Bis(N‐picolinamido)cobalt(II) Complexes Display Antifungal Activity toward Candida albicans and Aspergillus fumigatus

This report highlights the synthesis and characterization of ten new bis(N‐picolinamido)cobalt(II) complexes of the type [(L)2CoX2]0/2+, whereby L=N‐picolinamide ligand and X=diisothiocyanato (−NCS), dichlorido (−Cl) or diaqua (−OH2) ligands. Single crystal X‐ray (SC‐XRD) analysis for nine of the structures are reported and confirm the picolinamide ligand is bound to the Co(II) center through a neutral N,O binding mode. With the addition of powder X‐ray diffraction (PXRD), we have confirmed the cis and trans ligand arrangements of each complex. All complexes were screened against several fungal species and show increased antifungal activity. Notably, these complexes had significant activity against strains of Candida albicans and Aspergillus fumigatus, with several compounds exhibiting growth inhibition of >80 %, and onecompound inhibiting Aspergillus fumigatus hyphal growth by >90 %. Conversely, no antifungal activity was exhibited toward Cryptococcus neoformans and no cytotoxicity towards mammalian cell lines. Bis(N‐picolinamide)cobalt(II) complexes containing trans isothiocyanate ligands are reported to have significantly enhanced activity toward fungal species, when compared the cis complexes. They display >80 % growth inhibition of fungal strains and no reported toxicity toward bacterial species or mammalian cells.