Synthesis and SAR Studies of Isoquinoline and Tetrahydroisoquinoline Derivatives as Melatonin Receptor Ligands.

In our constant search for new successors of agomelatine, we report herein a new series of compounds resulting from bioisosteric modulation of the naphthalene ring. The isoquinoline and tetrahydroisoquinoline derivatives were synthesized and pharmacologically evaluated. This isosteric replacement of the naphthalene group of agomelatine has led to potent agonist and partial agonist compounds with nanomolar melatonergic binding affinities. Overall, the presence of a nitrogen atom was accompanied with a decrease in the binding affinity toward both MT1 and MT2 and the loss of 5HT2C response, especially for tetrahydroisoquinoline in comparison with the parent compound. Interestingly, due to the presence of this nitrogen atom, a notable improvement in the pharmacokinetic properties was observed for all compounds.

Effect of 6-Benzoyl-benzothiazol-2-one scaffold on the pharmacological profile of α-alkoxyphenylpropionic acid derived PPAR agonists.

A series of nitrogen heterocycles containing α-ethoxyphenylpropionic acid derivatives were designed as dual PPARα/γ agonist ligands for the treatment of type 2 diabetes (T2D) and its complications. 6-Benzoyl-benzothiazol-2-one was the most tolerant of the tested heterocycles in which incorporation of O-methyl oxime ether and trifluoroethoxy group followed by enantiomeric resolution led to the (S)-stereoisomer 44 b displaying the best in vitro pharmacological profile. Compound 44 b acted as a very potent full PPARγ agonist and a weak partial agonist on the PPARα receptor subtype. Compound 44 b showed high efficacy in an ob/ob mice model with significant decreases in serum triglyceride, glucose and insulin levels but mostly with limited body-weight gain and could be considered as a selective PPARγ modulator (SPPARγM).

Tetrahydroquinoline Ring as a Versatile Bioisostere of Tetralin for Melatonin Receptor Ligands.

A new family of melatonin receptor ligands, characterized by a tetrahydroquinoline (THQ) scaffold carrying an amide chain in position 3, was devised as conformationally constrained analogs of flexible N-anilinoethylamides previously developed. Molecular superposition models allowed to identify the patterns of substitution conferring high receptor binding affinity and to support the THQ ring as a suitable scaffold for the preparation of melatonin ligands. The biological activity of 3-acylamino-THQs was compared with that of the corresponding tetralin derivatives. The THQ ring proved to be a versatile scaffold for easy feasible MT1 and MT2 ligands, which resulted as more polar bioisosteres of their tetralin analogs. Potent partial agonists, with subnanomolar binding affinity for the MT2 receptor, were obtained, and a new series of THQ derivatives is presented. The putative binding mode of potent THQs and tetralines was discussed on the basis of their conformational equilibria as inferred from molecular dynamics simulations and experimental NMR data.

Synthesis and biological evaluation of new naphtho- and quinolinocyclopentane derivatives as potent melatoninergic (MT1/MT2) and serotoninergic (5-HT2C) dual ligands.

We recently reported a series of naphthofuranic compounds as constrained agomelatine analogues. Herein, in order to explore alternative ethyl amide side chain rigidification, naphthocyclopentane and quinolinocyclopentane derivatives with various acetamide modulations were synthesized and evaluated at both melatonin (MT1, MT2) and serotonin (5-HT2C) receptors. These modifications has led to compounds with promising dual affinity and high MTs receptors agonist activity. Enantiomeric separation was then performed on selected compounds allowing us to identify levogyre enantiomers (-)-17g and (-)-17k as the highest (MT1, MT2)/5-HT2C dual ligands described nowadays.

Anti-diabetic activity of fused PPARγ-SIRT1 ligands with limited body-weight gain by mimicking calorie restriction and decreasing SGK1 expression.

A series of benzothiazol-2-one containing α-ethoxyphenylpropionic acid derivatives incorporating resveratrol or butein scaffolds were designed as fused full PPARγ agonist ligands and SIRT1-activating compounds for the treatment of type 2 diabetes (T2D) and its complications. Compound 14d displayed the best in vitro pharmacological profile with full PPARγ agonist activity (Emax = 98%, EC50 = 200 nM), SIRT1 enzymatic activation (+128%) and SGK1 expression inhibition (- 57%) which is known to limit side effects as fluid retention and body-weight gain. Compound 14d showed high efficacy in an ob/ob mice model with significant decreases in serum triglyceride, glucose and insulin levels but mostly with limited body-weight gain by mimicking calorie restriction (CR) and inhibiting SGK1 expression.

New quinolinic derivatives as melatonergic ligands: Synthesis and pharmacological evaluation.

New series of melatonergic ligands issued from two methoxy-quinolinic scaffolds (2-MQ and 3-MQ), were designed and synthesized. Herein we report the synthetic scheme and pharmacological results of the new prepared compounds. Investigation of compound 11a, the strict 2-MQ analogue, revealed the promising potential of this series. Therefore, pharmacomodulation of the acetamide function of 11a has led to compounds with different pharmacological profiles and the emergence of an MT2 selectivity. Besides, sulphonamide 11b showed the most important MT2 selectivity of this series (167 folds) while methyl and ethyl-ureas 11f and 11g represented the most potent melatonergic ligands of this study.

Melatonergic ligands: Design, synthesis and pharmacological evaluation of novel series of naphthofuranic derivatives.

Following our research for new melatonergic ligands, herein we report the design, synthesis and biological evaluation of new series of naphthofuranic derivatives as MT1 and MT2 ligands. Binding affinity results of the prepared compounds revealed good binding affinities at both melatonin receptor subtypes. Particularly, compound 6a behaved as an MT1 partial agonist and MT2 full agonist and exhibited an excellent binding affinity at MT2 (Ki = 0.09 nM). In addition, lateral chain displacement from position 1 to 2 of the furan core had no effect on the binding affinity at both MT1 and MT2, while elongation of this side chain, led to decreased melatonergic binding affinities.

Synthesis of 2-arylfuro[3,2-b]pyridines: Effect of the C2-aryl group on melatoninergic activity.

We report herein an efficient synthesis of 2-substituted furo[3,2-b]pyridines and their biological evaluation as melatonin receptors ligands. The proposed eight-step sequence ending with a Suzuki coupling allowed a rapid access to various analogues. The steric hindrance and the conformation of the aryl group in C2-position were evaluated regarding the selectivity of the molecule for one of the two high affinity melatonin receptors as well as the activity profile of the compound. Introduction of 1-naphthyl substituent gave the best result in terms of selectivity with a MT1/MT2 ratio of about 150 (MT1 Ki = 198 nM, MT2 Ki = 1.3 nM).

Synthesis and Pharmacology of Mono-, Di-, and Trialkyl-Substituted 7-Chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-Dioxides Combined with X-ray Structure Analysis to Understand the Unexpected Structure-Activity Relationship at AMPA Receptors.

Positive allosteric modulators of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA)-type ionotropic glutamate receptors are promising compounds for treatment of neurological disorders, for example, Alzheimer's disease. Here, we report synthesis and pharmacological evaluation of a series of mono-, di-, or trialkyl-substituted 7-chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides, comprising in total 16 new modulators. The trisubstituted compounds 7b, 7d, and 7e revealed potent activity (EC2× = 2.7-4.3 µM; concentration of compound responsible for a 2-fold increase of the AMPA mediated response) as AMPA receptor potentiators in an in vitro cellular fluorescence assay (FLIPR). The 4-cyclopropyl compound 7f was found to be considerably less potent (EC2× = 60 µM), in contrast to previously described 4-monoalkyl-substituted benzothiadiazine dioxides for which the cyclopropyl group constitutes the best choice of substituent. 7b was subjected to X-ray structural analysis in complex with the GluA2 ligand-binding domain. We propose an explanation of the unexpected structure-activity relationship of this new series of mono-, di-, and trialkyl-substituted 1,2,4-benzothiadiazine 1,1-dioxide compounds. The methyl substituent in the 3-position directs the binding mode of the 1,2,4-benzothiadiazine 1,1-dioxide (BTD) scaffold. When a methyl substituent is present in the 3-position of the BTD, additional methyl substituents in both the 2- and 4-positions increase potency, whereas introduction of a 4-cyclopropyl group does not enhance potency of 2,3,4-alkyl-substituted BTDs. A hydrogen bond donor in the 2-position of the BTD is not necessary for modulator potency.

Highly Potent and Selective MT2 Melatonin Receptor Full Agonists from Conformational Analysis of 1-Benzyl-2-acylaminomethyl-tetrahydroquinolines.

Molecular superposition models guided the design of novel melatonin receptor ligands characterized by a 2-acylaminomethyltetrahydroquinoline scaffold. Starting from the structure of N-anilinoethylamide ligands, the flexible chain was conformationally constrained to reproduce the bioactive conformation of melatonin. Structure-activity relationships were investigated, focusing on the substituent at the nitrogen atom, the position of the methoxy group, and the replacement of the amide side chain by urea and thiourea groups. The compounds were tested for binding affinity and intrinsic activity at human MT1 and MT2 receptors. Structural optimization resulted in N-[(1-benzyl-1,2,3,4-tetrahydro-5-methoxyquinolin-2-yl)methyl]propionamide (UCM1014), with picomolar MT2 binding affinity (K(i) = 0.001 nM), more than 10000-fold selectivity over the MT1 receptor, and a full agonist profile (GTPγS test), being the most potent MT2-selective full agonist reported to date. Molecular dynamics simulations provided a rationale for high binding affinity, stereoselectivity, and agonist behavior of these novel melatonin receptor ligands based on superposition models and conformational preference.

Novel N-Acetyl Bioisosteres of Melatonin: Melatonergic Receptor Pharmacology, Physicochemical Studies, and Phenotypic Assessment of Their Neurogenic Potential.

Herein we present a new family of melatonin-based compounds, in which the acetamido group of melatonin has been bioisosterically replaced by a series of reversed amides and azoles, such as oxazole, 1,2,4-oxadiazole, and 1,3,4-oxadiazole, as well as other related five-membered heterocycles, namely, 1,3,4-oxadiazol(thio)ones, 1,3,4-triazol(thio)ones, and an 1,3,4-thiadiazole. New compounds were fully characterized at melatonin receptors (MT1R and MT2R), and results were rationalized by superimposition studies of their structures to the bioactive conformation of melatonin. We also found that several of these melatonin-based compounds promoted differentiation of rat neural stem cells to a neuronal phenotype in vitro, in some cases to a higher extent than melatonin. This unique profile constitutes the starting point for further pharmacological studies to assess the mechanistic pathways and the relevance of neurogenesis induced by melatonin-related structures.

Neurogenic Potential Assessment and Pharmacological Characterization of 6-Methoxy-1,2,3,4-tetrahydro-ß-carboline (Pinoline) and Melatonin-Pinoline Hybrids.

6-Methoxy-1,2,3,4-tetrahydro-ß-carboline (pinoline) and N-acetyl-5-methoxytryptamine (melatonin) are both structurally related to 5-hydroxytryptamine (serotonin). Here we describe the design, synthesis, and characterization of a series of melatonin rigid analogues resulting from the hybridization of both pinoline and melatonin structures. The pharmacological evaluation of melatonin-pinoline hybrids comprises serotonergic and melatonergic receptors, metabolic enzymes (monoamine oxidases), antioxidant potential, the in vitro blood-brain barrier permeability, and neurogenic studies. Pinoline at trace concentrations and 2-acetyl-6-methoxy-1,2,3,4-tetrahydro-ß-carboline (2) were able to stimulate early neurogenesis and neuronal maturation in an in vitro model of neural stem cells isolated from the adult rat subventricular zone. Such effects are presumably mediated via serotonergic and melatonergic stimulation, respectively.

Synthesis and pharmacological evaluation of dual ligands for melatonin (MT1/MT2) and serotonin 5-HT2C receptor subtypes (II).

In this paper we report the investigation of C-3 and ß-acetamide positions of agomelatine analogues. Concomitant insertion of a hydroxymethyl in the ß-acetamide position and aliphatic groups in C-3 position produced a positive effect on both melatonin (MT1, MT2) and serotonin (5-HT2C) binding affinities. In particular, the allyl 6b and ethyl 15a represented the more interesting compounds of this series. Furthermore, the introduction of methyl cycloalkyl groups (compounds 11a, 12a) exhibited no change in both MT2 and 5-HT2C binding affinities while a decrease of MT1 binding affinity occurred leading to an MT2 selectivity. Finally, the acetamide modulation has led to methyl thiourea 11h, with a weak MT2 selectivity.

Efficient synthesis of hexahydroindenopyridines and their potential as melatoninergic ligands.

Hexahydroindenopyridine (HHIP) is an interesting tricyclic piperidine nucleus that is structurally related to melatonin, a serotonin-derived neurohormone. Melatonin receptor ligands have applications in several cellular, neuroendocrine and neurophysiological disorders, including depression and/or insomnia. We report herein an efficient two-step method to prepare new HHIP via enamine C-alkylation-cyclization. The influence of substituents on the benzene ring and the nitrogen atom on melatoninergic receptors has been studied. Among the 25 synthesized HHIPs, some of them containing methylenedioxy (series 2) and 8-chloro-7-methoxy substituents (series 4) on the benzene ring revealed affinity for the MT1 and/or the MT2 receptors within the nanomolar range or low micromolar. Similar activities were also encountered for those presenting urea (4g), N-aryl (2e) and N-alkyl (2f) acetamide functions. Therefore, new synthesized compounds with a HHIP nucleus have emerged as new promising leads towards the discovery of melatoninergic ligands which could provide new therapeutic agents.

Synthesis of new melatoninergic hexahydroindenopyridines.

Hexahydroindenopyridine (HHIP) is an interesting heterocyclic framework that contains an indene core similar to ramelteon. This type of tricyclic piperidines aroused our interest as potential melatoninergic ligands. Melatonin receptor ligands have applications in insomnia and depression. We report herein an efficient two-step method to prepare new HHIP by the reaction of an enamine with 3-bromopropylamine hydrobromide. Some synthesized compounds showed moderate affinity for melatonin receptors in the nanomolar or low micromolar range. Furthermore, the methylenedioxy HHIPs 2d (N-phenylacetamide) and 2f (N,N-diethylacetamide), exhibited high selectivity at MT1 or MT2 receptors, respectively, when compared with melatonin. It seems that the methylenedioxy group on the indene ring system and the N-acetamide substituent are important structural features to bind selectively MT1 or MT2 subtypes.

New melatonin (MT1/MT2) ligands: design and synthesis of (8,9-dihydro-7H-furo[3,2-f]chromen-1-yl) derivatives.

Herein we describe the synthesis of novel tricyclic analogues issued from the rigidification of the methoxy group of the benzofuranic analogue of melatonin as MT1 and MT2 ligands. Most of the synthesized compounds displayed high binding affinities at MT1 and MT2 receptors subtypes. Compound 6b (MT1, Ki=0.07nM; MT2, Ki=0.08nM) exhibited with the vinyl 6c and allyl 6d the most interesting derivatives of this series. Functional activity of these compounds showed full agonist activity with EC50 in the nanomolar range. Compounds 6a (EC50=0.8nM and Emax=98%) and 6b (EC50=0.2nM and Emax=121%) exhibited good pharmacological profiles.

Development of thiophenic analogues of benzothiadiazine dioxides as new powerful potentiators of 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptors.

On the basis of the results obtained in previous series of AMPA potentiators belonging to 3,4-dihydro-2H-benzo- and 3,4-dihydro-2H-pyrido-1,2,4-thiadiazine 1,1-dioxides, the present work focuses on the design of original isosteric 3,4-dihydro-2H-thieno-1,2,4-thiadiazine 1,1-dioxides. Owing to the sulfur position, three series of compounds were developed and their activity as AMPA potentiators was characterized. In each of the developed series, potent compounds were discovered. After screening the selected active compounds on a safety in vivo test, 6-chloro-4-ethyl-3,4-dihydro-2H-thieno[2,3-e]-1,2,4-thiadiazine 1,1-dioxide (24) appeared as the most promising compound and was further evaluated. Its effects on long-term potentiation in vivo and on AMPA-mediated noradrenaline release were measured to predict its potential cognitive enhancing properties. Finally, an object recognition test performed in mice revealed that 24 was able to significantly enhance cognition, after oral administration, at doses as low as 0.3 mg/kg. This study validates the interest of the isosteric replacement of the benzene or pyridine nuclei by the thiophene nucleus in the ring-fused thiadiazine dioxides class of AMPA potentiators.

Synthesis and pharmacological evaluation of a series of the agomelatine analogues as melatonin MT1 /MT2 agonist and 5-HT2C antagonist.

Agomelatine is a naphthalenic analogue of melatonin that is in clinical use for the treatment of major depressive disorders. Interestingly, while agomelatine exhibits potent affinity for melatonin receptors, it binds with only moderate affinity to the serotonin 5-HT2C receptor. Optimization of agomelatine toward this target could further potentiate its clinical efficacy. To explore this hypothesis and to access derivatives in which a key point of agomelatine metabolism is blocked, a series of naphthalenic derivatives was designed and synthesized as novel analogues of agomelatine. Most of the prepared compounds exhibited good binding affinity at the melatonin MT1 and MT2 receptor subtypes. Two compounds, an acetamide and an acrylamide derivative, exhibited good binding affinities at both the human melatonin (MT) receptors and the serotonin 5-HT2C receptor subtype, with pKi values of 7.96 and 7.95 against MT1, 7.86 and 8.68 against MT2, and 6.64 and 6.44 against 5-HT2C, respectively.

New radioligands for describing the molecular pharmacology of MT1 and MT2 melatonin receptors.

Melatonin receptors have been studied for several decades. The low expression of the receptors in tissues led the scientific community to find a substitute for the natural hormone melatonin, the agonist 2-[125I]-iodomelatonin. Using the agonist, several hundreds of studies were conducted, including the discovery of agonists and antagonists for the receptors and minute details about their molecular behavior. Recently, we attempted to expand the panel of radioligands available for studying the melatonin receptors by using the newly discovered compounds SD6, DIV880, and S70254. These compounds were characterized for their affinities to the hMT1 and hMT2 recombinant receptors and their functionality in the classical GTPS system. SD6 is a full agonist, equilibrated between the receptor isoforms, whereas S70254 and DIV880 are only partial MT2 agonists, with Ki in the low nanomolar range while they have no affinity to MT1 receptors. These new tools will hopefully allow for additions to the current body of information on the native localization of the receptor isoforms in tissues.

Synthesis of new N-(arylcyclopropyl)acetamides and N-(arylvinyl)acetamides as conformationally-restricted ligands for melatonin receptors.

N-(Arylcyclopropyl)acetamides and N-(arylvinyl)acetamides or methyl ureas have been prepared as constrained analogues of melatonin. The affinity of these new compounds for chicken brain melatonin receptors and recombinant human MT(1) and MT(2) receptors was evaluated using 2-[(125)I]-iodomelatonin as radioligand. Strict ethylenic or cyclopropyl analogues of the commercialized agonist agomelatine (Valdoxan®) were equipotent to agomelatine in binding bioassays. However, the ethylenic analogue was more effective than the cyclopropyl one in the melanophore aggregation bioassay, but was still less potent than the disubstituted 2,7-dimethoxy-naphtalenic compounds.