Discovery of noscapine derivatives as potential β-tubulin inhibitors

Twenty novel 1,2,3-triazole noscapine derivatives were synthesized starting from noscapine by consecutive N-demethylation, reduction of lactone ring, N-propargylation and Huisgen 1,3-dipolar cycloaddition reaction. In order to select the most promising molecules to subject to further biophysical and biological evaluation, a molecular docking analysis round was performed using noscapine as reference compound. The molecules featuring docking predicted binding affinity better than that of noscapine were then subjected to MTT assay against MCF7 cell line. The obtained results disclosed that all the selected triazole derivatives exhibited a remarkably lower cell viability compared to noscapine in the range of 20 μM in 48 h. In an attempt to correlate the biological activity with the ability to bind tubulin, the surface plasmon resonance (SPR) assay was employed. Compounds 8a, 8h, 9c, 9f and 9j were able to bind tubulin with affinity constant values in the nanomolar range and higher if compared to noscapine. Integrating computational predictions and experimental evaluation, two promising compounds (8h and 9c) were identified, whose relevant cytotoxicity was supposed to be correlated with tubulin binding affinity. These findings shed lights onto structural modifications of noscapine toward the identification of more potent cytotoxic agents targeting tubulin.     

6-Oxooxazolidine–quinazolines as noncovalent inhibitors with the potential to target mutant forms of EGFR

Despite the remarkable benefits of gefitinib, the clinical efficacy is eventually diminished due to the acquired point mutations in the EGFR (T790M). To address this unmet medical need, we demonstrated a strategy to prepare a hybrid analogue consisting of the oxooxazolidine ring and the quinazoline scaffold and provided alternative noncovalent inhibitors targeting mutant forms of EGFR. Most of the derivatives displayed moderate to good anti-proliferative activity against gefitinib-resistant NCI-H1975. Some of them exhibited potent EGFR kinase inhibitory activities, especially on EGFR^T790M and EGFR^L858R kinases. SAR studies led to the identification of a hit 9a that can target both of the most common EGFR mutants: L858R and T790M. Also, 9a displayed weaker inhibitory against cancer cell lines with low level of EGFR expression and good chemical stability under different pH conditions. The work presented herein showed the potential for developing noncovalent inhibitors targeting EGFR mutants.     

Synthesis and evaluation of β-carboline derivatives as potential monoamine oxidase inhibitors

Previous studies have shown that harmine is a reversible inhibitor of human monoamine oxidase A (MAO-A). Moreover, the crystal structure of human MAO-A in complex with harmine has been recently solved. This crystal structure shows that close to the methoxy group of the harmine moiety, a lipophilic pocket is left vacant within the binding site of human MAO-A. Our objective was to optimize the ??-carboline series against human MAO-A in order to explore this pocket. Therefore, a series of ??-carboline derivatives has been synthesized. The compounds were evaluated for their human monoamine oxidase A and B inhibitory potency and their K_i values were estimated. The results show that O-alkylated compounds with lipophilic groups like cyclohexyl, phenyl and aliphatic chains increase the inhibition of MAO-A compared to harmine. Compound 3e, with the trifluorobutyloxy group, was the most active of this series, with a K_i against MAO-A of 3.6 nM. Molecular docking studies show that the trifluorobutyloxy chain occupies the hydrophobic pocket vacant with harmine. The O-alkylated compounds are less active on MAO-B than on MAO-A. However, several compounds show a better inhibition on MAO-B compared to harmine. Compound 3f, with the cyclohexylmethoxy chain, displayed the best inhibitory activity against MAO-B with a K_i value of 221.6 nM. This cyclohexyl bearing analogue is also a potent MAO-A inhibitor with a K_i value of 4.3 nM. Molecular docking studies show that the cyclohexyl chain also occupies a hydrophobic pocket but in different ways in MAO-A or MAO-B.     

The use of β-amino acids in the design of protease and peptidase inhibitors

Summary The use of β-amino acids as peptidomimetics has emerged in recent years with significant potential in a number of applications. The incorporation of β-amino acids has been successful in creating peptidomimetics that not only have potent biological activity, but are also resistant to proteolysis. This article reviews the recent applications of β-amino acids in the design of protease and peptidase inhibitors. Given their structural diversity, together with the ease of synthesis and incorporation into peptide sequences using standard solid-phase peptide synthesis techniques, β-amino acids have the potential to form a new platform technology for peptidomimetic design and synthesis.     

Bicyclic γ-amino acids as inhibitors of γ-aminobutyrate aminotransferase

The γ-aminobutyrate (GABA)-degradative enzyme GABA aminotransferase (GABA-AT) is regarded as an attractive target to control GABA levels in the central nervous system: this has important implications in the treatment of several neurological disorders and drug dependencies. We have investigated the ability of newly synthesized compounds to act as GABA-AT inhibitors. These compounds have a unique bicyclic structure: the carbocyclic ring bears the GABA skeleton, while the fused 3-Br-isoxazoline ring contains an electrophilic warhead susceptible of nucleophilic attack by an active site residue of the target enzyme. Out of the four compounds tested, only the one named (+)-3 was found to significantly inhibit mammalian GABA-AT in vitro. Docking studies, performed on the available structures of GABA-AT, support the experimental findings: out of the four tested compounds, only (+)-3 suitably orients the electrophilic 3-Br-isoxazoline warhead towards the active site nucleophilic residue Lys329, thereby explaining the irreversible inhibition of GABA-AT observed experimentally.     

Ammonia lyases and aminomutases as biocatalysts for the synthesis of α-amino and β-amino acids

Ammonia lyases catalyse the reversible addition of ammonia to cinnamic acid (1: R=H) and p-hydroxycinnamic (1: R=OH) to generate L-phenylalanine (2: R=H) and L-tyrosine (2: R=OH) respectively (Figure 1a). Both phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL) are widely distributed in plants, fungi and prokaryotes. Recently there has been interest in the use of these enzymes for the synthesis of a broader range of L-arylalanines. Aminomutases catalyse a related reaction, namely the interconversion of α-amino acids to β-amino acids (Figure 1b). In the case of L-phenylalanine, this reaction is catalysed by phenylalanine aminomutase (PAM) and proceeds stereospecifically via the intermediate cinnamic acid to generate β-Phe 3. Ammonia lyases and aminomutases are related in sequence and structure and share the same active site cofactor 4-methylideneimidazole-5-one (MIO). There is currently interest in the possibility of using these biocatalysts to prepare a wide range of enantiomerically pure l-configured α-amino and β-amino acids. Recent reviews have focused on the mechanism of these MIO containing enzymes. The aim of this review is to review recent progress in the application of ammonia lyase and aminomutase enzymes to prepare enantiomerically pure α-amino and β-amino acids.     

A novel piperazine linked β-amino alcohols bearing a benzosuberone scaffolds as anti-proliferative agents

A new series of 1-((9-chloro-2,3-dimethyl-6,7-dihydro-5H-benzo[7]annulen-8-yl)methoxy)-3-(4-phenylpiperzin-1-yl) propan-2-ols (6a-k) have been designed, synthesized and their structures were established by spectroscopic data (FT-IR, ¹H NMR, ¹³C NMR, HRMS) and further confirmed by X-ray analysis. The newly synthesized compounds 6a-k were evaluated for their in vitro anti-proliferative activity against four cancer cell lines such as HeLa (cervical), MDA-MB-231 (breast), A549 (lung) and MIAPACA (pancreatic). Among the compounds tested, the compound 6e displayed most potent activity against four cancer cell lines with GI₅₀ values ranging from 0.010 to 0.097 μM. The structure and anti-proliferative activity relationship was further supported by in silico molecular docking study of the active compounds against Colchicine binding site of β-tubulin.     

Stereoselective synthesis of β-arabino glycosyl sulfones as potential inhibitors of mycobacterial cell wall biosynthesis

A series of β-arabino glycosyl sulfones with varying alkyl chain lengths were synthesised in a stereoselective fashion as putative mimics of decaprenolphosphoarabinose (DPA), and as potential inhibitors of mycobacterial cell wall biosynthesis. Biological testing against Mycobacterium bovis BCG revealed low to moderate anti-mycobacterial activity with marked dependence on alkyl chain length, which was maximal for a C-12 chain.     

Arthrobacter sp. lipase immobilization for preparation of enantiopure masked β-amino alcohols

Recent reports on immobilization of lipase from Arthrobacter sp. (ABL, MTCC 5125; IIIM isolate) on insoluble polymers have shown altered properties including stability and enantioselectivity. Present work demonstrates a facile method for the preparation of enantiopure β-amino alcohols by modulation of ABL enzyme properties via immobilization on insoluble as well as soluble supports using entrapment/covalent binding techniques. Efficacies of immobilized ABL on insoluble supports prepared from tetraethylorthosilicate/aminopropyltriethoxy silane and soluble supports derived from copolymerization of N-vinyl pyrrolidone-allylglycidyl ether (ANP type)/N-vinyl pyrrolidone-glycidyl methacrylate (GNP type) for kinetic resolution of masked β-amino alcohols have been studied vis-à-vis free ABL enzyme/wet cell biomass. The immobilized lipase on different insoluble/soluble supports has shown 21–110 mg/g protein binding and 30–700 U/g activity for hydrolyzing tributyrin substrate. The findings have shown a significant enhancement in enantioselectivity (ee 99%) vis-à-vis wet cell biomass providing ee 70–90% for resolution of β-amino alcohols.     

Synthesis and structure–activity relationships evaluation of benzothiazinone derivatives as potential anti-tubercular agents

N-Alkyl and heterocycle substituted 1,3-benzothiazin-4-one (BTZ) derivatives were synthesized. The anti-mycobacterial activities of these compounds were evaluated by determination of minimal inhibitory concentration (MIC) for Mycobacterium tuberculosis H37Ra and M. tuberculosis H37Rv. It was found that an extended or branched alkyl chain analog could enhance the potency, and activities of N-alkyl substituted BTZs were not affected by either nitro or trifluoromethyl at 6-position. Trifluoromethyl plays an important role in maintaining anti-tubercular activity in the piperazine or piperidine analogs. Compound 8o, which contains an azaspirodithiolane group, showed a MIC of 0.0001 μM against M. tuberculosis H37Rv, 20-fold more potent than BTZ043 racemate. These results suggested that the volume and lipophilicity of the substituents were important in maintaining activity. In addition, compound 8o was nontoxic to Vero cells and orally bioavailable in a preliminary pharmacokinetics study.     

Synthesis of benzimidazole derivatives as potent β-glucuronidase inhibitors

Twenty five 4, 6-dichlorobenzimidazole derivatives (1–25) have been synthesized and evaluated against β-glucuronidase inhibitory activity. The compounds which actively inhibit β-glucuronidase activity have IC₅₀ values ranging between 4.48 and 46.12 μM and showing better than standard d-saccharic acid 1,4 lactone (IC₅₀ = 48.4 ± 1.25 μM). Molecular docking provided potential clues to identify interactions between the active molecules and the enzyme which further led us to identify plausible binding mode of all the benzimidazole derivatives. This study confirmed that presence of hydrophilic moieties is crucial to inhibit the human β-glucuronidase.     

Synthesis of indole analogs as potent β-glucuronidase inhibitors

Natural products are the main source of motivation to design and synthesize new molecules for drug development. Designing new molecules against β-glucuronidase inhibitory is utmost essential. In this study indole analogs (1–35) were synthesized, characterized using various spectroscopic techniques including ¹H NMR and EI-MS and evaluated for their β-glucuronidase inhibitory activity. Most compounds were identified as potent inhibitors for the enzyme with IC₅₀ values ranging between 0.50 and 53.40 μM, with reference to standard d-saccharic acid 1,4-lactone (IC₅₀ = 48.4 ± 1.25 μM). Structure-activity relationship had been also established. The results obtained from docking studies for the most active compound 10 showed that hydrogen bond donor features as well as hydrogen bonding with (Oε1) of nucleophilic residue Glu540 is believed to be the most importance interaction in the inhibition activity. It was also observed that hydroxyl at fourth position of benzylidene ring acts as a hydrogen bond donor and interacts with hydroxyl (OH) on the side chain of catalysis residue Tyr508. The enzyme-ligand complexed were being stabilized through electrostatic π-anion interaction with acid-base catalyst Glu451 (3.96 Å) and thus preventing Glu451 from functioning as proton donor residue.     

Thiadiazole derivatives as New Class of β-glucuronidase inhibitors

Thiadiazole derivatives 1–24 were synthesized via a single step reaction and screened for in vitro β-glucuronidase inhibitory activity. All the synthetic compounds displayed good inhibitory activity in the range of IC₅₀ = 2.16 ± 0.01–58.06 ± 1.60 μM as compare to standard d-saccharic acid 1,4-lactone (IC₅₀ = 48.4 ± 1.25 μM). Molecular docking study was conducted in order to establish the structure–activity relationship (SAR) which demonstrated that thiadiazole as well as both aryl moieties (aryl and N-aryl) involved to exhibit the inhibitory potential. All the synthetic compounds were characterized by spectroscopic techniques ¹H, ¹³C NMR, and EIMS.     

Phenoxypropanolamine derivatives as selective inhibitors of the 20S proteasome β1 and β5 subunits

New series of thiophene-containing phenoxypropanolamines were synthesized and evaluated for their potency to inhibit the three proteolytic activities of the mammalian 20S proteasome. Noticeable inhibition of both ChT-L and PA activities was obtained with three compounds: one with unsubstituted phenoxypropanolamine group (7) and the two others with a p-Cl-substituted group (4 and 9). For three other compounds (3, 8 and 10), ChT-L activity alone was significantly inhibited. In silico docking performed on the β5 and β1 subunits bearing the respective ChT-L and PA catalytic sites showed features common to poses associated with active compounds. These features may constitute a selectivity criterion for structure-guided inhibitor design.     

Serendipitous discovery of aryl boronic acids as β-lactamase inhibitors

High throughput screening for β-lactamase inhibitors afforded biphenyl hits such as 1. Hit confirmation and X-ray soaking experiments with Pseudomonas Aeruginosa AmpC enzyme led to the identification of an aryl boronic acid-serine complex 4, which was formed from phenyl boronic acid 8 (an impurity in compound 1) and ethylene glycol (the cryoprotectant in the soaking experiment).     

Design,synthesis and biological evaluation of novel tripeptidyl epoxyketone derivatives constructed from β-amino acid as proteasome inhibitors

A series of novel tripeptidyl epoxyketone derivatives constructed from β-amino acid were designed, synthesized and evaluated as proteasome inhibitors. All target compounds were tested for their proteasome inhibitory activities and selected compounds were tested for their anti-proliferation activities against two multiple myeloma (MM) cell lines RPMI 8226 and NCI-H929. Among them, eleven compounds exhibited proteasome inhibitory rates of more than 50% at the concentration of 1 μg/mL and nine compounds showed anti-proliferation activities with IC₅₀ values at low micromolar level. Compound 20h displayed the most potent proteasome inhibitory activities (IC₅₀: 0.11 ± 0.01 μM) and anti-proliferation activities with IC₅₀ values at 0.23 ± 0.01 and 0.17 ± 0.02 μM against two tested cell lines. Additionally, the poly-ubiquitin accumulation in the western blot analysis supported that proteasome inhibition in a cellular system was induced by compound 20h. All these experimental results confirmed that β-amino acid can be introduced as a building block for the development of proteasome inhibitors.     

Design,synthesis and structure–activity relationships of 3,5-diaryl-1H-pyrazoles as inhibitors of arylamine N-acetyltransferase

The synthesis and inhibitory potencies of a novel series of 3,5-diaryl-1H-pyrazoles as specific inhibitors of prokaryotic arylamine N-acetyltransferase enzymes is described. The series is based on hit compound 1 3,5-diaryl-1H-pyrazole identified from a high-throughout screen that has been carried out previously and found to inhibit the growth of Mycobacterium tuberculosis.     

Triazolyl tryptoline derivatives as β-secretase inhibitors

Tryptoline, a core structure of ochrolifuanine E, which is a hit compound from virtual screening of the Thai herbal database against BACE1 was used as a scaffold for the design of BACE1 inhibitors. The tryptoline was linked with different side chains by 1,2,3-triazole ring readily synthesized by catalytic azide-alkyne cycloaddition reactions. Twenty two triazolyl tryptoline derivatives were synthesized and screened for the inhibitory action against BACE1. JJCA-140 was the most potent inhibitor (IC(50)=1.49 μM) and was 100 times more selective for BACE1 than for Cat-D.     

Synthesis of optically active lipidicα-amino acids and lipidic 2-amino alcohols

Summary Lipidic-amino acids (LAAs) are a class of compounds combining structural features of amino acids with those of fatty acids. They are non-natural-amino acids with saturated or unsaturated long aliphatic side chains. Synthetic approaches to optically active LAAs and lipidic 2-amino alcohols (LAALs) are summarized in this review. A general approach to enantioselective synthesis of saturated LAAs is based on the oxidative cleavage of 3-amino -1,2-diols obtained by the regioselective opening of enantiomerically enriched long chain 2,3-epoxy alcohols. Unsaturated LAAs are prepared in their enantiomeric forms by Wittig reactionvia methyl (S)-2di-tert-butoxycarbonylamino-5-oxo-pentanoate. This key intermediate aldehyde is obtained by selective reduction of dimethyl N,N-di-Boc glutamate with DIBAL. (R) or (S) LAALs may be prepared starting from D-mannitol or L-serine. LAAs are converted into LAALs by chemoselective reduction of their fluorides using sodium borohydride with retention of optical purity. Replacement of the hydroxyl group of LAALs by the azido group, followed by selective reduction leads to unsaturated optically active lipidic 1,2-diamines.Abbreviations Bn benzyl - Boc tert-butoxycarbonyl - DDQ 2,3-dichloro-5,6-dicyano-1,4-benzoquinone - DET diethyl tartrate - DIBAL diisobutyl aluminum hydride - DMAP 4-dimethylaminopyridine - DMF N,N-dimethylformamide - DMSO dimethyl sulfoxide - EDC N-ethyl-N-(3-dimethylaminopropyl)carbodiimide - Et₃N triethylamine - HMPA hexamethylphosphoramide - HOBt 1-hydroxybenzotriazole - KN(TMS)₂ potassium bis(trimethylsilyl)-amide - LAA lipidic-amino acid - LAAAl lipidic 2-amino alcohol - LDA lipidic 1,2-diamine - LP lipidic peptide - MPM-Cl p-methoxybenzyl chloride - MsCl methanesulphonyl chloride - MTPA -methoxy--(trifluoromethyl)phenylaccitc - PLA₂ phospholipase A₂ - TBIIP tert-butyl hydroperoxide - THF tetrahydrofuran - TMSCl trimethylsilyl chloride - Tr trityl - Z benzyloxycarbonyl