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The effect of a steric hindrance around the protonation center of the model 4-substituted 1-(3-chlorophenyl)-piperazines 1-9 and 11-14 on their affinity for 5-HT1A and 5-HT2 receptor sites was investigated. Additional evidence for hydrophobic interactions between the N-4 hydrocarbon substituents and 5-HT1A receptors has been presented. However, the hydrophobic forces play a minor role in stabilization of the bioactive complex with 5-HT2 receptors. It has also been found that even bulky substituents around the protonation center of 1-aryl-piperazines are well tolerated at both 5-HT1A and 5-HT2 sites.

Nine new N-acyl derivatives of 2-amino-1-alcohols and 1-amino-2-alcohols with a potential arrhythmic activity have been obtained. In the preliminary screening 2-[N-(7-theophyllineacetyl)-amino]-2-methyl-1-propanol, 5, was more active in the chloroform-induced arrhythmia than quinidine. Unlike to propranolol and quinidine, compound 5 in doses of 5-30 mg/kg, iv, did not prevent distortions of the cardiac rhythm evoked by adrenaline and strophanthine. When administered at the peak of arrhythmia, it did not abolish disturbances of the cardiac rhythm. Compound 5 had a low toxicity (LD50 = 3000 mg/kg, ip), did not change the control ECG curve, showed no cardiodepressive activity, and had weaker local anesthetic properties than lignocaine.