Schiff bases are aldehyde-or ketone-like compounds in which the carbonyl group is replaced by an imine or azomethine group. They are widely used for industrial purposes and also exhibit a broad range of biological activities. This short review compiles examples of the most promising antimalarial, antibacterial, antifungal, and antiviral Schiff bases. An overview of synthetic methodologies used for the preparation of Schiff bases is also described.

Aldimines are aldehyde-derived compounds that contain a C=N group. Besides its broad industrial applications, this class of non-naturally occurring compounds are found to possess antibacterial, antifungal, antimalarial, antiproliferative, anti-inflammatory, antiviral, and antipyretic properties. Based on this, six aryl aldimines were synthesized from the condensation of aromatic amines with benzaldehydes. The antifungal activities of synthesized compounds were evaluated against nineteen fungal strains that included Candida and Aspergillus species, Cryptococcus neoformans. The aryl aldimines 2-(benzylideneamino)phenol (3) and 4-(benzylideneamino)phenol (8) were the most active compounds against the fungi studied. Compounds 3 and 8 efficiently inhibited the metabolism of C. neoformans mature biofilm.

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Copper(II) complexes of the Schiff base ligands 2-((5-nitrofuran-2-yl)methyleneamino) phenol (HL1) and 2-(4-nitrobenzylideneamino)phenol (HL2) were prepared and characterized using physicochemical and spectroscopic techniques. In these complexes the Schiff base ligands acted as a bidentate donor bound to Cu 2+ through the oxygen and nitrogen atoms in the deprotonated form. The electron paramagnetic resonance spectra, carried out on [CuCl(L1)(phen)].0.5H 2 O and [CuCl(L2)(phen)].2H 2 O complexes, showed the presence of only mononuclear forms. The Cu 2+ complexes and ligands were evaluated for their in vitro trypanocidal activity. The complex [CuCl(L1)(phen)].0.5H 2 O was more active than the free Schiff base and also presented a superior effect to benznidazole, the reference drug. The antiproliferative activity of the Schiff bases and Cu 2+ complexes were evaluated for their effect on seven tumor cell lines and showed a cytostatic and in some cases a cytotoxic effect. These compounds also presented binding properties to deoxyribonucleic acid (DNA) and moderate ability to quench the intrinsic fluorescence of albumins.