Nature-Inspired 1-Phenylpyrrolo[2,1-a]isoquinoline Scaffold for Novel Antiproliferative Agents Circumventing P-Glycoprotein-Dependent Multidrug Resistance

Previous studies have shown that some lamellarin-resembling annelated azaheterocyclic carbaldehydes and related imino adducts, sharing the 1-phenyl-5,6-dihydropyrrolo[2,1-a]isoquinoline (1-Ph-DHPIQ) scaffold, are cytotoxic in some tumor cells and may reverse multidrug resistance (MDR) mediated by P-glycoprotein (P-gp). Herein, several novel substituted 1-Ph-DHPIQ derivatives were synthesized which carry carboxylate groups (COOH, COOEt), nitrile (CN) and Mannich bases (namely, morpholinomethyl derivatives) in the C2 position, as replacements of the already reported aldehyde group. They were evaluated for antiproliferative activity in four tumor cell lines (RD, HCT116, HeLa, A549) and for the ability of selectively inhibiting P-gp-mediated MDR. Lipophilicity descriptors and molecular docking calculations helped us in rationalizing the structure-activity relationships in the P-gp inhibition potency of the investigated 1-Ph-DHPIQs. As a main outcome, a morpholinomethyl Mannich base (8c) was disclosed which proved to be cytotoxic to all the tested tumor cell lines in the low micromolar range (IC50 < 20 μM) and to inhibit in vitro the efflux pumps P-gp and MRP1 responsible for MDR, with IC50s of 0.45 and 12.1 μM, respectively.

Novel 6-alkyl-bridged 4-arylalkylpiperazin-1-yl derivatives of azepino[4,3-b]indol-1(2H)-one as potent BChE-selective inhibitors showing protective effects against neurodegenerative insults

Due to the putative role of butyrylcholinesterase (BChE) in regulation of acetylcholine levels and functions in the late stages of the Alzheimer's disease (AD), the potential of selective inhibitors (BChEIs) has been envisaged as an alternative to administration of acetylcholinesterase inhibitors (AChEIs). Starting from our recent findings, herein the synthesis and in vitro evaluation of cholinesterase (ChE) inhibition of a novel series of some twenty 3,4,5,6-tetrahydroazepino[4,3-b]indol-1(2H)-one derivatives, bearing at the indole nitrogen diverse alkyl-bridged 4-arylalkylpiperazin-1-yl chains, are reported. The length of the spacers, as well as the type of arylalkyl group affected the enzyme inhibition potency and BChE/AChE selectivity. Two compounds, namely 14c (IC50 = 163 nM) and 14d (IC50 = 65 nM), bearing at the nitrogen atom in position 6 a n-pentyl- or n-heptyl-bridged 4-phenethylpiperazin-1-yl chains, respectively, proved to be highly potent mixed-type inhibitors of both equine and human BChE isoforms, showing more than two order magnitude of selectivity over AChE. The study of binding kinetics through surface plasmon resonance (SPR) highlighted differences in their BChE residence times (8 and 47 s for 14c and 14d, respectively). Moreover, 14c and 14d proved to hit other mechanisms known to trigger neurodegeneration underlying AD and other CNS disorders. Unlike 14c, compound 14d proved also capable of inhibiting by more than 60% the in vitro self-induced aggregation of neurotoxic amyloid-β (Aβ) peptide at 100 μM concentration. On the other hand, 14c was slightly better than 14d in counteracting, at 1 and 10 μM concentration, glutamate excitotoxicity, due to over-excitation of NMDA receptors, and hydrogen peroxide-induced oxidative stress assessed in neuroblastoma cell line SH-SY5Y. This paper is dedicated to Prof. Marcello Ferappi, former dean of the Faculty of Pharmacy of the University of Bari, in the occasion of his 90th birthday.

Novel Dual-Acting Hybrids Targeting Type-2 Cannabinoid Receptors and Cholinesterase Activity Show Neuroprotective Effects In Vitro and Amelioration of Cognitive Impairment In Vivo

Alzheimer's disease (AD) is a neurodegenerative form of dementia characterized by the loss of synapses and a progressive decline in cognitive abilities. Among current treatments for AD, acetylcholinesterase (AChE) inhibitors have efficacy limited to symptom relief, with significant side effects and poor compliance. Pharmacological agents that modulate the activity of type-2 cannabinoid receptors (CB2R) of the endocannabinoid system by activating or blocking them have also been shown to be effective against neuroinflammation. Herein, we describe the design, synthesis, and pharmacological effects in vitro and in vivo of dual-acting compounds that inhibit AChE and butyrylcholinesterase (BChE) and target CB2R. Within the investigated series, compound 4g proved to be the most promising. It achieved IC50 values in the low micromolar to submicromolar range against both human cholinesterase isoforms while antagonizing CB2R with Ki of 31 nM. Interestingly, 4g showed neuroprotective effects on the SH-SY5Y cell line thanks to its ability to prevent oxidative stress-induced cell toxicity and reverse scopolamine-induced amnesia in the Y-maze forced alternation test in vivo.

A second life for MAO inhibitors? From CNS diseases to anticancer therapy

Monoamine oxidases A and B (MAO A, B) are ubiquitous enzymes responsible for oxidative deamination of amine neurotransmitters and xenobiotics. Despite decades of studies, MAO inhibitors (MAOIs) find today limited therapeutic space as second-line drugs for the treatment of depression and Parkinson's disease. In recent years, a renewed interest in MAOIs has been raised up by several studies investigating the role of MAOs, particularly MAO A, in tumor insurgence and progression, and the efficacy of MAOIs as coadjutants in the therapy of chemoresistant tumors. In this survey, we highlight the implication of MAOs in the biochemical pathways of tumorigenesis and review the state-of-the-art of preclinical and clinical studies of MAOIs as anticancer agents used in monotherapy or in combination with antitumor chemotherapeutics.

Radiosynthesis and whole-body distribution in mice of a 18 F-labeled azepino[4,3-b]indole-1-one derivative with multimodal activity for the treatment of Alzheimer's disease

Recently, the azepino[4,3-b]indole-1-one derivative 1 showed in vitro nanomolar inhibition against butyrylcholinesterase (BChE), the ChE isoform that plays a role in the progression and pathophysiology of Alzheimer's disease (AD), and protects against N-methyl- d-aspartate-induced neuronal toxicity. Three 9-R-substituted (R = F, Br, OMe) congeners were investigated. The 9-F derivative (2a) was found more potent as BChE inhibitors (half-maximal inhibitory concentration value = 21 nM) than 2b (9-Br) and 2c (9-OMe), achieving a residence time (38 s), assessed by surface plasmon resonance, threefold higher than that of 1. To progress in featuring the in vivo pharmacological characterization of 2a, herein the 18 F-labeled congener 2a was synthesized, by applying the aromatic 18 F-fluorination method, and its whole-body distribution in healthy mice, including brain penetration, was evaluated through positron emission tomography imaging. [18 F]2a exhibited a rapid and high brain uptake (3.35 ± 0.26% ID g-1 at 0.95 ± 0.15 min after injection), followed by a rapid clearance (t1/2  = 6.50 ± 0.93 min), showing good blood-brain barrier crossing. After a transient liver accumulation of [18 F]2a, the intestinal and urinary excretion was quantified. Finally, ex vivo pharmacological experiments in mice showed that the unlabeled 2a affects the transmitters' neurochemistry, which might be favorable to reverse cognition impairment in mild-to-moderate AD-related dementias.

A Critical Appraisal of the Protective Activity of Polyphenolic Antioxidants against Iatrogenic Effects of Anticancer Chemotherapeutics

Polyphenolic compounds, encompassing flavonoids (e.g., quercetin, rutin, and cyanidin) and non-flavonoids (e.g., gallic acid, resveratrol, and curcumin), show several health-related beneficial effects, which include antioxidant, anti-inflammatory, hepatoprotective, antiviral, and anticarcinogenic properties, as well as the prevention of coronary heart diseases. Polyphenols have also been investigated for their counteraction against the adverse effects of common anticancer chemotherapeutics. This review evaluates the outcomes of clinical studies (and related preclinical data) over the last ten years, with a focus on the use of polyphenols in chemotherapy as auxiliary agents acting against oxidative stress toxicity induced by antitumor drugs. While further clinical studies are needed to establish adequate doses and optimal delivery systems, the improvement in polyphenols' metabolic stability and bioavailability, through the implementation of nanotechnologies that are currently being investigated, could improve therapeutic applications of their pharmaceutical or nutraceutical preparations in tumor chemotherapy.

In-vitro and in-silico studies of annelated 1,4,7,8-tetrahydroazocine ester derivatives as nanomolar selective inhibitors of human butyrylcholinesterase

Based on previous finding showing 2,3,6,11-tetrahydro-1H-azocino[4,5-b]indole as suitable scaffold of novel inhibitors of acetylcholinesterase (AChE), a main target of drugs for the treatment of Alzheimer's disease and related dementias, herein we investigated diverse newly and previously synthesized β-enamino esters (and ketones) derivatives of 1,4,7,8-tetrahydroazocines (and some azonines) fused with benzene, 1H-indole, 4H-chromen-4-one and pyrimidin-4(3H)-one. Twenty derivatives of diversely annelated eight-to-nine-membered azaheterocyclic ring, prepared through domino reaction of the respective tetrahydropyridine and azepine with activated alkynes, were assayed for the inhibitory activity against AChE and butyrylcholinesterase (BChE). As a major outcome, compound 7c, an alkylamino derivative of tetrahydropyrimido[4,5-d]azocine, was found to be a highly potent BChE-selective inhibitor, which showed a noncompetitive/mixed-type inhibition mechanism against human BChE with single digit nanomolar inhibition constant (Ki = 7.8 ± 0.2 nM). The four-order magnitude BChE-selectivity of 7c clearly reflects the effect of lipophilicity upon binding to the BChE binding cavity. The ChEs' inhibition data, interpreted by chemoinformatic tools and an in-depth in-silico study (molecular docking combined with molecular dynamics calculations), not only highlighted key structural factors enhancing inhibition potency and selectivity toward BChE, but also shed light on subtle differences distinguishing the binding sites of equine BChE from the recombinant human BChE. Compound 7c inhibited P-glycoprotein with IC50 of 0.27 μM, which may support its ability to permeate blood-brain barrier, and proved to be no cytotoxic in human liver cancer cell line (HepG2) at the BChE bioactive concentrations. Overall, the biological profile allows us to envision 7c as a promising template to improve design and development of BChE-selective ligands of pharmaceutical interest, including inhibitors and fluorogenic probes.

Synthesis, computational and experimental pharmacological studies for (thio)ether-triazine 5-HT6R ligands with noticeable action on AChE/BChE and chalcogen-dependent intrinsic activity in search for new class of drugs against Alzheimer's disease

Alzheimer's disease is becoming a growing problem increasing at a tremendous rate. Serotonin 5-HT6 receptors appear to be a particularly attractive target from a therapeutic perspective, due to their involvement not only in cognitive processes, but also in depression and psychosis. In this work, we present the synthesis and broad biological characterization of a new series of 18 compounds with a unique 1,3,5-triazine backbone, as potent 5-HT6 receptor ligands. The main aim of this research is to compare the biological activity of the newly synthesized sulfur derivatives with their oxygen analogues and their N-demethylated O- and S-metabolites obtained for the first time. Most of the new triazines displayed high affinity (Ki < 200 nM) and selectivity towards 5-HT6R, with respect to 5-HT2AR, 5-HT7R, and D2R, in the radioligand binding assays. For selected, active compounds crystallographic studies, functional bioassays, and ADME-Tox profile in vitro were performed. The exciting novelty is that the sulfur derivatives exhibit an agonistic mode of action contrary to all other compounds obtained to date in this chemical class herein and previously reported. Advanced computational studies indicated that this intriguing functional shift might be caused by presence of chalcogen bonds formed only by the sulfur atom. In addition, the N-demethylated derivatives have emerged highly potent antioxidants and, moreover, show a significant improvement in metabolic stability compared to the parent structures. The cholinesterase study present micromolar inhibitory AChE and BChE activity for both 5-HT6 agonist 19 and potent antagonist 5. Finally, the behavioral experiments of compound 19 demonstrated its antidepressant-like properties and slight ability to improve cognitive deficits, without inducing memory impairments by itself. Described pharmacological properties of both compounds (5 and 19) allow to give a design clue for the development of multitarget compounds with 5-HT6 (both agonist and antagonist)/AChE and/or BChE mechanism in the group of 1,3,5-triazine derivatives.

Investigation on Novel E/Z 2-Benzylideneindan-1-One-Based Photoswitches with AChE and MAO-B Dual Inhibitory Activity

The multitarget therapeutic strategy, as opposed to the more traditional 'one disease-one target-one drug', may hold promise in treating multifactorial neurodegenerative syndromes, such as Alzheimer's disease (AD) and related dementias. Recently, combining a photopharmacology approach with the multitarget-directed ligand (MTDL) design strategy, we disclosed a novel donepezil-like compound, namely 2-(4-((diethylamino)methyl)benzylidene)-5-methoxy-2,3-dihydro-1H-inden-1-one (1a), which in the E isomeric form (and about tenfold less in the UV-B photo-induced isomer Z) showed the best activity as dual inhibitor of the AD-related targets acetylcholinesterase (AChE) and monoamine oxidase B (MAO-B). Herein, we investigated further photoisomerizable 2-benzylideneindan-1-one analogs 1b-h with the unconjugated tertiary amino moiety bearing alkyls of different bulkiness and lipophilicity. For each compound, the thermal stable E geometric isomer, along with the E/Z mixture as produced by UV-B light irradiation in the photostationary state (PSS, 75% Z), was investigated for the inhibition of human ChEs and MAOs. The pure E-isomer of the N-benzyl(ethyl)amino analog 1h achieved low nanomolar AChE and high nanomolar MAO-B inhibition potencies (IC50s 39 and 355 nM, respectively), whereas photoisomerization to the Z isomer (75% Z in the PSS mixture) resulted in a decrease (about 30%) of AChE inhibitory potency, and not in the MAO-B one. Molecular docking studies were performed to rationalize the different E/Z selectivity of 1h toward the two target enzymes.

Chemical and Biological Evaluation of Novel 1H-Chromeno[3,2-c]pyridine Derivatives as MAO Inhibitors Endowed with Potential Anticancer Activity

About twenty molecules sharing 1H-chromeno[3,2-c]pyridine as the scaffold and differing in the degree of saturation of the pyridine ring, oxidation at C10, 1-phenylethynyl at C1 and 1H-indol-3-yl fragments at C10, as well as a few small substituents at C6 and C8, were synthesized starting from 1,2,3,4-tetrahydro-2-methylchromeno[3,2-c]pyridin-10-ones (1,2,3,4-THCP-10-ones, 1) or 2,3-dihydro-2-methyl-1H-chromeno[3,2-c]pyridines (2,3-DHPCs, 2). The newly synthesized compounds were tested as inhibitors of the human isoforms of monoamine oxidase (MAO A and B) and cholinesterase (AChE and BChE), and the following main SARs were inferred: (i) The 2,3-DHCP derivatives 2 inhibit MAO A (IC₅₀ about 1 μM) preferentially; (ii) the 1,2,3,4-THCP-10-one 3a, bearing the phenylethynyl fragment at C1, returned as a potent MAO B inhibitor (IC₅₀ 0.51 μM) and moderate inhibitor of both ChEs (IC₅₀s 7-8 μM); (iii) the 1H-indol-3-yl fragment at C10 slightly increases the MAO B inhibition potency, with the analog 6c achieving MAO B IC₅₀ of 3.51 μM. The MAO B inhibitor 3a deserves further pharmacological studies as a remedy in the symptomatic treatment of Parkinson's disease and neuroprotectant for Alzheimer's disease. Besides the established neuroprotective effects of MAO inhibitors, the role of MAOs in tumor insurgence and progression has been recently reported. Herein, antiproliferative assays with breast (MCF-7), colon (HCT116) and cisplatin-resistant ovarian (SK-OV-3) tumor cells revealed that the 10-indolyl-bearing 2,3,4,10-THCP analog 6c exerts anti-tumor activity with IC₅₀s in the range 4.83-11.3 μM.

Hansch-Type QSAR Models for the Rational Design of MAO Inhibitors: Basic Principles and Methodology

Hansch-type regression analysis enables the derivation of quantitative structure-activity relationship (QSAR) equations correlating bioactivity data with physicochemical parameters accounting for hydrophobicity, electronic properties, and steric effects of molecules or functional groups (substituents). Two datasets of MAO A and B inhibitors were enrolled in prototypical workflows employing multiparametric stepwise regression analysis, which includes linear and nonlinear (generally quadratic) terms. The optimal choice of variables (and/or combinations thereof) along with statistical validation yielded two robust equations describing MAO B potency and B/A selectivity, which included three and one parameter(s), respectively, and explained more than 80% of y-variance (r²) with low standard deviation (s) and good statistical significance (F, Fisher value).

Exploring Mannosylpurines as Copper Chelators and Cholinesterase Inhibitors with Potential for Alzheimer's Disease

Alzheimer's Disease (AD) is characterized by a progressive cholinergic neurotransmission imbalance, with a decrease of acetylcholinesterase (AChE) activity followed by a significant increase of butyrylcholinesterase (BChE) in the later AD stages. BChE activity is also crucial for the development of Aβ plaques, the main hallmarks of this pathology. Moreover, systemic copper dyshomeostasis alters neurotransmission leading to AD. In the search for structures targeting both events, a set of novel 6-benzamide purine nucleosides was synthesized, differing in glycone configuration and N⁷/N⁹ linkage to the purine. Their AChE/BChE inhibitory activity and metal ion chelating properties were evaluated. Selectivity for human BChE inhibition required N⁹-linked 6-deoxy-α-d-mannosylpurine structure, while all three tested β-d-derivatives appeared as non-selective inhibitors. The N⁹-linked l-nucleosides were cholinesterase inhibitors except the one embodying either the acetylated sugar or the N-benzyl-protected nucleobase. These findings highlight that sugar-enriched molecular entities can tune bioactivity and selectivity against cholinesterases. In addition, selective copper chelating properties over zinc, aluminum, and iron were found for the benzyl and acetyl-protected 6-deoxy-α-l-mannosyl N^9-linked purine nucleosides. Computational studies highlight molecular conformations and the chelating molecular site. The first dual target compounds were disclosed with the perspective of generating drug candidates by improving water solubility.

Synthesis of Isomeric 3-Benzazecines Decorated with Endocyclic Allene Moiety and Exocyclic Conjugated Double Bond and Evaluation of Their Anticholinesterase Activity

Transformations of 1-methoxymethylethynyl substituted isoquinolines triggered by terminal alkynes in alcohols were studied and new 3-benzazecine-containing compounds synthesized, such as 6-methoxymethyl-3-benzazecines incorporating an endocyclic C6–C8 allene fragment and the -ylidene derivatives 6-methoxymethylene-3-benzazecines. The reaction mechanisms were investigated and a preliminary in vitro screening of their potential inhibitory activities against human acetyl- and butyrylcholinesterases (AChE and BChE) and monoamine oxidases A and B (MAO-A and MAO-B) showed that the allene compounds were more potent than the corresponding -ylidene ones as selective AChE inhibitors. Among the allenes, 3e (R³ = CH₂OMe) was found to be a competitive AChE inhibitor with a low micromolar inhibition constant value (K_i = 4.9 μM), equipotent with the corresponding 6-phenyl derivative 3n (R³ = Ph, K_i = 4.5 μM), but 90-fold more water-soluble.

Evaluation of Novel Guanidino-Containing Isonipecotamide Inhibitors of Blood Coagulation Factors against SARS-CoV-2 Virus Infection

Coagulation factor Xa (fXa) and thrombin (thr) are widely expressed in pulmonary tissues, where they may catalyze, together with the transmembrane serine protease 2 (TMPRSS2), the coronaviruses spike protein (SP) cleavage and activation, thus enhancing the SP binding to ACE2 and cell infection. In this study, we evaluate in vitro the ability of approved (i.e., dabigatran and rivaroxaban) and newly synthesized isonipecotamide-based reversible inhibitors of fXa/thr (cmpds 1-3) to hinder the SARS-CoV-2 infectivity of VERO cells. Nafamostat, which is a guanidine/amidine antithrombin and antiplasmin agent, disclosed as a covalent inhibitor of TMPRSS2, was also evaluated. While dabigatran and rivaroxaban at 100 μM concentration did not show any effect on SARS-CoV-2 infection, the virus preincubation with new guanidino-containing fXa-selective inhibitors 1 and 3 did decrease viral infectivity of VERO cells at subtoxic doses. When the cells were pre-incubated with 3, a reversible nanomolar inhibitor of fXa (K_i = 15 nM) showing the best in silico docking score toward TMPRSS2 (pdb 7MEQ), the SARS-CoV-2 infectivity was completely inhibited at 100 μM (p < 0.0001), where the cytopathic effect was just about 10%. The inhibitory effects of 3 on SARS-CoV-2 infection was evident (ca. 30%) at lower concentrations (3-50 μM). The covalent TMPRSS2 and the selective inhibitor nafamostat mesylate, although showing some effect (15-20% inhibition), did not achieve statistically significant activity against SARS-CoV-2 infection in the whole range of test concentrations (3-100 μM). These findings suggest that direct inhibitors of the main serine proteases of the blood coagulation cascade may have potential in SARS-CoV-2 drug discovery. Furthermore, they prove that basic amidino-containing fXa inhibitors with a higher docking score towards TMPRSS2 may be considered hits for optimizing novel small molecules protecting guest cells from SARS-CoV-2 infection.

Design, synthesis and biological evaluation of light-driven on-off multitarget AChE and MAO-B inhibitors

Neurodegenerative diseases are multifactorial disorders characterized by protein misfolding, oxidative stress, and neuroinflammation, finally resulting in neuronal loss and cognitive dysfunctions. Nowadays, an attractive strategy to improve the classical treatments is the development of multitarget-directed molecules able to synergistically interact with different enzymes and/or receptors. In addition, an interesting tool to refine personalized therapies may arise from the use of bioactive species able to modify their activity as a result of light irradiation. To this aim, we designed and synthesized a small library of cinnamic acid-inspired isomeric compounds with light modulated activity able to inhibit acetylcholinesterase (AChE) and monoamine oxidase B (MAO-B), with remarkable selectivity over butyrylcholinesterase (BChE) and MAO-A, which have been investigated as the enzyme targets related to Alzheimer's disease (AD). The inhibitory activities were evaluated for the pure E-diastereomers and the E/Z-diastereomer mixtures, obtained upon UV irradiation. Molecular docking studies were carried out to rationalize the differences in the inhibition potency of the E and Z diastereomers of the best performing analogue 1c. Our preliminary findings may open-up the way for developing innovative multitarget photo-switch drugs against neurodegenerative diseases.

Assessing the Role of a Malonamide Linker in the Design of Potent Dual Inhibitors of Factor Xa and Cholinesterases

The rational discovery of new peptidomimetic inhibitors of the coagulation factor Xa (fXa) could help set more effective therapeutic options (to prevent atrial fibrillation). In this respect, we explored the conformational impact on the enzyme inhibition potency of the malonamide bridge, compared to the glycinamide one, as a linker connecting the P1 benzamidine anchoring moiety to the P4 aryl group of novel selective fXa inhibitors. We carried out structure–activity relationship (SAR) studies aimed at investigating para- or meta-benzamidine as the P1 basic group as well as diversely decorated aryl moieties as P4 fragments. To this end, twenty-three malonamide derivatives were synthesized and tested as inhibitors of fXa and thrombin (thr); the molecular determinants behind potency and selectivity were also studied by employing molecular docking. The malonamide linker, compared to the glycinamide one, does significantly increase anti-fXa potency and selectivity. The meta-benzamidine (P1) derivatives bearing 2′,4′-difluoro-biphenyl as the P4 moiety proved to be highly potent reversible fXa-selective inhibitors, achieving inhibition constants (K_i) in the low nanomolar range. The most active compounds were also tested against cholinesterase (ChE) isoforms (acetyl- or butyrylcholinesterase, AChE, and BChE), and some of them returned single-digit micromolar inhibition potency against AChE and/or BChE, both being drug targets for symptomatic treatment of mild-to-moderate Alzheimer’s disease. Compounds 19h and 22b were selected as selective fXa inhibitors with potential as multimodal neuroprotective agents.

Probing Fluorinated Motifs onto Dual AChE-MAO B Inhibitors: Rational Design, Synthesis, Biological Evaluation, and Early-ADME Studies

Bioisosteric H/F or CH₂OH/CF₂H replacement was introduced in coumarin derivatives previously characterized as dual AChE-MAO B inhibitors to probe the effects on both inhibitory potency and drug-likeness. Along with in vitro screening, we investigated early-ADME parameters related to solubility and lipophilicity (Sol_7.4, CHI_7.4, log D_7.4), oral bioavailability and central nervous system (CNS) penetration (PAMPA-HDM and PAMPA-blood-brain barrier (BBB) assays, Caco-2 bidirectional transport study), and metabolic liability (half-lives and clearance in microsomes, inhibition of CYP3A4). Both specific and nonspecific tissue toxicities were determined in SH-SY5Y and HepG2 lines, respectively. Compound 15 bearing a -CF₂H motif emerged as a water-soluble, orally bioavailable CNS-permeant potent inhibitor of both human AChE (IC₅₀ = 550 nM) and MAO B (IC₅₀ = 8.2 nM, B/A selectivity > 1200). Moreover, 15 behaved as a safe and metabolically stable neuroprotective agent, devoid of cytochrome liability.

Away from Flatness: Unprecedented Nitrogen-Bridged Cyclopenta[a]indene Derivatives as Novel Anti-Alzheimer Multitarget Agents

Nature-inspired, bridged polycyclic molecules share low similarity with currently available drugs, containing preferentially planar and/or achiral moieties. This "Escape from Flatland" scenario, aimed at exploring pharmacological properties of atypical molecular scaffolds, finds interest in synthetic routes leading to tridimensional-shaped molecules. Herein we report on the synthesis of N-bridged cyclopenta[a]indene derivatives, achieved through microwave-assisted thermal rearrangement of allene 3-benzazecines with high diastereoselectivity. The biological evaluation disclosed selective inhibition of human acetylcholinesterase or butyrylcholinesterase, depending on the substitution around the molecular core, which was rationalized by means of docking simulations. The most potent BChE inhibitor 31 was effective in neuroprotection from glutamatergic excitotoxicity and displayed low intrinsic cytotoxicity and good brain penetration. Overall, compound 31 and its close congeners 34 and 35 acted as multitarget agents addressing different biological events involved in neurodegeneration, particularly in the progression of Alzheimer's disease.

Pharmacophore Modeling and 3D-QSAR Study of Indole and Isatin Derivatives as Antiamyloidogenic Agents Targeting Alzheimer's Disease

Thirty-six novel indole-containing compounds, mainly 3-(2-phenylhydrazono) isatins and structurally related 1H-indole-3-carbaldehyde derivatives, were synthesized and assayed as inhibitors of beta amyloid (Aβ) aggregation, a hallmark of pathophysiology of Alzheimer’s disease. The newly synthesized molecules spanned their IC₅₀ values from sub- to two-digit micromolar range, bearing further information into structure-activity relationships. Some of the new compounds showed interesting multitarget activity, by inhibiting monoamine oxidases A and B. A cell-based assay in tau overexpressing bacterial cells disclosed a promising additional activity of some derivatives against tau aggregation. The accumulated data of either about ninety published and thirty-six newly synthesized molecules were used to generate a pharmacophore hypothesis of antiamyloidogenic activity exerted in a wide range of potencies, satisfactorily discriminating the ‘active’ compounds from the ‘inactive’ (poorly active) ones. An atom-based 3D-QSAR model was also derived for about 80% of ‘active’ compounds, i.e., those achieving finite IC₅₀ values lower than 100 μM. The 3D-QSAR model (encompassing 4 PLS factors), featuring acceptable predictive statistics either in the training set (n = 45, q² = 0.596) and in the external test set (n = 14, r²_ext = 0.695), usefully complemented the pharmacophore model by identifying the physicochemical features mainly correlated with the Aβ anti-aggregating potency of the indole and isatin derivatives studied herein.

Evaluation of Water-Soluble Mannich Base Prodrugs of 2,3,4,5-Tetrahydroazepino[4,3-b]indol-1(6H)-one as Multitarget-Directed Agents for Alzheimer's Disease

Different Mannich base derivatives have been studied with the aim of addressing the poor aqueous solubility of the recently disclosed 6-phenethyl-2,3,4,5-tetrahydroazepino[4,3-b]indol-1(6H)-one (1), a human butyrylcholinesterase inhibitor (hBChE, IC₅₀ 13 nM) and protective agent in NMDA-induced neurotoxicity, in in vivo assays. The N-(4-methylpiperazin-1-yl)methyl derivative 2 c showed a 50-fold increase in solubility in pH 7.4-buffered solution, high stability in serum and (half-life >24 h) and rapid (<3 min) conversion to 1 at acidic pH. Although less active than 1, 2 c retained moderate hBChE inhibition (IC₅₀ =3.35 μM) and a significant protective effect against NMDA-induced neurotoxicity at 0.1 μM. Moreover, 2 c resulted a weaker serum albumin binder than 1, could pass the blood-brain barrier, and exerted negligible cytotoxicity on HepG2 cells. These findings suggest that 2 c could be a water-soluble prodrug candidate of 1 for oral administration or a slow-release injectable derivative in in vivoAlzheimer's disease models.

Interplay between Ionization and Tautomerism in Bioactive β-Enamino Ester-Containing Cyclic Compounds: Study of Annulated 1,2,3,6-Tetrahydroazocine Derivatives

Depending on the chemical scaffold, a bioactive species could reflect the interplay between ionization and tautomerism, which is often complicated by the possibility of populating different conformational states, in the case of flexible ligands. In this context, theoretical methods can be valuable to discern the role of these factors, as shown here for β-enamino esters of 1,2,3,6-tetrahydroazocino-fused ring systems, some of which had proven to be suitable scaffolds for designing novel acetylcholinesterase inhibitors. The compounds investigated herein form two clusters with distinctive experimental pK_a values (i.e., α,β-diesters and β-esters ranging within 6.1-7.3 and 8.2-9.0 pK_a intervals, respectively), which implies a drastic difference in the most populated species at physiological conditions. While chemoinformatic tools did not provide a consistent description of the actual pK_a values, the theoretical analysis performed for the protonated and neutral species of these compounds revealed a marked change in the tautomeric preference of the tetrahydroazocine moiety upon (de)protonation. Excellent agreement between the calculated and experimental pK_a values was found when the tautomeric preference of the protonated and neutral species was considered. Overall, this study highlights the potential use of high-level computational methods to disclose the mutual influence between ionization, tautomerism, and conformational preferences in multifunctional (bio)organic compounds.

Chasing ChEs-MAO B Multi-Targeting 4-Aminomethyl-7-Benzyloxy-2H-Chromen-2-ones

A series of 4-aminomethyl-7-benzyloxy-2H-chromen-2-ones was investigated with the aim of identifying multiple inhibitors of cholinesterases (acetyl- and butyryl-, AChE and BChE) and monoamine oxidase B (MAO B) as potential anti-Alzheimer molecules. Starting from a previously reported potent MAO B inhibitor (3), we studied single-point modifications at the benzyloxy or at the basic moiety. The in vitro screening highlighted triple-acting compounds (6, 8, 9, 16, 20) showing nanomolar and selective MAO B inhibition along with IC50 against ChEs at the low micromolar level. Enzyme kinetics analysis toward AChE and docking simulations on the target enzymes were run in order to get insight into the mechanism of action and plausible binding modes.

Investigating 1,2,3,4,5,6-hexahydroazepino[4,3-b]indole as scaffold of butyrylcholinesterase-selective inhibitors with additional neuroprotective activities for Alzheimer's disease

Due to the role of butyrylcholinesterase (BChE) in acetylcholine hydrolysis in the late stages of the Alzheimer's disease (AD), inhibitors of butyrylcholinesterase (BChE) have been recently envisaged, besides acetylcholinesterase (AChE) inhibitors, as candidates for treating mild-to-moderate AD. Herein, synthesis and AChE/BChE inhibition activity of some twenty derivatives of 1,2,3,4,5,6-hexahydroazepino[4,3-b]indole (HHAI) is reported. Most of the newly synthesized HHAI derivatives achieved the inhibition of both ChE isoforms with IC₅₀s in the micromolar range, with a structure-dependent selectivity toward BChE. Apparently, molecular volume and lipophilicity do increase selectivity toward BChE, and indeed the N²-(4-phenylbutyl) HHAI derivative 15d, which behaves as a mixed-type inhibitor, resulted the most potent (IC₅₀ 0.17 μM) and selective (>100-fold) inhibitor toward either horse serum and human BChE. Moreover, 15d inhibited in vitro self-induced aggregation of neurotoxic amyloid-β (Aβ) peptide and displayed neuroprotective effects in neuroblastoma SH-SY5Y cell line, significantly recovering (P < 0.001) cell viability when impaired by Aβ_1-42 and hydrogen peroxide insults. Overall, this study highlighted HHAI as useful and versatile scaffold for developing new small molecules targeting some enzymes and biochemical pathways involved in the pathogenesis of AD.

A New Class of 1-Aryl-5,6-dihydropyrrolo[2,1-a]isoquinoline Derivatives as Reversers of P-Glycoprotein-Mediated Multidrug Resistance in Tumor Cells

A number of aza-heterocyclic compounds, which share the 5,6-dihydropyrrolo[2,1-a]isoquinoline (DHPIQ) scaffold with members of the lamellarin alkaloid family, were synthesized and evaluated for their ability to reverse in vitro multidrug resistance in cancer cells through inhibition of P-glycoprotein (P-gp) and/or multidrug-resistance-associated protein 1. Most of the investigated DHPIQ compounds proved to be selective P-gp modulators, and the most potent modulator, 8,9-diethoxy-1-(3,4-diethoxyphenyl)-3-(furan-2-yl)-5,6-dihydropyrrolo[2,1-a]isoquinoline-2-carbaldehyde, attained sub-micromolar inhibitory potency (IC₅₀ : 0.19 μm). Schiff bases prepared by the condensation of some 1-aryl-DHPIQ aldehydes with p-aminophenol also proved to be of some interest, and one of them, 4-((1-(4-fluorophenyl)-5,6-dihydro-8,9-dimethoxypyrrolo[2,1-a]isoquinolin-2-yl)methyleneamino)phenol, had an IC₅₀ value of 1.01 μm. In drug combination assays in multidrug-resistant cells, some DHPIQ compounds, at nontoxic concentrations, significantly increased the cytotoxicity of doxorubicin in a concentration-dependent manner. Studies of structure-activity relationships and investigation of the chemical stability of Schiff bases provided physicochemical information useful for molecular optimization of lamellarin-like cytotoxic drugs active toward chemoresistant tumors as well as nontoxic reversers of P-gp-mediated multidrug resistance in tumor cells.

Delivery of Proapoptotic Agents in Glioma Cell Lines by TSPO Ligand-Dextran Nanogels

Translocator protein 18-kDa (TSPO) is a versatile mitochondrial target for molecular imaging and therapy. Moreover, selective TSPO ligands have been widely investigated for diagnostic purposes and explored to target drug delivery systems directed to cancer cells overexpressing TSPO. Indeed, poly(d,l-lactic-co-glycolic acid (PLGA) polymers and nanocarriers decorated with TSPO ligands are capable of transporting TSPO ligands inside cancer cells, inducing survival inhibition in cancer cells and producing mitochondrial morphology modification. The aim of this work was to prepare nanogels (NGs) made with TSPO ligand dextran conjugates (TSPO-Dex) that are useful as potential delivery systems of two TSPO ligands as apoptotic agents. Synthesis and complete characterization of TSPO–dextran conjugates, an average molecular weights analysis, TSPO ligand release profiles, thermal behaviour and swelling studies were achieved. NG preparation, characterization and in vitro biological studies were also performed. The release of TSPO ligands released from dextran conjugates at 37 °C occurred in human serum at a faster rate than that detected in phosphate buffer. Cytotoxicity studies demonstrated that NGs produced from TSPO ligand–dextran conjugates induce survival inhibition in rat C6 glioma cell lines. Cellular uptake was also proven by fluorescence microscopy.

Oxazepam-Dopamine Conjugates Increase Dopamine Delivery into Striatum of Intact Rats

The neurotransmitter dopamine (DA) was covalently linked to oxazepam (OXA), a well-known positive allosteric modulator of γ-aminobutyric acid type-A (GABA_A) receptor, through a carbamate linkage (4) or a succinic spacer (6). These conjugates were synthesized with the aim of improving the delivery of DA into the brain and enhancing GABAergic transmission, which may be useful for the long-term treatment of Parkinson disease (PD). Structure-based permeability properties, in vitro stability, and blood-brain barrier (BBB) permeability studies led to identify the OXA-DA carbamate conjugate 4a as the compound better combining sufficient stability and ability to cross BBB. Finally, in vivo microdialysis experiments in freely moving rats demonstrated that 4a (20 mg/kg, i.p.) significantly increases extracellular DA levels into striatum, with a peak (more than 15-fold increase over the baseline) at about 80 min after a single administration. The stability and delivery data proved that 4a may be a promising candidate for further pharmacological studies in animal models of PD.

The position of fluorine in CP-118,954 affects AChE inhibition potency and PET imaging quantification for AChE expression in the rat brain

The in vitro inhibition potency against acetylcholinesterase (AChE) of fluorinated derivatives of CP-118,954 (1) has been shown to depend upon the position of aromatic fluorine (F) substitution on the N-benzyl moiety. Indeed, the meta-F-substituted compound 3 (IC₅₀=1.4nM) shows similar potency with the parent compound 1 (IC₅₀=1.2nM), whereas the ortho-F derivative 2 (IC₅₀=3.2nM) and para-F derivative 4 (IC₅₀=10.8nM) were found to be less potent AChE inhibitors. A comparative in vivo microdialysis study in rats showed that 3 has the strongest effect on the neuropharmacological properties as AChE inhibitor. For PET imaging studies, a radiolabeled ligand ([¹⁸F]3) was synthesized through nucleophilic aromatic substitution reaction of diaryliodonium salt-based aldehyde precursor followed by reductive alkylation in a two-step radiolabeling procedure with 11.5 ± 1.2% (n=24, non-decay corrected) radiochemical yield and over 99% radiochemical purity. In a comparative PET imaging study of the three ¹⁸F-containing derivatives of CP-118,954 ([¹⁸F]2-4), [¹⁸F]3 showed the highest radioactivity in the AChE-rich region of normal rat brain which visually reflected the in vitro AChE-binding affinity of 3. These findings support [¹⁸F]3 as a promising AChE-targeted PET imaging ligand for the assessment of cholinergic activity into the brain, providing also insights into the AChE ligand disposition, which depends upon the position of the aromatic fluorine in the benzyl moiety.

Investigating Structural Requirements for the Antiproliferative Activity of Biphenyl Nicotinamides

A number of trimethoxybenzoic acid anilides, previously studied as permeability glycoprotein (P-gp) modulators, were screened with the aim of identifying new anticancer agents. One of these compounds, which showed antiproliferative activity against resistant MCF-7 cell line, was selected as the hit structure. Replacement of the trimethoxybenzoyl moiety with a nicotinoyl group, in order to overcome solubility issues, led to a new series of N-biphenyl nicotinoyl anilides, among which a nitro derivative, N-(3',5'-difluoro-3-nitro-[1,1'-biphenyl]-4-yl)nicotinamide (3), displayed antiproliferative activity against MCF-7 and MDA-MB-231 cells in the nanomolar range. The search for a bioisostere of the nitro group led to nitrile analogue N-(3-cyano-4'-fluoro-[1,1'-biphenyl]-4-yl)nicotinamide (36), which shows a strong increase in activity against MCF-7 and MDA-MB-231 cells. Compound 36 induced a dose-dependent accumulation of G₂ - and M-phase MCF-7 cell populations, and a decrease in S-phase cells. Relative to vinblastine, a well-known potent antimitotic agent, compound 36 also induced G₁ -phase arrest at low doses (20-40 nm), but did not inhibit in vitro tubulin polymerization.

A greener and efficient access to substituted four- and six-membered sulfur-bearing heterocycles

The regioselective functionalization of four- and six-membered cyclic sulfones was investigated using a lithiation/functionalization strategy.

Galloyl benzamide-based compounds modulating tumour necrosis factor α-stimulated c-Jun N-terminal kinase and p38 mitogen-activated protein kinase signalling pathways

OBJECTIVES

The aim of this work is to investigate whether and how two newly synthesized 3,4,5-trimethoxygalloyl-containing compounds 1 and 3 interfere with the mitogen-activated protein kinase (MAPK) signalling pathways involved in several pathological events, ranging from inflammatory diseases to cancer.

METHODS

The effects on the phosphorylation of MAP kinases (c-Jun N-terminal kinases (JNKs), p38) and activation of nuclear factor-kappa B (NF-κB) pathways of 1 and its 1H-indazole-containing analogue 3, compared with those elicited by the known Adenosine Triphosphate (ATP)-competitive JNK inhibitor SP600125, were evaluated through Western blot analysis in murine fibroblasts NIH-3T3 and human endothelial cells EA.hy926 acutely treated with tumour necrosis factor-α (TNF-α). Their effects on cell viability were also assessed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay.

KEY FINDINGS

In cultured murine fibroblasts, 1 inhibited JNK signalling with a different mechanism from SP600125. It reduced c-Jun phosphorylation without altering phosphorylation levels of JNK protein. Compound 3, showing a profile similar to SP600125, inhibited JNK phosphorylation and partially inhibited p38 MAPK at 50 μm concentration. Compound 3 and SP600125 showed similar behaviour in both cell cultures. In contrast, compound 1 in EA.hy926 cells significantly interfered with JNK phosphorylation, did not decrease phosphorylation of c-Jun (Ser73), whereas significantly suppressed phosphorylation of p38 MAPK and reversed degradation of NF-κB signalling components.

CONCLUSIONS

3,4,5-Trimethoxygalloyl-based compounds 1 and 3, which did not show significant cell toxicity, modulate the TNF-α-induced activation of MAPK signalling, mainly inhibiting phosphorylation of JNK, c-Jun and p38 MAPK, in murine fibroblasts and human endothelial cells with different MAPK selectivity profiles. These compounds deserve future investigation in specific cell-based disease models and in-vivo pharmacology.

Synthesis and biological evaluation of direct thrombin inhibitors bearing 4-(piperidin-1-yl)pyridine at the P1 position with potent anticoagulant activity

The design and synthesis of a new class of nonpeptide direct thrombin inhibitors, built on the structure of 1-(pyridin-4-yl)piperidine-4-carboxamide, are described. Starting from a strongly basic 1-amidinopiperidine derivative (6) showing poor thrombin (fIIa) and factor Xa (fXa) inhibition activities, anti-fIIa activity and artificial membrane permeability were considerably improved by optimizing the basic P1 and the X-substituted phenyl P4 binding moieties. Structure-activity relationship studies, usefully complemented with molecular modeling results, led us to identify compound 13b, which showed excellent fIIa inhibition (Ki = 6 nM), weak anti-Xa activity (Ki = 5.64 μM), and remarkable selectivity over other serine proteases (e.g., trypsin). Compound 13b showed in vitro anticoagulant activity in the low micromolar range and significant membrane permeability. In mice (ex vivo), 13b demonstrated anticoagulant effects at 2 h after oral dosing (100 mg·kg(-1)), with a significant 43% prolongation of the activated partial thromboplastin time (aPTT), over controls (P < 0.05).

Targeting of the translocator protein 18 kDa (TSPO): a valuable approach for nuclear and optical imaging of activated microglia

The aim of the present review is to give a concise and updated analysis of the imaging tools for the visualization of activated microglia. After an overview on the important pathologies where activated microglia are involved, we first describe the role played by the translocator protein-18 kDa (TSPO) as an important target for the visualization of activated microglia. Second, imaging tools based on TSPO ligands radiolabeled for positron emission tomography (PET) are summarized with particular emphasis to the TSPO ligands alternative to the standard radioligand [(11)C]PK11195 or (R)-[(11)C]PK11195. In this regard, an updated list of (11)C- and (18)F-labeled TSPO radioligands is shown. Moreover, a detailed analysis based on TSPO ligands bearing fluorescent probes for fluorescence microscopy is also provided. This last optical imaging technique represents an area of large and increasing interest due to the advantages offered by the use of simple instrumentation and safer experimental conditions. The scope and limitations of the nuclear and optical imaging techniques are discussed. Finally, a perspective on the plausible advances in this area is also presented.

Biarylmethoxy isonipecotanilides as potent and selective inhibitors of blood coagulation factor Xa

New chloro-substituted biarylmethoxyphenyl piperidine-4-carboxamides were synthesized and assayed in vitro as inhibitors of the blood coagulation enzymes factor Xa (fXa) and thrombin. An investigation of effects of the amidine and isopropyl groups attached at the piperidine nitrogen and 5-(halogenoaryl)isoxazol-3-yl groups as biaryl substituents led us to identify new compounds which proved to be selective fXa inhibitors, with inhibition constants in the low nanomolar range. The most potent compound 21e, that incorporates 2-Cl-thiophen-5-yl group as the P1 motif and 1-isopropylpiperidine P4 group, inhibited fXa with K(i) value of 0.3nM and very high selectivity over thrombin and some other tested serine proteases, achieving moderate levels of anticoagulant activity in the low micromolar range, as assessed by the prothrombin time clotting assay (PT(2)=3.30μM). Based on reliable docking simulations, molecular modeling provided a rationale for interpreting structure-activity relationships. The predicted binding modes highlighted the structural requirements for addressing the subsites S1 and S4 of the fXa enzyme.

Novel factor Xa inhibitors: a patent review

IMPORTANCE OF THE FIELD

New oral anticoagulants with favorable safety profiles and fixed doses are required for the management of thromboembolism and stroke prevention in patients with atrial fibrillation. Among them, fXa inhibitors (the so-called xabans) are attractive options that can overcome limitations (e.g., bleeding) of the current oral antithrombotic therapy. The rational design of small-molecule direct fXa inhibitors, whose importance is testified by the growing number of publications and patents recently registered, has been fully supported by the X-ray crystallography of enzyme-ligand complexes.

AREAS COVERED IN THIS REVIEW

Pubmed, SciFinder Scholar, ISI web of knowledge(SM), http://ep.espacenet.com/ and Google websites were used as the main sources for literature retrieving, and > 100 patents filed between 2006 and April 2009, reviewed and discussed herein, highlight the variety among the P1 and P4 moieties on suitable scaffolds.

WHAT THE READER WILL GAIN

The replacement of the benzamidine P1 moiety, which characterizes the first generation, with less basic bioisosteric or nonpolar neutral P1 groups led to the disclosure of numerous fXa inhibitors with high potency, selectivity and oral bioavailability. Novel selective fXa inhibitors with stable pharmacokinetics, better therapeutic windows and ease-of-use than the existing anticoagulants are currently under advanced stage clinical trials.

TAKE-HOME MESSAGE

Available data from Phase II and Phase III studies reflect the drive towards fXa inhibitors as potentially more effective and safer antithrombotic drugs. Their development is expected to address two major needs for anticoagulation, namely safety and ease-of-use, and to significantly affect the anticoagulant market.

Ester derivatives of annulated tetrahydroazocines: A new class of selective acetylcholinesterase inhibitors

A series of ester derivatives of annulated tetrahydroazocines, namely 2,3,6,11-tetrahydro-1H-azocino[4,5-b]indoles (5-10), 2,3,6,7-tetrahydro-1H-azocino[5,4-b]indoles (11-14), and 4,7,8,9-tetrahydro-1H-pyrrolo[2,3-d]azocines (15-18), synthesized through an efficient 6-->8 membered ring expansion procedure, were investigated for their acetylcholinesterase (AChE) inhibitory activities. Most of the compounds acted as AChE inhibitors in vitro, with IC(50) values ranging from 5 to 40 microM. The most potent compounds 11 and 15, both as racemic mixtures, proved selective toward AChE, exhibiting selectivity ratios versus butyrylcholinesterase (BuChE) of ca. 15 and more than 20, respectively. Structure-activity studies highlighted, among other factors, lipophilicity as a property modulating the AChE inhibition potency, as shown by a reasonable parabolic correlation between pIC(50) and experimental 1-octanol/water partition coefficient (logP), which described the prevailing behavior of the examined compounds (r(2)=0.665). Molecular docking simulations using the X-ray crystal structure of AChE from Torpedo californica suggested possible binding modes of the tetrahydroazocine ester derivatives 11 and 15.

Insights into structure-activity relationships from lipophilicity profiles of pyridin-2(1H)-one analogs of the cardiotonic agent milrinone

The pH-dependent distribution profiles of a series of pyridin-2(1H)-one analogs of the inotropic/vasodilator agent milrinone, determined in 1-octanol/water (and for a number of them also in chloroform-water) using a pH-metric technique, showed that partition coefficients of the neutral forms (logP(N)) significantly encode for 2-pyridone/2-hydroxypyridine tautomerism. A comparison between experimental and calculated logP (CLOG P) values indicated that electron-withdrawing substituents, at the C(6) position, and to a lesser extent at the C(3) and C(5) positions, push up logPs toward the values of the more lipophilic 2-hydroxypyridine tautomers. RP-HPLC parameters (log k'omega) carry for large part similar information related to tautomerism-dependent lipophilicity, but they were also found to reasonably correlate with the solute molar volumes (r2 = 0.75). Investigating the implications of ionization and partition properties in modulating the in vitro cardiotonic activity of the examined compounds revealed that a high fraction of the neutral species at physiological pH, predominantly in the more polar pyridone (OX) tautomer, increases the positive inotropic potency.

Investigation of platelet aggregation inhibitory activity by phenyl amides and esters of piperidinecarboxylic acids

A series of anilides and phenyl esters of piperidine-3-carboxylic acid (nipecotic acid) were synthesized and tested for the ability to inhibit aggregation of human platelet rich-plasma triggered by adenosine 5'-diphosphate (ADP) and adrenaline. As a rule, amides were about two times more active than the corresponding esters, and derivatives bearing substituents at the para position of the phenyl ring were significantly more active than the meta-substituted ones. Among the tested compounds, 4-hexyloxyanilide of nipecotic acid (18a) was found to be the most active one, its IC(50) value being close to that of the most active bis-3-carbamoylpiperidines reported in literature (ca. 40 micro M) and aspirin (ca. 60 microM) in ADP- and adrenaline-induced aggregation, respectively. Compared with the isomeric 4-hexyloxyanilides of piperidine-2-carboxylic (pipecolinic) and piperidine-4-carboxylic (isonipecotic) acids, compound 18a showed higher activity, and a Hansch-type quantitative structure-activity relationship (QSAR) study highlighted lipophilicity and increase in electron density of the phenyl ring as the properties which mainly increase the antiplatelet activity (r(2)=0.74, q(2)=0.64). The interaction of nipecotoyl anilides with phosphatidylinositol, a major component of the inner layer of the platelet membranes, was investigated by means of flexible docking calculation methods to give an account of a key event underlying their biological action.

Investigation on the antiplatelet activity of pyrrolo[3,2-c]pyridine-containing compounds

A series of 4,5,6,7-tetrahydro-1H-pyrrolo[3,2-c]pyridines (THPPs), mostly C(2)-substituted derivatives, and some 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indoles (THPIs) were synthesized and tested in-vitro for their ability to inhibit aggregation of human platelet-rich plasma (PRP) induced by adenosine 5'-diphosphate (ADP) and adrenaline (epinephrine). 5-Benzyl THPP (3), 2-(benzylamino)methyl THPP (5f) and 2-ethyl THPI (6) moderately and dose-dependently inhibited platelet aggregation induced by adrenaline and, to a lesser extent, by ADP. These compounds inhibited the second phase of the PRP aggregation triggered by adrenaline, which largely depends upon thromboxane A(2) production and ADP release. In the adrenaline stimulated aggregation, the THPI derivative 6 was found to be nearly equipotent with aspirin, their IC50 values (concentration effecting 50% inhibition of aggregation) being 90 and 60 microM, respectively. A relation between activity and calculated octanol-water partition coefficient suggested that a log P value around 2.5 should be the optimal lipophilicity value for the activity of THPP-containing compounds.