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The coronavirus disease 2019 (COVID-19) pandemic, due to the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in December 2019 and has rapidly spread globally. As the confirmed number of cases has reached to 83 million worldwide, the potential severity and the deadly complications of the disease requires urgent development of effective drugs for prevention and treatment. No proven effective treatment for this virus currently exists. Most of the antiviral discovery efforts are focused on the repurposing of approved or clinical stage drugs. This review highlights the small-molecule repurposed antiviral agents that are currently under investigation in clinical trials for COVID19. These include viral polymerase and protease inhibitors remdesivir, galidesivir, favipiravir, ribavirin, sofosbuvir, tenofovir/emtricitabine, baloxavir marboxil, EIDD-2801, lopinavir/ritonavir; virus-/host-directed viral entry and fusion inhibitors arbidol chloroquine/hydroxychloroquine, chlorpromazine, camostat mesylate, nafamostat mesylate, bromhexine and agents with diverse/unclear mechanism of actions as oseltamivir, triazavirin, ivermectin, nitazoxanide, niclosamide and BLD-2660. The published preclinical and clinical data to date on these drugs as well as the mechanisms of action are reviewed.
A novel series of indolylthiosemicarbazides (6a-6g) and their cyclization products, 4-thiazolidinones (7a-7g), have been designed, synthesized and evaluated, in vitro, for their antiviral activity against a wide range of DNA and RNA viruses. Compounds 6a, 6b, 6c and 6d exhibited notable antiviral activity against Coxsackie B4 virus, at EC50 values ranging from 0.4 to 2.1 μg/mL. The selectivity index (ratio of cytotoxic to antivirally effective concentration) values of these compounds were between 9 and 56. Besides, 6b, 6c and 6d also inhibited the replication of two other RNA viruses, Sindbis virus and respiratory syncytial virus, although these EC50 values were higher compared to those noted for Coxsackie B4 virus. The SAR analysis indicated that keeping the free thiosemicarbazide moiety is crucial to obtain this antiviral activity, since the cyclization products (7a-7g) did not produce any antiviral effect.
A series of indole-based spirothiazolidinones have been designed, synthesized and evaluated, in vitro, for their antitubercular, antiviral, antibacterial, and antifungal activities. The structures of the new compounds were established by IR, 1 H NMR, 13 C NMR (proton decoupled, APT, and DEPT), electrospray ionization mass spectrometry, and microanalysis. Compounds bearing a phenyl substituent at position 8 of the spiro ring, exhibited significant antitubercular activity against Mycobacterium tuberculosis H37Rv ATCC 27294 at concentrations of 3.9 and 7.8 µM. Still, some of the tested compounds displayed activity on mycobacteria with MIC values of 16 and 31 µM. Four of the indole-spirothiazolidinone derivatives were found to be moderately active against Punta Toro virus, yellow fever virus or Sindbis virus in Vero cells. The antiviral EC 50 values were in the range of 1.9-12 µM and the selectivity index (ratio of cytotoxic to antivirally effective concentration) was above 10 in some cases. The most potent effect was seen with the compound that is methylated at positions 2 and 8 of the spirothiazolidinone system.
Graphic abstract
A new series of 5-fluoro-N(2)-(cyclohexylidene)-3-phenyl-1H-indole-2-carbohydrazides (6a-6e) and their cyclization products 5-fluoro-N-(3-oxo-1-thia-4-azaspiro [4.5]dec-4-yl)-3-phenyl-1H-indole-2-carboxamides (7a-7e, 8a-8e) have been synthesized and evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv using the Microplate Alamar Blue Assay (MABA). Compounds showed moderate to good inhibitory activity at 6.25 μg/mL. Among them, 7b, 7d, 8b, and 8d were the most potent analogs with an inhibition range of 91-95 %. Additionally, compounds 6a, 7a, 7e, 8a, and 8e were subjected to the National Cancer Institute's (NCI) in vitro disease-oriented antitumor screening to be evaluated for antitumor activity. 8e, the most potent compound examined, displayed broad spectrum antiproliferative activity with particular selectivity against four leukemia cell lines (CCRF-CEM, HL-60 (TB), K-562, and RPMI-8226) with log (10) GI (50) values between -5.68 and -6.09.
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