Synthesis and structure-activity relationships of a new model of arylpiperazines.: 5.: Study of the physicochemical influence of the pharmacophore on 5-HT1A/α1-adrenergic receptor affinity:: Synthesis of a new derivative with mixed 5-HT1A/D2 antagonist properties

In this paper we have designed and synthesized a test series of 32 amide arylpiperazine derivatives VI in order to gain insight into the physicochemical influence of the pharmacophores of 5-HT1A and alpha (1)-adrenergic receptors. The training set was designed applying a fractional factorial design using six physicochemical descriptors. The amide moiety is a bicyclohydantoin or a diketopiperazine (X = -(CH2)(3)-, -(CH2)(4)-; m = 0, 1), the spacer length is 3 or 4 methylene units, which are the optimum values for both receptors, and the aromatic substituent R occupies the ortho- or meta-position and has been selected from a database of 387 substituents using the EDISFAR program. The 5-HT1A and alpha (1)-adrenergic receptor binding affinities of synthesized compounds VI (1-32) have been determined. This data set has been used to derive classical quantitative structure-activity relationships (QSAR) and neural-networks models for both receptors (following paper). A comparison of these models gives information for the design of the new ligand EF-7412 (46) (5-HT1A: K-i = 27 nM; alpha (1): K-i > 1000 nM). This derivative displays affinity for the dopamine D-2 receptor (K-i = 22 nM) and is selective versus all other receptors examined (5-HT2A, 5-HT3, 5-HT4 and Bz; K-i > 1000 nM). EF-7412 (46) acts as an antagonist in vivo in pre- and postsynaptic 5-HT1A receptor sites and; as an antagonist in the dopamine D-2 receptor. Thus, EF-7412 (46) is a derivative with mixed 5-HT1A/D-2 antagonist properties and this derivative could be useful as a pharmacological tool.