Pivalase catalytic antibodies: Towards abzymatic activation of prodrugs

Screening of monoclonal-antibody libraries generated against the tert-butyl phosphonate hapten 2 and the chloromethyl phosphonate hapten 3 with pivalo yloxymethyl-umbelliferone I as a fluorogenic substrate led to the isolation of eleven catalytic antibodies with rate accelerations around k(cat)/ k(un cat)=10(3). The antibodies are not inhibited by the product and accept diff erent acyloxymethyl derivatives of acidic phenols as substrates. The highes t activity was found for the bulky, chemically less-reactive pivaloyloxymet hyl. group; there is no activity with acetoxymethyl or acetyl esters. This difference might reflect the preference of the immune system for hydrophobi c interactions in binding and catalysis. Pivalase catalytic antibodies migh t be useful for activating orally available pivaloyloxymethyl prodrugs.