Low Nanomolar Levels Research Articles

Sensitive and robust colorimetric assay for the detection of Hg2+ at nanomolar level from real samples by TMPM functionalized Ag-Fe NCs and it's photocatalytic and antimicrobial activities

In this study, a selective and sensitive colorimetric probe for the detection of mercury at nanomolar level was reported and the effective detection by the probe was performed with environmental samples. The colorimetric sensing platform was prepared based on Ag-Fe bimetallic- 3-(Trimethoxysilyl) propyl methacrylate framework. The UV–vis spectroscopy, X-Ray diffraction, high resolution transmission electron microscope, energy dispersive X-ray spectroscopy (EDS), thermal gravimetric analyzer, zeta sizer and particle size analyzer were used for the characterization of Ag-Fe nanocomposite. The detection of mercury by Ag-Fe-glycine nanoconjugate was indicated by the colour change from yellowish brown to colourless. The environmental sample was collected from Noyyal river and the estimated amount by the probe was almost similar to the result of atomic absorption spectroscopy analysis. The detailed study on the effect of pH, temperature and saline concentration on the detection was performed. In addition, metal interference study was performed to understand the influence of other metal ions on detection and quantification of Hg2+ by Ag-Fe-glycine nanoconjugate and the study reveals the practical application of the prepared probe. The limit of detection of Hg2+ by Ag-Fe nanocomposite was determined to be 1.8 nM. The prepared probe is found to be an effective system to detect mercury at very low nanomolar level from aqueous samples. In addition, the nanocomposite exhibited multifunctional properties including efficient photocatalytic and antimicrobial applications, indicates its wide applications in various sectors.

Novel 2‐hydroxynaphthalene‐based fluorescent turn‐on sensor for highly sensitive and selective detection of Al3+ and its application in imaging in vitro and in vivo

Excessive aluminum exposure in the human body has been held responsible for multiple adverse effects, and existing data underscore the significance of aluminum detection in environmental and biological systems. Developing high‐performance Al3+ fluorescent chemosensors can revolutionize our understanding of the physiological and pathological processes of Al3+ ions. Herein, we reported a highly sensitive and selective Schiff base fluorescence sensor, bis‐NAPPD (1,1'‐((1E,1'E)‐(pyridine‐2,3‐diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen‐2‐ol)), which can recognize Al3+ ions and exhibits a remarkable turn‐on dual emission response (by ~23 fold) with a low nanomolar level detection limit (1.67 × 10−8 M) in methanol. Furthermore, the binding behavior and the turn‐on fluorescence probing mechanism of bis‐NAPPD were illustrated in detail by UV–vis titration, 1H NMR, and ESI‐MS spectroscopy as well as density functional theory calculations. Notably, bis‐NAPPD showed great potential for tracing Al3+ distribution in cells and living zebrafish larvae, and can also be applied in the fluorimetric detection of aluminum in sucralfate tablets with good precision and satisfactory accuracy, which may represent a promising Al3+ probe in bioimaging and biomedical applications.

Rapid biomonitoring of perfluoroalkyl substance exposures in serum by multisegment injection-nonaqueous capillary electrophoresis-tandem mass spectrometry.

Perfluoroalkyl substances (PFASs) are a major contaminant class due to their ubiquitous prevalence, persistence, and putative endocrine disrupting activity that may contribute to chronic disease risk notably with exposures early in life. Herein, multisegment injection-nonaqueous capillary electrophoresis-tandem mass spectrometry (MSI-NACE-MS/MS) is introduced as a high throughput approach for PFAS screening in serum samples following a simple methyl-tert-butyl ether (MTBE) liquid extraction. Separation and ionization conditions were optimized to quantify low nanomolar concentration levels of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) from serum extracts when using multiple reaction monitoring under negative ion mode conditions. Multiplexed separations of PFOA and PFOS were achieved with excellent throughput(<3min/sample), adequate concentration sensitivity (LOD ∼ 20nM, S/N=3) and good technical precision over three consecutive days of analysis (mean CV=9.1%, n=84). Accurate quantification of PFASs was demonstrated in maternal serum samples (n=16) when using MSI-CE-MS/MS following pre-column sample enrichment with median concentrations of 3.46nM (0.7-9.0nM) and 3.29nM (1.5-6.6nM) for PFOA and PFOS, respectively. This was lower than average PFAS exposures measured in pregnant women who had serum collected prior to 2009 likely due to subsequent phase out of their production. Overall, this method offers a convenient approach for large-scale biomonitoring of environmental exposures to legacy PFASs and their emerging replacements that is relevant to maternal health and chronic disease risk assessment in children.

Synthesis, bioactivity and binding energy calculations of novel 3-ethoxysalicylaldehyde based thiosemicarbazone derivatives.

In recent decade, the entrance of α-N-heterocyclic thiosemicarbazones derivates (Triapne, COTI-2 and DpC) in clinical trials for cancer and HIV-1 has vastly increased the interests of medicinal chemists towards this class of organic compounds. In the given study, a series of eighteen new (3a-r) 3-ethoxy salicylaldehyde-based thiosemicarbazones (TSC), bearing aryl and cycloalkyl substituents, were synthesized and assayed for their pharmacological potential against carbonic anhydrases (hCA I and hCA II), cholinesterases (AChE and BChE) and α-glycosidase. The hCA I isoform was inhibited by these novel 3-ethoxysalicylaldehyde thiosemicarbazone derivatives (3a-r) in low nanomolar levels, the Ki of which differed between 144.18±26.74 and 454.92±48.32nM. Against the physiologically dominant isoform hCA II, the novel compounds demonstrated Kis varying from 110.54±14.05 to 444.12±36.08nM. Also, these novel derivatives (3a-r) effectively inhibited AChE, with Ki values in the range of 385.38±45.03 to 983.04±104.64nM. For BChE was obtained with Ki values in the range of 400.21±35.68 to 1003.02±154.27nM. For α-glycosidase the most effective Ki values of 3l, 3n, and 3q were with Ki values of 12.85±1.05, 16.03±2.84, and 19.16±2.66nM, respectively. Moreover, the synthesized TCSs were simulated using force field methods whereas the binding energies of the selected compounds were estimated using MM-GBSA method. The findings indicate the present novel 3-ethoxy salicylaldehyde-based thiosemicarbazones to be excellent hits for pharmaceutical applications.

Cocaine Receptor Identified as BASP1

Cocaine exerts its behavioral actions mainly through inhibition of dopamine reuptake. However, cocaine is a weak and non-selective inhibitor of the monoamine transporters. In addition, many dopamine reuptake inhibitors do not produce psychotropic effects in drug-experienced volunteers. On the other hand, previous evidence indicates more potent effects of cocaine. For example, low nanomolar cocaine regulates dopamine D2 receptor signaling. In planarians, low nanomolar levels of cocaine produces environmental place conditioning. These signaling and behavioral actions of cocaine could not be mediated through the inhibition of monoamine transporters. Furthermore, previous a study describes 16 nM cocaine binding in rat striatal synaptosomes suggesting the existence of a high-affinity receptor for cocaine. However, the identity of such receptor is unknown.

Cryptophycin-55/52 based antibody-drug conjugates: Synthesis, efficacy, and mode of action studies

Cryptophycin-52 (CR52), a tubulin inhibitor, exhibits promising antitumor activity in vitro (picomolar level) and in mouse xenograft models. However, the narrow therapeutic window in clinical trials limits its further development. Antibody-drug conjugate (ADC), formed by coupling cytotoxic compound (payload) to an antibody via a linker, can deliver drug to tumor locations in a targeted manner by antibody, enhancing the therapeutic effects and reducing toxic and side effects. In this study, we aim to explore the possibility of CR52-based ADC for tumor targeted therapy. Due to the lack of a coupling site in CR52, its prodrug cryptophycin-55 (CR55) containing a free hydroxyl was synthesized and conjugated to the model antibody trastuzumab (anti-HER2 antibody drug approved by FDA for breast cancer therapy) via the linkers based on Mc-NHS and Mc-Val-Cit-PAB-PNP. The average drug-to-antibody ratios (DARs) of trastuzumab-CR55 conjugates (named T-L1-CR55, T-L2-CR55, and T-L3-CR55) were 3.50, 3.29, and 3.35, respectively. These conjugates exhibited potent cytotoxicity in HER2-positive tumor cell lines with IC50 values at low nanomolar levels (0.58–1.19 nM). Further, they displayed significant antitumor activities at the doses of 10 mg/kg in established ovarian cancer (SKOV3) and gastric cancer (NCI–N87) xenograft models without overt toxicities. Finally, the drug releases were analyzed and the results indicated that T-L3-CR55 was able to effectively release CR55 and further epoxidized to CR52, which may be responsible for its best performance in antitumor activities. In conclusion, our results demonstrated that these conjugates have the potential for tumor targeted therapy, which provides insights to further research the CR55/CR52-based ADC for tumor therapy.

Discovery of Highly Potent Benzimidazole Derivatives as Indoleamine 2,3-Dioxygenase-1 (IDO1) Inhibitors: From Structure-Based Virtual Screening to in Vivo Pharmacodynamic Activity.

In this study, a successful medicinal chemistry campaign that exploited virtual, biophysical, and biological investigations led to the identification of a novel class of IDO1 inhibitors based on a benzimidazole substructure. This family of compounds is endowed with an extensive bonding network in the protein active site, including the interaction with pocket C, a region not commonly exploited by previously reported IDO1 inhibitors. The tight packing of selected compounds within the enzyme contributes to the strong binding interaction with IDO1, to the inhibitory potency at the low nanomolar level in several tumoral settings, and to the selectivity toward IDO1 over TDO and CYPs. Notably, a significant reduction of L-Kyn levels in plasma, together with a potent effect on abrogating immunosuppressive properties of MDSC-like cells isolated from patients affected by pancreatic ductal adenocarcinoma, was observed, pointing to this class of molecules as a valuable template for boosting the antitumor immune system.

Synthesis of Combretastatin A-4 and 3'-Aminocombretastatin A-4 derivatives with Aminoacid Containing Pendants and Study of Their Interaction with Tubulin and as Downregulators of the VEGF, hTERT and c-Myc Gene Expression.

Natural product combretastatin A-4 (CA-4) and its nitrogenated analogue 3′-aminocombretastatin A-4 (AmCA-4) have shown promising antitumor activities. In this study, a range of CA-4 and AmCA-4 derivatives containing amino acid pendants have been synthesized in order to compare their biological actions with those of their parent compounds. Thus, inhibition of cell proliferation on tumor cell lines HT-29, MCF-7 and A-549, as well as on the nontumor cell line HEK-273; in vitro tubulin polymerization; mitotic cell arrest; action on the microtubule cell network and inhibition of VEGF, hTERT, and c-Myc genes have been evaluated. Some AmCA-4 derivatives bearing L-amino acids exhibited inhibition of cell proliferation at low nanomolar levels exceeding the values shown by AmCA-4. Furthermore, while CA-4 and AmCA-4 derivatives do not show significant effects on the in vitro tubulin polymerization and cell cycle arrest, some selected CA-4 and AmCA-4 derivatives are able to cause total depolymerization of the microtubule network on A-549 cells. The best results were obtained in the inhibition of gene expression, particularly on the VEGF gene, in which some AmCA-4 derivatives greatly exceeded the inhibition values achieved by the parent compound.

Electrochemical Nitric Oxide Microsensors Based on a Fluorinated Xerogel Screening Layer for in Vivo Brain Monitoring.

Nitric oxide (NO) is an important free radical synthesized and released by brain cells. At low (nanomolar) levels, it modulates synaptic transmission and neuronal activity, but at much higher levels mediates neuronal injury through oxidative stress. However, the precise concentrations at which these biological actions are exerted are still poorly defined. Electrochemical detection of NO in vivo requires rigorous exclusion of endogenous redox molecules such as ascorbate or nitrite. A fluorinated xerogel composed of trimethoxymethylsilane and heptadecafluoro-1,1,2,2-tetrahydrodecyl silane has been proposed to create a screening layer around NO sensors, protecting against such chemical interference in vitro. Here we detected NO in the living brain using carbon fiber microelectrodes covered with nickel porphyrin and this fluorinated xerogel. These microsensors were insensitive to interfering redox molecules and surpassed similar microelectrodes coated with a Nafion screening layer. In vivo, in the rat parietal cortex, these electrodes could detect brain NO released by local microinjection of the glutamatergic agonist N-methyl-d-aspartate (NMDA). NMDA-evoked NO release peaked at 1.1 μM and lasted more than 20 min. This fluorinated xerogel screening layer can therefore be applied in vivo, allowing for the fabrication of highly specific microsensors to study NO physio-pathological actions in the brain.

Bisphenol A and several derivatives exert neural toxicity in human neuron-like cells by decreasing neurite length

Bisphenol A (BPA) and its derivatives, including bisphenols S (BPS), F (BPF), E (BPE), B (BPB), Z (BPZ), and AF (BPAF), are widely used in consumer products. Moreover, they are typically detected in the environment, food, and humans. Previous studies have linked BPA to several health risks, but it is still unclear whether BPA replacements are safe. In this study, we developed an in vitro model based on human embryonic stem cells (hESCs) to explore the potential neural toxicity of these compounds. We observed that the bisphenols affected the viability of hESCs and hESC-derived neural stem cells (NSCs) at high concentrations, with BPS being the least cytotoxic and BPAF the strongest cytotoxic compound. At human-relevant concentrations, the bisphenols did not significantly interfere with gene expression and protein levels during hESC differentiation into the neural epithelium, as well as during specification of neuron-like cells from NSCs. Nevertheless, monitoring of cell morphology changes indicated that exposure to BPA and its derivatives impaired neurite length in neuron-like cells. Thus, our findings provide insights into the molecular mechanisms of bisphenol-dependent neurotoxicity at low nanomolar levels and support the view that BPA substitutes may not be sufficiently safe for widespread use as industrial chemicals.

4,5-Disubstituted 1,2,3-triazoles: Effective Inhibition of Indoleamine 2,3-Dioxygenase 1 Enzyme Regulates T cell Activity and Mitigates Tumor Growth

The improvement of body’s own immune system is considered one of the safest approaches to fight against cancer and several other diseases. Excessive catabolism of the essential amino acid, L-tryptophan (L-Trp) assists the cancer cells to escape normal immune obliteration. The formation of disproportionate kynurenine and other downstream metabolites suppress the T cell functions. Blocking of this immunosuppressive mechanism is considered as a promising approach against cancer, neurological disorders, autoimmunity, and other immune-mediated diseases. Overexpression of indoleamine 2,3-dioxygenase 1 (IDO1) enzyme is directly related to the induction of immunosuppressive mechanisms and represents an important therapeutic target. Several classes of small molecule-based IDO1 inhibitors have been already reported, but only few compounds are currently being evaluated in various stages of clinical trials as adjuvants or in combination with chemo- and radiotherapies. In the quest for novel structural class(s) of IDO1 inhibitors, we developed a series of 4,5-disubstituted 1,2,3-triazole derivatives. The optimization of 4,5-disubstituted 1,2,3-triazole scaffold and comprehensive biochemical and biophysical studies led to the identification of compounds, 3i, 4i, and 4k as potent and selective inhibitors of IDO1 enzyme with IC50 values at a low nanomolar level. These potent compounds also showed strong IDO1 inhibitory activities in MDA-MB-231 cells with no/negligible level of cytotoxicity. The T cell activity studies revealed that controlled regulation of IDO1 enzyme activity in the presence of these potent compounds could induce immune response against breast cancer cells. The compounds also showed excellent in vivo antitumor efficacy (of tumor growth inhibition = 79–96%) in the female Swiss albino mice. As a consequence, this study describes the first example of 4,5-disubstituted 1,2,3-triazole based IDO1 inhibitors with potential applications for immunotherapeutic studies.

Two instantaneous fluorogenic steps for detection of nanomolar amyloid beta monomer and its interaction with stoichiometric copper(II) ion

A small molecule SEA-SC2 exhibited fluorescence in response to 10–60 nM amyloid beta (Aβ)40 and Aβ42 monomers at pH 7.4, in the presence of gold nanoparticle (AuNP). Here we report the fluorogenic detection due to the response from low nanomolar level of Aβ peptide monomer. The small organic molecule or AuNP has been reported to show detection limit up to 200 nM Aβ peptide. Furthermore, fluorescence enhancement studies with different stoichiometries of Aβ:Cu(II) confirmed the initial Aβ:Cu(II) adduct at the nanomolar level. This methodology has been applied to the detection of nanomolar concentrations of Aβ monomer in artificial cerebrospinal fluid and human serum albumin.

Synthesis and in vitro evaluation of piperazinyl-ureido sulfamates as steroid sulfatase inhibitors

Two new piperazinyl-ureido single ring aryl sulfamate-based inhibitor series were designed against the emerging oncology drug target steroid sulfatase (STS), for which there are existing potent steroidal and non-steroidal agents in clinical trials. 4-(Piperazinocarbonyl)aminosulfamates (5–31) were obtained by reacting 4-hydroxyarylamines with phenylchloroformate, subsequent sulfamoylation of the resulting hydroxyarylcarbamates and coupling of the product with 1-substituted piperazines. Pyrimidinyl-piperazinourea sulfamates (35–42) were synthesized by pyrimidine ring closure of 4-Boc-piperazine-1-carboxamidine with 3-(dimethylamino)propenones, deprotection and coupling with the sulfamoylated building block. Target ureidosulfamates 5–31 and 35–42 were evaluated both as STS inhibitors in vitro using a lysate of JEG-3 human placenta choriocarcinoma cell line and in a whole cell assay. SAR conclusions were drawn from both series. In series 35–42 the best inhibitory activity is related to the presence of a benzofuryl on the pyrimidine ring. In series 5–31 the best inhibitory activity was shown by the ureas bearing 4-chlorophenyl, 3,4-dichlorophenyl groups or aliphatic chains at the piperazino 4-nitrogen displaying IC50 in the 33–94 nM concentration range. Final optimization to the low nanomolar level was achieved through substitution of the arylsulfamate ring with halogens. Four halogenated arylsulfamates of high potency were achieved and two of these 19 and 20 had IC50 values of 5.1 and 8.8 nM respectively and are attractive for potential in vivo evaluation and further development. We demonstrate the optimization of this new series to low nanomolar potency, employing fluorine substitution, providing potent membrane permeant inhibitors with further development potential indicating piperazinyl-ureido aryl sulfamate derivatives as an attractive new class of STS inhibitors.

Rapid Discovery and Structure-Property Relationships of Metal-Ion Fluorescent Sensors via Macroarray Synthesis

A macroarray immobilisation of fluorophores on filter papers for sensing metal ions by in-situ reductive amination and carbodiimide coupling is reported herein. Chemometric approaches resulted in a rapid discovery of sensors that can synergistically discriminate up to 12 metal ions with great prediction accuracies. Covalently bound on paper, sensoring scaffolds that were synthesised from the macroarray format can readily be adopted as practical paper-based sensors with great reusability and sensitivity, achieving the limit of detection at low nanomolar level with some repeating spotting. Lastly, the discovered scaffolds were also confirmed to be functional as unbound molecules, thus paving the way for more diverse applications.

α,γ-Diketocarboxylic Acids and Their Esters Act as Carbonic Anhydrase IX and XII Selective Inhibitors.

Among human carbonic anhydrase (CA) inhibitors, the α,γ-diketocarboxylic acids and esters are still poorly investigated. Here, we report the first compounds of this class (1-6) acting as potent inhibitors at low nanomolar level against the cancer-related human CA IX and XII, and 2-3 magnitude orders selective toward the cytosolic isoforms hCA I and II. At enzymatic level, the α,γ-diketoacids 1-3 were more effective inhibitors compared to the corresponding ethyl esters 4-6. The phenyl- and α-naphthyl-containing compounds (1, 3, 4, and 6) behaved as dual hCA IX/XII inhibitors, while the β-naphthyl analogues (2 and 5) exhibited hCA IX-selective inhibition. In MG63 and HOS osteosarcoma (OS) cell lines, the ethyl esters 5 and 6 displayed dose-dependent reduction of viability and proliferation after 72 h treatment, with 6 being more potent than 5 likely for its dual hCA IX/XII inhibition.

Melamine-Mediated Base Mismatch for Label-Free and Amplified Sensitive Fluorescent Detection of Melamine in Milk

Sensitive identification and detection of melamine illegally added to food to increase false protein content is important for food safety monitoring because melamine can cause tissue injury or even death above the safety regulation level. Melamine can coordinate with two thymines to form stable T-melamine-T structures. On the basis of such a unique interaction, we have developed a T-melamine-T base mismatch-mediated rolling circle amplification (RCA) signal enhancement means for amplified sensitive and label-free fluorescent detection of melamine in milk. The presence of melamine facilitates the hybridization between two T:T base mismatch containing DNA strands, which triggers RCA generation of many long sequences with repeated G-quadruplex segments. The fluorescent dye, thioflavin T, further binds the resulting G-quadruplexes to exhibit substantially enhanced fluorescence for sensitive detection of melamine at the low nanomolar level in a label-free manner. Besides, the developed approach is highly selective toward the discrimination and detection of melamine in milk samples.

Discovery of New Cyclopentaquinoline Analogues as Multifunctional Agents for the Treatment of Alzheimer's Disease.

Here we report the two-step synthesis of 8 new cyclopentaquinoline derivatives as modifications of the tetrahydroacridine structure. Next, the biological assessment of each of them was performed. Based on the obtained results we identified 6-chloro-N-[2-(2,3-dihydro-1H-cyclopenta[b]quinolin-9-ylamino)-hexyl]]-nicotinamide hydrochloride (3e) as the most promising compound with inhibitory potencies against EeAChE and EqBuChE in the low nanomolar level 67 and 153 nM, respectively. Moreover, 3e compound is non-hepatotoxic, able to inhibit amyloid beta aggregation, and shows a mix-type of cholinesterase’s inhibition. The mixed type of inhibition of the compound was confirmed by molecular modeling. Then, yeast three-hybrid (Y3H) technology was used to confirm the known ligand-receptor interactions. New derivatives do not show antioxidant activity (confirmed by the use of two different tests). A pKa assay method was developed to identify the basic physicochemical properties of 3e compound. A LogP assay confirmed that 3e compound fulfills Lipinsky’s rule of five

Design of a Novel and Selective IRAK4 Inhibitor Using Topological Water Network Analysis and Molecular Modeling Approaches.

Protein kinases are deeply involved in immune-related diseases and various cancers. They are a potential target for structure-based drug discovery, since the general structure and characteristics of kinase domains are relatively well-known. However, the ATP binding sites in protein kinases, which serve as target sites, are highly conserved, and thus it is difficult to develop selective kinase inhibitors. To resolve this problem, we performed molecular dynamics simulations on 26 kinases in the aqueous solution, and analyzed topological water networks (TWNs) in their ATP binding sites. Repositioning of a known kinase inhibitor in the ATP binding sites of kinases that exhibited a TWN similar to interleukin-1 receptor-associated kinase 4 (IRAK4) allowed us to identify a hit molecule. Another hit molecule was obtained from a commercial chemical library using pharmacophore-based virtual screening and molecular docking approaches. Pharmacophoric features of the hit molecules were hybridized to design a novel compound that inhibited IRAK4 at low nanomolar levels in the in vitro assay.

Artemisinin resistance phenotypes and K13 inheritance in a Plasmodium falciparum cross and Aotus model

Concerns about malaria parasite resistance to treatment with artemisinin drugs (ARTs) have grown with findings of prolonged parasite clearance t1/2s (>5 h) and their association with mutations in Plasmodium falciparum Kelch-propeller protein K13. Here, we describe a P. falciparum laboratory cross of K13 C580Y mutant with C580 wild-type parasites to investigate ART response phenotypes in vitro and in vivo. After genotyping >400 isolated progeny, we evaluated 20 recombinants in vitro: IC50 measurements of dihydroartemisinin were at similar low nanomolar levels for C580Y- and C580-type progeny (mean ratio, 1.00; 95% CI, 0.62-1.61), whereas, in a ring-stage survival assay, the C580Y-type progeny had 19.6-fold (95% CI, 9.76-39.2) higher average counts. In splenectomized Aotus monkeys treated with three daily doses of i.v. artesunate, t1/2 calculations by three different methods yielded mean differences of 0.01 h (95% CI, -3.66 to 3.67), 0.80 h (95% CI, -0.92 to 2.53), and 2.07 h (95% CI, 0.77-3.36) between C580Y and C580 infections. Incidences of recrudescence were 57% in C580Y (4 of 7) versus 70% in C580 (7 of 10) infections (-13% difference; 95% CI, -58% to 35%). Allelic substitution of C580 in a C580Y-containing progeny clone (76H10) yielded a transformant (76H10C580Rev) that, in an infected monkey, recrudesced regularly 13 times over 500 d. Frequent recrudescences of ART-treated P. falciparum infections occur with or without K13 mutations and emphasize the need for improved partner drugs to effectively eliminate the parasites that persist through the ART component of combination therapy.

1H-pyrrolo[2,3-b]pyridine: A new scaffold for human neutrophil elastase (HNE) inhibitors.

Human neutrophil elastase (HNE) is a potent serine protease belonging to the chymotrypsin family. It is an important target for the development of novel and selective inhibitors for the treatment of inflammatory diseases, especially pulmonary pathologies. Here, we report the synthesis and biological evaluation of a new series of HNE inhibitors with a pyrrolo[2,3-b]pyridine scaffold, which is an isomer of our previously reported indazoles, in order to assess how a shift of the nitrogen from position 2 to position 7 influences activity. The majority of new compounds were effective HNE inhibitors and had IC50 values in the micromolar/submicromolar range, with some compounds active in low nanomolar levels. For example, 2a and 2b inhibited HNE with IC50 values of 15 and 14 nM, respectively. Molecular modeling of compounds differing in the position of heteroatom(s) in the bicyclic moiety and in the oxadiazole ring demonstrated that the calculated geometries of enzyme-inhibitor complexes were in agreement with the observed biological activities. Docking experiments showed that orientation of the active pyrrolo[2,3-b]pyridines in the HNE catalytic triad Ser195-His57-Asp102 correlated with effectiveness of the inhibitor interaction with the enzyme. Thus, the pyrrolo[2,3-b]pyridine scaffold represents a novel scaffold for the development of potent HNE inhibitors.