FH-510, a potent and selective ligand for rat brain sigma recognition sites

Nonpeptide analogues of dynorphin A(1-8): design, synthesis, and pharmacological evaluation of kappa-selective agonists

Two novel series of kappa opioid receptor agonist analogues of MPCB-GRRI and MPCB-RRI, hybrid ligands of MPCB ((-)-cis-N-(2-phenyl-2-carbomethoxy)cyclopropylmethyl-N-normetazocine ) and of the C-terminal fragments of dynorphin A(1-8), have been synthesized. The critical functional groups of the peptide fragments of hybrid compounds were maintained, and the binding affinities and selectivities for compounds 1-40 to mu, delta, and kappa opioid receptors were analyzed. Compounds 15 and 16, MPCB-Gly-Leu-NH-(CH(2))(n)()-NH-C(=NH)-C(4)H(9) (n = 5, 6), displayed high affinity and selectivity for kappa opioid receptors (K(i)(kappa) = 6.7 and 5.3 nM, K(i)(mu)/K(i)(kappa) = 375 and 408, and K(i)(delta)/K(i)(kappa) = 408 and 424, respectively). Since kappa agonists may also cause psychotomimetic effects by interaction with sigma sites, binding assays to sigma(1) sites were performed where compounds 15 and 16 showed negligible affinity (K(i) > 10 000). Compounds 15 and 16 were further characterized in vivo and showed potent antinociceptive activity in mouse abdominal constriction tests (ED(50) = 0.88 and 1.1 mg/kg, respectively), fully prevented by nor-BNI. Thus, these novel analogues open an exciting avenue for the design of peptidomimetics of dynorphin A(1-8).

Chemical modification of apomorphine to discover sigma ligands: 6H-dibenzo[b,d]pyran and carbazole analogues

It seems that many sigma ligands have been designed from known sigma ligands. We focused on a difference in structural flexibility between haloperidol and apomorphine, and studied chemical modification of apomorphine, a compound with high affinity for dopamine D2 receptors but not for sigma receptors, for discovery of sigma ligands. The first modification yielded good results with 6H-dibenzo[b,d]pyran analogues with weak affinity for sigma receptors but not D2 receptors. Furthermore, carbazole analogues, compounds designed from 6H-dibenzo[b,d]pyran analogues, potentially acted at sigma receptors with high selectivity. This paper describes the design, synthesis and sigma/D2 selectivity of 6H-dibenzo[b,d]pyran and carbazole analogues.

Design, synthesis, structure-activity relationships, and biological characterization of novel arylalkoxyphenylalkylamine sigma ligands as potential antipsychotic drugs

sigma Receptor antagonists may be effective antipsychotic drugs that do not induce motor side effects caused by ingestion of classical drugs such as haloperidol. We obtained evidence that 1-(2-dipropylaminoethyl)-4-methoxy-6H-dibenzo[b,d]pyran hydrochloride 2a had selective affinity for sigma receptor over dopamine D2 receptor. This compound was designed to eliminate two bonds of apomorphine 1 to produce structural flexibility for the nitrogen atom and to bridge two benzene rings with a -CH2O- bond to maintain the planar structure. In light of the evidence, N, N-dipropyl-2-(4-methoxy-3-benzyloxylphenyl)ethylamine hydrochloride 10b was designed. Since compound 10b had eliminated a biphenyl bond of 6H-dibenzo[b,d]pyran derivative 2a, it might be more released from the rigid structure of apomorphine 1 than compound 2a. The chemical modification of compound 10b led to the discovery that N, N-dipropyl-2- [4-methoxy-3-(2-phenylethoxyl)phenyl]ethylamine hydrochloride 10g (NE- 100), the best compound among arylalkoxyphenylalkylamine derivatives 3, had a high and selective affinity for sigma receptor and had a potent activity in an animal model when the drug was given orally. We report here the design, synthesis, structure-activity relationships, and biological characterization of novel arylalkoxyphenylalkylamine derivatives 3.

(+)-cis-N-ethyleneamino-N-normetazocine derivatives. Novel and selective sigma ligands with antagonist properties

A series of (+)-cis-N-normetazocine derivatives has been described, and their affinities for sigma1, sigma2, and phencyclidine (PCP) sites and opioid, muscarinic (M2), dopamine (D2), and serotonin (5-HT2) receptors were evaluated. The effect of the N-substitution with a substituted ethylamino spacer was investigated. Compounds 8c-11c displayed high affinities for sigma1 sites and for opioid receptors. Substitution of the second basic nitrogen either with alkyl or cycloalkyl substituents give compounds (1a-6a) with high affinity and selectivity for sigma1 binding sites. Compounds 1a-5a were further characterized in vivo, and their agonist/antagonist activity was evaluated. In mouse, compound 1a and 2a as well as haloperidol suppressed in a dose-related manner the stereotyped behavior induced by (+)-SKF 10,047. Compounds 3a-5a and (+)-pentazocine do not affect the stereotyped behavior induced by ip injection of (+)-SKF 10,047. Therefore, from this series of compounds we identified potent and selective sigma1 ligands which might prove useful to unveil the functional role of sigma1 sites.

Modulation of NMDA and dopaminergic neurotransmissions by sigma ligands: possible implications for the treatment of psychiatric disorders

Sigma (sigma) receptors, improperly classified as belonging to the opiate receptor family when discovered in 1976, were subsequently confused with phencyclidine binding sites for several years. It's only recently, with the emergence of new selective ligands that their functional significance could be meaningfully addressed. Several subtypes of sigma receptors are present in high densities in the limbic structures as well as in motor-related areas of the CNS. Different lines of evidence suggest that a major role for sigma receptors might be to regulate the activity of the glutamatergic system via the modulation one of its subtype of receptor, the NMDA receptor. This modulation of the glutamatergic system could in turn interfere with the dopaminergic neurotransmission with which, however, sigma ligands could also interact directly. The potential involvement of sigma receptors in schizophrenia has been considered ever since their discovery. The initial suggestion to this respect emerged from the observation that several of the earliest sigma ligands induced psychotomimetic symptoms such as delusions, hallucinations and depersonalization. This link was later reinforced with the demonstration that several neuroleptics, such as haloperidol, have a high affinity for sigma receptors, whereas, some new molecules with a high affinity for sigma receptors, but a low affinity for dopaminergic receptors demonstrated a "neuroleptic-like" pharmacological profile. However, the therapeutic efficacy of selective sigma ligands in schizophrenia has not yet been established and it has even been suggested that sigma receptors might be responsible for some side effects of the classical neuroleptics. The possible implication of sigma receptors in affective disorders has also been suggested by reports showing that some antidepressant drugs have a high affinity for sigma receptors and that long-term treatments with anti- depressant drugs, even with those devoid of affinity for sigma receptors, modify their binding characteristics. In conclusion, indirect evidence suggests possible etiological and/or therapeutic roles for sigma receptors in some psychiatric disorders. However, despite several attempts, no clear indications of a therapeutic efficacy of sigma ligands has yet emerged. More selective ligands and fundamental studies on the respective role of the different subtypes of sigma receptors are needed before clear concepts can be formulated. p3

Discrimination of (+)-3-PPP sites from DTG sites by FH-510, a novel potent sigma ligand, in rat brain

The effect of 5,8-dimethyl-4-(2-di-n-propylaminoethyl)carbazol monohydrochloride (FH-510) on the binding of sigma ligands such as [3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ([3H](+)-3-PPP) and [3H]1,3-di-o-tolylguanidine ([3H]DTG) to rat brain membranes was studied. The inhibitory effect of FH-510 on [3H](+)-3-PPP binding to membranes of rat brain was 260 times more potent than that on [3H]DTG binding. Scatchard plot analysis showed that FH-510 inhibited [3H](+)-3-PPP binding in a competitive manner, while the inhibitory effect of FH-510 on [3H]DTG binding was noncompetitive. These results suggest that (+)-3-PPP sites could be discriminated from DTG sites, and that FH-510 binds preferentially to (+)-3-PPP recognition sites in rat brain.