Synthesis and pharmacological evaluation of 1-benzylpiperazine and 4-benzylpiperidine as potent sigma ligands.

It is now well established that sigma receptors are an independent class of receptors expressed in peripheral organs and in the central nervous system. There are at least two identified subtypes, namely sigma1 and sigma2, with distinct functional roles and different pharmacological characteristics. On the basis of their neuroregulative and neuropotective functions sigma1 agents could be potentially used for the treatment of depression and psychiatric disorders. The finding of high concentration of sigma2 receptors in neuronal and non-neuronal tumor cell lines provides evidence of a possible role in anticancer therapy. A variety of chemically unrelated compounds is able to bind sigma receptors, however only few bind with high affinity and selectivity to sigma receptor subtypes. This situation has given new impulse to medicinal chemists for the search of new and more selective ligands.We have recently reported that substituted 1-benzylpiperazine and 4-benzylpiperidine derivatives were shown to be high-affinity sigma ligands (Ki in the nanomolar range) with a slight preference for sigma1 over sigma2 receptors1-2. With the aim to improve sigma1/sigma2 selectivity we have studied the effect of some substitutions of the oxygen atoms on the 1,3-dioxolane ring by synthesizing 1,3-oxathiolane, 1,3-dithiolane, tetrahydro-furan, cyclopentanone and cyclopentanol derivatives as depicted below. A spiro derivative was additionally prepared and tested to study the influence of the two aromatic rings on receptor affinity. The preliminary pharmacological results show a significant improvement of sigma1 selectivity for compound A. Structure-activity relationship will be extensively discussed during the congress.