Identification and characterization of pyrrolidine diastereoisomers as potent functional agonists and antagonists of the human melanocortin-4 receptor

A series of trans-4-phenylpyrrolidine-3-carboxamides were synthesized and characterized as potent ligands of the human melanocortin-4 receptor. Interestingly, a pair of diastereoisomers 13b displayed potent functional agonist and antagonist activity, respectively. Thus, the 3S,4R-pyrrolidine 13b-1 possessed a Ki of 1.0 nM and an EC50 of 3.8 nM, while its 3R,4S-isomer 13b-2 exhibited a Ki of 4.7 and an IC50 of 64 nM. Both compounds were highly selective over other melanocortin receptor subtypes. The MC4R agonist 13b-1 also demonstrated efficacy in a diet-induced obesity model in rats.     

Pyrrolidines as potent functional agonists of the human melanocortin-4 receptor

A series of pyrrolidine derivatives were synthesized and characterized as potent agonists of the human melanocortin-4 receptor. For example, 28c had a K(i) of 13 nM in binding affinity and EC(50) of 6.9 nM in agonist potency with an intrinsic activity of 100% of the endogenous ligand alpha-MSH.     

Structure-activity relationships of piperazinebenzylamines as potent and selective agonists of the human melanocortin-4 receptor

SAR studies on a series of piperazinebenzenes directed toward the human melanocortin-4 receptor resulted in potent MC4R agonists. Replacement of the triazole moiety of an initial lead 4 by a basic nitrogen baring a lipophilic side-chain increased the binding affinities of these compounds. Analogs bearing an additional hetero-atom in the side-chain possessed good agonist potency. Thus, 11h had a Ki of 11 nM, and 13g exhibited an EC50 of 3.8 nM and a Ki of 6.4 nM.     

Pyrrolidinones as potent functional antagonists of the human melanocortin-4 receptor

A series of pyrrolidinones derived from phenylalaninepiperazines were synthesized and characterized as potent and selective antagonists of the melanocortin-4 receptor. In addition to their high binding affinities, these compounds displayed high functional potencies. 12a had a K(i) of 0.94 nM in binding and IC(50) of 21 nM in functional activity. 12a also demonstrated efficacy in a mouse cachexia model.     

Piperazinebenzylamines as potent and selective antagonists of the human melanocortin-4 receptor

SAR studies of a series of piperazinebenzylamines resulted in the discovery of potent antagonists of the human melanocortin-4 receptor. Compounds 11c, 11d, and 11l, which had K(i) values of 21, 14, and 15 nM, respectively, possessed low efficacy in cAMP stimulation ( approximately 15% of alpha-MSH maximal level) mediated by MC4R, and functioned as antagonists in inhibition of alpha-MSH-stimulated cAMP release in a dose-dependent manner (11l, IC(50)=36 nM).     

D-4'-thioadenosine derivatives as highly potent and selective agonists at the human A3 adenosine receptor

4'-Thionucleoside derivatives as potent and selective A3 adenosaine receptor agonists were synthesized, starting from D-gulono-gamma-lactone via D-thioribosyl acetate as a key intermediate, among which the 2-chloro-N6-methyladenosine-5-methyluronamide showed the most potent and selective binding affinity (Ki = 0.28 +/- 0.09 nM) at the human A3 adenosine receptor.     

Pharmacological and pharmacokinetic characterization of 2-piperazine-alpha-isopropyl benzylamine derivatives as melanocortin-4 receptor antagonists

A series of 2-piperazine-alpha-isopropylbenzylamine derivatives were synthesized and characterized as melanocortin-4 receptor (MC4R) antagonists. Attaching an amino acid to benzylamines 7 significantly increased their binding affinity, and the resulting compounds 8-12 bound selectively to MC4R over other melanocortin receptor subtypes and behaved as functional antagonists. These compounds were also studied for their permeability using Caco-2 cell monolayers and metabolic stability in human liver microsomes. Most compounds exhibited low permeability and high efflux ratio possibly due to their high molecular weights. They also showed moderate metabolic stability which might be associated with their moderate to high lipophilicity. Pharmacokinetic properties of these MC4R antagonists, including brain penetration, were studied in mice after oral and intravenous administrations. Two compounds identified to possess high binding affinity and selectivity, 10d and 11d, were studied in a murine cachexia model. After intraperitoneal (ip) administration of 1mg/kg dose, mice treated with 10d had significantly more food intake and weight gain than the control animals, demonstrating efficacy by blocking the MC4 receptor. Similar in vivo effects were also observed when 11d was dosed orally at 20mg/kg. These results provide further evidence that a potent and selective MC4R antagonist has potential in the treatment of cancer cachexia.     

Identification of agonists and antagonists of the human melanocortin-4 receptor from piperazinebenzylamines

SAR studies of a series of piperazinebenzylamines resulted in identification of potent agonists and antagonists of the human melanocortin-4 receptor. Thus, the 1,2,3,4-tetrahydroisoquinolin-1-ylacetyl compound 12e and the quinolin-3-ylcarbonyl analogue 12l possessed K(i) values of 6.3 and 4.5 nM, respectively. Interestingly, 12e was a full agonist with an EC(50) value of 31 nM, and 12l was a weak partial agonist (IA=17%) and functioned as an antagonist (IC(50)=300 nM).     

Propionylpiperazines as human melanocortin-4 receptor ligands

A series of alpha-benzylpropionylpiperazines were synthesized and tested as antagonists of the melanocortin-4 receptor. In addition to its high potency and selectivity, R-11a had desirable pharmacokinetic properties including high brain penetration in mice.     

Novel malonamide derivatives as potent kappa opioid receptor agonists

A novel series of malonamide derivatives was synthesized. These amides were shown to be potent and selective kappa opioid receptor agonists.     

Arylpropionylpiperazines as antagonists of the human melanocortin-4 receptor

A series of 3-arylpropionylpiperazines were synthesized as antagonists of the melanocortin-4 receptor. Their potency was found to be increased by replacing the alpha-methyl substituent of the initial lead 11 with a larger s-Bu or i-Bu group. Further potency enhancement was observed when a glycine or beta-alanine was incorporated onto the benzylamine. Some compounds demonstrated good potency, moderate selectivity, and oral bioavailability.     

Design and synthesis of potent and selective 1,3,4-trisubstituted-2-oxopiperazine based melanocortin-4 receptor agonists

The design and synthesis of a series of potent 1,3,4-trisubstituted-2-oxopiperazine based MC4 agonists are described. The tripeptidomimetic analogs (12a,b and 23) and the dipeptidomimetic 27 displayed single-nanomolar binding affinity and agonist potency for MC4R and excellent selectivity for MC4R relative to MC1R.     

1-Amino-1,2,3,4-tetrahydronaphthalene-2-carboxylic acid as a Tic mimetic: application in the synthesis of potent human melanocortin-4 receptor selective agonists

The discovery of 1-amino-1,2,3,4-tetrahydronaphthalene-2-carboxylic acid analogs as potent human melanocortin-4 selective agonists is described.     

Identification of a novel series of benzimidazoles as potent and selective antagonists of the human melanocortin-4 receptor

A novel series of benzimidazoles was identified and optimized, leading to the discovery of potent and selective antagonists of the human melanocortin-4 receptor. In addition, compound 5i was shown to cross the blood-brain barrier after intravenous dosing in rats.     

Synthesis and pharmacological properties of benzamide derivatives as selective serotonin 4 receptor agonists

A series of 4-amino-5-chloro-2-methoxy-N-(piperidin-4-ylmethyl)benzamides with a polar substituent group at the 1-position of the piperidine ring was synthesized and evaluated for its effect on gastrointestinal motility. The benzoyl, phenylsulfonyl, and benzylsulfonyl derivatives accelerated gastric emptying and increased the frequency of defecation. One of them, 4-amino-N-[1-[3-(benzylsulfonyl)propyl]piperidin-4-ylmethyl]-5-chloro-2-methoxybenzamide (13a, Y-36912), was a selective 5-HT4 receptor agonist offering potential as a novel prokinetic with reduced side effects derived from 5-HT3- and dopamine D2 receptor-binding affinity. In the oral route of administration, this compound enhanced gastric emptying and defecation in mice, and has a possibility as a prokinetic agent, which is effective on both the upper and the lower gastrointestinal tract.     

New oxadiazolidinedione derivatives as potent and selective human beta3 agonists

As part of our investigation into the development of potent and selective human beta3 agonists, a series of thiazolidinedione analogues was prepared and evaluated for their biological activity on the human beta3-adrenergic receptor. The oxadiazolidinedione derivative 17 was found to be the most potent and selective compound in this study, with an EC50 value of 0.02 microM at the beta3 receptor, 259-fold selectivity over the beta1 receptor, and 745-fold selectivity over the beta2 receptor.     

Novel phenylamino acetamide derivatives as potent and selective kappa opioid receptor agonists

A novel series of phenylamino acetamide derivatives was synthesized. These amides were shown to be potent and selective kappa opioid receptor agonists.     

Antibodies against the melanocortin-4 receptor act as inverse agonists in vitro and in vivo

Functionally active antibodies (Abs) against central G-protein-coupled receptors have not yet been reported. We selected the hypothalamic melanocortin-4 receptor (MC4-R) as a target because of its crucial role in the regulation of energy homeostasis. A 15 amino acid sequence of the N-terminal (NT) domain was used as an antigen. This peptide showed functional activity in surface plasmon resonance experiments and in studies on HEK-293 cells overexpressing the human MC4-R (hMC4-R). Rats immunized against the NT peptide produced specific antibodies, which were purified and characterized in vitro. In HEK-293 cells, rat anti-NT Abs showed specific immunofluorescence labeling of hMC4-R. They reduced the production of cAMP under basal conditions and after stimulation with a synthetic MC4-R agonist. Rats immunized against the NT peptide developed a phenotype consistent with MC4-R blockade, that is, increased food intake and body weight, increased liver and fat pad weight, and elevated plasma triglycerides. In a separate experiment in rats, an increase in food intake could be produced after injection of purified Abs into the third ventricle. Similar results were obtained in rats injected with anti-NT Abs raised in rabbits. Our data show for the first time that active immunization of rats against the NT sequence of the MC4-R results in specific Abs, which appear to stimulate food intake by acting as inverse agonists in the hypothalamus.     

Synthesis and evaluation of 8-oxoadenine derivatives as potent Toll-like receptor 7 agonists with high water solubility

We report the discovery of novel series of highly potent TLR7 agonists based on 8-oxoadenines, 1 and 2 by introducing and optimizing various tertiary amines onto the N(9)-position of the adenine moiety. The introduction of the amino group resulted in not only improved water solubility but also enhanced TLR7 agonistic activity. In particular compound 20 (DSR-6434) indicated an optimal balance between the agonistic potency and high water solubility. It also demonstrated a strong antitumor effect in vivo by intravenous administration in a tumor bearing mice model.     

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.