(+)-and (-)-Phenazocine enantiomers: Evaluation of their dual opioid agonist/σ1 antagonist properties and antinociceptive effects.

cis-N-Substituted N-normetazocine enantiomers possess peculiar pharmacological profiles. Indeed, dextro enantiomers bind with high affinity σ1 receptor while opposite enantiomers bind opioid receptors. In spite of their stereochemistry, cis-N-2-phenylethyl N-normetazocine (phenazocine) enantiomers showed mixed opioid/σ1 receptor profiles and a significant in vivo analgesia. To the best of our knowledge, there is no information available regarding the evaluation of σ1 pharmacological profile in the antinociceptive effects of (+)- and (-)-phenazocine. Therefore, the present study was designed to ascertain this component by in vitro and in vivo studies. In particular, we tested the σ1 affinity of both enantiomers by a predictive binding assay in absence or presence of phenytoin (DPH). Our results showed that DPH (1 mM) did not increase the σ1 receptor affinity of (+)-and (-)-phenazocine (Ki = 3.8 ± 0.4 nM, Ki = 85 ± 2.0 nM, respectively) suggesting a σ1 antagonist profile of both enantiomers. This σ1 antagonistic component of two phenazocine enantiomers was corroborated by in vivo studies in which the selective σ1 receptor agonist PRE-084, was able to unmask their σ1 antagonistic component associated with the opioid activity. The σ1 antagonistic component of (+)- and (-)-phenazocine may justify their analgesic activity and it suggests that they may constitute useful lead compounds to develop new ligands with this dual activity.

Design and synthesis of new bifunctional sigma-1 selective ligands with antioxidant activity.

Herein we report the synthesis of new bifunctional sigma-1 (σ1)-selective ligands with antioxidant activity. To achieve this goal, we combined the structure of lipoic acid, a universal antioxidant, with an appropriate sigma aminic moiety. Ligands 14 and 26 displayed high affinity and selectivity for σ1 receptors (Kiσ1 = 1.8 and 5.5 nM; Kiσ2/σ1 = 354 and 414, respectively). Compound 26 exhibited in vivo antiopioid effects on kappa opioid (KOP) receptor-mediated analgesia. In rat liver and brain mitochondria (RLM, RBM), this compound significantly reduced the swelling and the oxidation of thiol groups induced by calcium ions. Our results demonstrate that the tested compound has protective effects against oxidative stress.

New benzomorphan derivatives of MPCB as MOP and KOP receptor ligands.

There is considerable interest in developing KOP Opioid receptor ligands as clinically useful analgesics. Moreover, compounds with mixed KOP receptor and mu-opioid peptide (MOP) receptor agonist/antagonist properties could have a better therapeutic potential. The benzomorphan-based synthetic ligands MPCB and CCB have been shown to bind KOP receptors with high affinity and selectivity. We report here a series of compounds synthesized to perform structure-affinity relationship (SAR) studies on MPCB. The aim of this study was to optimise KOP receptor-ligand interaction and to modulate MOP receptor selectivity. In the benzylamide analogue of MPCB (compound 9) the presence of a third aromatic nucleus, at an appropriate distance and conformation with respect to aromatic pharmacophoric residues, increased KOP receptor affinity by about 6-fold compared to MPCB (Ki = 35 nM and Ki = 240 nM, respectively). Instead, compound 28 with a tertiary amino group in the nitrogen substituent displayed a comparable KOP receptor affinity (Ki = 179 nM) but also high MOP receptor affinity (Ki = 45 nM). Thus, the present study shows that in benzomorphan-based ligands the presence of different functional groups in the nitrogen substituent, ranging from a positive charged amine to an additional aromatic ring, is able to promote the correct aligment of aromatic pharmacophoric residues with MOP and KOP receptor types. Evaluation of docking simulations of compounds 9 and 28 into the KOP and MOP receptor displayed selective ligand interactions with the important amino acid residues Tyr320 (TMVII) and Trp318 (TMVII), respectively.

Synthesis and anti-measles virus activity of new isoquinolin-4-one derivatives.

Despite intense efforts to increase vaccine coverage, measles virus (MV) still causes significant morbidity and mortality in the world sometimes as a results of severe, chronic and lethal diseases. In an effort to develop therapies to supplement immunization strategies a number of 1-oxo-2-[[(1E)-phenylmethylene]amino]-1,2-dihydroisoquinoline-4-carboxylic acid derivatives were synthesized and evaluated for anti-measles activity. The substituents on the aromatic ring were chosen in order to evaluate the influence of electron-withdrawing or electron-donating effects on the electronic density of the aromatic moiety. We also evaluated the introduction of a vinyl chain between the exocyclic nitrogen and phenyl moiety. The biological results allow to outline some preliminary considerations on structure-activity relationship.

Synthesis and pharmacological evaluation of potent and enantioselective sigma 1, and sigma 2 ligands.

In a previous study we found that substitutions of the (+)-cis-N-normetazocine nucleus of (+)-MPCB with 1-adamantanamine provide the compound (+/-)-10 with high affinity and selectivity for sigma receptors. Starting with this result we have synthesized a new series of eight 1-phenyl-2-cyclopropylmethylamines structurally related to (+/-)-10, and binding affinities, with respect to sigma 1, sigma 2, opioid and dopaminergic D2 receptors, have been reported. All compounds showed a negligible opioid and dopaminergic affinity and high selectivity for sigma receptors. Modifications on the amino moiety and methylcarboxyester group of 10 provide compounds with different sigma 1 and sigma 2 binding affinity and selectivity. Moreover, we have also synthesized the respective enantiomers of componds (+/-)-10 and (+/-)-18 in order to evaluate the enantioselectivity for sigma 1 and sigma 2 receptors. The binding data showed that carboxymethylester on the cyclopropane ring was more critical for enantioselectivity than the hydroxymethylenic group. In fact, the (-)-10 enantiomer showed a preference for sigma 1 whereas (+)-10 showed a preference for sigma 2.

Specific kappa opioid receptor agonists.

The results of studies on the design of a heterocyclic scaffold for the dynorphin A pharmacophore and on structure-affinity relationships in the MPCB/CCB series are described. The representative ligands provide insights to binding modes of benzomorphan derivatives to the kappa opioid receptor.

Synthesis and binding affinity of cis-(-)- and cis-(+)-N-ethyleneamino-N-nordeoxymetazocine and cis-(-)-N-normetazocine analogues at sigma1, sigma2 and kappa opioid receptors.

The synthesis of cis-(+)- and cis-(-)-N-ethyleneamino-N-nordeoxymetazocine and cis-(-)-N-normetazocine analogues is described and their affinities to sigma1, sigma2 and kappa opioid receptors are evaluated. The cis-(+)-deoxy compounds displayed high sigma/kappa selectivity with nanomolar K(i) values for sigma1 receptors, whereas in the cis-(-)-N-normetazocine series the compound (-)-7b was found to bind with nanomolar affinity to the kappa opioid receptor (K(i)=21.5 nM). Compound (-)-7b showed good selectivity for the kappa opioid receptor in comparison to the sigma1 and sigma2 sites and to the mu and delta opioid receptors. A correlation of the binding affinities between cis-(-)- and cis-(+)-N-deoxynormetazocine derivatives show that both isomers of the deoxy analogs have similar sigma1 and sigma2 binding profiles as the cis-(+)-N-normetazocine derivatives.

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).

Substituted 1-phenyl-2-cyclopropylmethylamines with high affinity and selectivity for sigma sites.

A series of 1-phenyl-2-cyclopropylmethylamines structurally related to (+)- and (-)-MPCB were synthesized and their binding affinities for sigma1, sigma2, opioid and dopamine (D2) receptors were evaluated. Substitution of the cis-N-normetazocine with different aminic moieties provided compounds with high affinity and selectivity for sigma binding sites with respect to opioid and dopamine (D2) receptors. The observed increase in sigma2 affinity as compared to the parent (+)-MPCB, supports the idea that the particular stereochemistry of (+)-cis-N-normetazocine affects sigma1 selectivity but does not affect sigma1 affinity. The (+/-)-cis isomers of methyl 2-[(1-adamantylamino)methyl]-1-phenylcyclopropane-1-carboxyl ate (18) displayed a higher affinity and selectivity for the sigma1 and sigma2 receptor subtypes compared to the (+/-)-trans 19. Interestingly, the enantiomer (-)-cis 18 displayed a preference for sigma1 receptor subtype whereas the (+)-cis 18 did for sigma2. These results prompt us to synthesize compounds with modification of nitrogen and carboxyl groups. The compounds obtained showed high affinities and selectivity for sigma sites. Moreover, modifications of carboxyl groups provided compounds with the highest affinities in the series. In particular, compound 25 with reverse-type ester showed a Ki of 0.6 and 4.05 nM for sigma1 and sigma2 binding sites, respectively.

(+)-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.

Synthesis of (+)-(1'R,2'S) and (1'S,2'R)-6,11-dimethyl-1,2,3,4,5,6 -hexahydro-3-[[2'-(alkoxycarbonyl)-2'-phenylcyclopropyl]methyl]-2 ,6 -methano-3-benzazocin-8-ol. Comparison of the affinities for sigma 1 and opioid receptors with in the diastereoisomeric MPCB and CCB.

The synthesis and the in vitro receptor affinity for sigma 1 and opiod receptors of the two diastereoisomers of (+)-cis-MPCB namely, (+)-cis-(1'S,2'R)-6,11-Dimethyl-1,2,3,4,5,6 -hexahydro-3-[[2'-(methoxycarbonyl)-2'-phenylcyclopropyl]methyl]-2 ,6 -methano-3-benzazocin-8-ol, (1'S,2'R)6a and (+)-cis-(1'R,2'S)-6,11-Dimethyl-1,2,3,4,5,6-hexahydro-3- [[2-(methoxycarbonyl)-2'-phenylcyclopropyl]methyl]-2,6-methano-3-+ ++benzazocin-8 -ol, (1'R,2'S)6a are reported. Affinities of (1'S,2'R)6a and (1'R,2'S)6a were compared with those of the (-)-cis-diastereoisomers of MPCB(1), and of its p-Cl phenyl derivative CCB(2). The (+)-cis-N-normetazocine derivatives showed higher affinity for the sigma 1 sites, labeled with [3H]-(+)-pentazocine than the corresponding (-)-cis- analogs. In particular, compound (1'S,2'R)6a showed a Ki = 66.7 nM for sigma 1 receptor, associated with a good selectivity for sigma 1 with respect to kappa, mu, delta opioid receptors subtypes (Ki = > 1,000 nM). Analysis of the data seem to support the hypothesis that the (+)-cis-N-normetazocine nucleus posses a specific enantioselectivity for sigma 1 sites, when supporting bulkier N-substituents functionalized with a carboxy ester group.

CCB, a novel specific kappa opioid agonist, which discriminates between opioid and sigma 1 recognition sites.

CCB, 6,11-Dimethyl-1,2,3,4,5,6-hexahydro-3-([2'-methoxycarbonyl-2'-(4- chlorophenyl)cyclopropyl]methyl)-2,6-methano-3-benzazocin-8-ol, displays specificity and very high affinity for kappa opioid receptor types (Ki = 0.41 +/- 0.19 nM). In contrast to other kappa opioid agonists, CCB is also selective with respect to sigma 1 sites (Ki = 1,050 +/- 55 nM). CCB displays antinociceptive and sedative effects in the mouse comparable to those of U50,488H and morphine. Naltrexone fully antagonizes these effects. The sedative effects of CCB are blocked in mice pretreated with naltrexone or nor-BNI. CCB and U50,488H produce a superimposable diuresis in rats. Naltrexone and nor-BNI, both are effective in antagonizing the effect. CCB does not produce any stereotyped behavior or ataxia in the behavioral assay in doses up to 40 mg/kg s.c. These findings suggest that CCB might be a useful tool to investigate the physiological role of kappa opioid receptors.