Development of a fluorescence assay for the characterization of brevenal binding to rat brain synaptosomes.

The marine dinoflagellate Karenia brevis produces a family of neurotoxins known as brevetoxins. Brevetoxins elicit their effects by binding to and activating voltage-sensitive sodium channels (VSSCs) in cell membranes. K. brevis also produces brevenal, a brevetoxin antagonist, which is able to inhibit and/or negate many of the detrimental effects of brevetoxins. Brevenal binding to VSSCs has yet to be fully characterized, in part due to the difficulty and expense of current techniques. In this study, we have developed a novel fluorescence binding assay for the brevenal binding site. Several fluorescent compounds were conjugated to brevenal to assess their effects on brevenal binding. The assay was validated against the radioligand assay for the brevenal binding site and yielded comparable equilibrium inhibition constants. The fluorescence-based assay was shown to be quicker and far less expensive and did not generate radioactive waste or need facilities for handling radioactive materials. In-depth studies using the brevenal conjugates showed that, while brevenal conjugates do bind to a binding site in the VSSC protein complex, they are not displaced by known VSSC site specific ligands. As such, brevenal elicits its action through a novel mechanism and/or currently unknown receptor site on VSSCs.

Structure activity relationship of brevenal hydrazide derivatives.

Brevenal is a ladder frame polyether produced by the dinoflagellate Karenia brevis. This organism is also responsible for the production of the neurotoxic compounds known as brevetoxins. Ingestion or inhalation of the brevetoxins leads to adverse effects such as gastrointestinal maladies and bronchoconstriction. Brevenal shows antagonistic behavior to the brevetoxins and shows beneficial attributes when administered alone. For example, in an asthmatic sheep model, brevenal has been shown to increase tracheal mucosal velocity, an attribute which has led to its development as a potential treatment for Cystic Fibrosis. The mechanism of action of brevenal is poorly understood and the exact binding site has not been elucidated. In an attempt to further understand the mechanism of action of brevenal and potentially develop a second generation drug candidate, a series of brevenal derivatives were prepared through modification of the aldehyde moiety. These derivatives include aliphatic, aromatic and heteroaromatic hydrazide derivatives. The brevenal derivatives were tested using in vitro synaptosome binding assays to determine the ability of the compounds to displace brevetoxin and brevenal from their native receptors. A sheep inhalation model was used to determine if instillation of the brevenal derivatives resulted in bronchoconstriction. Only small modifications were tolerated, with larger moieties leading to loss of affinity for the brevenal receptor and bronchoconstriction in the sheep model.

The selective mu-opioid receptor antagonist ADL5510 reduces levodopa-induced dyskinesia without affecting antiparkinsonian action in MPTP-lesioned macaque model of Parkinson's disease.

In Parkinson's disease (PD), dyskinesia develops following long-term treatment with 3,4-dihydroxyphenylalanine (L-dopa). Given the prominent role of the opioid system in basal ganglia function, nonselective opioid receptor antagonists have been tested for antidyskinetic efficacy in the clinic (naltrexone and naloxone), although without success. In the current study, ADL5510, a novel, orally active opioid antagonist with mu opioid receptor selectivity, was examined in L-dopa-treated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) macaques. Antidyskinetic effects were compared with those of naltrexone. Parkinsonian monkeys with established L-dopa-induced dyskinesia (LID) received acute challenges with L-dopa (subcutaneously) in combination with either vehicle, ADL5510 (0.1, 1, 3 or 10 mg/kg by mouth), or naltrexone (1, 3, or 10 mg/kg subcutaneously). Following treatments, behavior was monitored for 6 hours. Parameters assessed were total activity, parkinsonism, and dyskinesia. ADL5510 (1, 3, and 10 mg/kg) reduced activity and LID (chorea and dystonia) without affecting the antiparkinsonian benefits of L-dopa. The antidyskinetic effect of ADL5510 showed a U-shaped dose-response. It was inactive at 0.1 mg/kg, efficacious at 1 and 3 mg/kg (72% and 40% reductions, respectively), and then less effective at 10 mg/kg. The quality of ON time produced by L-dopa was improved, as indicated by a reduction in the percentage of ON time spent experiencing disabling dyskinesia (70% and 61% reductions with 1 and 3 mg/kg, respectively, compared with L-dopa). Naltrexone, in contrast, did not alleviate LID or affect the antiparkinsonian actions of L-dopa. Mu-selective opioid antagonists have the potential to form the basis of novel antidyskinetic therapies for PD.

Synthesis and SAR of heterocyclic carboxylic acid isosteres based on 2-biarylethylimidazole as bombesin receptor subtype-3 (BRS-3) agonists for the treatment of obesity.

SAR around non-peptidic potent bombesin receptor subtype-3 (BRS-3) agonist lead 2 is presented. Attempts to replace the carboxylic acid with heterocyclic isosteres to improve oral bioavailability and brain penetration are described.

Synthesis and SAR of derivatives based on 2-biarylethylimidazole as bombesin receptor subtype-3 (BRS-3) agonists for the treatment of obesity.

This Letter describes a series of potent and selective BRS-3 agonists containing a biarylethylimidazole pharmacophore. Extensive SAR studies were carried out with different aryl substitutions. This work led to the identification of a compound 2-{2-[4-(pyridin-2-yl)phenyl]ethyl}-5-(2,2-dimethylbutyl)-1H-imidazole 9 with excellent binding affinity (IC(50)=18 nM, hBRS-3) and functional agonist activity (EC(50)=47 nM, 99% activation). After oral administration, compound 9 had sufficient exposure in diet induced obese mice to demonstrate efficacy in lowering food intake and body weight via BRS-3 activation.

Discovery of substituted biphenyl imidazoles as potent, bioavailable bombesin receptor subtype-3 agonists.

We report SAR studies on a novel non-peptidic bombesin receptor subtype-3 (BRS-3) agonist lead series derived from high-throughput screening hit RY-337. This effort led to the discovery of compound 22e with significantly improved potency at both rodent and human BRS-3.

Novel sulfamoyl benzamides as selective CB(2) agonists with improved in vitro metabolic stability.

A lead optimization campaign in our previously reported sulfamoyl benzamide class of CB(2) agonists was conducted to improve the in vitro metabolic stability profile in this series while retaining high potency and selectivity for the CB(2) receptor. From this study, compound 14, N-(3,4-dimethyl-5-(morpholinosulfonyl)phenyl)-2,2-dimethylbutanamide, was identified as a potent and selective CB(2) agonist exhibiting moderate in vitro metabolic stability and oral bioavailability. Compound 14 demonstrated in vivo efficacy in a rat model of post-surgical pain.

Novel pyridine derivatives as potent and selective CB2 cannabinoid receptor agonists.

Replacement of the phenyl ring in our previous (morpholinomethyl)aniline carboxamide cannabinoid receptor ligands with a pyridine ring led to the discovery of a novel chemical series of CB2 ligands. Compound 3, that is, 2,2-dimethyl-N-(5-methyl-4-(morpholinomethyl)pyridin-2-yl)butanamide was identified as a potent and selective CB2 agonist exhibiting in vivo efficacy after oral administration in a rat model of neuropathic pain.

CB2 selective sulfamoyl benzamides: optimization of the amide functionality.

Previous research within our laboratories identified sulfamoyl benzamides as novel cannabinoid receptor ligands. Optimization of the amide linkage led to the reverse amide 40. The compound exhibited robust antiallodynic activity in a rodent pain model when administered intraperitoneally. Efficacy after oral administration was observed only when ABT, a cytochrome P450 suicide inhibitor, was coadministered.

Mu opioid receptor antagonists: recent developments.

For thousands of years mu opioid agonists such as morphine have been utilized for their analgesic properties. Today, morphine and related compounds are still used as a first line therapy in the treatment of moderate to severe pain. However, despite the clear benefits of mu agonists in pain management, severe side effects such as dependence and respiratory depression are associated with use of these drugs. To date, there are only two approved mu opioid antagonists for use in the treatment of these adverse effects, that is, naloxone and naltrexone. However, many other clinical and therapeutic areas have been linked to mu opioid receptor antagonism. These include treatment of opioid induced pruritus of the skin, obesity, and Parkinson-induced tardive dyskinesia. Currently there are two compounds, N-methylnaltrexone and alvimopan, under FDA review as possible treatments for opioid induced bowel dysfunction and postoperative ileus. These compounds are of special interest as they are peripherally restricted. This attribute enables treatment of peripheral side effects induced by opioid agonists without reversal of the centrally mediated analgesia of the agonist. In this article we discuss the structural classes of mu opioid antagonists, their potential clinical applications, and review the relevant patents of the last ten years.

Elucidation of the bioactive conformation of the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of mu-opioid receptor antagonists.

The series of trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines have been widely investigated as opioid receptor antagonists. One of our research goals was to explore the bioactive conformation of the N-phenethyl trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine derivative 3, prototypical mu-opioid antagonist in this series. In this effort, the rotational degrees of freedom of the N-substituent of 3 were limited by incorporation of an ethylene bridge between the piperidine 2- or 6-position of 3 and the benzylic position of the N-phenethyl moiety. The overall modification led to a novel series of fused bicyclic derivatives of the octahydroquinolizine chemical class, conformationally restricted analogue of 3. The constrained analogues 6 and 9 showed high affinity toward the mu-opioid receptor. Compound 6 was found to be a mu-opioid antagonist, whereas the constrained analogue 9 displayed potent mu-agonist activity in vitro. This study provides additional information about the molecular determinants for mu recognition, the structural features affecting ligand binding, and the structure function relationships.

Synthesis and pharmacological evaluation of novel octahydro-1H-pyrido[1,2-a]pyrazine as mu-opioid receptor antagonists.

To better understand structural requirements for a mu ligand of the trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class to interact with the mu opioid receptor, we have described in the previous article (Le Bourdonnec, B. et al. J. Med. Chem. 2006, 25, 7278-7289) new, constrained analogues of the N-phenethyl derivative 3. One of the active constrained analogues, compound 4, exhibited subnanomolar mu-opioid receptor affinity (K(i) = 0.62 nM) and potent mu-opioid antagonist activity (IC(50) = 0.54 nM). On the basis of structure 4, a new series of mu-opioid receptor antagonists were designed. In these compounds the octahydroquinolizine template of 4 was replaced by an octahydro-1H-pyrido[1,2-a]pyrazine scaffold. The new derivatives were tested for their binding affinities and in vitro functional activity against the cloned human mu-, delta-, and kappa-opioid receptors. From this study, we identified compound 36, which displays high affinity toward the mu-opioid receptor (K(i) = 0.47 nM), potent mu in vitro antagonist activity (IC(50) = 1.8 nM) and improved binding selectivity profile mu/kappa and mu/delta, when compared to 4.

Synthesis and structure-activity relationships of a new series of 2alpha-substituted trans-4,5-dimethyl-4-(3-hydroxyphenyl)piperidine as mu-selective opioid antagonists.

Structure-activity relationships at the 2alpha-position of the piperidine ring of the trans-4,5-dimethyl-4-(3-hydroxyphenyl)piperidine mu-opioid antagonist series were investigated. This study showed that only small linear alkyl groups (methyl, propyl) are tolerated at the 2alpha-position of the piperidine ring of this series.

Model systems for flavoenzyme activity: interplay of hydrogen bonding and aromatic stacking in cofactor redox modulation.

[structure: see text] A model system has been developed to study the synergy between aromatic stacking and hydrogen bonding in the binding of a flavin derivative. The results show that the identity of both the hydrogen bonding and pi-stacking units strongly determine the overall receptor affinity for flavin in both the oxidized and radical anion forms.