Serendipitous discovery of α-hydroxyalkyl esters as β-lactamase substrates

O-(1-Carboxy-1-alkyloxycarbonyl) hydroxamates were found to spontaneously decarboxylate in aqueous neutral buffer to form O-(2-hydroxyalkylcarbonyl) hydroxamates. While the former molecules do not react rapidly with serine β-lactamases, the latter are quite good substrates of representative class A and C, but not D, enzymes, and particularly of a class C enzyme. The enzymes catalyze hydrolysis of these compounds to a mixture of the α-hydroxy acid and hydroxamate. Analogous compounds containing aryloxy leaving groups rather that hydroxamates are also substrates. Structure-activity experiments showed that the α-hydroxyl group was required for any substantial substrate activity. Although both d- and l-α-hydroxy acid derivatives were substrates, the former were preferred. The response of the class C activity to pH and to alternative nucleophiles (methanol and d-phenylalanine) suggested that the same active site functional groups participated in catalysis as for classical substrates. Molecular modeling was employed to explore how the α-hydroxy group might interact with the class C β-lactamase active site. Incorporation of the α-hydroxyalkyl moiety into novel inhibitors will be of considerable interest.