Synthesis of novel pentacyclic triterpene-Neu5Ac2en derivatives and investigation of their in vitro anti-influenza entry activity

Synthesis and evaluation of pentacyclic triterpenoids conjugates as novel HBV entry inhibitors targeting NTCP receptor

Chronic liver diseases caused by hepatitis B virus (HBV) are the accepted main cause leading to liver cirrhosis, hepatic fibrosis, and hepatic carcinoma. Sodium taurocholate cotransporting polypeptide (NTCP), a specific membrane receptor of hepatocytes for triggering HBV infection, is a promising target against HBV entry. In this study, pentacyclic triterpenoids (PTs) including glycyrrhetinic acid (GA), oleanolic acid (OA), ursolic acid (UA) and betulinic acid (BA) were modified via molecular hybridization with podophyllotoxin respectively, and resulted in thirty-two novel conjugates. The anti-HBV activities of conjugates were evaluated in HepG2.2.15 cells. The results showed that 66% of the conjugates exhibited lower toxicity to the host cells and had significant inhibitory effects on the two HBV antigens, especially HBsAg. Notably, the compounds BA-PPT1, BA-PPT3, BA-PPT4, and UA-PPT3 not only inhibited the secretion of HBsAg but also suppressed HBV DNA replication. A significant difference in the binding of active conjugates to NTCP compared to the HBV PreS1 antigen was observed by SPR assays. The mechanism of action was found to be the competitive binding of these compounds to the NTCP 157-165 epitopes, blocking HBV entry into host cells. Molecular docking results indicated that BA-PPT3 interacted with the amino acid residues of the target protein mainly through π-cation, hydrogen bond and hydrophobic interaction, suggesting its potential as a promising HBV entry inhibitor targeting the NTCP receptor.

Curcumin as a natural potential drug candidate against important zoonotic viruses and prions: A narrative review

Zoonotic diseases are major public health concerns and undeniable threats to human health. Among Zoonotic diseases, zoonotic viruses and prions are much more difficult to eradicate, as they result in higher infections and mortality rates. Several investigations have shown curcumin, the active ingredient of turmeric, to have wide spectrum properties such as anti-microbial, anti-vascular, anti-inflammatory, anti-tumor, anti-neoplastic, anti-oxidant, and immune system modulator properties. In the present study, we performed a comprehensive review of existing in silico, in vitro, and in vivo evidence on the antiviral (54 important zoonotic viruses) and anti-prion properties of curcumin and curcuminoids in PubMed, Google Scholar, Science Direct, Scopus, and Web of Science databases. Database searches yielded 13,380 results, out of which 216 studies were eligible according to inclusion criteria. Of 216 studies, 135 (62.5%), 24 (11.1%), and 19 (8.8%) were conducted on the effect of curcumin and curcuminoids against SARS-CoV-2, Influenza A virus, and dengue virus, respectively. This review suggests curcumin and curcuminoids as promising therapeutic agents against a wide range of viral zoonoses by targeting different proteins and signaling pathways.

Conformationally locked sugar derivatives and analogues as potential neuraminidase inhibitors

The influenza virus remains a major health concern for mankind because it tends to mutate frequently and cause high morbidity. Influenza prevention and treatment are greatly aided by the use of antivirals. One such class of antivirals is neuraminidase inhibitors (NAIs), effective against influenza viruses. A neuraminidase on the virus's surface serves a vital function in viral propogation by assisting in the release of viruses from infected host cells. Neuraminidase inhibitors are the backbone in stoping such virus propagation thus helps in the treatment of influenza viruses infections. Two NAI medicines are licensed globally: Oseltamivir (Tamiflu™) and Zanamivir (Relanza™). There are two molecules that have acquired Japanese approval recently: Peramivir and Laninamivir, whereas Laninamivir octanoate is in Phase III clinical trials. The need for novel NAIs is due to frequent mutations in viruses and the rise in resistance against existing medication. The NA inhibitors (NAIs) are designed to have (oxa)cyclohexene scaffolds (a sugar scaffold) to mimic the oxonium transition state in the enzymatic cleavage of sialic acid. This review discusses in details and comprises all such conformationally locked (oxa)cyclohexene scaffolds and their analogues which have been recently designed and synthesized as potential neuraminidase inhibitors, thus as antiviral molecules. The structure-activity relationship of such diverese molecules has also been discussed in this review.

Recent advances in medicinal chemistry of oleanolic acid derivatives

Oleanolic acid (OA), a ubiquitous pentacyclic oleanane-type triterpene isolated from edible and medicinal plants, exhibits a wide spectrum of pharmacological activities and tremendous therapeutic potential. However, the undesirable pharmacokinetic properties limit its application and development. Numerous researches on structural modifications of OA have been carried out to overcome this limitation and improve its pharmacokinetic and therapeutic properties. This review aims to compile and summarize the recent progresses in the medicinal chemistry of OA derivatives, especially on structure-activity relationship in the last few years (2010-2021). It gives insights into the rational design of bioactive derivatives from OA scaffold as promising therapeutic agents.

Synthesis of Four Pentacyclic Triterpene-Sialylglycopeptide Conjugates and Their Affinity Assays with Hemagglutinin

Influenza outbreaks pose a serious threat to human health. Hemagglutinin (HA) is an important target for influenza virus entry inhibitors. In this study, we synthesized four pentacyclic triterpene conjugates with a sialylglycopeptide scaffold through the Cu(I)-catalyzed alkyne-azide cycloaddition reaction (CuAAC) and prepared affinity assays of these conjugates with two HAs, namely H1N1 (A/WSN/1933) and H5N1 (A/Hong Kong/483/97), respectively. With a dissociation constant (KD) of 6.89 μM, SCT-Asn-betulinic acid exhibited the strongest affinity with the H1N1 protein. Furthermore, with a KD value of 9.10 μM, SCT-Asn-oleanolic acid exhibited the strongest affinity with the H5N1 protein. The conjugates considerably enhanced antiviral activity, which indicates that pentacyclic triterpenes can be used as a ligand to improve the anti-influenza ability of the sialylglycopeptide molecule by acting on the HA protein.

Structure-aided optimization of 3-O-β-chacotriosyl epiursolic acid derivatives as novel H5N1 virus entry inhibitors

It is urgent to develop new antiviral agents due to the continuous emergence of drug-resistant strains of influenza virus. Our earlier studies have identified that certain pentacyclic triterpene saponins with 3-O-β-chacotriosyl residue are novel H5N1 virus entry inhibitors. In the present study, a series of C-28 modified 3-O-β-chacotriosyl epiursolic acid derivatives via conjugation with different kinds of sides were synthesized, of which anti-H5N1 activities in A549 cells were evaluated in vitro. Among them, 10 exhibited strongest anti-H5N1 potency at the low-micromole level without cytotoxicity, surpassing the potency of ribavirin. Further mechanism studies of the lead compound 10 based on HI, SPR and molecular modeling revealed that these new 3-epiursolic acid saponins could bind tightly to the viral envelope HA protein, thus blocking the invasion of H5N1 viruses into host cells.

Design and synthesis of pentacyclic triterpene conjugates and their use in medicinal research

Triterpenoids are natural products from plants and many other organisms that have various biological activities, such as antitumor, antiviral, antimicrobial, and protective activities. This review covers the synthesis and biological evaluation of pentacyclic triterpene (PT) conjugates with other molecules that have been found to increase the IC₅₀ or improve the pharmacological profile of the parent PT. Some of these molecules are designed to target specific proteins or cellular organelles, which has resulted in highly selective lead structures for drug development. Other PT conjugates are useful for investigating their mechanism of action. This concept has been very successful: 1) Many compounds, especially mitochondria-targeting PT conjugates, have reached a selective cytotoxicity at low nanomolar concentrations in cancer cells. 2) A number of PT conjugates have had high activity against HIV or the influenza virus. 3) Fluorescent PT conjugates have been able to visualize the PT in living cells, which has allowed quantification of the uptake and distribution of the PT within the cell. 4) Biotinylated PT conjugates have been used to identify target proteins, which may help to show their mechanism of action. 5) A large number of PT conjugates with polyethylene glycol (PEG), polyamines, etc. form nanometer-sized micelles that have a much better pharmacological profile than the PT alone. In summary, the connection of a PT to an appropriate modifying molecule has resulted in extremely useful semisynthetic compounds with a high potential to treat cancer or viral infections or compounds that are useful for the study of the mechanism of action of PTs at the molecular level.

Recent progress in the antiviral activity and mechanism study of pentacyclic triterpenoids and their derivatives

Viral infections cause many serious human diseases with high mortality rates. New drug‐resistant strains are continually emerging due to the high viral mutation rate, which makes it necessary to develop new antiviral agents. Compounds of plant origin are particularly interesting. The pentacyclic triterpenoids (PTs) are a diverse class of natural products from plants composed of three terpene units. They exhibit antitumor, anti‐inflammatory, and antiviral activities. Oleanolic, betulinic, and ursolic acids are representative PTs widely present in nature with a broad antiviral spectrum. This review focuses on the recent literatures in the antiviral efficacy of this class of phytochemicals and their derivatives. In addition, their modes of action are also summarized.

Synthesis and In Vitro Anti-Influenza Virus Evaluation of Novel Sialic Acid (C-5 and C-9)-Pentacyclic Triterpene Derivatives

The emergence of drug resistant variants of the influenza virus has led to a great need to identify novel and effective antiviral agents. In our previous study, a series of sialic acid (C-2 and C-4)-pentacyclic triterpene conjugates have been synthesized, and a five-fold more potent antiviral activity was observed when sialic acid was conjugated with pentacyclic triterpene via C-4 than C-2. It was here that we further reported the synthesis and anti-influenza activity of novel sialic acid (C-5 and C-9)-pentacyclic triterpene conjugates. Their structures were confirmed by ESI-HRMS, ¹H-NMR, and ¹³C-NMR spectroscopic analyses. Two conjugates (26 and 42) showed strong cytotoxicity to MDCK cells in the CellTiter-Glo assay at a concentration of 100 μM. However, they showed no significant cytotoxicity to HL-60, Hela, and A549 cell lines in MTT assay under the concentration of 10 μM (except compound 42 showed weak cytotoxicity to HL-60 cell line (10 μM, ~53%)). Compounds 20, 28, 36, and 44 displayed weak potency to influenza A/WSN/33 (H1N1) virus (100 μM, ~20–30%), and no significant anti-influenza activity was found for the other conjugates. The data suggested that both the C-5 acetylamide and C-9 hydroxy of sialic acid were important for its binding with hemagglutinin during viral entry into host cells, while C-4 and C-2 hydroxy were not critical for the binding process and could be replaced with hydrophobic moieties. The research presented herein had significant implications for the design of novel antiviral inhibitors based on a sialic acid scaffold.