Schiff bases : synthesis, characterization and antimicrobial properties

D.Tech. (Biotechnology)Abstract: Pathogenic microorganisms as well as those microrganisms that are toxigenic in producing various types of secondary metabolites including mycotoxins in foods continue to be a challenge worldwide. This is partly because of their ability to develop resistance over a wide range of drugs resulting in increased mortality amongst humans and animals. There is need for a continuous search for alternative means in managing their occurrence as well as in the treatment of diseases they cause in both animal and man. In an approach to counter the ravaging effects of microorganisms on health, a class of imine (compounds with C=N) compounds known as Schiff bases with benzimidazole moiety and benzimidazole derivatives, together with those of salicylaldehyde thiosemicarbazone, aniline, and tryptamine scaffolds were successfully synthesized by condensation of aromatic amines and carbonyls and screened for their antimicrobial as well as other biological properties against bacteria, fungi, human immunodeficiency virus (HIV), trypanosoma and plasmodia parasites. Data obtained revealed the potencies of the synthesized compounds against the studied microbes. The antimicrobial activities of these compounds were structurally dependent with all of the synthesized compounds found to significantly alter the metabolic activities in the studied microorganisms. When compared to Gram positive bacteria, the antibacterial activity of a series of benzimidazole Schiff bases established following the microdilution method was found to be more pronounced against such Gram negative representatives as Enterobacter cloacae, E. aergenes, Klebsiella oxytoca, K. pneumonia and Escherischia coli, presenting minimum inhibitory concentrations (MICs) ranging between of 7.8 and 15.6 μg/mL. Against the fungi under study, the genus Aspergillus was more sensitive to the synthesized benzimidazole Schiff bases when compared to Fusarium species. The same benzimidazole Schiff bases also demonstrated a high cytotoxic effect on Aspergillus flavus and A. carbonarius as they displayed minimum fungicidal concentrations (MFC) that ranged from 7.8 to 15.6 μg/mL. All test compounds exhibited moderate to high antimalarial activity inducing between 13 and 95% toxicity against Plasmodium falciparum strain 3D7 and IC50 of 27.0 and 28.3 μg/mL exhibited by N-(1,3-Dihydro-benzoimidazol-2-ylidene)-N'-pyridin-2-yl-oct-2-ynamidine (Compound 7.9) and 4-[1-(1,3-Dihydro-benzoimidazol-2-ylideneamino)-oct-2-ynylideneamino]-benzoic acid (Compound 7.10), respectively. In addition, these compounds showed strong trypanocidal..