Antiviral Activity of Diterpene Esters on Chikungunya Virus and HIV Replication

Antiviral and Cytotoxic Activities of Ilex aquifolium Silver Queen in the Context of Chemical Profiling of Two Ilex Species

The leaves of Ilex paraguariensis (known as Yerba mate), used as a popular beverage, are a very well-recognized plant material with various biological activities, including analeptic (because of caffeine), anti-obesity (phenolics, saponins), antimicrobial, and antiviral (phenolics, saponins). Here, the chemical compositions of the leaves of two European Ilex species (× meserveae and aquifolium) with three varieties each were investigated. The terpenoid, saponin, and polyphenolic fractions were submitted for LC-MS or GC-MS analysis against a standard Mate leaf. In addition, the aroma profiles of all the species were analysed using HS-SPME-Arrow prior to GC-MS analysis. All fractions were subjected to antiviral and cytotoxic assays. We found 86 compounds in all accessions, with limonene, linalool, and p-cymene being predominant. There were minor similarities between the volatile compositions of the European and South American species. We found ursolic and oleanolic acid to be the main compounds in the terpenoid fraction. Mono-caffeoylquinic acids and di-caffeoylquinic acids were the main constituents of the polar fractions. About 180 compounds from the saponin group were tentatively identified, of which 9 and 3 were selected as distinctive markers for I. meserveae and I. aquifolium, respectively. Based on chemical screening, I. aquifolium Silver Queen was chosen as the source of terpenoid and saponin fractions and polyphenol extracts. The most substantial inhibition of cancer cell growth was observed with saponin in the case of the MCF7 (human breast cancer) cell line, while for LoVo and L929 cell lines (human colorectal cancer and reference mouse fibroblasts), it was slightly weaker. These results should be analysed further as a promising chemoprevention of colorectal and gastrointestinal cancers. Saponin and polyphenolic extracts exhibited similar activities against HSV-1 and HAdV-5, with 4-log reduction in virus titres. This study focuses our attention on a field of potential antiviral formulations derived from European holly.

Total Syntheses of Phorbol and 11 Tigliane Diterpenoids and Their Evaluation as HIV Latency-Reversing Agents

Tigliane diterpenoids possess exceptionally complex structures comprising common 5/7/6/3-membered ABCD-rings and disparate oxygen functionalities. While tiglianes display a wide range of biological activities, compounds with HIV latency-reversing activity can eliminate viral reservoirs, thereby serving as promising leads for new anti-HIV agents. Herein, we report collective total syntheses of phorbol (13) and 11 tiglianes 14-24 with various acylation patterns and oxidation states, and their evaluation as HIV latency-reversing agents. The syntheses were strategically divided into five stages to increase the structural complexity. First, our previously established sequence enabled the expeditious preparation of ABC-tricycle 9 in 15 steps. Second, hydroxylation of 9 and ring-contractive D-ring formation furnished phorbol (13). Third, site-selective attachment of two acyl groups to 13 produced four phorbol diesters 14-17. Fourth, the oxygen functionalities were regio- and stereoselectively installed to yield five tiglianes 18-22. Fifth, further oxidation to the most densely oxygenated acerifolin A (23) and tigilanol tiglate (24) was realized through organizing a 3D shape of the B-ring. Assessment of the HIV latency-reversing activities of the 12 tiglianes revealed seven tiglianes (14-17 and 22-24) with 20- to 300-fold improved efficacy compared with prostratin (12), a representative latency-reversing agent. Therefore, the robust synthetic routes to a variety of tiglianes with promising activities devised in this study provide opportunities for advancing HIV eradication strategies.

Daphnanes diterpenes from the latex of Hura crepitans L. and their PKCζ-dependent anti-proliferative activity on colorectal cancer cells

Hura crepitans L. (Euphorbiaceae) is a thorn-covered tree widespread in South America, Africa and Asia which produces an irritating milky latex containing numerous secondary metabolites, notably daphnane-type diterpenes known as Protein Kinase C activators. Fractionation of a dichloromethane extract of the latex led to the isolation of five new daphnane diterpenes (1-5), along with two known analogs (6-7) including huratoxin. Huratoxin (6) and 4',5'-epoxyhuratoxin (4) were found to exhibit significant and selective cell growth inhibition against colorectal cancer cell line Caco-2 and primary colorectal cancer cells cultured as colonoids. The underlying mechanism of 4 and 6 was further investigated revealing the involvement of PKCζ in the cytostatic activity.

Anti-inflammatory kaurane diterpenoids of Erythroxylum bezerrae

Five unusual kaurane diterpenes, designated as bezerraditerpenes A-E (1-5), along with six known ones (6-11), were isolated from the hexane extract of the stems of Erythroxylum bezerrae. Their structures were elucidated based on the interpretation of the NMR spectroscopy, mass spectrometry, and X-ray diffraction analysis. The anti-inflammatory potential of the diterpenes 1-11 was screened through cellular viability and lipopolysaccharide (LPS)-induced nitric oxide (NO) production on murine macrophage-like cells RAW 264.7. Diterpene 6 (cauren-6β-ol) showed potent cytotoxicity and increased ability to inhibit NO production. Diterpenes 1 (bezerraditerpene A), 2 (bezerraditerpene B), and 8 (ent-kaur-16-ene-3β,15β-diol) exhibited the same significant anti-inflammatory activity with NO CI₅₀ inhibition (3.21-3.76 μM) without cytotoxicity, in addition to decreasing the levels of pro-inflammatory cytokines TNF-α and IL-6 in LPS-induced RAW264.7 cells.

Growth in chikungunya virus-related research in ASEAN and South Asian countries from 1967 to 2022 following disease emergence: a bibliometric and graphical analysis

BACKGROUND

ASEAN (Association of Southeast Asian Nations) is composed of ten Southeast Asian countries bound by socio-cultural ties that promote regional peace and stability. South Asia, located in the southern subregion of Asia, includes nine countries sharing similarities in geographical and ethno-cultural factors. Chikungunya is one of the most significant problems in Southeast and South Asian countries. Much of the current chikungunya epidemic in Southeast Asia is caused by the emergence of a virus strain that originated in Africa and spread to Southeast Asia. Meanwhile, in South Asia, three confirmed lineages are in circulation. Given the positive correlation between research activity and the improvement of the clinical framework of biomedical research, this article aimed to examine the growth of chikungunya virus-related research in ASEAN and South Asian countries.

METHODS

The Scopus database was used for this bibliometric analysis. The retrieved publications were subjected to a number of analyses, including those for the most prolific countries, journals, authors, institutions, and articles. Co-occurrence mapping of terms and keywords was used to determine the current state, emerging topics, and future prospects of chikungunya virus-related research. Bibliometrix and VOSviewer were used to analyze the data and visualize the collaboration network mapping.

RESULTS

The Scopus search engine identified 1280 chikungunya-related documents published by ASEAN and South Asian countries between 1967 and 2022. According to our findings, India was the most productive country in South Asia, and Thailand was the most productive country in Southeast Asia. In the early stages of the study, researchers investigated the vectors and outbreaks of the chikungunya virus. In recent years, the development of antivirus agents has emerged as a prominent topic.

CONCLUSIONS

Our study is the first to present the growth of chikungunya virus-related research in ASEAN and South Asian countries from 1967 to 2022. In this study, the evaluation of the comprehensive profile of research on chikungunya can serve as a guide for future studies. In addition, a bibliometric analysis may serve as a resource for healthcare policymakers.

Integration of LC/MS, NMR and Molecular Docking for Profiling of Bioactive Diterpenes from Euphorbia mauritanica L. with in Vitro Anti-SARS-CoV-2 Activity

In spite of tremendous efforts exerted in the management of COVID-19, the absence of specific treatments and the prevalence of delayed and long-term complications termed post-COVID syndrome still urged all concerned researchers to develop a potent inhibitor of SARS-Cov-2. The hydromethanolic extracts of different parts of E. mauritanica were in vitro screened for anti-SARS-Cov-2 activity. Then, using an integrated strategy of LC/MS/MS, molecular networking and NMR, the chemical profile of the active extract was determined. To determine the optimum target for these compounds, docking experiments of the active extract's identified compounds were conducted at several viral targets. The leaves extract showed the best inhibitory effect with IC₅₀ 8.231±0.04 μg/ml. The jatrophane diterpenes were provisionally annotated as the primary metabolites of the bioactive leaves extract based on multiplex of LC/MS/MS, molecular network, and NMR. In silico studies revealed the potentiality of the compounds in the most active extract to 3CLpro, where compound 20 showed the best binding affinity. Further attention should be paid to the isolation of various jatrophane diterpenes from Euphorbia and evaluating their effects on SARS-Cov-2 and its molecular targets.

Discovery of Taxus chinensis fruit wine as potentially functional food against Alzheimer's disease by UHPLC-QE-MS/MS, network pharmacology and molecular docking

Nowadays, there is no specific cure for Alzheimer's disease (AD), but the progression of AD can be improved by preventive interventions. The wine of Taxus chinensis fruit (TCFW) has the effect of improving human immunity and anti-aging as a long history of health care wine in folk, especially popular in the longevity villages in China, which may be potentially effective dietary products to improve AD. However, the chemical constituents and molecular mechanisms of TCFW still remain unknown. In this study, chemical profiling with UHPLC-QE-MS/MS, network pharmacology and molecular docking were integrated to fastly explore the potential chemicals and mechanisms of TCFW against AD. A total of 31 chemical components in TCFW were detected and identified compared with the solvent wine of TCFW by UHPLC-QE-MS/MS. Then, 27 potential key targets and 14 chemical compounds of TCFW were uncovered for the improvement of AD by network pharmacology and molecular docking. These 14 compounds were reported to have diverse bioactivities such as neuroprotective activity, antifibrotic activity, anticancer activity, antiviral activity and effectiveness in the treatment of neuronal injury, Alzheimer's disease, etc. Among these 27 targets affected by TCFW predicted by our approach, AKT1, PTGS2, NOS3, NOS2, INS, ESR1, ESR2, BDNF, IL6, IL1B, DRD2 and ACHE were significantly altered in AD. The GO and KEGG enrichment analyses revealed that TCFW mainly acted on oxidative response, inflammatory response, insulin secretion, amyloid fibril formation, neurodegenerative pathway-multiple diseases, Alzheimer's disease, longevity regulation pathway, PI3K-Akt signaling pathway, MAPK signaling pathway, etc, which were the main pathogenesis of AD. PRACTICAL APPLICATIONS: Alzheimer's disease (AD) is a degenerative neurological disorder characterized by cognitive and behavioral dysfunction. Nowadays, there is no specific cure for AD, but the progression of AD can be improved by preventive interventions. The wine of Taxus chinensis fruit (TCFW) has the effect of improving human immunity and anti-aging as a long history of health care wine in folk, especially popular in the longevity villages in China, which may be potentially effective dietary products to improve AD. This study proposed a fastly integrated method to explore the potential chemicals and mechanisms of TCFW against AD by UHPLC-QE-MS/MS, network pharmacology and molecular docking. Here, we found that TCFW may ameliorate AD by reversing many biological events, including oxidative stress, inflammatory response, neuronal apoptosis, insulin secretion, amyloid fibril formation, and T cell co-stimulation, which may provide some insights for the development and research of anti-AD drugs.

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.

Euphorbia diterpenoids: isolation, structure, bioactivity, biosynthesis, and synthesis (2013-2021)

Covering: 2013 to 2021As the characteristic metabolites of Euphorbia plants, Euphorbia diterpenoids have always been a hot topic in related science communities due to their intriguing structures and broad bioactivities. In this review, we intent to provide an in-depth and extensive coverage of Euphorbia diterpenoids reported from 2013 to the end of 2021, including 997 new Euphorbia diterpenoids and 78 known ones with latest progress. Multiple aspects will be summarized, including their occurrences, chemical structures, bioactivities, and syntheses, in which the structure-activity relationship and biosynthesis of this class will be discussed for the first time.

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.

Gene discovery and virus-induced gene silencing reveal branched pathways to major classes of bioactive diterpenoids in Euphorbia peplus

SignificanceEuphorbia peplus, a member of the Euphorbia genus, is rich in jatrophane and ingenane diterpenoids. Using a metabolomics-guided transcriptomic approach to gene candidate identification, we have discovered a short-chain dehydrogenase gene involved in the production of the lathyrane jolkinol E. We have developed a virus-induced gene-silencing method in E. peplus that has allowed us to demonstrate the direct relationship between casbene and polycyclic diterpenoids and that jolkinol C acts as a key branch point intermediate in the production of ingenanes and jatrophanes. This work contributes both knowledge and tools for engineering production of bioactive diterpenoids in heterologous host systems, thus enabling their further evaluation and development.

Phytoconstituents from Moringa oleifera fruits target ACE2 and open spike glycoprotein to combat SARS-CoV-2: An integrative phytochemical and computational approach

Therapeutic drugs based on natural products for the treatment of SARS-CoV-2 are currently unavailable. This study was conducted to develop an anti-SARS-CoV-2 herbal medicine to face the urgent need for COVID-19 treatment. The bioactive components from ethanolic extract of Moringa oleifera fruits (MOFs) were determined by gas chromatography-mass spectroscopy (GC-MS). Molecular-docking analyses elucidated the binding effects of identified phytocomponents against SARS-CoV-2 spike glycoprotein (PDB ID: 6VYB) and human ACE2 receptor (PDB ID: 1R42) through the Glide module of Maestro software. GC-MS analysis unveiled the presence of 33 phytocomponents. Eighteen phytocomponents exhibited good binding affinity toward ACE2 receptor, and thirteen phytocomponents had a high affinity with spike glycoprotein. This finding suggests that the top 11 hits (Docking score ≥ -3.0 kcal/mol) could inhibit SARS-CoV-2 propagation. Intriguingly, most of the phytoconstituents displayed drug-likeness with no predicted toxicity. However, further studies are needed to validate their effects and mechanisms of action. PRACTICAL APPLICATIONS: Moringa oleifera (MO) also called "drumstick tree" has been used as an alternative food source to combat malnutrition and may act as an immune booster. GC-MS analysis unveiled that ethanolic extract of Moringa oleifera fruits (MOFs) possessed 33 active components of pyridine, aromatic fatty acid, oleic acid, tocopherol, methyl ester, diterpene alcohol, triterpene and fatty acid ester and their derivatives, which have various pharmacological and medicinal values. Virtual screening study of phytocomponents of MOF with human ACE2 receptor and SARS-CoV-2 spike glycoprotein exhibited good binding affinity. Based on molecular docking, the top 11 hits (Docking score ≥-3.0 kcal/mol) might serve as potential lead molecules in antiviral drug development. Intriguingly, most of the phytoconstituents displayed drug-likeness with no predicted toxicity. Thus, MOF might be used as a valuable source for antiviral drug development to combat COVID-19, an ongoing pandemic.

Potential of diterpene compounds as antivirals, a review

Viruses cause widely transmitted diseases resulting in pandemic conditions. Currently, the world is being hit by the Covid-19 pandemic caused by the SAR-CoV-2 infection. Countries in the world are competing to develop antivirals to overcome this problem. Diterpene compounds derived from natural ingredients (plants, corals, algae, fungi, sponges) and synthesized products have potential as antivirals. This article summarizes the different types of diterpenes such as daphnane, tiglilane, kaurane, abietane, pimarane, labdane, dollabelane, jatrophane, dolastane, prenylated guaiane, tonantzitlolone, casbane, have antivirals activity such as targeting HIV, Coxsackie virus, herpes virus, hepatitis virus, influenza virus, Chikungunya virus, Zika virus, dengue virus, and SARS-CoV. Some compounds such as andrographolide and its derivatives show promising activity in inhibiting the influenza virus. Additionally, compounds such as pineolidic acid, forskolin, sugiol, and many other diterpene compounds showed anti-SAR-CoV activity. The diterpene compound class's high antivirals potential does not rule out the possibility that these compounds can also act as anti-SAR-CoV-2 drugs in the future.

DrugRepV: a compendium of repurposed drugs and chemicals targeting epidemic and pandemic viruses

Viruses are responsible for causing various epidemics and pandemics with a high mortality rate e.g. ongoing SARS-CoronaVirus-2 crisis. The discovery of novel antivirals remains a challenge but drug repurposing is emerging as a potential solution to develop antivirals in a cost-effective manner. In this regard, we collated the information of repurposed drugs tested for antiviral activity from literature and presented it in the form of a user-friendly web server named ‘DrugRepV’. The database contains 8485 entries (3448 unique) with biological, chemical, clinical and structural information of 23 viruses responsible to cause epidemics/pandemics. The database harbors browse and search options to explore the repurposed drug entries. The data can be explored by some important fields like drugs, viruses, drug targets, clinical trials, assays, etc. For summarizing the data, we provide overall statistics of the repurposed candidates. To make the database more informative, it is hyperlinked to various external repositories like DrugBank, PubChem, NCBI-Taxonomy, Clinicaltrials.gov, World Health Organization and many more. ‘DrugRepV’ database (https://bioinfo.imtech.res.in/manojk/drugrepv/) would be highly useful to the research community working to develop antivirals.

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.

Ligand and Structure-based Virtual Screening of Lamiaceae Diterpenes with Potential Activity against a Novel Coronavirus (2019-nCoV)

BACKGROUND

The emergence of a new coronavirus (CoV), named 2019-nCoV, as an outbreak originated in the city of Wuhan, China, has resulted in the death of more than 3,400 people this year alone and has caused worldwide an alarming situation, particularly following previous CoV epidemics, including the Severe Acute Respiratory Syndrome (SARS) in 2003 and the Middle East Respiratory Syndrome (MERS) in 2012. Currently, no exists for infections caused by CoVs; however, some natural products may represent potential treatment resources, such as those that contain diterpenes.

OBJECTIVE

This study aimed to use computational methods to perform a virtual screening (VS) of candidate diterpenes with the potential to act as CoV inhibitors.

METHODS

1,955 diterpenes, derived from the Nepetoideae subfamily (Lamiaceae), were selected using the SistematX tool (https://sistematx.ufpb.br), which were used to make predictions. From the ChEMBL database, 3 sets of chemical structures were selected for the construction of predictive models.

RESULTS

The chemical structures of molecules with known activity against SARS CoV, two of which were tested for activity against specific viral proteins and one of which was tested for activity against the virus itself, were classified according to their pIC50 values [-log IC50 (mol/l)].

CONCLUSION

In the consensus analysis approach, combining both ligand- and structure-based VSs, 19 compounds were selected as potential CoV inhibitors, including isotanshinone IIA (01), tanshinlactone (02), isocryptotanshinone (03), and tanshinketolactone (04), which did not present toxicity within the evaluated parameters.

The Revaluation of Plant-Derived Terpenes to Fight Antibiotic-Resistant Infections

The discovery of antibiotics has revolutionized the medicine and treatment of microbial infections. However, the current scenario has highlighted the difficulties in marketing new antibiotics and an exponential increase in the appearance of resistant strains. On the other hand, research in the field of drug-discovery has revaluated the potential of natural products as a unique source for new biologically active molecules and scaffolds for the medicinal chemistry. In this review, we first contextualized the worldwide problem of antibiotic resistance and the importance that natural products of plant origin acquire as a source of new lead compounds. We then focused on terpenes and their potential development as antimicrobials, highlighting those studies that showed an activity against conventional antibiotic-resistant strains.

The Revaluation of Plant-Derived Terpenes to Fight Antibiotic-Resistant Infections

The discovery of antibiotics has revolutionized the medicine and treatment of microbial infections. However, the current scenario has highlighted the difficulties in marketing new antibiotics and an exponential increase in the appearance of resistant strains. On the other hand, research in the field of drug-discovery has revaluated the potential of natural products as a unique source for new biologically active molecules and scaffolds for the medicinal chemistry. In this review, we first contextualized the worldwide problem of antibiotic resistance and the importance that natural products of plant origin acquire as a source of new lead compounds. We then focused on terpenes and their potential development as antimicrobials, highlighting those studies that showed an activity against conventional antibiotic-resistant strains.

The Revaluation of Plant-Derived Terpenes to Fight Antibiotic-Resistant Infections

The discovery of antibiotics has revolutionized the medicine and treatment of microbial infections. However, the current scenario has highlighted the difficulties in marketing new antibiotics and an exponential increase in the appearance of resistant strains. On the other hand, research in the field of drug-discovery has revaluated the potential of natural products as a unique source for new biologically active molecules and scaffolds for the medicinal chemistry. In this review, we first contextualized the worldwide problem of antibiotic resistance and the importance that natural products of plant origin acquire as a source of new lead compounds. We then focused on terpenes and their potential development as antimicrobials, highlighting those studies that showed an activity against conventional antibiotic-resistant strains.

Anti-HIV tigliane diterpenoids from Reutealis trisperma

Bioassay-guided fractionation of the n-butanol extract from the branches and leaves of Reutealis trisperma resulted in the isolation of six undescribed (crotignoids L ~ Q) together with two known (12-deoxyphorbol-13-hexadecanoate and 12-deoxyphorbol-13-myristate) tigliane diterpenoids. Their structures, especially the absolute configurations, were determined from extensive spectroscopic studies, including 2D NMR spectra, CD data analysis and electronic circular dichroism (ECD) calculations. All isolates were tested for anti-HIV activity against HL4-3 virus in MT4 cells. Except for crotignoid Q, the remaining seven tigliane diterpenoids exhibited potent anti-HIV activity with IC₅₀ values ranging from 0.0023 to 4.03 μM.

In vitro Studies on The Inhibition of Replication of Zika and Chikungunya Viruses by Dolastane Isolated from Seaweed Canistrocarpus cervicornis

The lack of vaccines and antiviral treatment, along with the increasing number of cases of Zika virus (ZIKV) and Chikungunya virus (CHIKV) infections, emphasize the need for searching for new therapeutic strategies. In this context, the marine brown seaweed Canistrocarpus cervicornis has been proved to hold great antiviral potential. Hence, the aim of this work was to evaluate the anti-ZIKV and anti-CHIKV activity of a marine dolastane isolated from brown seaweed C. cervicornis and its crude extract. Vero cells were used in antiviral assays, submitted to ZIKV and CHIKV, and treated with different concentrations of C. cervicornis extract or dolastane. The crude extract of C. cervicornis showed inhibitory activities for both ZIKV and CHIKV, with EC50 values of 3.3 μg/mL and 3.1 μg/mL, respectively. However, the isolated dolastane showed a more significant and promising inhibitory effect (EC50 = 0.95 µM for ZIKV and 1.3 µM for CHIKV) when compared to both the crude extract and ribavirin, which was used as control. Also, the dolastane showed a very potent virucidal activity against CHIKV and was able to inhibit around 90% of the virus infectivity at 10 μM. For the ZIKV, the effects were somewhat lower, although interesting, at approximately 64% in this same concentration. Further, we observed that both the extract and the dolastane were able to inhibit the replication of ZIKV and CHIKV at different times of addition post-infection, remaining efficient even if added after 8 hours post-infection, but declining soon after. A synergistic effect using sub-doses of the extract and isolates was associated with ribavirin, inhibiting above 80% replication even at the lowest concentrations. Therefore, this work has unveiled the anti-ZIKV and CHIKV potential of C. cervicornis crude extract and an isolated dolastane, which, in turn, can be used as a preventive or therapeutic strategy in the future.

Discovery of sclareol and sclareolide as filovirus entry inhibitors

Filoviruses cause severe hemorrhagic fever in humans. Ebola virus (EBOV) is the most contagious filovirus. Although compassionate treatments have been used during the latest Ebola outbreak, novel anti-EBOV agents are still urgently needed. In this study, sclareol and sclareolide, two natural products in Salvia sclarea, were identified as EBOV entry inhibitors with EC₅₀s of 2.4 μmol/L and 8.0 μmol/L, respectively, through blocking the viral fusion process. Moreover, both compounds exhibited inhibitory effects on all tested filoviruses' entry, indicating their wide-spectrum activities against filoviruses. This study provides insights into the two natural products and their applications against filovirus infectious diseases.

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.

Jatrophane and rearranged jatrophane-type diterpenes: biogenesis, structure, isolation, biological activity and SARs (1984-2019)

Diterpene compounds specially macrocyclic ones comprising jatrophane, lathyrane, terracinolide, ingenane, pepluane, paraliane, and segetane skeletons occurring in plants of the Euphorbiaceae family are of considerable interest in the context of natural product drug discovery programs. They possess diverse complex skeletons and a broad spectrum of therapeutically relevant biological activities including anti-inflammatory, anti-chikungunya virus, anti-HIV, cytotoxic, and multidrug resistance-reversing activities as well as curative effects on thrombotic diseases. Among macrocyclic diterpenes of Euphorbia, the discovery of jatrophane and modified jatrophane diterpenes with a wide range of structurally unique polyoxygenated polycyclic derivatives and as a new class of powerful inhibitors of P-glycoprotein has opened new frontiers for research studies on this genus. In this review, an attempt has been made to give in-depth coverage of the articles on the naturally occurring jatrophanes and rearranged jatrophane-type diterpenes isolated from species belonging to the Euphorbiaceae family published from 1984 to March 2019, with emphasis on the biogenesis, isolation methods, structure, biological activity, and structure-activity relationship.

Application of an integrated cheminformatics-molecular docking approach for discovery for physicochemically similar analogs of fluoroquinolones as putative HCV inhibitors

BACKGROUND

Hepatitis C Virus (HCV) infection is a major public health concern across the globe. At present, direct-acting antivirals are the treatment of choice. However, the long-term effect of this therapy has yet to be ascertained. Previously, fluoroquinolones have been reported to inhibit HCV replication by targeting NS3 protein. Therefore, it is logical to hypothesize that the natural analogs of fluoroquinolones will exhibit NS3 inhibitory activity with substantially lesser side effects.

METHOD

In this study, we tested the application of a recently devised integrated in-silico Cheminformatics-Molecular Docking approach to identify physicochemically similar natural analogs of fluoroquinolones from the available databases (Ambinter, Analyticon, Indofines, Specs, and TimTec). Molecular docking and ROC curve analyses were performed, using PatchDock and Graphpad software, respectively, to compare and analyze drug-protein interactions between active natural analogs, Fluoroquinolones, and HCV NS3 protein.

RESULT

In our analysis, we were able to shortlist 18 active natural analogs, out of 10,399, that shared physicochemical properties with the template drugs (fluoroquinolones). These analogs showed comparable binding efficacy with fluoroquinolones in targeting 32 amino acids in the HCV NS3 active site that are crucial for NS3 activity. Our approach had around 80 % sensitivity and 70 % specificity in identifying physicochemically similar analogs of fluoroquinolones.

CONCLUSION

Our current data suggest that our approach can be efficiently applied to identify putative HCV drug inhibitors that can be taken for in vitro testing. This approach can be applied to discover physicochemically similar analogs of virtually any drug, thus providing a speedy and inexpensive approach to complement drug discovery and design, which can tremendously economize on time and money spent on the screening of putative drugs.

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.

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.

Potent Anti-HIV Ingenane Diterpenoids from Euphorbia ebracteolata

Two new (1 and 2) and 14 known (3-16) ingenane diterpenoids were isolated from the roots of Euphorbia ebracteolata by bioassay-guided fractionation together with UPLC-MS ⁿ analysis. The absolute configurations of the new diterpenoids were established from electronic circular dichroism (ECD) data and ECD calculations. Except for ingenol (16), the ingenane diterpenoids with long aliphatic chain substituents (1-15) exhibited potent activities against HIV-1, with IC₅₀ values of 0.7 to 9.7 nM and selectivity index values of 96.2 to 20 263. From the results, it was concluded that long aliphatic chain substituents are required for the enhanced anti-HIV activity of ingenane diterpenoids.

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.

Jatrophane Diterpenoids from Euphorbia glomerulans

In a phytochemical investigation of the whole plant of Euphorbia glomerulans, 17 new (1-17) and five known jatrophane diterpenoids (18-22) were identified. The X-ray crystallographic data of compounds 1, 4, and 21 permitted the definition of the absolute configurations of these compounds. The cytotoxicity and multidrug resistance reversal activities of the 17 new compounds were evaluated on multidrug-resistant MCF-7/ADR cells overexpressing P-glycoprotein. Several compounds showed different chemoreversal activities and considerably decreased cytotoxicity. Compounds 11 (IC₅₀ value of 5.0 ± 0.8 μM) and 12 (IC₅₀ value of 5.2 ± 2.0 μM) possessed MDR reversal activities that were as good as that of verapamil (IC₅₀ value of 4.7 ± 0.6 μM).

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.

Current Strategies for Inhibition of Chikungunya Infection

Increasing incidences of Chikungunya virus (CHIKV) infection and co-infections with Dengue/Zika virus have highlighted the urgency for CHIKV management. Failure in developing effective vaccines or specific antivirals has fuelled further research. This review discusses updated strategies of CHIKV inhibition and provides possible future directions. In addition, it analyzes advances in CHIKV lifecycle, drug-target development, and potential hits obtained by in silico and experimental methods. Molecules identified with anti-CHIKV properties using traditional/rational drug design and their potential to succeed in subsequent stages of drug development have also been discussed. Possibilities of repurposing existing drugs based on their in vitro findings have also been elucidated. Probable modes of interference of these compounds at various stages of infection, including entry and replication, have been highlighted. The use of host factors as targets to identify antivirals against CHIKV has been addressed. While most of the earlier antivirals were effective in the early phases of the CHIKV life cycle, this review is also focused on drug candidates that are effective at multiple stages of its life cycle. Since most of these antivirals require validation in preclinical and clinical models, the challenges regarding this have been discussed and will provide critical information for further research.

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.

Bioactivity-Based Molecular Networking for the Discovery of Drug Leads in Natural Product Bioassay-Guided Fractionation

It is a common problem in natural product therapeutic lead discovery programs that despite good bioassay results in the initial extract, the active compound(s) may not be isolated during subsequent bioassay-guided purification. Herein, we present the concept of bioactive molecular networking to find candidate active molecules directly from fractionated bioactive extracts. By employing tandem mass spectrometry, it is possible to accelerate the dereplication of molecules using molecular networking prior to subsequent isolation of the compounds, and it is also possible to expose potentially bioactive molecules using bioactivity score prediction. Indeed, bioactivity score prediction can be calculated with the relative abundance of a molecule in fractions and the bioactivity level of each fraction. For that reason, we have developed a bioinformatic workflow able to map bioactivity score in molecular networks and applied it for discovery of antiviral compounds from a previously investigated extract of Euphorbia dendroides where the bioactive candidate molecules were not discovered following a classical bioassay-guided fractionation procedure. It can be expected that this approach will be implemented as a systematic strategy, not only in current and future bioactive lead discovery from natural extract collections but also for the reinvestigation of the untapped reservoir of bioactive analogues in previous bioassay-guided fractionation efforts.

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.

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.

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.

Euphorbia dendroides Latex as a Source of Jatrophane Esters: Isolation, Structural Analysis, Conformational Study, and Anti-CHIKV Activity

An efficient process was used to isolate six new jatrophane esters, euphodendroidins J (3), K (5), L (6), M, (8), N (10), and O (11), along with seven known diterpenoid esters, namely, euphodendroidins A (4), B (9), E (1), and F (2), jatrophane ester (7), and 3α-hydroxyterracinolides G and B (12 and 13), and terracinolides J and C (14 and 15) from the latex of Euphorbia dendroides. Their 2D structures and relative configurations were established by extensive NMR spectroscopic analysis. The absolute configurations of compounds 1, 11, and 15 were determined by X-ray diffraction analysis. Euphodendroidin F (2) was obtained in 18% yield from the diterpenoid ester-enriched extract after two consecutive flash chromatography steps, making it an interesting starting material for chemical synthesis. Euphodendroidins K and L (5 and 6) showed an unprecedented NMR spectroscopic behavior, which was investigated by variable-temperature NMR experiments and molecular modeling. The structure-conformation relationships study of compounds 1, 5, and 6, using DFT-NMR calculations, indicated the prominent role of the acylation pattern in governing the conformational behavior of these jatrophane esters. The antiviral activity of compounds 1-15 was evaluated against Chikungunya virus (CHIKV) replication.

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.