Guanylthiourea derivatives as potential antimalarial agents: Synthesis, in vivo and molecular modelling studies

A review on quinolines: New green synthetic methods and bioactive potential

Quinolines have been an interest of study for a few decades due to the importance of this system in natural and pharmaceutical products. Since their discovery in the nineteenth century, many medicinal properties have been found for quinoline compounds. Firstly, as an anti-parasitic agent against malaria and then against many other diseases, such as, other parasitic infections, HIV, bacterial infections and cancer. Consequently, many synthetic methods have been developed to afford the quinoline ring. In this review we look back at traditional methods and look forward to the most recent and promising "green" methods for the synthesis of quinolines. Also, we review the newest advances in therapeutic compounds based on the quinoline skeleton for the treatment of parasitic and cancer diseases and the most recent applications of quinoline derivatives in drug delivery systems.

Neutral Cyclic Nitreones: Electronic Structure Analysis Reveals an Unorthodox Perspective of Several Zwitterionic Heterocyclic Species

Nitreones are compounds with the general formula L → N+ ← L'. These compounds exhibit medicinal properties and have found applications in phase transfer catalysis. A few nitreones are cyclic; protonated cycloguanil (an antimalarial agent) is the most prominent example. Recently, a few more cyclic compounds were experimentally reported, in which the central N+ was shown to exhibit nitreone character. This led to attention being paid to the chemistry of neutral cyclic nitreones. A thorough literature search led to two sets of cyclic nitreones: C → N ← C type and P → N ← P type. In this work, we report quantum chemical analysis in exploring the electronic structure of neutral cyclic nitreones. Molecular orbital analysis, electron density analysis, charge, electron localization function (ELF), complexation energy values, and Tolman electronic parameter (TEP) all indicate that the studied compounds do carry nitrogen in the N(I) oxidation state and the two lone pairs are at the central nitrogen; thus, they qualify to be considered as cyclic nitreones.

Identification of CYP3A4 inhibitors as potential anti-cancer agents using pharmacoinformatics approach

Biguanide derivatives exhibit a wide variety of therapeutic applications, including anti-cancer effects. Metformin is an effective anti-cancer agent against breast cancer, lung cancer, and prostate cancer. In the crystal structure (PDB ID: 5G5J), it was found that metformin is found in the active site of CYP3A4, and the associated anti-cancer effect was explored. Taking clues from this work, pharmacoinformatics research has been carried out on a series of known and virtual biguanide, guanylthiourea (GTU), and nitreone derivatives. This exercise led to the identification of more than 100 species that exhibit greater binding affinity toward CYP3A4 in comparison to that of metformin. Selected six molecules were subjected to molecular dynamics simulations, and the results are presented in this work.

Structure- and ligand-based drug design methods for the modeling of antimalarial agents: a review of updates from 2012 onwards

Malaria still persists as one of the deadliest infectious disease having a huge morbidity and mortality affecting the higher population of the world. Structure and ligand-based drug design methods like molecular docking and MD simulations, pharmacophore modeling, QSAR and virtual screening are widely used to perceive the accordant correlation between the antimalarial activity and property of the compounds to design novel dominant and discriminant molecules. These modeling methods will speed-up antimalarial drug discovery, selection of better drug candidates for synthesis and to achieve potent and safer drugs. In this work, we have extensively reviewed the literature pertaining to the use and applications of various ligand and structure-based computational methods for the design of antimalarial agents. Different classes of molecules are discussed along with their target interactions pattern, which is responsible for antimalarial activity. Communicated by Ramaswamy H. Sarma.

Recent contributions of quinolines to antimalarial and anticancer drug discovery research

Quinoline, a privileged scaffold in medicinal chemistry, has always been associated with a multitude of biological activities. Especially in antimalarial and anticancer research, quinoline played (and still plays) a central role, giving rise to the development of an array of quinoline-containing pharmaceuticals in these therapeutic areas. However, both diseases still affect millions of people every year, pointing to the necessity of new therapies. Quinolines have a long-standing history as antimalarial agents, but established quinoline-containing antimalarial drugs are now facing widespread resistance of the Plasmodium parasite. Nevertheless, as evidenced by a massive number of recent literature contributions, they are still of great value for future developments in this field. On the other hand, the number of currently approved anticancer drugs containing a quinoline scaffold are limited, but a strong increase and interest in quinoline compounds as potential anticancer agents can be seen in the last few years. In this review, a literature overview of recent contributions made by quinoline-containing compounds as potent antimalarial or anticancer agents is provided, covering publications between 2018 and 2020.

Identification of selective LdDHFR inhibitors using quantum chemical and molecular modeling approach

Among the various known targets for the treatment of Leishmaniasis, dihydrofolate reductase (DHFR) is an essential target which plays an important role in the folate metabolic pathway. In the current study, pharmacoinformatics approaches including quantum chemistry methods, molecular docking and molecular dynamics simulations have been utilized to identify selective Leishmania donovani DHFR (LdDHFR) inhibitors. Initially, for the design of new LdDHFR inhibitors, a virtual combinatorial library was created by considering various head groups (scaffolds), linkers and tail groups. The scaffolds utilized in the library design were selected on the basis of their proton affinity (PA) estimated using quantum chemical methods, required to make a strong H-bond interaction with negatively charged LdDHFR active site. Later on, molecular docking-based virtual screening was performed to screen the designed library. Selectivity of the chosen hits toward the LdDHFR was established through re-docking in the human DHFR enzyme (HsDHFR). Best five hits were subjected to molecular dynamics (MD) simulations to validate their selectivity as well as stability in LdDHFR. Out of the five hits, four were found to be energetically more favorable and promising for selective binding toward LdDHFR in comparison to HsDHFR.Communicated by Ramaswamy H. Sarma.

An insight into the recent development of the clinical candidates for the treatment of malaria and their target proteins

Malaria is an endemic disease, prevalent in tropical and subtropical regions which cost half of million deaths annually. The eradication of malaria is one of the global health priority nevertheless, current therapeutic efforts seem to be insufficient due to the emergence of drug resistance towards most of the available drugs, even first-line treatment ACT, unavailability of the vaccine, and lack of drugs with a new mechanism of action. Intensification of antimalarial research in recent years has resulted into the development of single dose multistage therapeutic agents which has advantage of overcoming the antimalarial drug resistance. The present review explored the current progress in the development of new promising antimalarials against prominent target proteins that have the potential to be a clinical candidate. Here, we also reviewed different aspects of drug resistance and highlighted new drug candidates that are currently in a clinical trial or clinical development, along with a few other molecules with excellent antimalarial activity overs ACTs. The summarized scientific value of previous approaches and structural features of antimalarials related to the activity are highlighted that will be helpful for the development of next-generation antimalarials.

Divalent NI Compounds: Identifying new Carbocyclic Carbenes to Design Nitreones using Quantum Chemical Methods

Nitreones are compounds with oxidation state 1 at the nitrogen, these compounds carry formal positive charge as well as two lone pairs of electrons at nitrogen center. These compounds are also known as divalent NI compounds and can be represented with the general formula L → N+ ← L, where L is an electron donating ligand. In the recent past, several divalent NI compounds have been reported with L = N-heterocyclic carbene (NHC), remote N-heterocyclic carbene (rNHC), carbocyclic carbene (CCC) and diaminocarbene. Recently, our group reported that a novel six-membered CCC (cyclohexa-2,5-diene-4-[diaminomethynyl]-1-ylidene) can stabilize N+ center in nitreones. As an independent carbene, this species is very unstable. In this work, modulation of this CCC using (a) annulation, (b) heterocyclic ring modification, (c) substitutions adjacent to the carbenic carbon, (d) exocyclic double bond insertion and (e) ring contraction, has been reported. These modulations and quantum chemical analyses helped in the identification of five new six-membered CCCs which carry improved donation and stability properties. Further, these CCCs were employed in the design of new divalent NI compounds (nitreones) which carry coordination bonds between ligands and N+ center. The molecular and electronic structure properties, and the donor→acceptor coordination interactions present in the resultant low oxidation state divalent NI compounds have been explored.

Substrate Specific Inhibitor Designed against the Immunomodulator GMF-beta Reversed the Experimental Autoimmune Encephalomyelitis

The concept of substrate inhibition to prevent its phosphorylation has potential in drug discovery and is envisioned to treat the autoimmune disorder multiple sclerosis (MS). Glia maturation factor-β (GMF-β) Ser83 phosphorylation by protein kinase A (PKA) is pivotal in the activation of GMF-β-p38MAPK-NFκB biochemical pathway towards proinflammatory response induction in experimental autoimmune encephalomyelitis (EAE). Using structure-based drug design, we identified the small molecule inhibitor 1-H-indazole-4yl methanol (GMFBI.1) that specifically blocked Ser83 phosphorylation site on GMF-β substrate. Using in vitro and in vivo techniques, molecular mechanism of action of GMFBI.1’s direct interaction with GMF-β substrate and prevention of its Ser83 phosphorylation was established. GMFBI.1 down regulated p38MAPK phosphorylation and NFκB expression essential for proinflammatory response. Further, GMFBI.1 administration at peak of EAE reversed clinical symptoms, immunopathology, proinflammatory cytokine response and up regulated the anti-inflammatory cytokines. Present strategy of substrate inhibition against the key immunomodulatory target has immense therapeutic potential in MS.

Design, synthesis and biological evaluation of 4-aminoquinoline-guanylthiourea derivatives as antimalarial agents

Guanylthiourea (GTU) has been identified as an important antifolate antimalarial pharmacophore unit, whereas, 4-amino quinolones are already known for antimalarial activity. In the present work molecules carrying 4-aminoquinoline and GTU moiety have been designed using molecular docking analysis with PfDHFR enzyme and heme unit. The docking results indicated that the necessary interactions (Asp54 and Ile14) and docking score (-9.63 to -7.36 kcal/mmol) were comparable to WR99210 (-9.89 kcal/mol). From these results nine molecules were selected for synthesis. In vitro analysis of these synthesized compounds reveal that out of the nine molecules, eight show antimalarial activity in the range of 0.61-7.55 μM for PfD6 strain and 0.43-8.04 μM for PfW2 strain. Further, molecular dynamics simulations were performed on the most active molecule to establish comparative binding interactions of these compounds and reference ligand with Plasmodium falciparum dihydrofolate reductase (PfDHFR).

Donor→acceptor coordination interactions in 1,3-bis(NHC)triazenyl Cations: An electronic structure analysis

Donor→acceptor coordination interactions (L → N) between ligands and nitrogen center as in L → N^⊕  ← L were reported in the recent past. This article describes the possibility of L → N coordination interactions in triazenyl cation species L → N₃ ^⊕  ← L. A few 1,3-bis(NHC)triazenyl cation species were experimentally known, the electronic structure analysis reported in this work reveals the presence of L → N (donor→acceptor) interactions in these species. Molecular orbital analysis, NBO charge analysis, energy decomposition analysis, and so forth, confirm the possibility of L → N coordination bond character. Ten molecules with the general formula L → N₃ ^⊕  ← L have been designed carrying L → N₃ ^⊕  ← L interactions. © 2019 Wiley Periodicals, Inc.

Synthesis of pyrazole acrylic acid based oxadiazole and amide derivatives as antimalarial and anticancer agents

Depravity of malaria in terms of morbidity and mortality in human beings makes it a major health issue in tropical and subtropical areas of the globe. Drug counterfeiting and non-adherence to the treatment regimen have significantly contributed to development and spread of multidrug resistance that has highlighted the need for development of novel and more efficient antimalarial drugs. Complexity associated with cancer disease and prevalence of diversified cell populations vindicates highly specific treatment options for treatment of cancer. Resistance to these anticancer agents has posed a great hindrance in successful treatment of cancer. Pondering this ongoing situation, it was speculated to develop novel compounds targeting malaria and cancer. Moving on the same aisle, we synthesized pyrazole acrylic acid based oxadiazole and amide derivatives using multi-step reaction pathways (6a-x; 6a'-h'). Schizont maturation inhibition assay was employed to determine antimalarial potential. Compound 6v emerged as the most potent antimalarial agent targeting falcipain-2 enzyme. Anticancer activity was done using sulforhodamine B assay. Compounds 6b' and 6g' demonstrated promising results against all the tested cell lines. Further, Microscopic view clearly indicated formation of apoptotic bodies, chromatin condensation, shrinkage of cells and bleb formation. Validation of the results was achieved using molecular docking studies. From the obtained results, it was observed that cyclization (oxadiazole) favored antimalarial activity while non-cyclized compounds (amides) emerged as better anticancer agents.