Synthesis and characterisation of Co( iii ) complexes of N -formyl hydroxylamines and antibacterial activity of a Co( iii ) peptide deformylase inhibitor complex

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The X-ray crystal structure and pKa values of GSK322, a well-known and effective peptide deformylase inhibitor and antibacterial drug candidate, are reported. The first examples of Co(iii) complexes of N-formyl hydroxylamines are reported. Reaction of N-hydroxy-N-phenylformamide (HFA) with [Co(tren)Cl2]Cl and [Co(tpa)Cl2]Cl (where tren = tris(2-aminoethyl)amine, tpa = tris(2-pyridylmethyl)amine) with one equivalent of NaOH in H2O afforded [Co(tren)(HFA-1H)](PF6)1.5Cl0.5 (1) and [Co(tpa)(HFA-1H)]Cl2 (2), respectively. X-ray crystal structures of both complexes revealed that the N-formyl hydroxylamine group acts as a bidentate ligand, coordinating the Co(iii) centres via the carbonyl oxygen and deprotonated hydroxy group (O,O'), a coordination mode typically observed for closely related mono-deprotonated hydroxamic acids. Reaction of the N-formyl hydroxylamine-based GSK322 with [Co(tpa)Cl2]Cl afforded the corresponding Co(iii) chaperone complex of the peptide deformylase inhibitor, [Co(tpa)(GSK322-1H)](PF6)2. GSK322 and [Co(tpa)(GSK322-1H)](PF6)2 exhibited better Gram-positive activity than Gram-negative, where low MICs (1.56-6.25 μM) were determined for S. aureus strains, independent of their antibiotic susceptibility.