Toward new classes of potent antibiotics: Synthesis and antimicrobial activity of novel metallosaldach-imidazolium salts

Imidazolium salts (Im(+)-(RR3)-R-2-Cl-) attached to the N,N'-bis(salicylidene)-(+/-)-trans-1,2-diamino-cyclohexane (saldach) backbone (4a-f) have been designed and successfully applied for the synthesis of the corresponding mononuclear complexes with Mn(III) and Fe(III) ions. The molecular structures of the saldach ligands H-2(R-1)(2)saldach(Im(+)-(RR3)-R-2-Cl-)(2) (R-1 = H, tert-Bu, R-2 = H, Et, n-Bu, R-3 = H, Me) and their [M(III)Cl{(R-1)(2)saldach(Im(+)-(RR3)-R-2-Cl-)(2)}] (M = Mn, Fe) complexes have been established. The free ligands exist as the phenol-OH and not as the zwitterionic (imine)N-H+center dot center dot center dot O-(phenol) tautomer. Antimicrobial activity of the target compounds revealed higher potent antibacterial activity against Salmonella aureus, B. subtilis while less effective against E. coli and C albicans and inactivity against A. flavus. Compound (4d) and its Fe(III) complex (6d) exhibit remarkable extra-potent bactericidal activity. (C) 2014 Elsevier Masson SAS. All rights reserved.