Tetrahydroquinoline and tetrahydroisoquinoline derivatives as potential selective PDE4B inhibitors

Tetrahydroquinoline and tetrahydroisoquinoline derivatives containing 2-phenyl-5-furan moiety were designed and synthesized as phosphodiesterase type 4 (PDE4) inhibitors. The bioassay results showed that title compounds showed good inhibitory activity against PDE4B and blockade of LPS (lipopolysaccharide) induced TNF-α release, which also exhibited considerable in vivo activity in animal models of asthma/COPD (chronic obstructive pulmonary disease) and sepsis induced by LPS. The bioactivity of compounds containing tetrahydroquinoline (series 4) was higher than that of tetrahydroisoquinoline derivatives (series 3). Compound 4?m with 4-methoxybenzene moiety exhibited the best potential selective activity against PDE4B. The primary structure–activity relationship study and docking results showed that the tetrahydroquinoline moiety of compound 4?m played a key role to form hydrogen bonds and π-π stacking interaction with PDE4B protein while the rest part of the molecule extended into the catalytic domain to block the access of cAMP and formed the foundation for inhibition of PDE4B. Based on LPS induced sepsis model for the measurement of TNF-α inhibition in Swiss Albino mice and neutrophilia inhibition for asthma and COPD in Sprague Dawley rats with the potential molecules, compound 4?m would be great promise as a hit inhibitor in the future study.     

Structure-based design and structure-activity relationships of 1,2,3,4-tetrahydroisoquinoline derivatives as potential PDE4 inhibitors

This paper describes our medicinal chemistry efforts on 7-(cyclopentyloxy)-6-methoxy1,2,3,4-tetrahydroisoquinoline scaffold: design, synthesis and biological evaluation using conformational restriction approach and bioisosteric replacement strategy. Biological data revealed that the majority of the synthesized compounds of this series displayed moderate to potent inhibitory activity against PDE4B and strong inhibition of LPS-induced TNFα release. Among them, compound 19 exhibited the strongest inhibition against PDE4B with an IC₅₀ of 0.88?µM and 21 times more potent selectivity toward PDE4B over PDE4D when compared to rolipram. A primary structure-activity relationship study showed that the attachment of CH₃O group or CF₃O group to the phenyl ring at the para-position was helpful to enhance the inhibitory activity against PDE4B. Moreover, sulfonamide group played a key role in improving the inhibitory activity against PDE4B and subtype selectivity. In addition, the attachment of the additional rigid substituents at the C-3 position of 1,2,3,4-tetrahydroisoquinoline ring was favored to subtype selectivity, which was consistent well with the observed docking simulation.     

Synthesis and biological evaluation of 5-carbamoyl-2-phenylpyrimidine derivatives as novel and potent PDE4 inhibitors

5-Carbamoyl-2-phenylpyrimidine derivative 2 has been identified as a phosphodiesterase 4 (PDE4) inhibitor with moderate PDE4B inhibitory activity (IC₅₀ = 200 nM). Modification of the carboxylic acid moiety of 2 gave N-neopentylacetamide derivative 10f, which had high in vitro PDE4B inhibitory activity (IC₅₀ = 8.3 nM) and in vivo efficacy against lipopolysaccharide (LPS)-induced pulmonary neutrophilia in mice (ID₅₀ = 16 mg/kg, ip). Furthermore, based on the X-ray crystallography of 10f bound to the human PDE4B catalytic domain, we designed 7,8-dihydro-6H-pyrido[4,3-d]pyrimidin-5-one derivative 39 which has a fused bicyclic lactam scaffold. Compound 39 exhibited excellent inhibitory activity against LPS-induced tumor necrosis factor alpha (TNF-α) production in mouse splenocytes (IC₅₀ = 0.21 nM) and in vivo anti-inflammatory activity against LPS-induced pulmonary neutrophilia in mice (41% inhibition at a dose of 1.0 mg/kg, i.t.).     

Discovery of triazines as selective PDE4B versus PDE4D inhibitors

In this study we report a series of triazine derivatives that are potent inhibitors of PDE4B. We also provide a series of structure activity relationships that demonstrate the triazine core can be used to generate subtype selective inhibitors of PDE4B versus PDE4D. A high resolution co-crystal structure shows that the inhibitors interact with a C-terminal regulatory helix (CR3) locking the enzyme in an inactive ‘closed’ conformation. The results show that the compounds interact with both catalytic domain and CR3 residues. This provides the first structure-based approach to engineer PDE4B-selective inhibitors.     

Identification of the fused bicyclic 4-amino-2-phenylpyrimidine derivatives as novel and potent PDE4 inhibitors

2-Phenyl-4-piperidinyl-6,7-dihydrothieno[3,4-d]pyrimidine derivative (2) was found to be a new PDE4 inhibitor with moderate PDE4B activity (IC₅₀ = 150 nM). A number of derivatives with a variety of 4-amino substituents and fused bicyclic pyrimidines were synthesized. Among these, 5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivative (18) showed potent PDE4B inhibitory activity (IC₅₀ = 25 nM). Finally, N-propylacetamide derivative (31b) was determined as a potent inhibitor for both PDE4B (IC₅₀ = 7.5 nM) and TNF-α production in mouse splenocytes (IC₅₀ = 9.8 nM) and showed good in vivo anti-inflammatory activity in the LPS-induced lung inflammation model in mice (ID₅₀ = 18 mg/kg). The binding mode of the new inhibitor (31e) in the catalytic site of PDE4B is presented based on an X-ray crystal structure of the ligand–enzyme complex.     

Novel Roflumilast analogs as soft PDE4 inhibitors

PDE4 inhibitors are of high interest for treatment of a wide range of inflammatory or autoimmune diseases. Their potential however has not yet been realized due to target-associated side effects, resulting in a low therapeutic window. We herein report the design, synthesis and evaluation of novel PDE4 inhibitors containing a γ-lactone structure. Such molecules are designed to undergo metabolic inactivation when entering circulation, thereby limiting systemic exposure and reducing the risk for side effects. The resulting inhibitors were highly active on both PDE4B1 and PDE4D2 and underwent rapid degradation in human plasma by paraoxonase 1. In contrast, their metabolites displayed markedly reduced permeability and/or on-target activity.     

Discovery of oral and inhaled PDE4 inhibitors

The optimization of oxazole-based PDE4 inhibitor 1 has led to the identification of both oral (compound 16) and inhaled (compound 34) PDE4 inhibitors. Selectivity against PDE10/PDE11, off target screening, and in vivo activity in the rat are discussed.     

Pyrazolopyridines as a novel structural class of potent and selective PDE4 inhibitors

Optimisation of a high-throughput screening hit resulted in the discovery of 4-(substituted amino)-1-alkyl-pyrazolo[3,4-b]pyridine-5-carboxamides as potent and selective inhibitors of Phosphodiesterase 4 (PDE4). Herein, we describe early SAR studies around this novel template highlighting preferred substituents and rationalization of SAR through X-ray crystal structures of analogues bound to the PDE4 active site. Pyrazolopyridine 20a was found to be a potent and selective PDE4 inhibitor which also inhibits LPS induced TNF-α production from isolated human peripheral blood mononuclear cells and has an encouraging rat PK profile suitable for oral dosing.     

Local anti-inflammatory effect and behavioral studies on new PDE4 inhibitors

Phosphodiesterase 4 (PDE4) inhibitors are effective anti-inflammatory drugs, although some adverse effects are observed in animals and humans. These effects have forced researchers to find new PDE4 inhibitors with less adverse effects. We recently reported the synthesis of novel heterocyclic-fused pyridazinones that inhibit PDE4. As a first step in the study of the anti-inflammatory properties of these compounds, we studied the effects of local administration of these pyridazinone derivatives in a mouse model of acute inflammation. We found that 6-Benzyl-3-methyl-4-phenylpyrazolo[3,4-d]pyridazin-7(6H)-one (CC4), ethyl 6,7-dihydro-6-ethyl-3-methyl-7-oxo-4-phenyl-thieno[2,3-d]pyridazine-2-carboxylate (CC6) and ethyl 6,7-dihydro-6-ethyl-3-methyl-4-phenyl-1H-pyrrolo[2,3-d]pyridazine-2-carboxylate (CC12) reduced the paw edema induced by zymosan in mice as rolipram (the PDE4 inhibitor prototype with anti-inflammatory activity) and indomethacin did. It is well known that rolipram locally administered induces some adverse effects such as hyperalgesia. Thus, we studied this effect after local administration of CC4, CC6 and CC12 in the formalin test. We found that CC6 induced hyperalgesic effects, whereas CC4 and CC12 did not change the nociceptive threshold. Furthermore, we found that rolipram and CC6 reduced locomotor activity, whereas CC4 and CC12 did not change locomotor performance of the mice. Since CC4 and CC12 neither affected the nociceptive threshold nor changed the locomotor performance of mice, they appear more suitable than CC6 for future studies on animals and could be developed as an anti-inflammatory drug for humans.     

Identification of the 5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivatives as highly selective PDE4B inhibitors

A PDE4B subtype selective inhibitor is expected to have a wider therapeutic window than non-selective PDE4 inhibitors. In this Letter, two series of 7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivatives and 5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivatives were evaluated for their PDE4B subtype selectivity using human PDE4B2 and PDE4D2 full length enzymes. To improve their PDE4B selectivity over PDE4D, we optimized the substituents on the pyrimidine ring and the side chain phenyl ring, resulting in several derivatives with more than 100-fold selectivity for PDE4B. Consequently, we identified 2-(3-chloro-4-methoxy-phenyl)-5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivative 54 as a highly selective PDE4B inhibitor, which had potent hPDE4B inhibitory activity with an IC₅₀ value of 3.0 nM and 433-fold PDE4B selectivity over PDE4D.     

Synthesis and biological evaluation of nimesulide based new class of triazole derivatives as potential PDE4B inhibitors against cancer cells

A new class of 1,2,3-triazol derivatives derived from nimesulide was designed as potential inhibitors of PDE4B. Synthesis of these compounds was carried out via a multi-step sequence consisting of copper-catalyzed azide–alkyne cycloaddition (CuAAC) as a key step in aqueous media. The required azide was prepared via the reaction of aryl amine (obtained from nimesulide) with α-chloroacetyl chloride followed by displacing the α-chloro group by an azide. Some of the synthesized compounds showed encouraging PDE4B inhibitory properties in vitro that is >50% inhibition at 30 μM that were supported by the docking studies of these compounds at the active site of PDE4B enzyme (dock scores ～ ?28.6 for a representative compound). Two of these PDE4 inhibitors showed promising cytotoxic properties against HCT-15 human colon cancer cells in vitro with IC₅₀ ～ 21–22 μg/mL.     

Discovery of triazines as potent,selective and orally active PDE4 inhibitors

Expanding on HTS hit 4 afforded a series of [1,3,5]triazine derivatives as novel PDE4 inhibitors. The SAR development and optimization process with the emphasis on ligand efficiency and physicochemical properties led to the discovery of compound 44 as a potent, selective and orally active PDE4 inhibitor.     

Synthesis,biological activity and molecular modeling studies on 1H-benzimidazole derivatives as acetylcholinesterase inhibitors

A series of N-{2-[4-(1H-benzimidazole-2-yl)phenoxy]ethyl}substituted amine derivatives were designed to assess cholinesterase inhibitor activities. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitor activities were evaluated in vitro by using Ellman’s method. It was discovered that most of the compounds displayed AChE and/or BuChE inhibitor activity and few compounds were selective against AChE/BuChE. Compound 3c and 3e were the most active compounds in the series against eeAChE and hAChE, respectively. Molecular docking studies and molecular dynamics simulations were also carried out.     

Pd-mediated functionalization of polysubstituted pyrroles: Their evaluation as potential inhibitors of PDE4

Novel polysubstituted pyrroles have been designed and accessed via a one-pot multicomponent reaction followed by Pd-mediated C-C bond forming reactions. All the compounds synthesized were tested for their PDE4B inhibitory properties in vitro and two of them obtained via Heck reaction showed significant inhibition. The docking results suggested that these alkenyl derivatives containing ester moiety interact well with the PDE4B protein in silico where the ester carbonyl oxygen played a key role. The pyrrole framework presented here could be a new template for the identification of small molecule based novel inhibitors of PDE4. The single crystal X-ray data of a representative compound is presented.     

Synthesis and structure-activity relationship studies of dihydronaphthyridinediones as a novel structural class of potent and selective PDE7 inhibitors

The synthesis and SAR studies of a series of structurally novel inhibitors of PDE7 are discussed. The best compounds from the series display low nanomolar inhibitory activity and are selective versus other PDE isoenzymes.     

Synthesis of quinoline derivatives as diabetic II inhibitors and molecular docking studies

In searchof the potenttherapeutic agent as an α-glucosidase inhibitor, we have synthesized twenty-five analogs (1–25) of quinoline-based Schiff bases as an inhibitoragainst α-glucosidase enzyme under positive control acarbose (IC₅₀ = 38.45 ± 0.80 µM). From the activity profile it was foundthat analogs 1, 2, 3, 4, 11, 12 and 20with IC₅₀values 12.40 ± 0.40, 9.40 ± 0.30, 14.10 ± 0.40, 6.20 ± 0.30, 14.40 ± 0.40, 7.40 ± 0.20 and 13.20 ± 0.40 µMrespectively showed most potent inhibition among the series even than standard drug acarbose (IC₅₀ = 38.45 ± 0.80 µM). Here in the present study analog 4 (IC₅₀ = 6.20 ± 0.30 µM) was found with many folds better α-glucosidase inhibitory activity than the reference drug. Eight analogs like 5, 7, 8, 16, 17, 22, 24 and 25 among the whole series displayed less than 50% inhibition. The substituents effects on phenyl ring thereby superficially established through SAR study. Binding interactions of analogs and the active site of ligands proteins were confirmed through molecular docking study. Spectroscopic techniques like ¹H NMR, ¹³C NMR and ESIMS were used for characterization.     

Design, synthesis and evaluation of flavonoid derivatives as potent AChE inhibitors

A new series of flavonoid derivatives have been designed, synthesized and evaluated as potent AChE inhibitors. Most of them showed more potent inhibitory activities to AChE than rivastigmine. The most potent inhibitor isoflavone derivative 10d inhibit AChE with a IC₅₀ of 4 nM and showed high BChE/AChE inhibition ratio (4575-fold), superior to donepezil (IC₅₀ = 12 nM, 389-fold). Molecular docking studies were also performed to explore the detailed interaction with AChE.     

Synthesis of 2,2,4-trimethyl-1,2-dihydroquinolinyl substituted 1,2,3-triazole derivatives: Their evaluation as potential PDE 4B inhibitors possessing cytotoxic properties against cancer cells

The 2,2,4-trimethyl-1,2-dihydroquinolinyl substituted 1,2,3-triazole derivatives were designed as potential inhibitors of PDE4B. These compounds were synthesized via a multi-step sequence consisting of copper-catalyzed azide-alkyne cycloaddition (CuAAC) as a key step in aqueous media. The required alkynes were prepared from nimesulide via N-propargylation and then nitro group reduction followed by a CAN mediated modified Skraup reaction of the resulting amine. All the synthesized compounds showed PDE4B inhibitory properties in vitro at 30 μM with two compounds showing >50% inhibition that were supported by the in silico docking results of these compounds at the active site of PDE4B. Three of these PDE4 inhibitors showed promising cytotoxic properties against A549 human lung cancer cells in vitro with IC₅₀ ∼8–9 μM.     

N-Acylhydrazones as inhibitors of PDE10A

Cyclic nucleotide phosphodiesterases (PDEs) are represented by a large superfamily of enzymes. A series of hydrazone-based inhibitors was synthesized and shown to be novel, potent, and selective against PDE10A. Optimized compounds of this class were efficacious in animal models of schizophrenia and may be useful for the treatment of this disease.