Substituted N-phenylpyrazine-2-carboxamides, their synthesis and evaluation as herbicides and abiotic elicitors

The condensation of substituted pyrazine-2-carboxylic acid chlorides with ring-substituted anilines yielded five substituted pyrazine-2-carboxylic acid amides. The synthesis, and analytical, lipophilicity and biological data of the newly synthesized compounds are presented in this paper. The photosynthesis inhibition, antialgal activity and the effect of a series of pyrazine derivatives as abiotic elicitors on the accumulation of flavonoids in a callus culture of Ononis arvensis (L.) were investigated. The most active inhibitor of the oxygen evolution rate in spinach chloroplasts was 6-chloro-pyrazine-2-carboxylic acid (3-iodo-4-methylphenyl)-amide (2, IC50 = 51.0 mu mol.L-1). The highest reduction of chlorophyll content in Chlorella vulgaris was found for 5-tert-butyl-N-(4-chloro-3-methylphenyl)-pyrazine-2-carboxamide (3, IC50 = 44.0 mu mol.L-1). The maximal flavonoid production (about 900%) was reached after a twelve-hour elicitation process with 6-chloropyrazine-2-carboxylic acid (3-iodo-4-methylphenyl)-amide (2).