Prostratin and 12-O-tetradecanoylphorbol 13-acetate are potent and selective inhibitors of Chikungunya virus replication

Development and Application of Treatment for Chikungunya Fever

The development and application of treatment for Chikungunya fever (CHIKF) remains complicated as there is no current standard treatment and many barriers to research exist. Chikungunya virus (CHIKV) causes serious global health implications due to its socioeconomic impact and high morbidity rates. In research, treatment through natural and pharmaceutical techniques is being evaluated for their efficacy and effectiveness. Natural treatment options, such as homeopathy and physiotherapy, give patients a variety of options for how to best manage acute and chronic symptoms. Some of the most used pharmaceutical therapies for CHIKV include non-steroidal anti-inflammatory drugs (NSAIDS), methotrexate (MTX), chloroquine, and ribavirin. Currently, there is no commercially available vaccine for chikungunya, but vaccine development is crucial for this virus. Potential treatments need further research until they can become a standard part of treatment. The barriers to research for this complicated virus create challenges in the efficacy and equitability of its research. The rising need for increased research to fully understand chikungunya in order to develop more effective treatment options is vital in protecting endemic populations globally.

Targeted in vitro gene silencing of E2 and nsP1 genes of chikungunya virus by biocompatible zeolitic imidazolate framework

Chikungunya fever caused by the mosquito-transmitted chikungunya virus (CHIKV) is a major public health concern in tropical, sub-tropical and temperate climatic regions. The lack of any licensed vaccine or antiviral agents against CHIKV warrants the development of effective antiviral therapies. Small interfering RNA (siRNA) mediated gene silencing of CHIKV structural and non-structural genes serves as a potential antiviral strategy. The therapeutic efficiency of siRNA can be improved by using an efficient delivery system. Metal-organic framework biocomposits have demonstrated an exceptional capability in protecting and efficiently delivering nucleic acids into cells. In the present study, carbonated ZIF called ZIF-C has been utilized to deliver siRNAs targeted against E2 and nsP1 genes of CHIKV to achieve a reduction in viral replication and infectivity. Cellular transfection studies of E2 and nsP1 genes targeting free siRNAs and ZIF-C encapsulated siRNAs in CHIKV infected Vero CCL-81 cells were performed. Our results reveal a significant reduction of infectious virus titre, viral RNA levels and percent of infected cells in cultures transfected with ZIF-C encapsulated siRNA compared to cells transfected with free siRNA. The results suggest that delivery of siRNA through ZIF-C enhances the antiviral activity of CHIKV E2 and nsP1 genes directed siRNAs.

Tigliane-Type Diterpene Esters from the Fruits of Shirakiopsis indica and Their Anti-HIV Activity

Four new diterpene esters, shirakindicans A-D (1-4), along with eight related known diterpene esters (5-12), were isolated from the fruits of the Bangladeshi medicinal plant Shirakiopsis indica. The structures of 1-4 were elucidated by spectroscopic data analysis and electronic circular dichroism (ECD) calculations. Shirakindican A (1) was assigned as a tigliane-type diterpene ester possessing an unusual 6β-hydroxy-1,7-dien-3-one structure, while shirakindican B (2) exhibits a tiglia-1,5-dien-3,7-dione structure. The anti-HIV activities of the isolated diterpene esters were evaluated and showed significant activities for sapintoxins A (5) and D (11), with EC₅₀ values of 0.0074 and 0.044 μM, respectively, and TI values of 1 100 and 5 290. Sapatoxin A (12) also exhibited anti-HIV activity with an EC₅₀ value of 0.13 μM and a TI value of 161.

Contemporary exploitation of natural products for arthropod-borne pathogen transmission-blocking interventions

An integrated approach to innovatively counter the transmission of various arthropod-borne diseases to humans would benefit from strategies that sustainably limit onward passage of infective life cycle stages of pathogens and parasites to the insect vectors and vice versa. Aiming to accelerate the impetus towards a disease-free world amid the challenges posed by climate change, discovery, mindful exploitation and integration of active natural products in design of pathogen transmission-blocking interventions is of high priority. Herein, we provide a review of natural compounds endowed with blockade potential against transmissible forms of human pathogens reported in the last 2 decades from 2000 to 2021. Finally, we propose various translational strategies that can exploit these pathogen transmission-blocking natural products into design of novel and sustainable disease control interventions. In summary, tapping these compounds will potentially aid in integrated combat mission to reduce disease transmission trends.

Study on components with neuroinflammation inhibitory activities from Croton tiglium L. var. xiaopadou

An undescribed tigliane diterpenoid 12- O -tiglyl-13-acetyl-17- O -tiglyl-phorbol, together with thirty-three known components, were isolated from the stems of Croton tiglium L. var. xiaopadou (Euphorbiaceae). Their structures were established based on spectroscopic data and calculated ECD spectra. Their anti-neuroinflammatory effects were evaluated in LPS-induced BV-2 microglia. Thirteen tested compounds showed significant inhibitory activities, especially compounds 10 , 16 , 18 and 21 exhibited an inhibitory effect with IC 50 values in the range of 12.39 to 17.80 μM, which are comparable with that of the positive control (minocycline, IC 50 13.92 μM).

Trigonostemon species in south China: Insights on its chemical constituents towards pharmacological applications

ETHNOPHARMACOLOGY RELEVANCE

The Euphorbiaceae family, which contains about 300 genera and more than 5000 species, is widely distributed in different regions. Trigonostemon genus comprises a wide group of tropical and temperate plants belonging to the Euphorbiaceae family. This genus includes at least 50 species throughout tropical Asia, extending from India and Sri Lanka to New Guinea. They have been employed by local populations for the treatment of asthma, poisonous snake bites, and food poisoning.

AIM OF THE REVIEW

The main aim of the review is to critically analyze the reported traditional uses, bioactive chemical constituents and pharmacological activities of Trigonostemon species.

MATERIALS AND METHODS

Scientific databases, including Google Scholar, PubMed, CNKI, SpringerLink, Web of Science, Wiley Online Library and SciFinder, were searched using keywords such as "Trigonostemon", "South China", "chemical constituents", or "traditional use". Thus, available articles from 2000 to 2020 were collected and analyzed.

RESULTS AND DISCUSSION

This paper provides systematic data that Trigonostemon species possess a diverse phytochemical composition, (including diterpenes, alkaloids, coumarins, lignins, sesquiterpenes, triterpenoids, flavonoids, and polyphenols) found in different plant organs. Research on Trigonostemon plants has revealed critical therapeutic properties, such as antiviral, anti-tumor, antimicrobial, anti-inflammatory, and insecticidal activities.

CONCLUSIONS

It is envisaged that the current review will add value to more scientific research on Trigonostemon species and enhance/promote the increased interest in the sustainable use of Trigonostemon species as well as lead to the validation of unverified ethnobotanical claims. Future studies on Trigonostemon species would focus on establishing the links between the traditional uses, active compounds and reported pharmacological activities.

Demystifying therapeutic potential of medicinal plants against chikungunya virus

Viral infections are posing a great threat to humanity for the last few years. Among these, Chikungunya which is a mosquito-borne viral infection has produced enormous epidemics around the world after been rebounded. Although this infection shows a low mortality rate, patients suffer from fever, arthralgia, and maculopapular rashes, which reduce the quality of life for several weeks to years. The currently available treatments only provide symptomatic relief based on analgesics, antipyretics, and anti-inflammatory drugs which are nonspecific without satisfactory results. Medicinal plants are a widely accepted source of new molecules for the treatment of infectious diseases including viral infections. The scientific reports, primarily focusing on the anti-chikungunya activity of plant extracts, natural origin pure compounds, and their synthetic analog published from 2011 to 2021, were selected from PubMed, Google Scholar, and Scopus by using related keywords like anti-chikungunya plants, natural antivirals for Chikungunya. The present review decodes scientific reports on medicinal plants against chikungunya virus (CHIKV) infection and demystifies the potential phytoconstituents which reveals that the screening of flavonoids containing plants and phytochemicals showing efficacy against other arbovirus infections, may prove as a potential lead for drug development against CHIKV. The present article also outlines pathogenesis, clinical aspects, molecular virology, and diagnostic approaches of CHIKV infection.

Mode-Dependent Antiviral Activity of Medicinal Plant Extracts against the Mosquito-Borne Chikungunya Virus

The lack of specific treatment for chikungunya fever makes the need for anti-chikungunya virus agents more crucial. This study was conducted to evaluate 132 extracts obtained by sequential solvent extraction from 21 medicinal plants for cytopathic effect inhibitory activity using virus-infected Vero cells in two different sample introduction modes. Among the extracts, 42 extracts (31.8%) from 12 plants in the concurrent mode and three extracts (2.3%) from a plant in the non-concurrent mode displayed strong cytopathic effect inhibitory activity (cell viability ≥70%). Viral load quantification analysis unveiled that the extracts of Clinacanthus nutans (chloroform, ethyl acetate, and ethanol), Hydrocotyle sibthorpioides (ethanol), and Ocimum americanum (ethanol and methanol) hindered the release of viral progeny from the infected cells while the extracts of Ficus deltoidea (ethanol), Gynura bicolor (water), H. sibthorpioides (water), and O. americanum (chloroform and ethyl acetate) blocked the entry of virus into the cells. The extracts of Diodella sarmentosa (ethyl acetate), Diplazium esculentum (chloroform, ethyl acetate, and ethanol), and G. bicolor (ethanol) possessed virucidal effect and caused 5.41-log to 6.63-log reductions of viral load compared to the virus control. The results indicate that these medicinal plants are potential sources of anti-chikungunya virus agents that have varied modes of action.

Antivirals against the Chikungunya Virus

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that has re-emerged in recent decades, causing large-scale epidemics in many parts of the world. CHIKV infection leads to a febrile disease known as chikungunya fever (CHIKF), which is characterised by severe joint pain and myalgia. As many patients develop a painful chronic stage and neither antiviral drugs nor vaccines are available, the development of a potent CHIKV inhibiting drug is crucial for CHIKF treatment. A comprehensive summary of current antiviral research and development of small-molecule inhibitor against CHIKV is presented in this review. We highlight different approaches used for the identification of such compounds and further discuss the identification and application of promising viral and host targets.

Current Status of Chikungunya in India

Chikungunya fever (CHIKF) is an arbovirus disease caused by chikungunya virus (CHIKV), an alphavirus of Togaviridae family. Transmission follows a human-mosquito-human cycle starting with a mosquito bite. Subsequently, symptoms develop after 2-6 days of incubation, including high fever and severe arthralgia. The disease is self-limiting and usually resolve within 2 weeks. However, chronic disease can last up to several years with persistent polyarthralgia. Overlapping symptoms and common vector with dengue and malaria present many challenges for diagnosis and treatment of this disease. CHIKF was reported in India in 1963 for the first time. After a period of quiescence lasting up to 32 years, CHIKV re-emerged in India in 2005. Currently, every part of the country has become endemic for the disease with outbreaks resulting in huge economic and productivity losses. Several mutations have been identified in circulating strains of the virus resulting in better adaptations or increased fitness in the vector(s), effective transmission, and disease severity. CHIKV evolution has been a significant driver of epidemics in India, hence, the need to focus on proper surveillance, and implementation of prevention and control measure in the country. Presently, there are no licensed vaccines or antivirals available; however, India has initiated several efforts in this direction including traditional medicines. In this review, we present the current status of CHIKF in India.

1,3-Thiazolbenzamide Derivatives as Chikungunya Virus nsP2 Protease Inhibitors

Chikungunya fever results from an infection with Chikungunya virus (CHIKV, genus Alphavirus) that is prevalent in tropical regions and is spreading fast to temperate climates with documented outbreaks in Europe and the Americas. Currently, there are no available vaccines or antiviral drugs for prevention or treatment of Chikungunya fever. The nonstructural proteins (nsPs) of CHIKV responsible for virus replication are promising targets for the development of new antivirals. This study was attempted to find out new potential inhibitors of CHIKV nsP2 protease using the ligand-based drug design. Two compounds 10 and 10c, identified by molecular docking, showed antiviral activity against CHIKV with IC₅₀ of 13.1 and 8.3 μM, respectively. Both compounds demonstrated the ability to inhibit the activity of nsP2 in a cell-free assay, and the impact of compound 10 on virus replication was confirmed by western blot. The molecular dynamics study of the interactions of compounds 10 and 10c with CHIKV nsP2 showed that a possible mechanism of action of these compounds is the blocking of the active site and the catalytic dyad of nsP2.

Catalytic radical cascade cyclization of alkene-tethered enones to fused bicyclic cyclopropanols

Fused bicyclic cyclopropanols were achieved via an unprecedented HAT-triggered radical cascade reaction of alkene-tethered enones in the presence of an iron catalyst.

Current and Promising Antivirals Against Chikungunya Virus

Chikungunya virus (CHIKV) is the causative agent of chikungunya fever (CHIKF) and is categorized as a(n) (re)emerging arbovirus. CHIKV has repeatedly been responsible for outbreaks that caused serious economic and public health problems in the affected countries. To date, no vaccine or specific antiviral therapies are available. This review gives a summary on current antivirals that have been investigated as potential therapeutics against CHIKF. The mode of action as well as possible compound targets (viral and host targets) are being addressed. This review hopes to provide critical information on the in vitro efficacies of various compounds and might help researchers in their considerations for future experiments.

Review of Phytochemical Compounds as Antiviral Agents Against Arboviruses from the Genera Flavivirus and Alphavirus

Arboviruses are a diverse group of viruses that are among the major causes of emerging infectious diseases. Arboviruses from the genera flavivirus and alphavirus are the most important human arboviruses from a public health perspective. During recent decades, these viruses have been responsible for millions of infections and deaths around the world. Over the past few years, several investigations have been carried out to identify antiviral agents to treat these arbovirus infections. The use of synthetic antiviral compounds is often unsatisfactory since they may raise the risk of viral mutation; they are costly and possess either side effects or toxicity. One attractive strategy is the use of plants as promising sources of novel antiviral compounds that present significant inhibitory effects on these viruses. In this review, we describe advances in the exploitation of compounds and extracts from natural sources that target the vital proteins and enzymes involved in arbovirus replication.

Computer-Aided Design, Synthesis, and Antiviral Evaluation of Novel Acrylamides as Potential Inhibitors of E3-E2-E1 Glycoproteins Complex from Chikungunya Virus

Chikungunya virus (CHIKV) causes an infectious disease characterized by inflammation and pain of the musculoskeletal tissues accompanied by swelling in the joints and cartilage damage. Currently, there are no licensed vaccines or chemotherapeutic agents to prevent or treat CHIKV infections. In this context, our research aimed to explore the potential in vitro anti-CHIKV activity of acrylamide derivatives. In silico methods were applied to 132 Michael’s acceptors toward the six most important biological targets from CHIKV. Subsequently, the ten most promising acrylamides were selected and synthesized. From the cytotoxicity MTT assay, we verified that LQM330, 334, and 336 demonstrate high cell viability at 40 µM. Moreover, these derivatives exhibited anti-CHIKV activities, highlighting the compound LQM334 which exhibited an inhibition value of 81%. Thus, docking simulations were performed to suggest a potential CHIKV-target for LQM334. It was observed that the LQM334 has a high affinity towards the E3-E2-E1 glycoproteins complex. Moreover, LQM334 reduced the percentage of CHIKV-positive cells from 74.07 to 0.88%, 48h post-treatment on intracellular flow cytometry staining. In conclusion, all virtual simulations corroborated with experimental results, and LQM334 could be used as a promising anti-CHIKV scaffold for designing new drugs in the future.

Antivirals against Chikungunya Virus: Is the Solution in Nature?

The worldwide outbreaks of the chikungunya virus (CHIKV) in the last years demonstrated the need for studies to screen antivirals against CHIKV. The virus was first isolated in Tanzania in 1952 and was responsible for outbreaks in Africa and Southwest Asia in subsequent years. Between 2007 and 2014, some cases were documented in Europe and America. The infection is associated with low rates of death; however, it can progress to a chronic disease characterized by severe arthralgias in infected patients. This infection is also associated with Guillain–Barré syndrome. There is no specific antivirus against CHIKV. Treatment of infected patients is palliative and based on analgesics and non-steroidal anti-inflammatory drugs to reduce arthralgias. Several natural molecules have been described as antiviruses against viruses such as dengue, yellow fever, hepatitis C, and influenza. This review aims to summarize the natural compounds that have demonstrated antiviral activity against chikungunya virus in vitro.

Unlocking the Drug Potential of the Bryostatin Family: Recent Advances in Product Synthesis and Biomedical Applications

Bryostatins are a class of naturally occurring macrocyclic lactones with a unique fast developing portfolio of clinical applications, including treatment of AIDS, Alzheimer's disease, and cancer. This comprehensive account summarizes the recent progress (2014-present) in the development of bryostatins, including their total synthesis and biomedical applications. An emphasis is placed on the discussion of bryostatin 1, the most-studied analogue to date. This review highlights the synthetic and biological challenges of bryostatins and provides an outlook on their future development.

Isolation of phenanthrenes and identification of phorbol ester derivatives as potential anti-CHIKV agents using FBMN and NAP from Sagotia racemosa

In an effort to identify inhibitors of Chikungunya virus (CHIKV) replication, a systematic study of 594 extracts of plant species originating from the French Guiana plateau region was performed in a virus-cell-based assay for CHIKV assay. The extract obtained from the stem bark of Sagotia racemosa was selected for its potent antiviral activity. Using a classical bioassay-guided procedure, three undescribed degraded diterpenoids, i.e. trigohowilols C and D and trigoflavidol D, as well as trigoxyphin K, stictic acid, hyperhomosekikaic acid and five known flavonoids were isolated. The structures of these compounds were elucidated by extensive NMR spectroscopic data analysis. Although trigohowilols C and D were isolated from the most active fraction they didn't show any antiviral activity. By using the Feature-Based Molecular Networking (FBMN) and Network Annotation Propagation (NAP) workflows, it has been shown that the strong anti-CHIKV activity found for this fraction might be due to the presence of analogues of 12-O-tetradecanoylphorbol-13-acetate (TPA), one of the most potent inhibitors of CHIKV replication identified to date.

Tri- and Diterpenoids from Stillingia loranthacea as Inhibitors of Zika Virus Replication

This study represents the first phytochemical analysis of Stillingia loranthacea (S. loranthacea) and describes new terpenoids obtained from the root bark of this species. The fractionation of the hexane extract from the root bark led to the isolation of two new 28-nor-taraxarenes derivatives, loranthones A and B (1 and 2), four new tigliane diterpenes (5-8), three known tigliane diterpenes (9-11), and three known flexibilene diterpenes, tonantzitlolones A-C (12-14). The investigation of these compounds and the use of a molecular networking-based prioritization approach afforded two other new 28-nor-taraxarenes, loranthones C and D (3 and 4). The cytotoxicity of compounds 1, 2, and 5-14 was evaluated against Vero cells, and their 20% cytotoxic concentration (CC₂₀) values varied from 8.7 to 328 μM; antiviral activity was tested against an epidemic Zika virus (ZIKV) strain circulating in Brazil. Six out of 12 compounds (2, 5, 9-11, and 14) exhibited significant antiviral effects against ZIKV. Specifically, compounds 2 and 5 offered the most promise as lead compounds as they had a 1.7 and 1.8 log₁₀ TCID₅₀/mL reduction in ZIKV replication, respectively. Together, the present findings have identified S. loranthacea terpenoids as potent anti-ZIKV inhibitors and pave the way to the development of possible new treatments against this devastating pathogen.

Inhibition by Marine Algae of Chikungunya Virus Isolated From Patients in a Recent Disease Outbreak in Rio de Janeiro

Chikungunya virus (CHIKV) infection is one of the most challenging re-emergent diseases caused by a virus, and with no specific antiviral treatment it has now become a major public health concern. In this investigation, 25 blood samples were collected from patients with characteristic CHIKV symptoms and submitted to a virus isolation protocol, which detected 3 CHIKV isolates. These samples were evaluated by sequencing for the characterization of the strains and any homology to viruses circulating in Brazil during a recent outbreak. These viruses were used for the development of antiviral assays. Subsequently, the inhibitory effects of seaweed extracts on CHIKV replication were studied. The marine species of algae tested were Bryothamnion triquetrum, Caulerpa racemosa, Laurencia dendroidea, Osmundaria obtusiloba, Ulva fasciata, and Kappaphycus alvarezii, all of which are found in different countries including Brazil. The results revealed high levels of CHIKV inhibition, including extracts of O. obtusiloba with inhibition values of 1.25 μg/mL and a selectivity index of 420. Viral inhibition was dependent on the time of addition of extract of O. obtusiloba to the infected cells, with the optimal inhibition occurring up to 16 h after infection. Neuron evaluations with O. obtusiloba were performed and demonstrated low toxicity, and in infected neurons we observed high inhibitory activity in a dose-dependent manner. These results indicate that the algal extracts may be promising novel candidates for the development of therapeutic agents against CHIKV infections.

Investigation of Premyrsinane and Myrsinane Esters in Euphorbia cupanii and Euphobia pithyusa with MS2LDA and Combinatorial Molecular Network Annotation Propagation

The species Euphorbia pithyusa and Euphorbia cupanii are two closely related Mediterranean spurges for which their taxonomic relationships are still being debated. Herein, the diterpene ester content of E. cupanii was investigated using liquid chromatography coupled to tandem mass spectrometry. The use of molecular networking coupled to unsupervised substructure annotation ( MS2LDA) indicated the presence of new premyrsinane/myrsinane diterpene esters in the E. cupanii fractions. A structure-guided isolation procedure yielded 16 myrsinane (11a-h, 12, and 13) and premyrsinane esters (14a-c and 15a-c), along with four 4β-phorbol esters (16a-c and 17) that showed inhibitory activity against chikungunya virus replication. The structures of the 16 new compounds (11a-c, 11h, 12, 13, 14a-c, 15a-c, 16a-c, and 17) were characterized by NMR spectroscopy and X-ray crystallography. To further uncover the diterpene ester content of these two species, the concept of combinatorial network annotation propagation (C-NAP) was developed. By leveraging the fact that the diterpene esters of Euphorbia species are made up of limited building blocks, a combinatorial database of theoretical structures was created and used for C-NAP that made possible the annotation of 123 premyrsinane or myrsinane esters, from which 74% are not found in any compound database.

Macrocyclic Diterpenoids from Euphorbiaceae as A Source of Potent and Selective Inhibitors of Chikungunya Virus Replication

Macrocyclic diterpenoids produced by plants of the Euphorbiaceae family are of considerable interest due to their high structural diversity; and their therapeutically relevant biological properties. Over the last decade many studies have reported the ability of macrocyclic diterpenoids to inhibit in cellulo the cytopathic effect induced by the chikungunya virus. This review; which covers the years 2011 to 2019; lists all macrocyclic diterpenoids that have been evaluated for their ability to inhibit viral replication. The structure-activity relationships and the probable involvement of protein kinase C in their mechanism of action are also detailed.

Spectrum of candidate molecules against Chikungunya virus - an insight into the antiviral screening platforms

INTRODUCTION

Chikungunya disease has undergone a phenomenal transition in its status from being recognized as a sporadic infection to acquiring a global prominence over the last couple of decades. The causative agent behind the explosive epidemics worldwide is the re-emerging pathogen, Chikungunya virus (CHIKV). Areas covered: The current review discusses all the possible avenues of antiviral research towards combating CHIKV infection. Aspects of antiviral drug discovery such as antiviral targets, candidate molecules screened, and the various criteria to be a potential inhibitor are all discussed at length. Existing antiviral drug screening tools for CHIKV and their applications are thoroughly described. Clinical trial status of agents with therapeutic potential has been updated with special mention of candidate molecules under patent approval. Databases such as PubMed, Google Scholar, ScienceDirect, Google Patent, and Clinical Trial Registry platforms were referred. Expert opinion: The massive outbreaks of Chikungunya viral disease in the recent past and the serious health concerns imposed thereby, have driven the search for effective therapeutics. The greatest challenge being the non-availability of robust, reproducible, cost-effective and biologically accurate assay models. Nevertheless, there is a need to identify good models mimicking the appropriate microenvironment of an infectious setting.

Antiviral Compounds from Codiaeum peltatum Targeted by a Multi-informative Molecular Networks Approach

From a set of 292 Euphorbiaceae extracts, the use of a molecular networking (MN)-based prioritization approach highlighted three clusters (MN1-3) depicting ions from the bark extract of Codiaeum peltatum. Based on their putative antiviral potential and structural novelty, the MS-guided purification of compounds present in MN1 and MN2 afforded two new daphnane-type diterpenoid orthoesters (DDO), codiapeltines A (1) and B (2), the new actephilols B (3) and C (4), and four known 1,4-dioxane-fused phenanthrene dimers (5-8). The structures of the new compounds were elucidated by NMR spectroscopic data analysis, and the absolute configurations of compounds 1 and 2 were deduced by comparison of experimental and calculated ECD spectra. Codiapeltine B (2) is the first daphnane bearing a 9,11,13-orthoester moiety, establishing a new major structural class of DDO. Compounds 1-8 and four recently reported monoterpenyl quinolones (9-12) detected in MN3 were investigated for their selective activities against chikungunya virus replication and their antipolymerase activities against the NS5 proteins of dengue and zika viruses. Compounds 3-8 exhibited strong inhibitory activities on both dengue and zika NS5 in primary assays, but extensive biological analyses indicated that only actephilol B (3) displayed a specific interaction with the NS5 targets.

Structural Simplification of Natural Products

Natural products (NPs) are important sources of clinical drugs due to their structural diversity and biological prevalidation. However, the structural complexity of NPs leads to synthetic difficulties, unfavorable pharmacokinetic profiles, and poor drug-likeness. Structural simplification by truncating unnecessary substructures is a powerful strategy for overcoming these limitations and improving the efficiency and success rate of NP-based drug development. Herein, we will provide a comprehensive review of the structural simplification of NPs with a focus on design strategies, case studies, and new technologies. In particular, a number of successful examples leading to marketed drugs or drug candidates will be discussed in detail to illustrate how structural simplification is applied in lead optimization of NPs.

Inhibition by Marine Algae of Chikungunya Virus Isolated From Patients in a Recent Disease Outbreak in Rio de Janeiro

Chikungunya virus (CHIKV) infection is one of the most challenging re-emergent diseases caused by a virus, and with no specific antiviral treatment it has now become a major public health concern. In this investigation, 25 blood samples were collected from patients with characteristic CHIKV symptoms and submitted to a virus isolation protocol, which detected 3 CHIKV isolates. These samples were evaluated by sequencing for the characterization of the strains and any homology to viruses circulating in Brazil during a recent outbreak. These viruses were used for the development of antiviral assays. Subsequently, the inhibitory effects of seaweed extracts on CHIKV replication were studied. The marine species of algae tested were Bryothamnion triquetrum, Caulerpa racemosa, Laurencia dendroidea, Osmundaria obtusiloba, Ulva fasciata, and Kappaphycus alvarezii, all of which are found in different countries including Brazil. The results revealed high levels of CHIKV inhibition, including extracts of O. obtusiloba with inhibition values of 1.25 μg/mL and a selectivity index of 420. Viral inhibition was dependent on the time of addition of extract of O. obtusiloba to the infected cells, with the optimal inhibition occurring up to 16 h after infection. Neuron evaluations with O. obtusiloba were performed and demonstrated low toxicity, and in infected neurons we observed high inhibitory activity in a dose-dependent manner. These results indicate that the algal extracts may be promising novel candidates for the development of therapeutic agents against CHIKV infections.

Structurally Diverse Diterpenoids from Sandwithia guyanensis

Bioassay-guided fractionation of an EtOAc extract of the trunk bark of Sandwithia guyanensis, using a chikungunya virus (CHIKV)-cell-based assay, afforded 17 new diterpenoids 1-17 and the known jatrointelones A and C (18 and 19). The new compounds included two tetranorditerpenoids 1 and 2, a trinorditerpenoid 3, euphoractines P-W (4-11), and euphactine G (13) possessing the rare 5/6/7/3 (4-7), 5/6/6/4 (8-11), and 5/6/8 (13) fused ring skeletons, sikkimenoid E (12), and jatrointelones J-M (14-17) possessing jatropholane and lathyrane carbon skeletons, respectively. Jatrointelones J (14) and M (17) represent the first naturally occurring examples of C-15 nonoxidized lathyrane-type diterpenoids. The structures of the new compounds were elucidated by NMR spectroscopic data analysis. The relative configuration of compound 16 and the absolute configurations of compounds 3-6 and 14 were determined by single-crystal X-ray diffraction analysis. In addition, jatrointelone K (15) was chemically transformed to euphoractine T (8) supporting the biosynthetic relationships between the two types of diterpenoids. Only compound 15 showed a moderate anti-CHIKV activity with an EC₅₀ value of 14 μM. Finally, using a molecular networking-based dereplication strategy, several close analogues of 12- O-tetradecanoylphorbol-13-acetate (TPA), one of the most potent inhibitors of CHIKV replication, were dereplicated.

Environmentally Friendly Procedure Based on Supercritical Fluid Chromatography and Tandem Mass Spectrometry Molecular Networking for the Discovery of Potent Antiviral Compounds from Euphorbia semiperfoliata

A supercritical fluid chromatography-based targeted purification procedure using tandem mass spectrometry and molecular networking was developed to analyze, annotate, and isolate secondary metabolites from complex plant extract mixture. This approach was applied for the targeted isolation of new antiviral diterpene esters from Euphorbia semiperfoliata whole plant extract. The analysis of bioactive fractions revealed that unknown diterpene esters, including jatrophane esters and phorbol esters, were present in the samples. The purification procedure using semipreparative supercritical fluid chromatography led to the isolation and identification of two new jatrophane esters (13 and 14) and one known (15) and three new 4-deoxyphorbol esters (16-18). The structure and absolute configuration of compound 16 were confirmed by X-ray crystallography. This compound was found to display antiviral activity against Chikungunya virus (EC₅₀ = 0.45 μM), while compound 15 proved to be a potent and selective inhibitor of HIV-1 replication in a recombinant virus assay (EC₅₀ = 13 nM). This study showed that a supercritical fluid chromatography-based protocol and molecular networking can facilitate and accelerate the discovery of bioactive small molecules by targeting molecules of interest, while minimizing the use of toxic solvents.

Bioactive Natural Products Prioritization Using Massive Multi-informational Molecular Networks

Natural products represent an inexhaustible source of novel therapeutic agents. Their complex and constrained three-dimensional structures endow these molecules with exceptional biological properties, thereby giving them a major role in drug discovery programs. However, the search for new bioactive metabolites is hampered by the chemical complexity of the biological matrices in which they are found. The purification of single constituents from such matrices requires such a significant amount of work that it should be ideally performed only on molecules of high potential value (i.e., chemical novelty and biological activity). Recent bioinformatics approaches based on mass spectrometry metabolite profiling methods are beginning to address the complex task of compound identification within complex mixtures. However, in parallel to these developments, methods providing information on the bioactivity potential of natural products prior to their isolation are still lacking and are of key interest to target the isolation of valuable natural products only. In the present investigation, we propose an integrated analysis strategy for bioactive natural products prioritization. Our approach uses massive molecular networks embedding various informational layers (bioactivity and taxonomical data) to highlight potentially bioactive scaffolds within the chemical diversity of crude extracts collections. We exemplify this workflow by targeting the isolation of predicted active and nonactive metabolites from two botanical sources (Bocquillonia nervosa and Neoguillauminia cleopatra) against two biological targets (Wnt signaling pathway and chikungunya virus replication). Eventually, the detection and isolation processes of a daphnane diterpene orthoester and four 12-deoxyphorbols inhibiting the Wnt signaling pathway and exhibiting potent antiviral activities against the CHIKV virus are detailed. Combined with efficient metabolite annotation tools, this bioactive natural products prioritization pipeline proves to be efficient. Implementation of this approach in drug discovery programs based on natural extract screening should speed up and rationalize the isolation of bioactive natural products.

The medicinal chemistry of Chikungunya virus

Arthropod-borne viruses (arboviruses) are an important threat to human and animal health globally. Among these, zoonotic diseases account for billions of cases of human illness and millions of deaths every year, representing an increasing public health problem. Chikungunya virus belongs to the genus Alphavirus of the family Togariridae, and is transmitted mainly by the bite of female mosquitoes of the Aedes aegypti and/or A. albopictus species. The focus of this review will be on the medicinal chemistry of Chikungunya virus, including synthetic and natural products, as well as rationally designed compounds.

Isolation of Premyrsinane, Myrsinane, and Tigliane Diterpenoids from Euphorbia pithyusa Using a Chikungunya Virus Cell-Based Assay and Analogue Annotation by Molecular Networking

Six new premyrsinol esters (1-6) and one new myrsinol ester (8) were isolated from an aerial parts extract of Euphorbia pithyusa, together with a known premyrsinol (7) and two known dideoxyphorbol esters (9 and 10), following a bioactivity-guided purification procedure using a chikungunya virus (CHIKV) cell-based assay. The structures of the new diterpene esters (1-6 and 8) were elucidated by MS and NMR spectroscopic data interpretation. Compounds 1-10 were evaluated against CHIKV replication, and results showed that the 4β-dideoxyphorbol ester 10 was the most active compound, with an EC₅₀ value of 4.0 ± 0.3 μM and a selectivity index of 10.6. To gain more insight into the structural diversity of diterpenoids produced by E. pithyusa, the initial extract and chromatographic fractions were analyzed by LC-MS/MS. The generated data were annotated using a molecular networking procedure and revealed that dozens of unknown premyrsinane, myrsinane, and tigliane analogues were present.

Chikungunya virus: an update on the biology and pathogenesis of this emerging pathogen

Re-emergence of chikungunya virus, a mosquito-transmitted pathogen, is of serious public health concern. In the past 15 years, after decades of infrequent, sporadic outbreaks, the virus has caused major epidemic outbreaks in Africa, Asia, the Indian Ocean, and more recently the Caribbean and the Americas. Chikungunya virus is mainly transmitted by Aedes aegypti mosquitoes in tropical and subtropical regions, but the potential exists for further spread because of genetic adaptation of the virus to Aedes albopictus, a species that thrives in temperate regions. Chikungunya virus represents a substantial health burden to affected populations, with symptoms that include severe joint and muscle pain, rashes, and fever, as well as prolonged periods of disability in some patients. The inflammatory response coincides with raised levels of immune mediators and infiltration of immune cells into infected joints and surrounding tissues. Animal models have provided insights into disease pathology and immune responses. Although host innate and adaptive responses have a role in viral clearance and protection, they can also contribute to virus-induced immune pathology. Understanding the mechanisms of host immune responses is essential for the development of treatments and vaccines. Inhibitory compounds targeting key inflammatory pathways, as well as attenuated virus vaccines, have shown some success in animal models, including an attenuated vaccine strain based on an isolate from La Reunion incorporating an internal ribosome entry sequence that prevents the virus from infecting mosquitoes and a vaccine based on virus-like particles expressing envelope proteins. However, immune correlates of protection, as well as the safety of prophylactic and therapeutic candidates, are important to consider for their application in chikungunya infections. In this Review, we provide an update on chikungunya virus with regard to its epidemiology, molecular virology, virus-host interactions, immunological responses, animal models, and potential antiviral therapies and vaccines.

Antiviral effect of compounds derived from the seeds of Mammea americana and Tabernaemontana cymosa on Dengue and Chikungunya virus infections

Background

The transmission of Dengue virus (DENV) and Chikungunya virus (CHIKV) has increased worldwide, due in part to the lack of a specific antiviral treatment. For this reason, the search for compounds with antiviral potential, either as licensed drugs or in natural products, is a research priority. The objective of this study was to identify some of the compounds that are present in Mammea americana (M. americana) and Tabernaemontana cymosa (T. cymosa) plants and, subsequently, to evaluate their cytotoxicity in VERO cells and their potential antiviral effects on DENV and CHIKV infections in those same cells.

Methods

Dry ethanolic extracts of M. americana and T. cymosa seeds were subjected to open column chromatographic fractionation, leading to the identification of four compounds: two coumarins, derived from M. americana; and lupeol acetate and voacangine derived from T. cymosa.. The cytotoxicity of each compound was subsequently assessed by the MTT method (at concentrations from 400 to 6.25 μg/mL). Pre- and post-treatment antiviral assays were performed at non-toxic concentrations; the resulting DENV inhibition was evaluated by Real-Time PCR, and the CHIKV inhibition was tested by the plating method. The results were analyzed by means of statistical analysis.

Results

The compounds showed low toxicity at concentrations ≤ 200 μg/mL. The compounds coumarin A and coumarin B, which are derived from the M. americana plant, significantly inhibited infection with both viruses during the implementation of the two experimental strategies employed here (post-treatment with inhibition percentages greater than 50%, p < 0.01; and pre-treatment with percentages of inhibition greater than 40%, p < 0.01). However, the lupeol acetate and voacangine compounds, which were derived from the T. cymosa plant, only significantly inhibited the DENV infection during the post-treatment strategy (at inhibition percentages greater than 70%, p < 0.01).

Conclusion

In vitro, the coumarins are capable of inhibiting infection by DENV and CHIKV (with inhibition percentages above 50% in different experimental strategies), which could indicate that these two compounds are potential antivirals for treating Dengue and Chikungunya fever. Additionally, lupeol acetate and voacangine efficiently inhibit infection with DENV, also turning them into promising antivirals for Dengue fever.

Spectral characterisation, antiviral activities, in silico ADMET and molecular docking of the compounds isolated from Tectona grandis to chikungunya virus

Chikungunya infection is treated symptomatically with antipyretics and anti-inflammatory drugs without any specific antiviral drug till date. The lack of an approved antiviral drug and the emergence of virulent strains after 2006 epidemics emphasize the need for the development of potential antiviral drugs to Chikungunya virus. Hence, we studied the antiviral activity of the extracts and compounds isolated from Tectona grandis leaves to both the Asian and East central South African strains of Chikungunya virus. Five compounds were isolated from the ethanolic extract of Tectona grandis by bioactivity guided fractionation followed by Spectral Characterisation through GC-MS and NMR spectroscopy and investigated for the antiviral activity. Also in silico ADMET and Molecular Docking of the characterised compounds against the structural and non structural proteins of Chikungunya virus were performed. The characterised compound Benzene-1-carboxylic acid hexadeconate was effective at IC 50 3.036μg/ml (7.5μM) and 76.46μg/ml (189.02μM) to Asian and ECSA strain of CHIKV respectively. The compound showed desirable pharmacokinetic properties and significant molecular interactions with the E1 protein of Chikungunya virus by in silico analysis. Thus Benzene-1-carboxylic acid-2-hexadeconate isolated from Tectona grandis was found to be a promising drug candidate to both the Asian and ECSA strains of Chikungunya virus with high selectivity indices in comparison to the reference RNA antiviral drug Ribavirin.

Protein kinases C as potential host targets for the inhibition of chikungunya virus replication

We have shown previously that prostratin, a non-tumor promoting phorbol ester, inhibits chikungunya virus (CHIKV)-induced cytopathic effects in vitro. Prostratin is a potent activator of protein kinases C (PKC), a family of related serine/threonine kinases that regulate many cellular processes such as proliferation and apoptosis. The objective of this study was to explore the mechanism of the anti-CHIKV activity of prostratin. Prostratin reduced the production of infectious virus particles and viral protein accumulation in a dose-dependent manner at a post-entry step during virus replication. The antiviral effect of the compound was cell-dependent, with potent antiviral activity observed in human skin fibroblasts cells, the primary target cells of CHIKV infection. The antiviral activity of prostratin was markedly reduced in the presence of PKC inhibitors, therefore confirming that the antiviral effect results from an activation of PKCs. Together these results showed that PKCs are potential host targets for the inhibition of CHIKV replication.

Diterpenes as lead molecules against neglected tropical diseases

Nowadays, neglected tropical diseases (NTDs) are reported to be present everywhere. Poor and developing areas in the world have received great attention to NTDs. Drug resistance, safety profile, and various challenges stimulate the search for alternative medications. Plant-based drugs are viewed with great interest, as they are believed to be devoid of side effects. Diterpenes, a family of essential oils, have showed attractive biological effects. A systematic review of the literature was carried out to summarize available evidences of diterpenes against NTDs. For this, databases were searched using specific search terms. Among the 2338 collected reports, a total of 181 articles were included in this review. Of them, 148 dealt with investigations using single organisms, and 33 used multiple organisms. No mechanisms of action were reported in the case of 164 reports. A total of 93.92% were related to nonclinical studies, and 4.42% and 1.66% dealt with preclinical and clinical studies, respectively. The review displays that many diterpenes are effective upon Chagas disease, chikungunya, echinococcosis, dengue, leishmaniasis, leprosy, lymphatic filariasis, malaria, schistosomiasis, and tuberculosis. Indeed, diterpenes are amazing drug candidates against NTDs. Copyright © 2016 John Wiley & Sons, Ltd.

Comparative analysis of the anti-chikungunya virus activity of novel bryostatin analogs confirms the existence of a PKC-independent mechanism

Previously, we reported that salicylate-based analogs of bryostatin protect cells from chikungunya virus (CHIKV)-induced cell death. Interestingly, 'capping' the hydroxyl group at C26 of a lead bryostatin analog, a position known to be crucial for binding to and modulation of protein kinase C (PKC), did not abrogate the anti-CHIKV activity of the scaffold, putatively indicating the involvement of a pathway independent of PKC. The work detailed in this study demonstrates that salicylate-derived analog 1 and two capped analogs (2 and 3) are not merely cytoprotective compounds, but act as selective and specific inhibitors of CHIKV replication. Further, a detailed comparative analysis of the effect of the non-capped versus the two capped analogs revealed that compound 1 acts both at early and late stages in the chikungunya virus replication cycle, while the capped analogs only interfere with a later stage process. Co-dosing with the PKC inhibitors sotrastaurin and Gö6976 counteracts the antiviral activity of compound 1 without affecting that of capped analogs 2 and 3, providing further evidence that the latter elicit their anti-CHIKV activity independently of PKC. Remarkably, treatment of CHIKV-infected cells with a combination of compound 1 and a capped analog resulted in a pronounced synergistic antiviral effect. Thus, these salicylate-based bryostatin analogs can inhibit CHIKV replication through a novel, yet still elusive, non-PKC dependent pathway.

Therapeutics and vaccines against chikungunya virus

Currently, there are no licensed vaccines or therapies available against chikungunya virus (CHIKV), and these were subjects discussed during a CHIKV meeting recently organized in Langkawi, Malaysia. In this review, we chart the approaches taken in both areas. Because of a sharp increase in new data in these fields, the present paper is complementary to previous reviews by Weaver et al. in 2012 and Kaur and Chu in 2013 . The most promising antivirals so far discovered are reviewed, with a special focus on the virus-encoded replication proteins as potential targets. Within the vaccines in development, our review emphasizes the various strategies in parallel development that are unique in the vaccine field against a single disease.

Inhibition of Chikungunya Virus-Induced Cell Death by Salicylate-Derived Bryostatin Analogues Provides Additional Evidence for a PKC-Independent Pathway

Chikungunya virus (CHIKV) has been spreading rapidly, with over one million confirmed or suspected cases in the Americas since late 2013. Infection with CHIKV causes devastating arthritic and arthralgic symptoms. Currently, there is no therapy to treat this disease, and the only medications focus on relief of symptoms. Recently, protein kinase C (PKC) modulators have been reported to inhibit CHIKV-induced cell death in cell assays. The salicylate-derived bryostatin analogues described here are structurally simplified PKC modulators that are more synthetically accessible than the natural product bryostatin 1, a PKC modulator and clinical lead for the treatment of cancer, Alzheimer's disease, and HIV eradication. Evaluation of the anti-CHIKV activity of these salicylate-derived bryostatin analogues in cell culture indicates that they are among the most potent cell-protective agents reported to date. Given that they are more accessible and significantly more active than the parent natural product, they represent new therapeutic leads for controlling CHIKV infection. Significantly, these analogues also provide evidence for the involvement of a PKC-independent pathway. This adds a fundamentally distinct aspect to the importance or involvement of PKC modulation in inhibition of chikungunya virus replication, a topic of recent and growing interest.

Simplified Bryostatin Analogues Protect Cells from Chikungunya Virus-Induced Cell Death

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus showing a recent resurgence and rapid spread worldwide. While vaccines are under development, there are currently no therapies to treat this disease, except for over-the-counter (OTC) analgesics, which alleviate the devastating arthritic and arthralgic symptoms. To identify novel inhibitors of the virus, analogues of the natural product bryostatin 1, a clinical lead for the treatment of cancer, Alzheimer's disease, and HIV eradication, were investigated for in vitro antiviral activity and were found to be among the most potent inhibitors of CHIKV replication reported to date. Bryostatin-based therapeutic efforts and even recent anti-CHIKV strategies have centered on modulation of protein kinase C (PKC). Intriguingly, while the C ring of bryostatin primarily drives interactions with PKC, A- and B-ring functionality in these analogues has a significant effect on the observed cell-protective activity. Significantly, bryostatin 1 itself, a potent pan-PKC modulator, is inactive in these assays. These new findings indicate that the observed anti-CHIKV activity is not solely mediated by PKC modulation, suggesting possible as yet unidentified targets for CHIKV therapeutic intervention. The high potency and low toxicity of these bryologs make them promising new leads for the development of a CHIKV treatment.

Antiviral Strategies Against Chikungunya Virus

In the last few decades the Chikungunya virus (CHIKV) has evolved from a geographically isolated pathogen to a virus that is widespread in many parts of Africa, Asia and recently also in Central- and South-America. Although CHIKV infections are rarely fatal, the disease can evolve into a chronic stage, which is characterized by persisting polyarthralgia and joint stiffness. This chronic CHIKV infection can severely incapacitate patients for weeks up to several years after the initial infection. Despite the burden of CHIKV infections, no vaccine or antivirals are available yet. The current therapy is therefore only symptomatic and consists of the administration of analgesics, antipyretics, and anti-inflammatory agents. Recently several molecules with various viral or host targets have been identified as CHIKV inhibitors. In this chapter, we summarize the current status of the development of antiviral strategies against CHIKV infections.

Towards antivirals against chikungunya virus

Chikungunya virus (CHIKV) has re-emerged in recent decades, causing major outbreaks of chikungunya fever in many parts of Africa and Asia, and since the end of 2013 also in Central and South America. Infections are usually associated with a low mortality rate, but can proceed into a painful chronic stage, during which patients may suffer from polyarthralgia and joint stiffness for weeks and even several years. There are no vaccines or antiviral drugs available for the prevention or treatment of CHIKV infections. Current therapy therefore consists solely of the administration of analgesics, antipyretics and anti-inflammatory agents to relieve symptoms. We here review molecules that have been reported to inhibit CHIKV replication, either as direct-acting antivirals, host-targeting drugs or those that act via a yet unknown mechanism. This article forms part of a symposium in Antiviral Research on "Chikungunya discovers the New World."