Substituted N-phenylpyrazine-2-carboxamides, Their Synthesis, Hydro-lipophilic Properties and Evaluation of Their Antimycobacterial, Antifungal and Photosynthesis-inhibiting Activity

A series of sixteen pyrazinamide analogues with the -CONH- linker connecting the pyrazine and benzene rings was synthesized by the condensation of chlorides of substituted pyrazinecarboxylic acids with ring-substituted (chlorine) anilines and characterized. The results of in vitro antimycobacterial screening indicated some interesting antimycobacterial activity. 6-Chloro-N-(4-chlorophenyl)pyrazine-2-carboxamide (6) has shown the highest activity against Mycobacterium tuberculosis strain H37Rv (65% inhibition at 6.25 μg mL^-1). The highest antifungal effect against Trichophyton mentagrophytes, the most susceptible fungal strain tested, was found for 6-chloro-5-tert-butyl-N-(3,4-dichlorophenyl)pyrazine-2-carboxamide (16) (MIC = 62.5 μmol mL^-1). 6-Chloro-5-tert-butyl-N-(4-chlorophenyl)pyrazine-2-carboxamide (8) was the most active in the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts (IC₅₀ = 43.0 μmol mL^-1). The compounds were analyzed using RP-HPLC to determine lipophilicity. Optimal log P value for studied series was not confirmed.For all the compounds, the relationships between the lipophilicity and the chemical structure of the studied compounds are discussed, as well as their structure-activity relationships (SAR).