Antibody-catalyzed formation of a 14-membered ring lactone

Abstract

Monoclonal antibody (MAb) F123, raised against a macrocyclic phosphonate transition-state analogue, catalyzed an intramolecular transesterification of the corresponding hydroxy ester to give a 14-membered ring lactone. The MAb reaction displayed enzyme-like Michaelis–Menten kinetics with a Km of 255 µM and a kcat of 0.01 min–1 based on p-nitrophenol release and calculated on an active-site basis. Substrate specificity and competitive inhibition by a transition state analogue (Ki = 3 µM) demonstrated that the catalytic activity was associated with binding in the antibody-combining site. The lactone product was isolated from a large-scale catalytic experiment through ether extraction and identified by gas chromatography – mass spectroscopy.Key words: macrocyclization, lactones, catalytic antibodies.