Structural Insights into the Marine Alkaloid Discorhabdin G as a Scaffold towards New Acetylcholinesterase Inhibitors.

In this study, Antarctic Latrunculia sponge-derived discorhabdin G was considered a hit for developing potential lead compounds acting as cholinesterase inhibitors. The hypothesis on the pharmacophore moiety suggested through molecular docking allowed us to simplify the structure of the metabolite. ADME prediction and drug-likeness consideration provided valuable support in selecting 5-methyl-2H-benzo[h]imidazo[1,5,4-de]quinoxalin-7(3H)-one as a candidate molecule. It was synthesized in a four-step sequence starting from 2,3-dichloronaphthalene-1,4-dione and evaluated as an inhibitor of electric eel acetylcholinesterase (eeAChE), human recombinant AChE (hAChE), and horse serum butyrylcholinesterase (BChE), together with other analogs obtained by the same synthesis. The candidate molecule showed a slightly lower inhibitory potential against eeAChE but better inhibitory activity against hAChE than discorhabdin G, with a higher selectivity for AChEs than for BChE. It acted as a reversible competitive inhibitor, as previously observed for the natural alkaloid. The findings from the in vitro assay were relatively consistent with the data available from the AutoDock Vina and Protein-Ligand ANTSystem (PLANTS) calculations.

Bioprospecting the potential of metabolites from a Saharan saline soil strain Nocardiopsis dassonvillei GSBS4.

Saharan soil samples collected in El-Oued province have been investigated for actinobacteria as a valuable source for the production of bioactive metabolites. A total of 273 isolates were obtained and subjected to antagonistic activity tests against human pathogenic germs. A strain with a broad-spectrum antimicrobial activity was selected and identified as Nocardiopsis dassonvillei GSBS4, with high sequence similarities to N. dassonvillei subsp. dassonvilleiT X97886.1 (99%) based on polyphasic taxonomy approach and 16S ribosomal ribonucleic acid gene sequence analysis. The GSBS4 ethyl acetate crude extract showed strong antibacterial activity towards pathogenic bacteria and Candida albicans. It inhibited biofilm formation by Staphylococcus aureus and methicillin-resistant S. aureus with minimum inhibitory concentrations estimated at 0.144 and 1.15 mg·mL-1 , respectively. A 44% biofilm reduction was obtained for S. aureus and 61% for Pseudomonas aeruginosa. Furthermore, phenols composition of the crude extract showed a significant dose-dependent antioxidant activity by α-diphenyl-ß-picrylhydrazyl (57.21%) and 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (64.29%) radicals scavenging assays. Although no inhibition was obtained on human coronavirus human coronavirus (HCoV) 229E and on model enterovirus (poliovirus 1) infection, a dose-dependent increase in cell viability of HCoV 229E-infected cells was noticed as the viability increased from 21% to 37%. Bioassay-guided fractionation of the crude extract gave a fraction showing antibacterial activity, which was analyzed by liquid chromatography-electrospray mass spectrometric technique, providing structural features on a major purple metabolite.

EGCG Disrupts the LIN28B/Let-7 Interaction and Reduces Neuroblastoma Aggressiveness.

Neuroblastoma (NB) is the most commonly diagnosed extracranial solid tumor in children, accounting for 15% of all childhood cancer deaths. Although the 5-year survival rate of patients with a high-risk disease has increased in recent decades, NB remains a challenge in pediatric oncology, and the identification of novel potential therapeutic targets and agents is an urgent clinical need. The RNA-binding protein LIN28B has been identified as an oncogene in NB and is associated with a poor prognosis. Given that LIN28B acts by negatively regulating the biogenesis of the tumor suppressor let-7 miRNAs, we reasoned that selective interference with the LIN28B/let-7 miRNA interaction would increase let-7 miRNA levels, ultimately leading to reduced NB aggressiveness. Here, we selected (-)-epigallocatechin 3-gallate (EGCG) out of 4959 molecules screened as the molecule with the best inhibitory activity on LIN28B/let-7 miRNA interaction and showed that treatment with PLC/PLGA-PEG nanoparticles containing EGCG (EGCG-NPs) led to an increase in mature let-7 miRNAs and a consequent inhibition of NB cell growth. In addition, EGCG-NP pretreatment reduced the tumorigenic potential of NB cells in vivo. These experiments suggest that the LIN28B/let-7 miRNA axis is a good therapeutic target in NB and that EGCG, which can interfere with this interaction, deserves further preclinical evaluation.

A Comprehensive Computational NMR Analysis of Organic Polyarsenicals including the Marine Sponge-Derived Arsenicins A-D and Their Synthetic Analogs.

The adamantane structure of arsenicin A and nor-adamantane structures of arsenicins B-D have gained attention as unique natural polyarsenicals, as well as hits showing promising anticancer activity. The purpose of this study is to apply the predictive power of NMR DFT calculations in order to identify a valid tool to be used in the structural elucidation of similar molecules. 1H- and 13C-NMR chemical shifts of twelve natural and synthetic polyarsenical analogs were calculated and validated by comparison with experimental data acquired in CDCl3 solutions, in regard to mean absolute error (MAE) values under various combinations of two methods (GIAO and CSGT), four functionals and five basis sets, also considering relativistic effects. The best computational approaches are highlighted for predicting the chemical shifts of 1H and 13C nuclei and J(1H,1H) coupling constants in the series of O- and S-polyarsenicals. This comprehensive analysis contributes to making NMR spectroscopy appealing for the structural elucidation of such molecules, contrary to the first structural elucidation of natural arsenicin A, in which the experimental NMR analysis was limited by the poor presence of proton and carbon atoms in its structure and by the shortage of reference data.

Expanding the Chemical Space of Arsenicin A-C Related Polyarsenicals and Evaluation of Some Analogs as Inhibitors of Glioblastoma Stem Cell Growth.

The marine polyarsenical metabolite arsenicin A is the landmark of a series of natural and synthetic molecules characterized by an adamantane-like tetraarsenic cage. Arsenicin A and related polyarsenicals have been evaluated for their antitumor effects in vitro and have been proven more potent than the FDA-approved arsenic trioxide. In this context, we have expanded the chemical space of polyarsenicals related to arsenicin A by synthesizing dialkyl and dimethyl thio-analogs, the latter characterized with the support of simulated NMR spectra. In addition, the new natural arsenicin D, the scarcity of which in the Echinochalina bargibanti extract had previously limited its full structural characterization, has been identified by synthesis. The dialkyl analogs, which present the adamantane-like arsenicin A cage substituted with either two methyl, ethyl, or propyl chains, were efficiently and selectively produced and evaluated for their activity on glioblastoma stem cells (GSCs), a promising therapeutic target in glioblastoma treatment. These compounds inhibited the growth of nine GSC lines more potently than arsenic trioxide, with GI50 values in the submicromolar range, both under normoxic and hypoxic conditions, and presented high selectivity toward non-tumor cell lines. The diethyl and dipropyl analogs, which present favorable physical-chemical and ADME parameters, had the most promising results.

Synthesis of Nucleoside-like Molecules from a Pyrolysis Product of Cellulose and Their Computational Prediction as Potential SARS-CoV-2 RNA-Dependent RNA Polymerase Inhibitors.

(1R,5S)-1-Hydroxy-3,6-dioxa-bicyclo[3.2.1]octan-2-one, available by an efficient catalytic pyrolysis of cellulose, has been applied as a chiral building block in the synthesis of seven new nucleoside analogues, with structural modifications on the nucleobase moiety and on the carboxyl- derived unit. The inverted configuration by Mitsunobu reaction used in their synthesis was verified by 2D-NOESY correlations, supported by the optimized structure employing the DFT methods. An in silico screening of these compounds as inhibitors of SARS-CoV-2 RNA-dependent RNA polymerase has been carried out in comparison with both remdesivir, a mono-phosphoramidate prodrug recently approved for COVID-19 treatment, and its ribonucleoside metabolite GS-441524. Drug-likeness prediction and data by docking calculation indicated compound 6 [=(3S,5S)-methyl 5-(hydroxymethyl)-3-(6-(4-methylpiperazin-1-yl)-9H-purin-9-yl)tetrahydrofuran-3-carboxylate] as the best candidate. Furthermore, molecular dynamics simulation showed a stable interaction of structure 6 in RNA-dependent RNA polymerase (RdRp) complex and a lower average atomic fluctuation than GS-441524, suggesting a well accommodation in the RdRp binding pocket.

Hybrid Molecules Containing Naphthoquinone and Quinolinedione Scaffolds as Antineoplastic Agents.

In recent decades, molecular hybridization has proven to be an efficient tool for obtaining new synthetic molecules to treat different diseases. Based on the core idea of covalently combining at least two pharmacophore fragments present in different drugs and/or bioactive molecules, the new hybrids have shown advantages when compared with the compounds of origin. Hybridization could be successfully applied to anticancer drug discovery, where efforts are underway to develop novel therapeutics which are safer and more effective than those currently in use. Molecules presenting naphthoquinone moieties are involved in redox processes and in other molecular mechanisms affecting cancer cells. Naphthoquinones have been shown to inhibit cancer cell growth and are considered privileged structures and useful templates in the design of hybrids. The present work aims at summarizing the current knowledge on antitumor hybrids built using 1,4- and 1,2-naphthoquinone (present in natural compounds as lawsone, napabucasin, plumbagin, lapachol, α-lapachone, and ß -lapachone), and the related quinolone- and isoquinolinedione scaffolds reported in the literature up to 2021. In detail, the design and synthetic approaches adopted to produce the reported compounds are highlighted, the structural fragments considered in hybridization and their biological activities are described, and the structure-activity relationships and the computational analyses applied are underlined.

Insight into the thermal stability of DNA in hydrated ionic liquids from multi-wavelength UV resonance Raman experiments.

The utility of ionic liquids (ILs) as alternative solvents for stabilizing and preserving the native structure of DNA over the long term may be envisaged for biotechnological and biomedical applications in the near future. The delicate balance between the stabilizing and destabilizing effects of IL-mediated interactions with the structure of DNA is complex and is still not well understood. This work reports a fundamental study dealing with the effect exerted by cations and anions in imidazolium-based ILs on the thermal structural stability of large nucleic acid molecules. Multi-wavelength UV resonance Raman spectroscopy is used for selectively detecting heat-induced structural transitions of DNA localized on specific base tracts. Our study reveals the establishment of preferential interactions between the imidazolium cations of ILs and the guanine bases in the DNA groove that lead to more effective stacking between the guanine bases even at high temperatures. Interestingly, we observe that this trend for ILs sharing the same chloride anion is further enhanced as the alkyl chain on the imidazolium cation gets shorter. The results from the present investigation lead to a more comprehensive view of the IL-mediated interactions with A-T and G-C base pairs during thermal unfolding.

Structural Isomerism and Enhanced Lipophilicity of Pyrithione Ligands of Organoruthenium(II) Complexes Increase Inhibition on AChE and BuChE.

The increasing number of Alzheimer's disease (AD) cases requires the development of new improved drug candidates, possessing the ability of more efficient treatment as well as less unwanted side effects. Cholinesterase enzymes are highly associated with the development of AD and thus represent important druggable targets. Therefore, we have synthesized eight organoruthenium(II) chlorido complexes 1a-h with pyrithione-type ligands (pyrithione = 1-hydroxypyridine-2(1H)-thione, a), bearing either pyrithione a, its methyl (b-e) or bicyclic aromatic analogues (f-h) and tested them for their inhibition towards electric eel acetylcholinesterase (eeAChE) and horse serum butyrylcholinesterase (hsBuChE). The experimental results have shown that the novel complex 1g with the ligand 1-hydroxyquinoline-2-(1H)-thione (g) improves the inhibition towards eeAChE (IC50 = 4.9 µM) and even more potently towards hsBuChE (IC50 = 0.2 µM) in comparison with the referenced 1a. Moreover, computational studies on Torpedo californica AChE have supported the experimental outcomes for 1g, possessing the lowest energy value among all tested complexes and have also predicted several interactions of 1g with the target protein. Consequently, we have shown that the aromatic ring extension of the ligand a, though only at the appropriate position, is a viable strategy to enhance the activity against cholinesterases.

Design, Synthesis and Cancer Cell Growth Inhibition Evaluation of New Aminoquinone Hybrid Molecules.

Molecular hybridization has proven to be a successful multi-target strategy in the design and development of new antitumor agents. Based on this rational approach, we have planned hybrid molecules containing covalently linked pharmacophoric units, present individually in compounds acting as inhibitors of the cancer protein targets tubulin, human topoisomerase II and ROCK1. Seven new molecules, selected by docking calculation of the complexes with each of the proteins taken into consideration, have been efficiently synthesized starting from 2,3-dichloro-1,4-naphtoquinone or 6,7-dichloro-5,8-quinolinquinone. By screening the full National Cancer Institute (NCI) panel, including 60 human cancer cell lines, four molecules displayed good and sometimes better growth inhibition GI50 than the ROCK inhibitor Y-27632, the Topo II inhibitor podophyllotoxin and the tubulin inhibitor combretastatin A-4. The relative position of N,N heteroatoms in the structures of the tested compounds was crucial in affecting bioactivity and selectivity. Furthermore, compound 3 (2-(4-(2-hydroxyethyl)piperazin-1-yl)-3-(3,4,5-trimethoxyphenoxy)naphthalene-1,4-dione) emerged as the most active in the series, showing a potent and selective inhibition of breast cancer BT-549 cells (GI50 < 10 nM).

Glucopyranosylbianthrones from the Algerian Asphodelus tenuifolius: Structural Insights and Biological Evaluation on Melanoma Cancer Cells.

Two new glucopyranosylbianthrones (1 and 2) were isolated from the aerial part of the plant Asphodelus tenuifolius, collected in Southwest Algeria. The 2D structures of 1 and 2 were defined by NMR analysis, HRESIMS data, and comparison with literature data. The comparison of experimental and calculated electronic circular dichroism and NMR data led to characterization of the ( M) and ( P) atropisomeric forms of the glucopyranosylbianthrones, asphodelins (1) and (2), respectively. The in vitro activities of these two metabolites were evaluated in human melanoma A375 cells, and both the compounds inhibited cell proliferation in a concentration-dependent manner, with IC50 values of 20.6 ± 0.8 and 23.2 ± 1.1 µM, respectively. Considering their biological profile, an inverse virtual screening approach was employed to identify and suggest putative anticancer interacting targets.

New Sulfur-Containing Polyarsenicals from the New Caledonian Sponge Echinochalina bargibanti.

Arsenicin A (C3H6As4O3) was isolated from the New Caledonian poecilosclerid sponge Echinochalina bargibanti, and described as the first natural organic polyarsenic compound. Further bioguided fractionation of the extracts of this sponge led us to isolate the first sulfur-containing organic polyarsenicals ever found in Nature. These metabolites, called arsenicin B and arsenicin C, are built on a noradamantane-type framework that is characterized by an unusual As⁻As bonding. Extensive NMR measurements, in combination with mass spectra, enabled the assignment of the structure for arsenicin B (C3H6As4S2) as 2. The scarcity of arsenicin C and its intrinsic chemical instability only allowed the collection of partial spectral data, which prevented the full structural definition. After the extensive computational testing of several putative structures, structure 3 was inferred for arsenicin C (C3H6As4OS) by comparing the experimental and density functional theory (DFT)-calculated ¹H and 13C NMR spectra. Finally, the absolute configurations of 2 and 3 were determined with a combined use of experimental and time-dependent (TD)-DFT calculated electronic circular dichroism (ECD) spectra and observed specific rotations. These findings pose great challenges for the investigation of the biosynthesis of these metabolites and the cycle of arsenic in Nature. Arsenicins B and C showed strong antimicrobial activities, especially against S. aureus, which is comparable to the reference compound gentamycin.

Synthesis of 2,6-Diamino-Substituted Purine Derivatives and Evaluation of Cell Cycle Arrest in Breast and Colorectal Cancer Cells.

Reversine is a potent antitumor 2,6-diamino-substituted purine acting as an Aurora kinases inhibitor and interfering with cancer cell cycle progression. In this study we describe three reversine-related molecules, designed by docking calculation, that present structural modifications in the diamino units at positions 2 and 6. We investigated the conformations of the most stable prototropic tautomers of one of these molecules, the N6-cyclohexyl-N6-methyl-N2-phenyl-7H-purine-2,6-diamine (3), by Density Functional Theory (DFT) calculation in the gas phase, water and chloroform, the last solvent considered to give insights into the detection of broad signals in NMR analysis. In all cases the HN(9) tautomer resulted more stable than the HN(7) form, but the most stable conformations changed in different solvents. Molecules 1⁻3 were evaluated on MCF-7 breast and HCT116 colorectal cancer cell lines showing that, while being less cytotoxic than reversine, they still caused cell cycle arrest in G2/M phase and polyploidy. Unlike reversine, which produced a pronounced cell cycle arrest in G2/M phase in all the cell lines used, similar concentrations of 1⁻3 were effective only in cells where p53 was deleted or down-regulated. Therefore, our findings support a potential selective role of these structurally simplified, reversine-related molecules in p53-defective cancer cells.

Muscarine-like compounds derived from a pyrolysis product of cellulose.

Cellulose represents a key component of a renewable biomass source, from which chiral compounds with a high added value in the application for the synthesis of potentially bioactive molecules can be obtained. The anhydrosugar (1R,5S)-1-hydroxy-3,6-dioxa-bicyclo[3.2.1]octan-2-one (LAC), produced on the gram-scale by catalytic pyrolysis of cellulose, was used as a building block in the synthesis of five new enantiomerically pure muscarine-like products. The structures of the target compounds 4-8 showed different substituents at the C-2 and C-4 positions, but each of them had the same (2S,4R) configuration as the natural (+)-muscarine. A renewed interest in new muscarinic analogues is due to the design and synthesis of molecules exhibiting a higher selectivity for a specific muscarinic receptor and due to the development of effective agents in the treatment of Alzheimer's disease and other cognitive disorders. In this context, products 4-8 were investigated with respect to their binding affinity to human M1-M5 muscarinic acetylcholine receptors. The data indicated that compound 8, emerging as the most active in the series with values comparable to natural (+)-muscarine and a moderate selectivity in favor of the hM2 subtype receptor, also exhibited the highest stability during the interaction with the hM2 (3UON) subtype muscarinic receptor by using a docking calculation.

Design, synthesis, and biological evaluation of novel 2H-pyran-2-one derivatives as potential HIV-1 reverse transcriptase inhibitors.

In search for more effective drugs against HIV infection acting as non-nucleoside reverse transcriptase inhibitors (NNRTIs), a series of new molecules with hybrid structures based on the natural product (+)-calanolide A and the synthetic molecule α-APA, known as potent and selective inhibitors of this enzyme, were selected by docking calculations. A convergent synthetic strategy gave 21 compounds with a 2H-pyran-2-one structural unit and bearing isosteric modifications, which were tested against HIV-infected CEM cell cultures. Only compound 6 (4-((2-(1H-indol-3-yl)ethyl)amino)-6-methyl-2H-pyran-2-one) displayed inhibitory activity (EC50 : 25-50 µM). However, it was associated with a relatively high cytostatic effect on human T lymphocyte (CEM) cell cultures, not easily predictable, neither by the chemical structure nor by the computational approach. Although this drug design has failed in selecting a novel scaffold for NNRTIs, the results have driven the interest towards new potential antitumor molecules showing activity against L1210 murine leukemia and HeLa cervix carcinoma cells, among which compound 21 (6-methyl-4-((2-(naphthalen-1-yl)ethyl)sulfonyl)-2H-pyran-2-one) was the most effective (IC50 : 0.95 and 2.9 µM, respectively).

p-Sulfonato-calix[n]arenes inhibit staphylococcal bicomponent leukotoxins by supramolecular interactions.

PVL (Panton-Valentine leukocidin) and other Staphylococcus aureus ß-stranded pore-forming toxins are important virulence factors involved in various pathologies that are often necrotizing. The present study characterized leukotoxin inhibition by selected SCns (p-sulfonato-calix[n]arenes): SC4, SC6 and SC8. These chemicals have no toxic effects on human erythrocytes or neutrophils, and some are able to inhibit both the activity of and the cell lysis by leukotoxins in a dose-dependent manner. Depending on the type of leukotoxins and SCns, flow cytometry revealed IC50 values of 6-22 µM for Ca2+ activation and of 2-50 µM for cell lysis. SCns were observed to affect membrane binding of class S proteins responsible for cell specificity. Electrospray MS and surface plasmon resonance established supramolecular interactions (1:1 stoichiometry) between SCns and class S proteins in solution, but not class F proteins. The membrane-binding affinity of S proteins was Kd=0.07-6.2 nM. The binding ability was completely abolished by SCns at different concentrations according to the number of benzenes (30-300 µM; SC8>SC6≫SC4). The inhibitory properties of SCns were also observed in vivo in a rabbit model of PVL-induced endophthalmitis. These calixarenes may represent new therapeutic avenues aimed at minimizing inflammatory reactions and necrosis due to certain virulence factors.

Targeted lipid analysis of haemolytic mycelial extracts of Aspergillus niger.

Ethanolic extracts of mycelia from Aspergillus niger (strain N402) grown in liquid media were observed to have haemolytic activity on bovine erythrocytes. This haemolytic activity decreased significantly during the time of growth (1-3 days). Moreover, when A. niger was grown on carbon-deprived medium, the efficiency of this haemolytic activity in the ethanolic extracts was much lower than when grown in carbon-enriched medium, and became almost undetectable after 3 days of growth in carbon-deprived medium. The lipid composition of these ethanolic extracts was analysed by liquid chromatography-electrospray ionisation tandem mass spectrometry. This haemolytic activity can be mainly linked to the relative levels of the molar ratios of the unsaturated fatty acids and lysophosphatidylcholines.

Chemical composition and biological activities of the Algerian Cymbalaria muralis aerial parts.

In the present study we report data about antioxidant (DPPH, ß-Carotene, reducing power), anti-inflammatory (xylene-induced ear oedema in mice (76 ± 1.0%) and membrane stabilisation (100%)) and antimicrobial (Escherichia coli ATCC25922, Staphylococcus aureus ATCC25923, Pseudomonas arugenosa ATCC27853 and Fusarium oxysporum ATCC62506) activities of the ethanolic extract from the Algerian Cymbalaria muralis P. Gaertn., B. Mey. & Scherb (CME). The LC-ESIMS analysis of CME chemical profile allowed to identify antirrhinoside (1), catalpol (2), linarioside (3), glucosyringic acid (4), angoroside C (5), apigenin 7-O-glucoside (6), acacetin 7-O-ß-D-glucopyranoside (7), apigenin (8), chrysoeriol 7-rutinoside (9), diosmin (10) and linarin (11). The evaluated total phenolic and flavonoid contents support the biological activities.

Local and cooperative structural transitions of double-stranded DNA in choline-based deep eutectic solvents.

The possibility of using deep eutectic solvents (DESs) as co-solvents for stabilizing and preserving the native structure of DNA provides an attractive opportunity in the field of DNA biotechnology. The rationale of this work is a systematic investigation of the effect of hydrated choline-based DES on the structural stability of a 30-base-pair double-stranded DNA model via a combination of spectroscopic experiments and MD simulations. UV absorption and CD experiments provide evidence of a significant contribution of DESs to the stabilization of the double-stranded canonical (B-form) DNA structure. Multi-wavelength synchrotron UV Resonance Raman (UVRR) measurements indicate that the hydration shell of adenine-thymine pairs is strongly perturbed in the presence of DESs and that the preferential interaction between H-bond sites of guanine residues and DESs is significantly involved in the stabilization of the dsDNA. Finally, MD calculations show that the minor groove of DNA is significantly selective for the choline part of the investigated DESs compared to the major groove. This finding is likely to have a significant impact not only in terms of thermal stability but also in the modulation of ligand-DNA interactions.

Bioactive poly(arsenic) compounds.

An overview of the biological activities of arsenic compounds containing more than one arsenic atom in their molecular structure is presented. This contribution covers the literature of the last 10-12 years concerning the in vitro and in vivo studies on arsenic species. They include inorganic oxides and sulfides, already employed for a long time in traditional Chinese medicine and currently investigated against hematological or solid malignancies, with arsenic trioxide clinically used in the treatment of acute promyelocytic leukemia. Chemical and biological aspects on the marine product arsenicin A, representing the first and only organic polyarsenical isolated from Nature, have also been reviewed, pointing out the characterization of its C3H6As4O3 molecular structure by experimental and theoretical vibrational spectroscopies, the potent antimicrobial activities, and the promising perspectives as an antitumor agent.