Toward an artificial acetylcholinesterase

The methanolysis of choline p-nitrophenylcarbonate in chloroform containing 1% methanal is catalyzed with turnover by ditopic receptors 1 and 2, consi sting of a calix[6]arene connected to a bicyclic guanidinium by means of a short spacer. The calix[6]arene subunit strongly binds to the trimethylammo nium head group through cation-ir interactions, whereas the guanidinium moi ety is deputed to stabilize through hydrogen bonding reinforced by electros tatic attraction the anionic tetrahedral intermediate resulting from methox ide addition to the ester carbonyl, The observed cholinesterase activity ha d been anticipated on the basis of the ability of the ditopic receptors 1 a nd 2 to bind strongly to the choline phosphate DOPC, which is a transition state analogue far the B(Ac)2-type cleavage of choline esters.