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 pivaloyloxymethyl-umbelliferone 1 as a fluorogenic substrate led to the isolation of eleven catalytic antibodies with rate accelerations around kcat/ kuncat = 10(3). The antibodies are not inhibited by the product and accept different acyloxymethyl derivatives of acidic phenols as substrates. The highest activity was found for the bulky, chemically less-reactive pivaloyloxymethyl group: there is no activity with acetoxymethyl or acetyl esters. This difference might reflect the preference of the immune system for hydrophobic interactions in binding and catalysis. Pivalase catalytic antibodies might be useful for activating orally available pivaloyloxymethyl prodrugs.