Structure-aided optimization of 3-O-β-chacotriosyl ursolic acid as novel H5N1 entry inhibitors with high selective index

Potential Pharmacological Properties of Triterpene Derivatives of Ursolic Acid

Ursolic acid (UA) and its derivatives have garnered significant attention due to their extensive pharmacological activity. UA is a pentacyclic triterpenoid found in a variety of plants, such as apples, rosemary, thyme, etc., and it possesses a range of pharmacological properties. Researchers have synthesized various derivatives of UA through structural modifications to enhance its potential pharmacological properties. Various in vitro and in vivo studies have indicated that UA and its derivatives possess diverse biological activities, such as anticancer, antifungal, antidiabetic, antioxidant, antibacterial, anti-inflammatory and antiviral properties. This review article provides a review of the biological activities of UA and its derivatives to show their valuable therapeutic properties useful in the treatment of different diseases, mainly focusing on the relevant structure-activity relationships (SARs), the underlying molecular targets/pathways, and modes of action.

Antiviral Compounds to Address Influenza Pandemics: An Update from 2016-2022

In recent decades, the world has gained experience of the dangerous effects of pandemic events caused by emerging respiratory viruses. In particular, annual epidemics of influenza are responsible for severe illness and deaths. Even if conventional influenza vaccines represent the most effective tool for preventing virus infections, they are not completely effective in patients with severe chronic disease and immunocompromised and new small molecules have emerged to prevent and control the influenza viruses. Thus, the attention of chemists is continuously focused on the synthesis of new antiviral drugs able to interact with the different molecular targets involved in the virus replication cycle. To date, different classes of influenza viruses inhibitors able to target neuraminidase enzyme, hemagglutinin protein, Matrix-2 (M2) protein ion channel, nucleoprotein or RNAdependent RNA polymerase have been synthesized using several synthetic strategies comprising the chemical modification of currently used drugs. The best results, in terms of inhibitory activity, are in the nanomolar range and have been obtained from the chemical modification of clinically used drugs such as Peramivir, Zanamivir, Oseltamir, Rimantadine, as well as sialylated molecules, and hydroxypyridinone derivatives. The aim of this review is to report, covering the period 2016-2022, the most recent routes related to the synthesis of effective influenza virus inhibitors.

Research progress on the antiviral activities of natural products and their derivatives: Structure–activity relationships

Viruses spread rapidly and are well-adapted to changing environmental events. They can infect the human body readily and trigger fatal diseases. A limited number of drugs are available for specific viral diseases, which can lead to non-efficacy against viral variants and drug resistance, so drugs with broad-spectrum antiviral activity are lacking. In recent years, a steady stream of new viral diseases has emerged, which has prompted development of new antiviral drugs. Natural products could be employed to develop new antiviral drugs because of their innovative structures and broad antiviral activities. This review summarizes the progress of natural products in antiviral research and their bright performance in drug resistance issues over the past 2 decades. Moreover, it fully discusses the effect of different structural types of natural products on antiviral activity in terms of structure–activity relationships. This review could provide a foundation for the development of antiviral drugs.

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.

Biological and Pharmacological Effects of Synthetic Saponins

Saponins are amphiphilic molecules consisting of carbohydrate and either triterpenoid or steroid aglycone moieties and are noted for their multiple biological activities-Fungicidal, antimicrobial, antiviral, anti-inflammatory, anticancer, antioxidant and immunomodulatory effects have all been observed. Saponins from natural sources have long been used in herbal and traditional medicines; however, the isolation of complexed saponins from nature is difficult and laborious, due to the scarce amount and structure heterogeneity. Chemical synthesis is considered a powerful tool to expand the structural diversity of saponin, leading to the discovery of promising compounds. This review focuses on recent developments in the structure optimization and biological evaluation of synthetic triterpenoid and steroid saponin derivatives. By summarizing the structure-activity relationship (SAR) results, we hope to provide the direction for future development of saponin-based bioactive compounds.

Ursolic acid derivatives are potent inhibitors against porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most devastating viral pathogens of swine and has a substantial economic impact on the global pork industry. Currently, vaccination strategies provide very limited protection against PRRSV transmission. Therefore, there is an urgent need to develop new antiviral strategies to prevent PRRSV pandemics. In this study, we showed that 3-O-β-chacotriosyl ursolic acid (1) and its ester analogs possessed anti-PRRSV activity in vitro, of which bioisosteric surrogates 7-15 were further generated with the aim of enhancing the selective index. Our results showed that amidation of the 17-COOH group of UA could significantly reduce cytotoxicity and enhance anti-PRRSV activity in MARC-145 cells. Among them, compound 9 displayed the strongest anti-PRRSV activity with the least cytotoxicity. Potent inhibition of representative compounds 9 and 12 on PRRSV infection was observed not only in MARC-145 cells, but also in primary porcine alveolar macrophages, PRRSV-target cells in vivo. Furthermore, compounds 8, 9, 12 and 14 exhibited broad-spectrum inhibitory activities in vitro against high pathogenic type 2 PRRSV NADC30-like and GD-XH strains as well as classical CH-1a and VR2332 strains. Mechanistically, compounds 9 and 12 inhibited PRRSV replication by directly inactivating virions and therefore affecting all tested stages of the virus life cycle, including viral entry, replication and progeny virus release, but did not affect cellular susceptibility to PRRSV. Our findings suggest that compound 9 could be a hit PRRSV inhibitor and deserves further in vivo studies in swine.

Synthesis and SARs of dopamine derivatives as potential inhibitors of influenza virus PAN endonuclease

Currently, influenza PA_N endonuclease has become an attractive target for development of new drugs to treat influenza infections. Herein we report the discovery of new PA_N endonuclease inhibitors derived from a chelating agent dopamine moiety. A series of dopamine amide derivatives and their conformationally constrained 1,2,3,4-tetrahydroisoquinoline-6,7-diol-based analogs were elaborated and assayed against influenza virus A/WSN/33 (H1N1). Most compounds exhibited moderate to excellent antiviral activities, generating a preliminary SARs. Among them, compounds 14 and 19 showed stronger anti-IAV activity compared with the reference Peramivir. Moreover, 14 and 19 demonstrated a concentration-dependent inhibition of PA_N endonuclease based on both FRET assay and SPR assay. Docking studies were also performed to elucidate the binding mode of 14 and 19 with the PA_N protein and to identify amino acids involved in their mechanism of action, which were well consistent with the biological data. This finding was beneficial to laying the foundation for the rational development of more effective PA_N endonuclease inhibitors.