H···O interactions at the lower rim. In effect, the conjugates exhibit a binding core at the lower rim along with hydrophobic cavity formed by the enclosure of arene moieties. Conformational mobility induced by the replacement of lower rim phenolic-OH by -OCH₃ has also been demonstrated by variable temperature NMR studies in case of the corresponding -OCH₃ derivatives. Differential receptor binding characteristics of these conjugates towards phosphate are demonstrated using absorption spectroscopy. The negatively charged phosphate group is received preferentially by the carboxylic terminal over the ester terminal conjugate.