A series of N-acylprolyltyrosine amides was designed as tripeptoid analogues of neurotensin. The substituted dipeptides were tested in vivo for antidopamine activity by their ability to inhibit the apomorphine-induced climbing in mice and the dopamine-induced extrapolatory behavior impairment in rats. The N-acylprolyltyrosine amides structure-activity relationships have indicated the size of the N-acyl group and the configuration of amino acids that are important for the activity. We found that the bioactivity has been increased dramatically when the n-hydrocarbon chain on the N-acyl group was increased from four to five carbon atoms. The activity seems to reside exclusively in the L-Tyr diastereomers. All of the compounds tested were inactive in the cataleptogenic action and did not exhibit the acute toxicity even at doses 500-1000 times higher than ED50 in climbing test. On this basis, the N-acylprolyltyrosine amides could potentially be a novel class of atypical antipsychotic agents.

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An approach to the design of dipeptide neuroleptics free of extrapyramidal effects is described. Proceeding from an original hypothesis about the peptidergic mechanism of action of the atypical neuroleptic drug sulpiride and using the method of drug-based peptide synthesis, a peptide prototype of sulpiride -Pro-Tyr-NH 2 dipeptide -was obtained whose neuroleptic activity and the absence of cataleptogenic properties were revealed by tests on experimental animals. An analysis of the structures of known neuropeptides showed that the Pro-Tyr dipeptide sequence coincides with a Pro 10 -Tyr 11 fragment of the tridecapeptide neurotensin referred to in the literature as a neuropeptide with neuroleptic properties. Further design based on the obtained active dipeptide structure and the supposed bioactive b-rotational conformation of the neurotensin 8 -13 sequence led to a group of new potential atypical neuroleptics, N-acylprolyltyrosines. The structure of these tripeptoid analogs of neurotensin contains an N-acyl group imitating the Leu 13 side chain of neurotensin, which plays an important role in receptor binding. One of these compounds, N-caproyl-Lprolyl-L-tyrosine methyl ester, was named Dilept and chosen for more extensive pharmacological characterization as a potential antipsychotic agent. Preclinical investigations showed that Dilept is effective in doses 0.4 -4.0 mg/kg (i.p.) and retains activity upon peroral administration. The drug is nontoxic and does not induce extrapyramidal disorders even when administered in amounts 1000 times higher than the effective dose. 230 0091-150X/05/3905-0230

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