Antiviral compounds in extracts of Korean seaweeds: Evidence for multiple activities

Extracts of 13 Korean seaweeds, previously shown to contain antiviral activity, were investigated in more detail in order to learn the nature of the antiviral compounds and their mechanisms of action. One extract, from Codium fragile, was active against all three test viruses (herpes simplex, HSV; Sindbis, SINV; polio), whereas the others were more selective. Thus four species, Enteromorpha linza, Colpomenia bullosa, Scytosiphon lomentaria, and Undaria pinnatifida, were active against HSV and SINV, but not poliovirus. The other eight were active against either HSV or SINV. In all cases there was evidence for photosensitizers, since the antiviral activities required or were enhanced substantially by light. In general UVA (long wave ultraviolet) was much more effective than visible light in promoting activity, although the extract of Sargassum sagamianum could be activated equally by either. In experiments to determine the site of action of these antiviral extracts, the predominant activity was virucidal (i.e. direct inactivation of virus particles), rather than inhibition of virus replication, although Sargassum sagamianum also could protect cells against subsequent virus infection. These results imply that different antiviral compounds are present among the extracts, and furthermore the activities cannot be explained in terms of common ingredients such as polysaccharides or tannins. We suggest that seaweeds may be a source of potentially useful and interesting antiviral compounds. This revised version was published online in June 2006 with corrections to the Cover Date.     

Antiviral Activity in Tissue Culture Systems of bis-Benzimidazoles, Potent Inhibitors of Rhinoviruses

(S,S)-1,2-bis(5-methoxy-2-benzimidazolyl)-1,2-ethanediol showed antiviral activity in monolayer tissue culture systems against 55 strains of rhinovirus, three types of poliovirus, and strains of type A and B coxsackieviruses. Neither the compound nor any of the analogues tested showed virucidal activity. Its antiviral activity was not associated with interference with viral attachment to or penetration into the cell. At a concentration of 0.1 mg/ml, this group of compounds was generally nontoxic to WI-38, primary bovine kidney, and African green monkey kidney cells and had antiviral activity with 100% inhibition of virus-induced cytopathic effects (CPE). At antiviral levels, these compounds prevented CPE of up to 10(6) median tissue culture infective dose units of virus and completely inhibited formation of new infective virions. The compounds showed antiviral activity both prophylactically and therapeutically against rhinoviruses. Infected cultures could be cleared of CPE up to 90 hr after infection.     

Novel P1 chain-extended HIV protease inhibitors possessing potent anti-HIV activity and remarkable inverse antiviral resistance profiles

A novel series of tyrosine-derived HIV protease inhibitors was synthesized and evaluated for in vitro antiviral activity against wild-type virus and two protease inhibitor-resistant viruses. All of the compounds had wild-type antiviral activities that were similar to or greater than several currently marketed HIV protease inhibitors. In addition, a number of compounds in this series were more potent against the drug-resistant mutant viruses than they were against wild-type virus.     

Ring substituent effects on biological activity of vinyl sulfones as inhibitors of HIV-1

In a previous study, we prepared a small library of chicoric acid analogs that possessed both potent anti-integrase and antiviral activity. It was also shown that active compounds fell into one of two groups: those that inhibited an early stage in viral replication and those that inhibited at a later stage. In this study, a series of vinyl geminal disulfone-containing compounds possessing a range of ring substituents has been synthesized to probe the impact of structure on inhibitory mechanisms. Four active compounds were identified using HIV drug susceptibility assays. Three of the inhibitors possessing either no substituents or electron-withdrawing substituents on the aromatic rings led to high levels of cytotoxicity and antiviral activity. Intrigued by the potential implications of electronic effects on activity, we probed whether the active compounds could be nonspecifically reacting via 1,4-addition. To investigate this hypothesis, the compounds were incubated with glutathione and upon LC/MS analysis, molecular ion peaks corresponding to both mono and double addition adducts were identified. Second, we synthesized analogs lacking the ability to participate in 1,4-addition and tested them for antiviral activity and cytotoxicity, and found the compounds inactive for both activities. Taken together, the studies reported herein suggest that compounds lacking electron-donating substituents on the aromatic ring are promiscuous acceptors of biological nucleophiles, whereas compounds possessing electron-donating substituents seem to resist addition or at least be more selective and significantly less toxic.     

Synthesis and antiviral activity of novel aza-acyclonucleosides

We have prepared a series of novel aza-acyclonucleosides as potential antiviral agents. These compounds were prepared from diethanolamine and the desired purine or pyrimidine base via a Mitsunobu coupling. No antiviral activity was observed against either HSV-1 or HCMV.     

Combination of N-methylisatin-β-thiosemicarbazone derivative (SCH16) with ribavirin and mycophenolic acid potentiates the antiviral activity of SCH16 against Japanese encephalitis virus in vitro

Aim: To investigate the drug to drug interaction of N-methylisatin-β-thiosemicarbazone (MIBT) derivative (SCH16) with ribavirin, mycophenolic acid and pentoxifylline against Japanese encephalitis virus in vitro. Our earlier studies have reported significant antiviral activity of these compounds against Japanese encephalitis virus in vitro and in vivo. Methods and Results: An in vitro drug to drug combination analysis was carried out to investigate whether or not the direct antiviral effect shown by the individual MIBT derivative could be effectively increased when lower concentrations of two compounds in combination were used. The results of this study showed that the combination of MIBT derivative (SCH16) with ribavirin or mycophenolic acid significantly enhanced the antiviral activity of SCH16 against JEV in vitro. In contrast, the combination of SCH16 and pentoxifylline resulted in antagonism. Conclusion: The antiviral activity showed by SCH16 was enhanced in the presence of ribavirin and mycophenolic Acid. Significance and Impact of the Study: Studying the synergistic/additive interaction of the compounds in combination would help in lowering the effective concentration so as to overcome the concern of toxicity.     

Effect of novel natural hypolipidemic compounds on human immunodeficiency virus]

Target screening among microbial products resulted in isolation of hypolipidemic compounds tested for activity against HIV in culture of transferable lymphoblastoid cells MT-4. The majority of the compounds showed antiviral activity. The highest antiviral effect was observed when before exposure to the virus the cells were preincubated for 1 hour in the presence of the isolated compounds. The compounds showed no effect when added to the cell culture preliminarily infected by HIV.     

Antiviral Activity of Carbobenzoxy Di- and Tripeptides on Measles Virus

A series of simple carbobenzoxy peptides showed high and consistent antiviral chemotherapeutic activity in cell culture. In general, greatest activity was found against the measles-distemper or herpesvirus groups, or both, but various representatives of the series had quantitatively and qualitatively different antiviral activities. Several of the compounds, showing the highest antimeasles activity, were investigated extensively. In human cell culture plaque assays, these compounds were active against measles virus at levels of from 15 to 500 mug/ml. At single doses of about 250 to 500 mg/kg, orally in three animal species, significant serum levels of drugs were detected in virus cell culture assays. The mode of action appeared to be therapeutic, as an effect was seen in cell systems infected for at least 24 hr before treatment.     

Anti-influenza virus activities of 2-alkoxyimino-n-(2-isoxazolin-3-ylmethyl)acetamides.

A series of 2-alkoxyimino-N-(2-isoxazolin-3-ylmethyl)acetamides and related compounds were synthesized and their antiviral activities against human influenza A virus were assessed. Studies of the structure-activity relationships revealed the strongest antiviral activity when position-5 of the isoxazoline ring was substituted with a tert-butyl group. When the alkoxyimino moiety was substituted with a methyl, ethyl, isopropyl or allyl group, good antiviral activity was obtained. Among the geometrical isomers at the oxime moiety, the E-isomers were more active than the Z-isomers. Among the compounds examined, (E)-2-allyloxyimino-2-cyano-N-(5-tert-butyl-2-isoxazolin-3-ylmethyl)acetamide (1j) was the most active inhibitor with an EC(50) of 3 microg/mL in vitro.     

Novel antiviral agents: a medicinal plant perspective

Several hundred plant and herb species that have potential as novel antiviral agents have been studied, with surprisingly little overlap. A wide variety of active phytochemicals, including the flavonoids, terpenoids, lignans, sulphides, polyphenolics, coumarins, saponins, furyl compounds, alkaloids, polyines, thiophenes, proteins and peptides have been identified. Some volatile essential oils of commonly used culinary herbs, spices and herbal teas have also exhibited a high level of antiviral activity. However, given the few classes of compounds investigated, most of the pharmacopoeia of compounds in medicinal plants with antiviral activity is still not known. Several of these phytochemicals have complementary and overlapping mechanisms of action, including antiviral effects by either inhibiting the formation of viral DNA or RNA or inhibiting the activity of viral reproduction. Assay methods to determine antiviral activity include multiple-arm trials, randomized crossover studies, and more compromised designs such as nonrandomized crossovers and pre- and post-treatment analyses. Methods are needed to link antiviral efficacy/potency- and laboratory-based research. Nevertheless, the relative success achieved recently using medicinal plant/herb extracts of various species that are capable of acting therapeutically in various viral infections has raised optimism about the future of phyto-antiviral agents. As this review illustrates, there are innumerable potentially useful medicinal plants and herbs waiting to be evaluated and exploited for therapeutic applications against genetically and functionally diverse viruses families such as Retroviridae, Hepadnaviridae and Herpesviridae     

in vitro inhibition of the measles virus by novel ring-expanded ('fat') nucleoside analogues containing the imidazo[4,5-e]diazepine ring system

The synthesis and in vitro anti-measles virus (anti-MV) activity of a class of ring-expanded ('fat') nucleoside analogues (1-4) containing the title heterocyclic ring system are reported. The target compounds were synthesized by base-catalyzed condensations of 4,5-dicarboxylic acid esters of the appropriately substituted imidazole-1-ribosides with suitably substituted guanidine derivatives. Compounds were screened for anti-MV activity in African green monkey kidney cells (CV-1), employing ribavirin as the control standard. While the parent compound 1 itself failed to show any significant antiviral activity against MV, its analogues containing hydrophobic substituents at the 2-position (2) or the 6-position (4) showed promising antiviral activity at submicromolar or micromolar concentration levels with no apparent toxicity to the host cell line. Both compounds showed higher anti-MV activity than the control drug ribavirin.     

Synthesis and antiviral activity of certain second generation methylenecyclopropane nucleosides

A second-generation series of substituted methylenecyclopropane nucleosides (MCPNs) has been synthesized and evaluated for antiviral activity against a panel of human herpesviruses, and for cytotoxicity. Although alkylated 2,6-diaminopurine analogs showed little antiviral activity, the compounds containing ether and thioether substituents at the 6-position of the purine did demonstrate potent and selective antiviral activity against several different human herpesviruses. In the 6-alkoxy series, antiviral activity depended on the length of the ether carbon chain, with the optimum chain length being about four carbon units long. For the corresponding thioethers, compounds containing secondary thioethers were more potent than those with primary thioethers.     

Synthesis,Antiviral and Cytostatic Activities of Carbocyclic Nucleosides Incorporating a Modified Cyclopentane Ring. Part 2:1 Adenosine and Uridine Analogues

Abstract

Six new carbocyclic nucleosides were prepared by mounting a purine (compounds 5–7), 8-azapurine (compounds 9 and 10) or pyrimidine (compound 13) base on the amino group of (1R,cis)-3-(aminornethyl)-1,2,2-trimethylcyclopentylmethanol (2). The antiviral activity of compounds 5–7, 10 and 13, and their cytostatic activity, were evaluated. At subtoxic concentrations, the compounds showed no or marginal antiviral activity. Compound 5 showed moderate inhibition on tumor cell proliferation.     

Antiviral and cytotoxic activities of new derivatives of natural sesquiterpenes and taxol

Common occurrences of serious viral infections and a small number of available antiviral chemotherapeutics necessitate research for new, biologically active substances, which might be of use as antiviral drugs. Natural compounds, e.g., derived from plants and fungi, which show significant and various biological activities, may be a source of potential drugs. Sesquiterpenes, as well as taxol, and their derivatives, may serve as an example. The aim of the present study was to investigate the antiviral, antibacterial and cytotoxic properties of 7 new compounds: derivatives of sesquiterpenes of Lactarius mushroom origin and taxol--N-benzoylphenylisoserinates of sesquiterpenoid alcohols. The cytotoxicity of the tested compounds against Vero, RD, LLC-MK2 and A549 cell lines were assessed using the formazan method. All compounds showed a lower cytotoxicity than taxol. Their antiviral activity in vitro was evaluated by assessing the reduction of virus titre in cells subjected to the compounds in comparison to the cells, which were not subjected to them. It was found that out of 7 investigated compounds 3 exhibited antiviral activity. These compounds inhibited replication of HSV-1 virus in Vero cells. It appears therefore that further investigation of these groups of compounds and their derivatives is justified because they may constitute a potential source of chemotherapeutics.     

Benzothiadiazine dioxides (BTD) derivatives as non-nucleoside human cytomegalovirus (HCMV) inhibitors. study of structural requirements for biological activity

Two new series of BTD derivatives have been synthesised allowing to explore the steric requirements for their biological activity. The N3-alkylBTD compounds have shown antiviral activity in the same order or lower than previously prepared compounds. However, the cytotoxicity values observed prevent this new series of BTD derivatives from its potential therapeutic application. Concerning BTD derivatives with the modified linker attached to N1 position, we have obtained new non-nucleoside anti-HCMV derivatives. The activity against HCMV is shown at concentrations that were 10-fold lower than the concentration that was toxic for the host cells, which confirm that these derivatives show a specific antiviral effect against HCMV. SAR conclusions derived from these last compounds have provided new knowledge about the structural requirements of BTD showing certain positions that could be modified for enhancing the anti-HCMV action.     

Chemical Derivatives of a Small Molecule Deubiquitinase Inhibitor Have Antiviral Activity against Several RNA Viruses

Most antiviral treatment options target the invading pathogen and unavoidably encounter loss of efficacy as the pathogen mutates to overcome replication restrictions. A good strategy for circumventing drug resistance, or for pathogens without treatment options, is to target host cell proteins that are utilized by viruses during infection. The small molecule WP1130 is a selective deubiquitinase inhibitor shown previously to successfully reduce replication of noroviruses and some other RNA viruses. In this study, we screened a library of 31 small molecule derivatives of WP1130 to identify compounds that retained the broad-spectrum antiviral activity of the parent compound in vitro but exhibited improved drug-like properties, particularly increased aqueous solubility. Seventeen compounds significantly reduced murine norovirus infection in murine macrophage RAW 264.7 cells, with four causing decreases in viral titers that were similar or slightly better than WP1130 (1.9 to 2.6 log scale). Antiviral activity was observed following pre-treatment and up to 1 hour postinfection in RAW 264.7 cells as well as in primary bone marrow-derived macrophages. Treatment of the human norovirus replicon system cell line with the same four compounds also decreased levels of Norwalk virus RNA. No significant cytotoxicity was observed at the working concentration of 5 µM for all compounds tested. In addition, the WP1130 derivatives maintained their broad-spectrum antiviral activity against other RNA viruses, Sindbis virus, LaCrosse virus, encephalomyocarditis virus, and Tulane virus. Thus, altering structural characteristics of WP1130 can maintain effective broad-spectrum antiviral activity while increasing aqueous solubility.     

In vitro cytotoxicity of nitroxyl radicals with respect to tumor and diploid human cells and estimation of their antiviral activity

Thirty nine water soluble nitroxyl radicals of various classes, belonging to piperidine, pyrrolidine and imidazolidine series were synthesized. Twenty seven of them were cytotoxic in vitro with respect to the tumor cell culture A431. The CC50 of the most active nitroxyl radicals with respect to cells SW480 and A431 was within 0.16-2.5 mM at the selectivity index of 3.91-7.81 in relation to cytotoxicity of the compounds for the cells of the normal L68 phenotype and tumor cells. The tests on the antiviral activity showed that 16 out of 22 nitroxyl radicals had antiviral activity in Vero cell culture with respect to the West Nile virus and Herpes simplex virus of type II respectively. The EC50 ranged within 0.09-3.45 mM. Some of the nitroxyl radicals had only antiviral activity, but a number of the compounds had both cytotoxic properties and antiviral activity.     

Synthesis and antiviral activities of N-9-oxypurine 1,3-dioxolane and 1,3-oxathiolane nucleosides

Two series of 1,3-dioxolanes and 1,3-oxathiolane nucleosides containing N-9-oxypurine were synthesized as potential antiviral agents. These compounds were prepared by reacting the sugar moieties with iodo- or bromotrimethylsilane, followed by treatment with a mixture of sodium hydride and the desired N-hydroxy purine base. The preparation of these N-hydroxybases was also described. No significant antiviral activity was observed against HIV, HBV, HSV-1, HSV-2, or HCMV.     

Pressurized liquids as an alternative green process to extract antiviral agents from the edible seaweed <Emphasis Type="Italic">Himanthalia elongata</Emphasis>

Pressurized liquid extraction (PLE), an environmentally friendly technique, was used to obtain antiviral compounds from the edible seaweed Himanthalia elongata. The antiviral properties of PLE extracts (hexane, ethanol, and water) were evaluated against herpes simplex virus type 1 (HSV-1) at different stages during viral infection. Pre-treatment of Vero cells with 75 μg mL⁻¹ of ethanol extract inhibited virus infection by approximately 90%, whereas the same concentration of water and hexane extracts reduced the virus infectivity to 78% and 70%, respectively. Moreover, ethanol extract was also more effective against HSV-1 intracellular replication than water and hexane extracts. The antiviral activity of water PLE extract was found to correlate with polysaccharides, since the polysaccharide-rich fraction isolated from this extract showed higher antiviral activity than the original water extract. A GC–MS characterization of the hexane and ethanol extracts showed that the antiviral activity of the hexane extract seemed to be related with the presence of fucosterol; meanwhile, in the case of the ethanol extract, other compounds, besides fucosterol, could be involved in this activity. Results demonstrated that PLE was an appropriate technique to obtain antiviral agents from H. elongata. These antiviral compounds were in addition to polysaccharides, which are the antiviral agents usually proposed when studying seaweeds.     

Synthesis and biological evaluation of novel amprenavir-based P1-substituted bi-aryl derivatives as ultra-potent HIV-1 protease inhibitors

A series of P1-substituted biaryl amprenavir derivatives was designed and synthesized. These compounds were evaluated for enzyme inhibition and antiviral activity in vitro. Several compounds showed highly efficient antiviral activity with EC(50) values down to 0.10nM, which are more potent than marketed HIV-1 protease inhibitors. Docking study indicated that 12c has similar binding mode to amprenavir with full occupancy in P1.