Hydrolysis of β-lactam antibiotics catalyzed by dinuclear zinc(II) complexes:: Functional mimics of metallo-β-lactamases

Three stable dinuclear zinc(II) complexes, [Zn2L1(mu-NO3)(NO3)(2)] and [Zn2L1(mu-OMe)(NO3)(2)], where L-1 is 2,6-bis {{N-(2-dimethylaminoethyl)-N-methyl]aminomethyl}-4-methylphenolate, and [Zn2L2(NO3)(3)], where L-2 is 2-{[N-(2-dimethylaminoethyl)-N-methyl]aminomethyl}-4-bromo-6-{[N'-2-(2'-pyridyl)ethyl]aminomethyl}phenolate, were synthesized and characterized in the solid stare and in aqueous solution. These complexes catalyze the hydrolysis of penicillin G and nitrocefin, serving as functional synthetic analogues of the metallo-beta-lactamases, bacterial enzymes responsible for antibiotic resistance. The mechanism of the hydrolysis was studied in detail for the catalyst precursor [Zn2L1(mu-NO3)(NO3)(2)], which converts into [Zn2L1(mu-OH)(NO3), (sol)(2-n)]((2-n)+) in the presence of water. The complex [Zn2L1(mu-OH)(No-3)(2)] (n = 2) was characterized in the solid state. Initial coordination of the substrate carboxylate group is followed by the rate-limiting nucleophilic attack of the bridging hydroxide at the beta-lactam carbonyl group in aqueous solution. The product is formed upon fast protonation of the intermediate. Mononuclear complexes Zn(cyclen)(NO3)(2) and Zn(bpta)(NO3)(2) are as reactive in the beta-lactam hydrolysis as the dinuclear complexes. Consequently, the second zinc ion is not required for catalytic activity.