Design, Chemical Synthesis and Biological Evaluation of Potential New Antiviral Agents

Acquired Immunodeficiency Syndrome (AIDS) is a disease caused by the Human Immunodeficiency Virus (HIV). Since its discovery in 1981, more than 25 million people died due to this disease. To date, an effective HIV-1 vaccine usable in prophylaxis or in the therapy of humans has not yet been identified. The failures and limited success of HIV vaccines have reinforced the role of chemotherapy and therefore research on the development of effective drugs. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) were the early agents introduced in the therapy and currently they are the most used, based on their concurrent high activity against the virus and low toxicity against human cells. In addition, the rapid development of virus resistance against these types of drugs, needs to find new molecules able to overcome this drawback. My thesis work started from the design of a small library of new molecules, with hybrid structures based on a template deriving from the natural product (+)-calanolide A and the synthetic molecule α-APA, both showing a potent and selective activity against reverse transcriptase. Docking calculation has allowed to select molecules having the best values of interaction energy with the viral enzyme. Chemical synthesis was carried out together with structural characterization by extensive spectroscopic analysis including NMR technique and mass spectrometry. In particular, the synthesis of the amide group present in the structure of some amino-pyrone compounds using the standard method, resulted in the expected N-acylation, but with a C-acyl byproduct. This result has suggested to look further into the study of N,C-acylation selectivity for the ambidentate amino-pyrone moiety, whose reactivity is poorly known. Regioselectivity was investigated under different conditions (organic bases, solvent, acylating agent), also for an enamino-ester taken as a model compound. Experimental procedures were optimized in order to synthesize selectively pure N- and C-acylated compounds. A preliminary enzymatic assay indicated a good activity in the early prepared compounds of the series, promising for the following in vitro tests on HIV infected cells of each molecule in the whole series. In addition, these compounds were tested against other common viruses for human infective pathologies. With the aim of identifying molecules with potential therapeutic applications, the antiviral activity must be related to cytostatic effect, in order to select the ones with a favored selectivity index. Unfortunately, the molecules showed paragonable values in antiviral and cytostatic effects, the latter one not easily predictable neither by the chemical structure, nor by a computational approach. If the drug design by molecular docking has failed in selecting a new scaffold for NNRTIs, the study has driven the interest towards new potential antitumoral molecules showing activity at sub-micromolar concentration against leukemic cell lines. Due to the structural similarity with recently studied antibacterial natural pyrones, the synthetic molecules showing the lowest values of cytotoxicity were investigated in the inhibition of bacterial strains. Some tested compounds have shown a good activity and selectivity against Gram(+) bacteria

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

3a-(4-Chlorophenyl)-1-methyl-3a,4-dihydroimidazo[1,5-<i>a</i>]quinazolin-5(3<i>H</i>)-one: Synthesis and In Silico Evaluation as a Ligand in the µ-Opioid Receptor

In the search for fused heterocycle molecules with potential biological activities, the new title compound was produced in racemic form via a four step-synthetic sequence with an overall yield of 60%. It was structurally characterised via 1H-, 13C-NMR and IR analyses, and the molecular composition was confirmed through a high-resolution MS experiment. After predicting its analgesic activity using PASS online software, wherein a good overlap between its enantiomers and the structure of the natural opioid morphine was observed, the compound was evaluated through docking calculations as a ligand of the µ-opioid receptor. The resulting energy values and interactions were comparable to the data obtained for morphine and its synthetic derivative fentanyl, which is used in the therapeutic treatment of severe forms of pain. Moreover, the title compound displayed favourable predicted blood–brain barrier permeation and drug-likeness

Antibacterial Polyketides from the Marine Alga-Derived Endophitic Streptomyces sundarbansensis: A Study on Hydroxypyrone Tautomerism

Polyketide 13 [=2-hydroxy-5-((6-hydroxy-4-oxo-4H-pyran-2-yl)methyl)-2- propylchroman-4-one] and three related known compounds 7, 9 and 11 were obtained and structurally characterized from Streptomyces sundarbansensis strain, an endophytic actinomycete isolated from the Algerian marine brown algae Fucus sp. Compound 13 was obtained as the major metabolite from optimized culture conditions, by using Agar state fermentation. Due to tautomeric equilibrium, 13 in CD3OD solution was able to incorporate five deuterium atoms, as deduced by NMR and ESI-MS/MS analysis. The 2-hydroxy-γ-pyrone form was established for these metabolites based on the comparison of their experimental IR spectra with the DFT calculated ones, for both the corresponding 4-hydroxy-α-pyrone and 2-hydroxy-γ-pyrone forms. During antibacterial evaluation, compound 13 stood out as the most active of the series, showing a selective activity against the gram positive pathogenic methicillin-resistant S. aureus (MRSA, MIC = 6 μΜ), with a bacteriostatic effect

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, &alpha;-lapachone, and &beta; -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&ndash;activity relationships and the computational analyses applied are underlined

Enhanced Production and Quantitative Evaluation of Nigericin from the Algerian Soil-Living Streptomyces youssoufiensis SF10 Strain

Nigericin, one of the main ionophoric polyethers produced by various Streptomyces strains, presents relevant biological activities including antibacterial and recently studied antitumor properties. This work describes the influence of different culture conditions on the production of this metabolite by Streptomyces sp. SF10, isolated from a semi-arid soil sample collected at Ch&eacute;lia Mountain, in Khenchela (Northeastern Algeria) and identified as Streptomyces youssoufiensis. The extracts from the strain, cultured in a solid state or submerged fermentation conditions, using several carbon sources at different pH values, in the presence or absence of iron (II) sulfate and in co-culture with other Streptomyces species, were analyzed using a high-performance liquid chromatography (HPLC) system equipped with an evaporative light scattering detector (ELSD). The best culture conditions provided a concentration of nigericin of 0.490 &plusmn; 0.001 mg/mL in the extract. The HPLC-ELSD method, optimized here for the quantitative detection of nigericin, can find wider applications in the analysis of several other metabolites characterized by a similar polycyclic polyether structure or, more generally, by the lack of significant chromophores in their molecular structure

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\u20138 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\u2019s disease and other cognitive disorders. In this context, products 4\u20138 were investigated with respect to their binding affinity to human M1\u2013M5 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