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

Imidazolium salts (Im(+)-R(2)R(3)-Cl(-)) attached to the N,N'-bis(salicylidene)-(±)-trans-1,2-diaminocyclohexane (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 H2(R(1))2saldach(Im(+)-R(2)R(3)-Cl(-))2 (R(1) = H, tert-Bu, R(2) = H, Et, n-Bu, R(3) = H, Me) and their [M(III)Cl{(R(1))2saldach(Im(+)-R(2)R(3)-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(+)· · ·(-)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.