Syntheses and pharmacological activity of substituted imidazolidinethiones and thiomidazolines

A series of imidazolidinethiones and thioimidazolines was synthesized and tested for their effects on both forced and spontaneous motor activity as well as for their ability to raise the convulsion threshold. The proton NMR spectra for the thioimidazolines synthesized were unusual in that they showed a sharp singlet for the ring ethylene unit rather than the expected A2B2 pattern. The thioimidazolines, 5 and 7, were the most active CNS depressants and had the highest safety index. Significantly, the isomeric imidazolidinethiones, 8 and 9, were comparatively much less effective while being considerably more toxic.