Synthesis of a dinuclear ZnII-calix[4]arene enzyme model with additional general base groups-catalytic activity in phosphate diester transesterification

Calix[4]arenes modified at the upper rim with two pairs of functional groups were synthesized and were used as starting materials for the synthesis of an enzyme model 3-Zn2 that has two ZnII centers and two dimethylamino groups. Under neutral conditions, this dinuclear metallo-enzyme model is catalytically active in the cleavage of the phosphate diester bond of the RNA model substrate 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP). The kinetics of 3-Zn2 were compared with a mononuclear complex 1-Zn and a dinuclear complex 2-Zn2 that lack the dimethylamino groups. A catalysis mechanism is proposed where the ZnII centers of 3-Zn2 cooperate in the activation of the phosphoryl group while one of the dimethylamino groups acts as a general base in the deprotonation of the hydroxyl group of HPNP.