2-[N-Acylamino(C1-C3)alkyl]indoles as MT1 melatonin receptor partial agonists, antagonists, and putative inverse agonists

Functionalization of Fe3O4@SiO2 nanoparticles with Cu(i)-thiosemicarbazone complex as a robust and efficient heterogeneous nanocatalyst for N-arylation of N-heterocycles with aryl halides

In this research, the functionalized silica-coated magnetite nanoparticles with Cu(i)-thiosemicarbazone complex (Fe3O4@SiO2-[CuL]) has been designed and synthesized as a magnetically retrievable nanocatalyst. Different techniques were employed to characterize the structure of Fe3O4@SiO2-[CuL] comprising FT-IR, FE-SEM, TEM, DLS, XRD, EDX, TGA, AAS, and VSM analysis. The catalytic performance of Fe3O4@SiO2-[CuL] was perused in Ullmann-type N-arylation of nucleobases, xanthines, and other N-heterocycles with diverse aryl halides which acquired the desired N-aryl products in good to excellent yields. Fe3O4@SiO2-[CuL] is a thermal and chemical stable, easy to prepare and recyclable, inexpensive, and ecofriendly catalyst that needs no additional additive or ligand as promoters. This catalyst could be separated without difficulty by a simple magnet and reused for at least seven sequential runs without a significant decline in its catalytic performance.

Enantioconvergent iso-Pictet-Spengler Reactions: Organocatalytic Synthesis of Chiral Tetrahydro-γ-carbolines

Enantioconvergent iso-Pictet-Spengler reactions of chiral racemic ß-formyl esters and a ß-keto ester are reported, providing complex tetrahydro-γ-carbolines containing two contiguous stereocenters. The reactions are catalyzed by a chiral thiourea and benzoic acid cocatalytic system and constitute rare cases of nonhydrogenative stereoconvergent additions to racemic α-stereogenic-ß-dicarbonyls. Elaboration of the products to chiral aminoalcohols and carbamates is demonstrated.

Early Clinical Development of Lufotrelvir as a Potential Therapy for COVID-19

Lufotrelvir was designed as a first in class 3CL protease inhibitor to treat COVID-19. Development of lufotrelvir was challenged by its relatively poor stability due to its propensity to epimerize and degrade. Key elements of process development included improvement of the supply routes to the indole and lactam fragments, a Claisen addition to homologate the lactam, and a subsequent phosphorylation reaction to prepare the prodrug as well as identification of a DMSO solvated form of lufotrelvir to enable long-term storage. As a new approach to preparing the indole fragment, a Cu-catalyzed C-O coupling using oxalamide ligands was demonstrated. The control of process-related impurities was essential to accommodate the parenteral formulation. Isolation of an MEK solvate followed by the DMSO solvate ensured that all impurities were controlled appropriately.

2-Arylmelatonin analogues: Probing the 2-phenyl binding pocket of melatonin MT1 and MT2 receptors

In crystal structures of melatonin MT₁ and MT₂ receptors, a lipophilic subpocket has been characterized which accommodates the phenyl ring of the potent agonist 2-phenylmelatonin. This subpocket appears a key structural element to achieve high binding affinity and selectivity for the MT₂ receptor. A series of 2-arylindole ligands was synthesized to probe the requirements for the optimal occupation and interaction with the 2-phenyl binding pocket. Thermodynamic integration simulations applied to MT₁ and MT₂ receptors in complex with the α-naphthyl derivative provided a rationale for the MT₂-selectivity and investigation on the binding mode of a couple of atropisomers allowed to define the available space and arrangement of substituents inside the subpocket. Interestingly, more hydrophilic 2-aza-substituted compounds displayed high binding affinity and molecular dynamics simulations highlighted polar interaction with residues from the subpocket that could be responsible for their potency.

Application of a Dual Catalytic Nickel/Iridium-Based Photoredox Reaction to Synthesize 2-Alkyl-N-Arylindoles in a Continuous Flow

A versatile one-pot procedure for the preparation of 2-alkyl-substituted N-arylindoles is described. The method combines a visible light-mediated Ni/Ir-photoredox dual catalytic N-arylation of alkynyl anilines under continuous flow conditions with a subsequent base-mediated cyclization to afford the desired substituted indoles. The initial Ni/Ir photoredox-promoted N-arylation of alkynylanilines proceeds efficiently in a continuous flow to afford the desired products in moderate to excellent yields with a short residence time (20 min) and mild conditions at ambient temperature and without the exclusion of air. The methodology was amenable for a multi-gram scale-up to deliver 2-alkyl-N-arylindoles in high yields followed with only a single purification step.

Melatonin receptor ligands: A pharmaco-chemical perspective

Melatonin MT₁ and MT₂ receptor ligands have been vigorously explored for the last 4 decades. Inspection of approximately 80 publications in the field revealed that most melatonergic ligands were structural analogues of melatonin combining three essential features of the parent compound: an aromatic ring bearing a methoxy group and an amide side chain in a relative arrangement similar to that present in melatonin. While several series of MT₂ -selective agents-agonists, antagonists, or partial agonists-were reported, the field was lacking MT₁ -selective agents. Herein, we describe various approaches toward the development of melatonergic ligands, keeping in mind that most of the molecules/pharmacophores obtained were essentially melatonin copies, even though diverse tri- or tetra-cyclic compounds were explored. In addition to lack of structural diversity, only few studies examined the activity of the reported melatonergic ligands in vivo. Moreover, an extensive pharmacological characterization including biopharmaceutical stability, pharmacokinetic properties, specificity toward other major receptors to name a few remained scarce. For example, many of the antagonists described were not stable in vivo, were not selective for the melatonin receptor subtype of interest, and were not fully characterized from a pharmacological standpoint. Indeed, virtual screening of large compound libraries has led to the recent discovery of potent and selective melatonin receptor agonists and partial agonists of new chemotypes. Having said this, the melatonergic field is still lacking subtype-selective melatonin receptor antagonists "active" in vivo, which are critical to our understanding of melatonin and melatonin receptors' role in basic physiology and disease.

Chiral Recognition of Flexible Melatonin Receptor Ligands Induced by Conformational Equilibria

N-anilinoethylamides are a class of melatoninergic agents with the aniline portion mimicking the indole ring of the natural ligand and the ethylamide chain reproducing that of melatonin. The simplest compound in this class, N-{2-[(3-methoxyphenyl)methylamino]ethyl}acetamide (UCM793), has nanomolar binding affinity for MT₁ and MT₂ membrane receptors. To explore the effect of chain conformation on receptor binding, a methyl group was inserted on the methylene alpha or beta to the amide nitrogen and conformational equilibria were investigated by NMR spectroscopy and molecular dynamics simulations. Receptor affinity was conserved only for the beta-methyl derivative, which also showed significant stereoselectivity, with the (S) enantiomer being the eutomer. Molecular dynamics simulations, validated by NMR spectroscopy, showed that the beta-methyl group affects the conformational preferences of the ethylamide chain. Docking into the receptor crystal structure provides a rationale for the observed chiral recognition, suggesting that the (S)-beta-methyl group favors the conformation that better fits the receptor binding site.

1,3-Iodo-amination of 2-methyl indoles via Csp2–Csp3 dual functionalization with iodine reagent

Remote iodo-amination of indole derivatives via C_sp2–C_sp3 dual functionalization under transition-metal-free conditions.

Antiproliferative and pro-apoptotic activity of melatonin analogues on melanoma and breast cancer cells

Melatonin plays different physiological functions ranging from the regulation of circadian rhythms to tumor inhibition, owing to its antioxidant, immunomodulatory and anti-aging properties. Due to its pleiotropic functions, melatonin has been shown to elicit cytoprotective processes in normal cells and trigger pro-apoptotic signals in cancer cells. The therapeutic potential of melatonin analogues prompted us to investigate the in vitro and in vivo antitumor activity of new melatonin derivatives and explore the underlying molecular mechanisms. The experiments revealed that the new melatonin analogues inhibited the growth of melanoma and breast cancer cells in a dose- and time-dependent manner. In addition, our results indicated that melatonin derivative UCM 1037 could induce apoptosis in melanoma and breast cancer cells, as well as cell necrosis, in MCF-7. Together, apoptosis and necrosis could be two possible mechanisms to explain the cytotoxic effect of the melatonin analogue against cancer cells. The suppression of tumor growth by the melatonin analogues was further demonstrated in vivo in a xenograft mice model. A decrease in the activation of MAPK pathway was observed in all cancer cells following UCM 1037 treatment. Overall, this study describes a promising antitumor compound showing antiproliferative and cytotoxic activity in melanoma and breast cancer cells.

Synthesis and biological evaluation of indolyl-pyridinyl-propenones having either methuosis or microtubule disruption activity

Methuosis is a form of nonapoptotic cell death characterized by an accumulation of macropinosome-derived vacuoles with eventual loss of membrane integrity. Small molecules inducing methuosis could offer significant advantages compared to more traditional anticancer drug therapies that typically rely on apoptosis. Herein we further define the effects of chemical substitutions at the 2- and 5-indolyl positions on our lead compound 3-(5-methoxy-2-methyl-1H-indol-3-yl)-1-(4-pyridinyl)-2-propene-1-one (MOMIPP). We have identified a number of compounds that induce methuosis at similar potencies, including an interesting analogue having a hydroxypropyl substituent at the 2-position. In addition, we have discovered that certain substitutions on the 2-indolyl position redirect the mode of cytotoxicity from methuosis to microtubule disruption. This switch in activity is associated with an increase in potency as large as 2 orders of magnitude. These compounds appear to represent a new class of potent microtubule-active anticancer agents.

Synthesis and characterization of new bivalent agents as melatonin- and histamine H3-ligands

Melatonin is an endogenous molecule involved in many pathophysiological processes. In addition to the control of circadian rhythms, its antioxidant and neuroprotective properties have been widely described. Thus far, different bivalent compounds composed by a melatonin molecule linked to another neuroprotective agent were synthesized and tested for their ability to block neurodegenerative processes in vitro and in vivo. To identify a novel class of potential neuroprotective compounds, we prepared a series of bivalent ligands, in which a prototypic melatonergic ligand is connected to an imidazole-based H₃ receptor antagonist through a flexible linker. Four imidazolyl-alkyloxy-anilinoethylamide derivatives, characterized by linkers of different length, were synthesized and their binding affinity for human MT₁, MT₂ and H₃ receptor subtypes was evaluated. Among the tested compounds, 14c and 14d, bearing a pentyl and a hexyl linker, respectively, were able to bind to all receptor subtypes at micromolar concentrations and represent the first bivalent melatonergic/histaminergic ligands reported so far. These preliminary results, based on binding affinity evaluation, pave the way for the future development of new dual-acting compounds targeting both melatonin and histamine receptors, which could represent promising therapeutic agents for the treatment of neurodegenerative pathologies.

Melatonin suppresses doxorubicin-induced premature senescence of A549 lung cancer cells by ameliorating mitochondrial dysfunction

Melatonin is an indolamine that is synthesized in the pineal gland and shows a wide range of physiological functions. Although the anti-aging properties of melatonin have been reported in a senescence-accelerated mouse model, whether melatonin modulates cellular senescence has not been determined. In this study, we examined the effect of melatonin on anticancer drug-induced cellular premature senescence. We found that the doxorubicin (DOX)-induced senescence of A549 human lung cancer cells and IMR90 normal lung cells was substantially inhibited by cotreatment with melatonin in a dose-dependent manner. Mechanistically, the DOX-induced G2/M phase cell cycle arrest and the decrease in cyclinB and cdc2 expression were not affected by melatonin. However, the DOX-induced increase in intracellular levels of ROS, which is necessary for premature senescence, was completely abolished upon melatonin cotreatment. In addition, the reduction in mitochondrial membrane potential that occurs upon DOX treatment was inhibited by melatonin. An aberrant increase in mitochondrial respiration was also significantly suppressed by melatonin, indicating that melatonin ameliorates the mitochondrial dysfunction induced by DOX treatment. The treatment of A549 cells with luzindole, a potent inhibitor of melatonin receptors, failed to prevent the effects of melatonin treatment on mitochondrial functions and premature senescence in cells also treated with DOX; this suggests that melatonin suppresses DOX-induced senescence in a melatonin receptor-independent manner. Together, these results reveal that melatonin has an inhibitory effect of melatonin on premature senescence at the cellular level and that melatonin protects A549 cells from DOX-induced senescence. Thus, melatonin might have the therapeutic potential to prevent the side effects of anticancer drug therapy.

Synthesis of chromeno[3,4-b]indoles as Lamellarin D analogues: a novel DYRK1A inhibitor class

A library of substituted chromeno[3,4-b]indoles was developed as Lamellarin isosters. Synthesis was achieved from indoles after a four-step pathway sequence involving C-3 iodination, a Suzuki cross-coupling reaction, and a one pot deprotection/lactonisation step. Twenty final compounds were tested in order to determine their activity against topoisomerase I and kinases, the two major biological activities of Lamellarins. One newly synthesized derivative exhibited a strong topoisomerase activity comparable to reference compounds such as campthotecin and Lamellarin with only a weak kinase inhibition. Two other lead compounds were identified as new nanomolar DYRK1A inhibitors and several other drugs affected the kinases in the sub-micromolar range. These results will enable us to use the chromeno[3,4-b]indole as a pharmacophore to develop potent treatments for neurological or oncological disorders in which DYRK1A is fully involved.

Diversity-oriented synthesis of polycyclic diazinic scaffolds

An efficient and versatile synthesis of a polycyclic diazinic system starting from oxazine has been developed using a two-step Michael/retro Michael and cyclization sequence. The substrates were synthesized with good to high yields giving rapid access to molecular diversity.

Cross-coupling reactions as valuable tool for the preparation of PET radiotracers

The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of new radiotracers and novel radiolabeling procedures with the most prominent short-lived positron emitters carbon-11 and fluorine-18. Radiolabeling with these radionuclides represents a remarkable challenge. Special attention has to be paid to synthesis time and specific labeling techniques due to the short physical half life of the respective radionuclides ¹¹C (t_1/2 = 20.4 min) and ¹⁸F (t_1/2 = 109.8 min). In the past, numerous transition metal-catalyzed reactions were employed in organic chemistry, even though only a handful of these coupling reactions were adopted in radiochemical practice. Thus, the implementation of modern synthesis methods like cross-coupling reactions offers the possibility to develop a wide variety of novel radiotracers. The introduction of catalysts based on transition metal complexes bears a high potential for rapid, efficient, highly selective and functional group-tolerating incorporation of carbon-11 and fluorine-18 into target molecules. This review deals with design, application and improvement of transition metal-mediated carbon-carbon as well as carbon-heteroatom cross-coupling reactions as a labeling feature with the focus on the preparation of radiolabeled compounds for molecular imaging.

Assessment of binding affinity to 5-hydroxytryptamine 2A (5-HT2A) receptor and inverse agonist activity of naftidrofuryl: comparison with those of sarpogrelate

Naftidrofuryl is a peripheral vasodilator that has been clinically used in the treatment of intermittent claudication and dementia. It has 5-hydroxytryptamine 2 (5-HT(2)) antiserotonergic activity and selectively binds with the 5-HT(2) receptor. The purpose of the present study is to assess the binding affinity and functional potency of naftidrofuryl to the 5-HT(2A) receptor, to find out the inverse agonist activity of this compound at a constitutively active mutant of 5-HT(2A) receptor, and finally to compare the findings with those of sarpogrelate. The investigation showed that the binding affinity (pK(i)) of naftidrofuryl was decreased 25- or 50-fold compared to sarpogrelate in the wild-type 5-HT(2A) receptor or Cys322Lys mutant receptor, respectively. Moreover, the functional potency (pK(b)) of naftidrofuryl was much lower compared to sarpogrelate at the 5-HT(2A) receptor. In addition, inverse agonist activity of naftidrofuryl was lower compared with sarpogrelate at the constitutively active mutant receptor. Thus, the data of the present study would be very important for the clarification of interaction sites of naftidrofuryl to 5-HT(2A) receptors and also may help to understand the mechanism of inverse agonist activity at the constitutively active mutant receptor.