Zinc complexes with 1,2,4-triazole functionalized amino acid derivatives: Synthesis, structure and b-lactamase assay

Coordinating abilities of 4R-1,2,4-triazole derivatives (R = glycine ethyl ester (L1), glycine (L2), diethylamino
malonate (L3), methionine (L4) and diethyl aminomethylphosphonate (L5)) towards ZnII ions have
been studied in solution, in solid state and versus three zinc-b-lactamases. The crystal structure of
[Zn3(L4)6(H2O)6] (6) is described; it is the first crystal structure involving a 1,2,4-triazole functionalized
methionine. It forms a trinuclear complex with central zinc octahedrally coordinated by only L4, whereas
terminal zinc ions coordination sphere is completed by three water molecules. L4 exhibits a dual functionality
of a bridging bidentate ligand as well as an anion. A dense hydrogen bonding network connects
these trinuclear entity into a 3D supramolecular network. The ZnII ions in 6 are held at equidistance
(3.848 Å) which coincidently matches with the corresponding Zn Zn distance in the binuclear zinc
enzyme from Bacillus cereus (3.848 and 4.365 Å). Among L1–L5 screened for b-lactamase assay, L4 shows
modest inhibition for BcII enzyme.