Analgesic activity of new pyrazine CH and NH acids and their hydrophobic and electron donating properties.

Analgesic efficacy was determined by the hot plate method for a group of 17 new pyrazine and 3 non-pyrazine CH and NH acids. The biological data were quantitatively related to the hydrophobicity of the compounds, expressed by fragmental constant, and to the orbital energy of the highest occupied molecular orbital, calculated quantumchemically. It has been found that the higher the electron donating properties, the more active is the agent, provided that its hydrophobicity allows it to reach its site of action. The results obtained support the charge transfer model for the biological interaction of analgesic agents.