Synthesis and SAR study of acridine, 2-methylquinoline and 2-phenylquinazoline analogues as anti-prion agents

Transmissible spongiform encephalopathies (TSEs) are thought to arise from aggregation of a protease resistant protein denoted PrP(Sc), which is a misfolded isoform of the normal cellular prion protein PrP(C). Using virtual high-throughput screening we have selected structures analogous to acridine, 2-methyquinoline and 2-phenylquinazoline as potential therapeutic candidates for the treatment of TSEs. From the synthesis and screening of constructed libraries we have shown that an electron-rich aromatic ring attached through an amine linker to the position para to the ring nitrogen is beneficial to both binding to PrP(C) and the suppression of PrP(Sc) accumulation for acridine and 2-methylquinoline analogues. 2-Phenylquinazoline analogues appear to utilise a different mode of action by binding at a different location and/or pose. We report IC50s in the nanomolar range.     

Synthesis and biological evaluation of helicid analogues as novel acetylcholinesterase inhibitors

A series of helicid analogues were prepared and evaluated in vitro for the cholinesterase (AChE and BuChE) inhibitory activities via UV spectroscopy. The results indicated that compounds 5, 6d and 8 exhibited potent AChE inhibitory activities with IC(50) values of 0.45+/-0.02microM, 0.49+/-0.02microM, and 0.20+/-0.01microM, respectively. High selectivity for AChE over BuChE was also observed. Kinetic study showed that the mechanism of AChE inhibition of compounds 5, 6d and 8 was all mixed-type.     

Synthesis and in vitro evaluation of new analogues as inhibitors for phosphodiesterase 10A

A series of analogues were synthesized by optimizing the structure of papaverine. The in vitro PDE10A binding affinity (IC₅₀) values for these new analogues were measured; for compounds that have IC₅₀ value less than 60 nM for PDE10A, the binding affinities (IC₅₀ value) for PDE3A and PDE3B were tested. Of these analogues, compounds 6a, 6b, 6n, 8b, 8c and 11 displayed relatively higher PDE10A potency with IC₅₀ value in the range of 28-60 nM. The most potent compound 1-(4-(2-(2-fluoroethoxy)ethoxy)-3-methoxybenzyl)-6,7-dimethoxyisoquinoline (8c) has the IC₅₀ value of 28 ± 1.2 nM for PDE10A, 2200 ± 437 nM for PDE3A and 2520 ± 210 nM for PDE3B. Compared to papaverine, compound 8c displayed similar PDE10A potency but improved selectivity to PDE10A versus PDE3A and PDE3B. To identify high potent PDE10A inhibitor, further optimization of the structures of these analogues is necessary.     

Synthesis of 3-substituted-2-oxoindole analogues and their evaluation as kinase inhibitors, anticancer and antiangiogenic agents

Several analogues of the 3-substituted-2-oxoindole chemotype were synthesized by condensing isatin or the appropriate haloisatin with some amino acids or histamine under neutral conditions. All the imino derivatives produced were tested for kinase inhibitory properties against three serine/threonine kinases, namely CDK1/cyclin B, CDK5/p25 and GSK3alpha/beta. Most of the histidine derivatives showed inhibitory properties to the three kinases in the low micromolar range. The histamine derivatives were less potent against CDK1/cyclin B and CDK5/p25 and totally inactive against GSK3alpha/beta. So, the management of the carboxyl function may be a tool to impart selectivity in such family of kinases. Docking of 2-[[-5-bromo-2-oxoindolin-3-ylidene]amino]-3-(1H-imidazol2-yl)propanoic acid 14 to CDK5/p25 indicates that this compound can interact with the enzyme through four hydrogen bonds; for GSK/3beta, the ligand poses itself in another orientation, also four hydrogen bonds can be formed between the ligand and the receptor, otherwise hydrophobic interactions seem to predominate. Also, all the final compounds were tested for their in vitro antitumor properties against MCF7 (breast), NCI-H460 (lung) and SF268 (CNS) cancer cell lines. None of the synthesized compounds was cytotoxic at 10(-4) molar concentration. Moreover, compounds 13 and 14 were tested for potential antiangiogenic properties by testing their ability to inhibit the proliferation of human umbilical vein endothelial cells (HUVECs), cord formation and migration in response to chemoattractant. Only compound 14 showed moderate inhibitory properties to HUVECs proliferation and cord formation while its non-brominated derivative 13 did not. Thus, the antiangiogenesis properties are not apparently caused by inhibition of any of the tested kinases.     

Synthesis and biological evaluation of new derivatives of 2-substituted 4-hydroxybutanamides as GABA uptake inhibitors

This study presents the synthesis of novel substituted 4-hydroxybutanamides and their influence on the activity of murine GABA transport proteins GAT1-GAT4. The active compounds, derivatives of N-arylalkyl-2-(4-diphenylmethylpiperazin-1-yl)-4-hydroxybutyramide, are characterized by pIC₅₀ values in range of 3.92-5.06 and by slight subtype-selectivity. Among them N-4-chlorobenzylamide was the most potent GAT inhibitor (mGAT3), while N-benzylamide was the most active in GAT1-binding assay (pK_i = 4.96). The results pointed out that benzhydryl and benzylamide moieties are crucial for the activity of this class of compounds as murine GAT inhibitors.     

Design, synthesis and docking studies of new quinoline-3-carbohydrazide derivatives as antitubercular agents

Three new series of 4-hydroxy-8-trifluoromethyl-quinoline derivatives were synthesized through multi step reactions. All the newly synthesized compounds were characterized by spectral and elemental analyses. The structure of 5j was evidenced by X-ray crystallographic study. The newly synthesized title compounds were evaluated for their antimicrobial activities including antimycobacterial activity. Amongst the tested compounds, 5b, 5e, 5h, 5j, 6c and 7c displayed promising antimicrobial activity. The mode of action of these active compounds was carried out by docking of receptor enoyl-ACP reductase with newly synthesized candidate ligands, 5b, 5e, 5h, 5j and 6c.     

Synthesis, molecular docking and binding studies of selective serotonin transporter inhibitors

With the aim of obtaining compounds possessing high SERT selectivity, in the present work we synthesized and studied the inhibition of serotonin (SERT), dopamine (DAT) and norepinephrine (NET) transporters by docking studies and experimental binding measurements of a series of 4-(aryl)piperidin-3-one O-4-benzyl oxime hydrochlorides (1-10) of both E and Z configuration. E configuration compounds showed high SERT binding affinities (K_i = 10-98 nM) and high SERT selectivities over both NET and DAT. The molecular docking studies allowed a rationalization of the molecular basis of drug-SERT interactions both of the synthesized compounds and paroxetine and fluoxetine used as reference antidepressant drugs.     

Synthesis and structure-activity relationship of 1- and 2-substituted-1,2,3-triazole letrozole-based analogues as aromatase inhibitors

A series of bis- and mono-benzonitrile or phenyl analogues of letrozole 1, bearing (1,2,3 and 1,2,5)-triazole or imidazole, were synthesized and screened for their anti-aromatase activities. The unsubstituted 1,2,3-triazole 10a derivative displayed inhibitory activity comparable with that of the aromatase inhibitor, letrozole 1. Compound 10a, bearing a 1,2,3-triazole, is also 10000-times more tightly binding than the corresponding analogue 25 bearing a 1,2,5-triazole, which confirms the importance of a nitrogen atom at position 3 or 4 of the 5-membered ring needed for high activity. The effect on human epithelial adrenocortical carcinoma cell line (H295R) proliferation was also evaluated. The compound 10j (IC₅₀ = 4.64 μM), a letrozole 1 analogue bearing para-cyanophenoxymethylene-1,2,3-triazole decreased proliferation rates of H295R cells by 76 and 99% in 24 and 72 h respectively. Computer calculations, using quantum ab initio structures, suggest a possible correlation between anti-aromatase activity and the distance between the nitrogen in position 3 or 4 of triazole nitrogen and the cyano group nitrogen.     

Synthesis and biological evaluation of pyrazoline analogues with beta-amino acyl group as dipeptidyl peptidase IV inhibitors

A series of pyrazoline derivatives with beta-amino acyl group were synthesized and evaluated for their ability to inhibit dipeptidyl peptidase IV. Several pyrazoline derivatives exhibited submicromolar inhibitory activities against DPP-IV. X-ray co-crystal structure of initial hit compound 1h was determined. Among this series, carboxylic acid substituted pyrazoline derivative 2u was the most active and greatly decreased the inhibitory activity toward CYP3A4 enzyme.     

Novel amide derivatives as inhibitors of histone deacetylase: design, synthesis and SAR

Enzymatic inhibition of histone deacetylase (HDAC) activity is emerging as an innovative and effective approach for the treatment of cancer. A series of novel amide derivatives have been synthesized and evaluated for their ability to inhibit human HDACs. Multiple compounds were identified as potent HDAC inhibitors (HDACi), with IC(50) values in the low nanomolar (nM) range against enzyme activity in HeLa cell extracts and sub-microM for their in vitro anti-proliferative effect on cell lines. The introduction of an unsaturated linking group between the terminal aryl ring and the amide moiety was the key to obtain good potency. This approach yielded compounds such as (E)-N-[6-(hydroxyamino)-6-oxohexyl]-3-(7-quinolinyl)-2-propenamide (27) (HDAC IC(50) 8 nM) which showed potent in vivo activity in the P388 mouse leukemia syngeneic model (an increased lifespan (ILS) of 111% was obtained).     

8-Aryl- and alkyloxycaffeine analogues as inhibitors of monoamine oxidase

Recently it was reported that a series of 8-benzyloxycaffeine analogues are potent reversible inhibitors of human monoamine oxidase (MAO) A and B. In an attempt to discover additional C8 oxy substituents of caffeine that lead to potent MAO inhibition, a series of related 8-aryl- and alkyloxycaffeine analogues were synthesized and their MAO-A and -B inhibition potencies were compared to those of the 8-benzyloxycaffeines. The results document that while the 8-substituted-oxycaffeine analogues inhibited both human MAO isoforms, they displayed a high degree of selectivity for MAO-B. 8-(3-Phenylpropoxy)caffeine, 8-(2-phenoxyethoxy)caffeine and 8-[(5-methylhexyl)oxy]caffeine were found to be the especially potent MAO-B inhibitors with IC₅₀ values ranging from 0.38 to 0.62 μM. These inhibitors are therefore 2.5-4.6 fold more potent MAO-B inhibitors than is 8-benzyloxycaffeine (IC₅₀ = 1.77 μM). It is also demonstrated that, analogous to 8-benzyloxycaffeine, halogen substitution on the phenyl ring of the C8 substituent significantly enhances MAO binding affinity. For example, the most potent MAO-B inhibitor of the present series is 8-[2-(4-bromophenoxy)ethoxy]caffeine with an IC₅₀ value of 0.166 μM. This study also reports possible binding orientations of selected oxy caffeines within the active site cavities of MAO-A and MAO-B.     

Carbonic anhydrase inhibitors. Synthesis, molecular structures, and inhibition of the human cytosolic isozymes I and II and transmembrane isozymes IX, XII (cancer-associated) and XIV with novel 3-pyridinesulfonamide derivatives

A series of novel 3-pyridinesulfonamide derivatives (2-5, 9-11 and 13-15) have been synthesized and investigated as inhibitors of five isoforms of zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1), that is, the cytosolic ubiquitous CA I and II, and isozymes CA IX and XII (cancer-associated), and XIV. Against the human isozyme hCA I the new compounds showed K_Is in the range of 0.089-251 μM, whereas toward hCA II, K_Is = 50.5-487 nM. Isozyme hCA IX was inhibited with K_Is in the range of 5.2-18.3 nM, while hCA XII with K_Is = 6.0-16.4 nM, and hCA XIV with K_Is = 76.4-152.0 nM. All of the new compounds 2-5, 9-11 and 13-15 showed excellent hCA IX inhibitory efficacy, with K_Is = 5.2-18.3 nM, being much more effective as compared to the clinically used AAZ, MZA, EZA, DCP and IND (K_Is = 24-50 nM).     

Synthesis and structure-activity relationship study of the new set of trypsin-like proteinase inhibitors

Anew set of 25 trypsin-like proteinase inhibitors was prepared and the inhibiting activity on trypsin, thrombin, plasmin and urokinase was measured. The structure-activity relationship is discussed. High inhibiting activities were observed in 4-guanidinobenzoic acid esters only. The replacement of this moiety for N-formamidinyl-isonipecotic acid or an arginine moiety caused almost total loss of the activity. In the series of 4-guanidinobenzoic acid esters, any important influence of the ester-groups reactivity was observed. The trypsin-thrombin selectivity in the compounds with the guanidine-remote carboxylic function was also observed.     

Synthesis and biological assessment of diversely substituted furo[2,3-b]quinolin-4-amine and pyrrolo[2,3-b]quinolin-4-amine derivatives, as novel tacrine analogues

The synthesis and pharmacological analyses of a number of furo[2,3-b]quinolin-4-amine, and pyrrolo[2,3-b]quinolin-4-amine derivatives are reported. Thus, we synthesized diversely substituted tacrine analogues 1–11 and 12–16 by Friedländer-type reaction of readily available o-amino(furano/pyrrolo)nitriles with suitable and selected cycloalkanones. The biological evaluation of furanotacrines1–11 and pyrrolotacrine13 showed that these are good, in the micromolar range, and highly selective inhibitors of BuChE. In the furanotacrine group, the most interesting inhibitor was 2-(p-tolyl)-5,6,7,8-tetrahydrofuro[2,3-b]quinolin-4-amine (3) [IC₅₀ (eqBuChE) = 2.9 ± 0.4 μM; IC₅₀ (hBuChE) = 119 ± 15 μM]. Conversely, pyrrolotacrines12 and 14 proved moderately equipotent for both cholinesterases, being 1,2-diphenyl-5,6,7,8-tetrahydro-1H-pyrrolo[2,3-b]quinolin-4-amine (12) the most potent for the inhibition of both enzymes [IC₅₀ (EeAChE) = 0.61 ± 0.04 μM; IC₅₀ (eqBuChE) = 0.074 ± 0.009 μM]. Moreover, pyrrolotacrine 12, at concentrations as low as 300 nM can afford significant neuroprotective effects against Aβ-induced toxicity. Docking studies show that compounds 3 and 12 bind in the middle of the AChE active site gorge, but are buried deeper inside BuChE active site gorge, as a consequence of larger BuChE gorge void. All these data suggest that these new tacrine analogues could be used for the potential treatment of Alzheimer’s disease.     

Synthesis and in vitro anti-HIV evaluation of a new series of 6-arylmethyl-substituted S-DABOs as potential non-nucleoside HIV-1 reverse transcriptase inhibitors

A series of new 5-alkyl-2-benzylsulfanylpyrimidin-4(3H)-ones (5a-y) bearing different substituted arylmethyl moieties at the C-6 position of the pyrimidine core have been synthesized and evaluated for their in vitro activities against HIV-1 and HIV-2 in MT-4 cell cultures. The majority of the title compounds showed moderate to good activities against HIV-1 with an IC(50) range from 6.67 microM to 0.12 microM. Among them, 6-(3,5-dimethylbenzyl) analogue 5q exhibited the most potent anti-HIV-1 activity (IC(50)=0.12 microM, SI>2642), which was about 40-fold more active than the reference compounds 1-[(2-hydroxyethoxy)methyl]-6-(phenylsulfanyl)thymine (HEPT) and 2',3'-dideoxyinosine (DDI). The structure-activity relationships (SARs) of these new congeners were further discussed.     

Synthesis, biological evaluation, and docking studies of gigantol analogs as calmodulin inhibitors

Several analogs of gigantol (1) were synthesized to evaluate their effect on the complexes Ca²⁺-calmodulin (CaM) and Ca²⁺-CaM-CaM sensitive phosphodiesterase 1 (PDE1). The compounds belong to four structural groups including, 1,2-diphenylethanes (2-11), diphenylmethanes (13-15), 1,3-diphenylpropenones (16-18), and 1,3-diphenylpropanes (20-22). In vitro enzymatic studies showed that all compounds except 11 inhibited the complex Ca²⁺-CaM-PDE1 with IC₅₀ values ranging from 9 to 146 μM. On the other hand, all analogs but 11, 12 and 15 quenched the extrinsic fluorescence of the CaM biosensor hCaM-M124C-mBBr to different extent, then revealing different affinities to CaM; their affinity constants (K_m) values were in the range of 3-80 μM. Molecular modeling studies indicated that all these compounds bound to CaM at the same site that the classical inhibitors trifluoperazine (TFP) and chlorpromazine (CPZ). Some of these analogs could be worthy candidates for developing new anti-tumor, local anesthetics, antidepressants, antipsychotic, or smooth muscle relaxant drugs, with anti-CaM properties due to their good affinity to CaM and the straightforwardness of their synthesis. In addition they could be valuable tools for the study of Ca²⁺-CaM functions.     

Synthesis and biological evaluation in U87MG glioma cells of (ethynylthiophene)sulfonamido-based hydroxamates as matrix metalloproteinase inhibitors

Matrix metalloproteinases (MMPs) are important factors in gliomas since these enzymes facilitate invasion into the surrounding brain and participate in neovascularization. In particular, the gelatinases (MMP-2 and MMP-9), and more recently MMP-25, have been shown to be highly expressed in gliomas and have been associated with disease progression. Thus, inhibition of these MMPs may represent a promising non-cytotoxic approach to glioma treatment. We report herein the synthesis and biological evaluation of a series of 4-butylphenyl(ethynylthiophene)sulfonamido-based hydroxamates. Among the new compounds tested, a promising derivative, 5a, was identified, which exhibits nanomolar inhibition of MMP-2, MMP-9, and MMP-25, but weak inhibitory activity toward other members of the MMP family. This compound also exhibited anti-invasive activity of U87MG glioblastoma cells at nanomolar concentrations, without affecting cell viability.     

Design, synthesis and pharmacobiological evaluation of novel acrylic acid derivatives acting as lipoxygenase and cyclooxygenase-1 inhibitors with antioxidant and anti-inflammatory activities

A series of novel acrylic acid derivatives bearing at the 3 position thienyl, furfuryl and 3,5-ditert-butyl-4-hydroxyphenyl substituents have been designed, synthesized and tested as potential dual lipoxygenase/cyclooxygenase-1 (LOX/COX-1) inhibitors and as antioxidant and anti-inflammatory agents. Some compounds have shown moderate antioxidant and COX-1 inhibitory activities, very good anti-inflammatory activity and an inhibition of soybean lipoxygenase (LOX) higher than caffeic acid. In particular, compound 4I disclosed a moderate in vitro LOX inhibition with an IC₅₀ = 100 μM whereas compounds 1I and 2II exhibited the best, albeit poor, activity as COX-1 inhibition (75% inhibition at 100 μM). Good radical scavenging properties were shown by compounds 4I, 3I and 1II. Docking simulations performed on LOX inhibitor 4I and COX-1 inhibitor 1I indicated that hydrophobic key interactions may govern the enzyme-inhibitor binding.     

Synthesis of novel 1,2,4-oxadiazoles and analogues as potential anticancer agents

A library of 3,5-disubstituted-1,2,4-oxadiazoles 7-9 and their bioisosters, 1,3,4-oxadiazole 14 and 1,3,4-thiadiazole 16, were synthesized and evaluated in vitro for their anticancer potential against a panel of six human cancer cell lines. The key step in the synthesis of oxadiazoles 7-9 involve coupling of amidoxime 6 with an appropriate carboxylic acid followed by thermal cyclization. The bioisosteres, 1,3,4-oxadiazole 14 and 1,3,4-thiadiazole 16 were prepared from the reaction of a common precursor diacylhydrazine 13 with thionyl chloride and Lawesson′s reagent, respectively. The anticancer studies on the synthesized compounds revealed that presence of a cyclopentyloxy or n-butyloxy on the C-3 aryl ring and piperdin-4-yl or trichloromethyl at the C-5 position of 1,2,4-oxadiazole is essential for good activity. In particular, 1,2,4-oxadiazole 7i and analogue 1,3,4-thiadiazole 16 exhibited significant activity against DU145 (IC₅₀: 9.3 μM) and MDA-MB-231 (IC₅₀: 9.2 μM) cell lines, respectively.     

Design,synthesis and structure-activity relationships of a series of 9-substituted adenine derivatives as selective phosphodiesterase type-4 inhibitors

Adenine derivatives substituted in position 9 have been demonstrated to have potent cyclic nucleotide phosphodiesterase (PDE) inhibition properties with high selectivity toward PDE-4. Starting from our initial lead compound 9-(2-fluorobenzyl)-N(6)-methyl-2-trifluoromethyladenine (4, NCS613), we designed and synthesized a new series of 9-substituted derivatives for developing structure-activity relationship studies. This new series of derivatives showed increased potencies and better selectivity profiles. Structural modifications were achieved in parallel on three different positions of the adenine ring, and led to the following observations: (i) introduction of a lipophilic substituent such as trifluoromethyl, n-propyl group or iodine in the C-2 position is favourable for both the PDE-4 inhibitory activity and the selectivity towards other isoenzymes; (ii) functionalization of the N9 benzyl group with a 2-methoxy substituent led to remarkably more active compounds; (iii) replacement of the N(6)-methylamino moiety by other amino groups is detrimental to the activity. Among all derivatives prepared, the 9-(2-methoxybenzyl)-N(6)-methyl-2-trifluoromethyladenine (9r), 9-(2-methoxybenzyl)-N(6)-methyl-2-n-propyladenine (9s), and the 2-iodo-9-(2-methoxybenzyl)-N(6)-methyladenine (13b) were found to be the most potent inhibitors within this series (PDE-4-IC(50)=1.4, 7.0, and 0.096 nM, respectively). Compared to our reference compound 4, which showed an IC(50) of 42 nM, the derivative 13b was found 450-fold more potent. Moreover, 2-iodo-9-(2-methoxybenzyl)-N(6)-methyladenine (13b) and 9-(2-methoxybenzyl)-N(6)-methyl-2-trifluoromethyladenine (9r), were at least 50000-150000 times more selective for the PDE-4 than for the other PDE families. Additionally, these new derivatives showed improved efficiency in inhibiting the TNFalpha release from mononuclear cells from healthy subjects (e.g. adenines 7l, 9s and 13b). Thus, compounds 7l, 9r, 9s and 13b are among the most potent and selective PDE-4 inhibitors reported so far and represent very promising pharmacological tools for a better understanding of the signal transduction involving cyclic AMP within the cell: this pathway is implicated in the physiology and the pathophysiology of inflammation, asthma and autoimmune disorders.