Substituted Amides of Pyrazine-2-carboxylic acids: Synthesis and Biological Activity.

Condensation of 6-chloro-, 5-tert-butyl- or 6-chloro-5-tert-butylpyrazine-2-carboxylic acid chloride with ring substituted anilines yielded a series of amides, which were tested for their in vitro antimycobacterial, antifungal and photosynthesis-inhibiting activities. The highest antituberculotic activity (72% inhibition) against Mycobacterium tuberculosis and the highest lipophilicity (log P = 6.85) were shown by the 3,5-bis-trifluoromethylphenyl amide of 5-tert-butyl-6-chloropyrazine-2-carboxylic acid (2o). The 3-methylphenyl amides of 6-chloro- and 5-tert-butyl-6-chloro-pyrazine-2-carboxylic acid (2d and 2f) exhibited only a poor in vitro antifungal effect (MIC = 31.25-500 μmol·dm(-3)) against all strains tested, although the latter was the most active antialgal compound (IC(50) = 0.063 mmol·dm(-3)). The most active inhibitor of oxygen evolution rate in spinach chloroplasts was the (3,5-bis-trifluoromethylphenyl)amide of 6-chloropyrazine-2-carboxylic acid (2m, IC(50) = 0.026 mmol·dm(-3)).