Indole-Containing Pyrazino[2,1-b]quinazoline-3,6-diones Active against Plasmodium and Trypanosomatids

Exploring the Recent Pioneering Developments of Small Molecules in Antimalarial Drug Armamentarium: A Chemistry Prospective Appraisal

Malaria is a very destructive and lethal parasitic disease that causes significant mortality worldwide, resulting in the loss of millions of lives annually. It is an infectious disease transmitted by mosquitoes, which is caused by different species of the parasite protozoan belonging to the genus Plasmodium. The uncontrolled intake of antimalarial drugs often employed in clinical settings has resulted in the emergence of numerous strains of plasmodium that are resistant to these drugs, including multidrug-resistant strains. This resistance significantly diminishes the effectiveness of many primary drugs used in the treatment of malaria. Hence, there is an urgent need for developing unique classes of antimalarial drugs that function with distinct mechanisms of action. In this context, the design and development of hybrid compounds that combine pharmacophoric properties from different lead molecules into a single unit gives a unique perspective towards further development of malaria drugs in the next generation. In recent years, the field of medicinal chemistry has made significant efforts resulting in the discovery and synthesis of numerous small novel compounds that exhibit potent antimalarial properties, while also demonstrating reduced toxicity and desirable efficacy. In light of this, we have reviewed the progress of hybrid antimalarial agents from 2021 up to the present. This manuscript presents a comprehensive overview of the latest advancements in the medicinal chemistry pertaining to small molecules, with a specific focus on their potential as antimalarial agents. As possible antimalarial drugs that might target both the dual stage and multi-stage stages of the parasite life cycle, these small hybrid molecules have been studied. This review explores a variety of physiologically active compounds that have been described in the literature in order to lay a strong foundation for the logical design and eventual identification of antimalarial drugs based on lead frameworks.

Synthesis and Evaluation of Marine-Inspired Compounds Result in Hybrids with Antitrypanosomal and Antileishmanial Activities

Natural products are a very rich source for obtaining new compounds with therapeutic potential. In the search for new antiparasitic and antimicrobial agents, molecular hybrids were designed based on the structures of antimicrobial marine quinazolinones and eugenol, a natural phenolic compound. Following reports of the therapeutic potential of quinazolinones and eugenol derivatives, it was expected that the union of these pharmacophores could generate biologically relevant substances. The designed compounds were obtained by classical synthetic procedures and were characterized by routine spectrometric techniques. Nine intermediates and final products were then evaluated in vitro against Trypanosoma brucei and Leishmania infantum. Antifungal and antibacterial activity were also evaluated. Six compounds (9b, 9c, 9d, 10b, 10c, and 14) showed mild activity against T. brucei with IC50 in the range of 11.17-31.68 μM. Additionally, intermediate 9c showed anti-Leishmania activity (IC50 7.54 μM) and was six times less cytotoxic against THP-1 cells. In conclusion, novel derivatives with a simple quinazolinone scaffold showing selectivity against parasites without antibacterial and antifungal activities were disclosed, paving the way for new antitrypanosomal agents.

Facile Access to Structurally Diverse Antimalarial Indoles Using a One-Pot A3 Coupling and Domino Cyclization Approach

A multistep and diversity-oriented synthetic route aiming at the A3 coupling/domino cyclization of o-ethynyl anilines, aldehydes and s-amines is described. The preparation of the corresponding precursors included a series of transformations, such as haloperoxidation and Sonogashira cross-coupling reactions, amine protection, desilylation and amine reduction. Some products of the multicomponent reaction underwent further detosylation and Suzuki coupling. The resulting library of structurally diverse compounds was evaluated against blood and liver stage malaria parasites, which revealed a promising lead with sub-micromolar activity against intra-erythrocytic forms of Plasmodium falciparum. The results from this hit-to-lead optimization are hereby reported for the first time.

Discovery, SAR and mechanistic studies of quinazolinone-based acetamide derivatives in experimental visceral leishmaniasis

Towards identification of novel therapeutic candidates, a series of quinazolinone-based acetamide derivatives were synthesized and assessed for their anti-leishmanial efficacy. Amongst synthesized derivatives, compounds F12, F27 and F30 demonstrated remarkable activity towards intracellular L. donovani amastigotes in vitro, with IC₅₀ values of 5.76 ± 0.84 μM, 3.39 ± 0.85 μM and 8.26 ± 1.23 μM against promastigotes, and 6.02 μM ± 0.52, 3.55 ± 0.22 μM and 6.23 ± 0.13 μM against amastigotes, respectively. Oral administration of compounds F12 and F27 entailed >85% reduction in organ parasite burden in L. donovani-infected BALB/c mice and hamsters, by promoting host-protective Th1 cytokine response. In host J774 macrophages, mechanistic studies revealed inhibition of PI3K/Akt/CREB axis, resulting in a decrease of IL-10 versus IL-12 release upon F27 treatment. In silico docking studies conducted with lead compound, F27 demonstrated plausible inhibition of Leishmania prolyl-tRNA synthetase, which was validated via detection of decreased proline levels in parasites and induction of amino acid starvation, leading to G₁ cell cycle arrest and autophagy-mediated programmed cell death of L. donovani promastigotes. Structure-activity analysis and study of pharmacokinetic and physicochemical parameters suggest oral availability and underscore F27 as a promising lead for anti-leishmanial drug development.

Effect of Indole-Containing Pyrazino[2,1-b]quinazoline-3,6-diones in the Virulence of Resistant Bacteria

Drug resistance is rising to alarming levels, constituting one of the major threats to global health. The overexpression of efflux pumps and the formation of biofilms constitute two of the most common resistance mechanisms, favoring the virulence of bacteria. Therefore, the research and development of effective antimicrobial agents that can also counteract resistance mechanisms are extremely important. Pyrazino[2,1-b]quinazoline-3,6-diones, from marine and terrestrial organisms and simpler synthetic analogues, were recently disclosed by us as having relevant antimicrobial properties. In this study, using a multi-step approach, it was possible to synthesize new pyrazino[2,1-b]quinazoline-3,6-diones focusing on compounds with fluorine substituents since, to the best of our knowledge, the synthesis of fluorinated fumiquinazoline derivatives had not been attempted before. The new synthesized derivatives were screened for antibacterial activity and, along with previously synthetized pyrazino[2,1-b]quinazoline-3,6-diones, were characterized for their antibiofilm and efflux-pump-inhibiting effects against representative bacterial species and relevant resistant clinical strains. Several compounds showed relevant antibacterial activity against the tested Gram-positive bacterial species with MIC values in the range of 12.5-77 μM. Furthermore, some derivatives showed promising results as antibiofilm agents in a crystal violet assay. The results of the ethidium bromide accumulation assay suggested that some compounds could potentially inhibit bacterial efflux pumps.

A recent update on new synthetic chiral compounds with antileishmanial activity

Parasitic diseases, including malaria, leishmaniasis, and trypanosomiasis, affect billions of people and are responsible for almost 500,000 deaths/year. In particular, leishmaniasis, a neglected tropical disease, is considered a global public health problem because current drugs have several drawbacks including to toxicity, high cost, and drug resistance, which result in a lack of effective and readily available therapies. Therefore, the synthesis of new, safe, and effective molecules still requires the attention of the scientific community. Moreover, it is well known that chirality plays a crucial role in the antiparasitic activity of molecules, driving the design of their synthesis. Therefore, in this review we report a recent update on new chiral compounds with promising antileishmanial activity, focusing on synthetic approaches. Where reported, in most cases the enantiopure compound has shown better potency against the protozoa than its enantiomer or corresponding racemic mixture.

Fiscalin Derivatives as Potential Neuroprotective Agents

Neurodegenerative diseases (ND) share common molecular/cellular mechanisms that contribute to their progression and pathogenesis. In this sense, we are here proposing new neuroprotection strategies by using marine-derived compounds as fiscalins. This work aims to evaluate the protective effects of fiscalin derivatives towards 1-methyl-4-phenylpyridinium (MPP⁺)- and iron (III)-induced cytotoxicity in differentiated SH-SY5Y cells, an in vitro disease model to study ND; and on P-glycoprotein (P-gp) transport activity, an efflux pump of drugs and neurotoxins. SH-SY5Y cells were simultaneously exposed to MPP⁺ or iron (III), and noncytotoxic concentrations of 18 fiscalin derivatives (0–25 μM), being the cytotoxic effect of both MPP⁺ and iron (III) evaluated 24 and 48 h after exposure. Fiscalins 1a and 1b showed a significant protective effect against MPP⁺-induced cytotoxicity and fiscalins 1b, 2b, 4 and 5 showed a protective effect against iron (III)-induced cytotoxicity. Fiscalins 4 and 5 caused a significant P-gp inhibition, while fiscalins 1c, 2a, 2b, 6 and 11 caused a modest increase in P-gp transport activity, thus suggesting a promising source of new P-gp inhibitors and activators, respectively. The obtained results highlight fiscalins with promising neuroprotective effects and with relevance for the synthesis of new derivatives for the treatment/prevention of ND.