Electrochemistry of ring-substituted 1-hydroxynaphthalene-2-carboxanilides: Relation to structure and biological activity
Abstract
Twenty-two novel antimycobacterial agents, 1-hydroxynaphthalene-2-carboxanilides, were studied by cyclic voltammetry on a glassy carbon electrode in a phosphate buffer pH 7.2 - dimethyl sulfoxide (DMSO) mixed medium (9:1; v/v). All compounds exhibited similar voltammetric behavior with one irreversible anodic signal in the range 100-300 mV corresponding to the oxidation of hydroxyl group on the naphthalene moiety.
A shift of the oxidation potential was caused solely by electron donating or withdrawing effects of substituents and their position on the benzene moiety. Mechanism of oxidation in the studied medium was briefly outlined.
Values of oxidation potentials exhibited very good linear correlation with calculated Hammett sigma substituent constants. For all active compounds, a relationship between oxidation potentials and MIC or IC50 values obtained from in vitro screening was investigated in detail.
Primary in vitro screening of synthesized compounds was previously performed against three species of Mycobacterium pathogens. Additionally, their activity related to the inhibition of photosynthetic electron transport (PET) in spinach chloroplasts was tested in previous publications.
In vitro screening against Mycobacterium tuberculosis was performed here for the first time with 1-hydroxy-N-(3-trifluoromethylphenyl)naphthalene-2-carboxamide being the most effective (MIC = 11.7 mmol L-1). Furthermore, several other compounds showed higher antimycobacterial activity than the standard isoniazid.
Relation of biological activities and oxidation potentials was successfully found in some cases; however, final correlations must also be considered with other physical and chemical factors contributing to the biological activity. Relation of structure, biological activity and electrochemical potential was also studied by cyclic voltammetry in cathodic area for three compounds containing reducible nitro moiety.