Synthesis and evaluation of diterpenic Mannich bases as antiviral agents against influenza A and SARS-CoV-2

Synthesis and Biological Activity of New Hydrazones Based on N-Aminomorpholine

The data on the synthesis of N-aminomorpholine hydrazones are presented. It is shown that the interaction of N-aminomorpholine with functionally substituted benzaldehydes and 4-pyridinaldehyde in isopropyl alcohol leads to the formation of corresponding hydrazones. The structure of the synthesized compounds was studied by 1H and 13C NMR spectroscopy methods, including the COSY (1H-1H), HMQC (1H-13C) and HMBC (1H-13C) methodologies. The values of chemical shifts, multiplicity, and integral intensity of 1H and 13C signals in one-dimensional NMR spectra were determined. The COSY (1H-1H), HMQC (1H-13C), and HMBC (1H-13C) results revealed homo- and heteronuclear interactions, confirming the structure of the studied compounds. The antiviral, cytotoxic, and antimicrobial activity of some synthesized hydrazones were investigated. It is shown that 2-((morpholinoimino)methyl)benzoic acid has a pronounced viral inhibitory property, comparable in its activity to commercial drugs Tamiflu and Remantadine. A docking study was performed using the influenza virus protein models (1930 Swine H1 Hemagglutinin and Neuraminidase of 1918 H1N1 strain). The potential binding sites that are complementary with 2-((morpholinoimino)methyl)benzoic acid were found.

In Silico and In Vitro Studies of Terpenes from the Fabaceae Family Using the Phenotypic Screening Model against the SARS-CoV-2 Virus

In 2019, the emergence of the seventh known coronavirus to cause severe illness in humans triggered a global effort towards the development of new drugs and vaccines for the SARS-CoV-2 virus. These efforts are still ongoing in 2024, including the present work where we conducted a ligand-based virtual screening of terpenes with potential anti-SARS-CoV-2 activity. We constructed a Quantitative Structure-Activity Relationship (QSAR) model from compounds with known activity against SARS-CoV-2 with a model accuracy of 0.71. We utilized this model to predict the activity of a series of 217 terpenes isolated from the Fabaceae family. Four compounds, predominantly triterpenoids from the lupane series, were subjected to an in vitro phenotypic screening in Vero CCL-81 cells to assess their inhibitory activity against SARS-CoV-2. The compounds which showed high rates of SARS-CoV-2 inhibition along with substantial cell viability underwent molecular docking at the SARS-CoV-2 main protease, papain-like protease, spike protein and RNA-dependent RNA polymerase. Overall, virtual screening through our QSAR model successfully identified compounds with the highest probability of activity, as validated using the in vitro study. This confirms the potential of the identified triterpenoids as promising candidates for anti-SARS-CoV-2 therapeutics.

Natural Product-Derived Phytochemicals for Influenza A Virus (H1N1) Prevention and Treatment

Influenza A (H1N1) viruses are prone to antigenic mutations and are more variable than other influenza viruses. Therefore, they have caused continuous harm to human public health since the pandemic in 2009 and in recent times. Influenza A (H1N1) can be prevented and treated in various ways, such as direct inhibition of the virus and regulation of human immunity. Among antiviral drugs, the use of natural products in treating influenza has a long history, and natural medicine has been widely considered the focus of development programs for new, safe anti-influenza drugs. In this paper, we focus on influenza A (H1N1) and summarize the natural product-derived phytochemicals for influenza A virus (H1N1) prevention and treatment, including marine natural products, flavonoids, alkaloids, terpenoids and their derivatives, phenols and their derivatives, polysaccharides, and derivatives of natural products for prevention and treatment of influenza A (H1N1) virus. We further discuss the toxicity and antiviral mechanism against influenza A (H1N1) as well as the druggability of natural products. We hope that this review will facilitate the study of the role of natural products against influenza A (H1N1) activity and provide a promising alternative for further anti-influenza A drug development.

Synthesis and bioevaluation of water-soluble β-cyclodextrin-diterpene acid conjugates

A series of β-cyclodextrin (β-CD)-conjugates were prepared by combining three abietane-type diterpene acids with two azide-functionalized β-CDs via click chemistry, and the antiviral activity against wild-type and omicron SARS-CoV-2 spike pseudovirus as well as the antibacterial activity against Escherichia coli were investigated. All the synthesised conjugates exhibited no significant cytotoxicity to BHK-21-hACE2 cells with cell viability over 80% at concentration of 15 µM. Among the conjugates, the heptavalent β-CD-dehydroabietic acid conjugate 6b exhibited higher anti-SARS-CoV-2 activity against the omicron variant compared to the other conjugates. This study suggested that the multivalent diterpene acid derivatives may have potential application against coronaviruses as entry inhibitors.

Antiviral opportunities of Mannich bases derived from triterpenic N-propargylated indoles

Oleanolic and glycyrrhetic acids alkyne derivatives were synthesized as a result of propargylation of the indole NH-group condensed with the triterpene A-ring, the following aminomethylation led to a series of Mannich bases. The synthesized compounds were tested for their potential inhibition of influenza A/PuertoRico/8/34 (H1N1) virus in Madin-Darby canine kidney (MDCK) cell culture and SARS-CoV-2 pseudovirus in baby hamster kidney-21-human angiotensin-converting enzyme 2 (BHK-21-hACE2) cells. Mannich bases of oleanolic and glycyrrhetic acids N-propargylated indoles 7, 8, and 12 were the most efficacious against influenza virus A with IC50 7-10 μM together with a low toxicity (CC50  > 145 μM) and high selectivity index SI value 20. Indolo-oleanolic acid morpholine amide Mannich base holding N-methylpiperazine moiety 9 showed anti-SARS-CoV-2 pseudovirus activity with EC50 value of 14.8 μM. Molecular docking and dynamics modeling investigated the binding mode of the compounds 7 and 12 into the binding pocket of influenza A virus M2 protein and compound 9 into the RBD domain of SARS-CoV-2 spike glycoprotein.

Evaluation of A-ring hydroxymethylene-amino- triterpenoids as inhibitors of SARS-CoV-2 spike pseudovirus and influenza H1N1

A set of triterpene A-ring hydroxymethylene-amino-derivatives was synthesized and their antiviral activity was studied. The synthesized compounds were tested for their potential inhibition of SARS-CoV-2 pseudovirus in BHK-21-hACE2 cells and influenza A/PuertoRico/8/34 (H1N1) virus in MDCK cell culture. Compounds 6, 8 and 19 showed significant anti-SARS-CoV-2 pseudovirus activity with EC50 value of 3.20-11.13 µM, which is comparable to the positive control amodiaquine (EC50 3.17 µM). Among them, 28-O-imidazolyl-azepano-betulin 6 and C3-hydroxymethylene-amino-glycyrrhetol-11,13-diene 19 were identified as the lead compounds with SI values of 7 and 10. The binding mode of compound 6 into the RBD domain of SARS-CoV-2 spike glycoprotein (PDB code: 7DK3) by docking and molecular dynamics simulation was investigated.

Anticoronavirus Evaluation of Antimicrobial Diterpenoids: Application of New Ferruginol Analogues

The abietane diterpene (+)-ferruginol (1), like other natural and semisynthetic abietanes, is distinguished for its interesting pharmacological properties such as antimicrobial activity, including antiviral. In this study, selected C18-functionalized semisynthetic abietanes prepared from the commercially available (+)-dehydroabietylamine or methyl dehydroabietate were tested in vitro against human coronavirus 229E (HCoV-229E). As a result, a new ferruginol analogue caused a relevant reduction in virus titer as well as the inhibition of a cytopathic effect. A toxicity prediction based on in silico analysis was also performed as well as an estimation of bioavailability. This work demonstrates the antimicrobial and specifically antiviral activity of two tested compounds, making these molecules interesting for the development of new antivirals.

A novel dehydroabietic acid-based multifunctional fluorescent probe for the detection and bioimaging of Cu2+/Zn2+/ClO. Analyst 2023;148:1867-1876. [PMID: 36942689 DOI: 10.1039/d3an00001j]

A multifunctional dehydroabietic acid-based fluorescent probe (CPS) was designed and synthesized by introducing the 2,6-bis(1H-benzo[d]imidazol-2-yl)phenol fluorophore. The probe CPS could selectively recognize Cu²⁺, Zn²⁺ and ClO^- ions from other analytes, and it showed fluorescence quenching behavior toward Cu²⁺ and a ratiometric response to Zn²⁺ and ClO^- by changing from green fluorescence to blue and cyan, respectively. The detection limits toward Cu²⁺, Zn²⁺ and ClO^- ions were 3.8 nM, 0.253 μM and 0.452 μM, respectively. In addition, CPS presented many fascinating merits, such as high selectivity, a short response time (15-20 s), a wide pH range (3-10) and high photostability. The sensing mechanisms of CPS were verified by ¹H-NMR, ESI-MS, FT-IR and Job's plot methods. Meanwhile, CPS exhibited satisfactory detection performance in water samples. More importantly, the probe could be applied as a promising tool for visual bioimaging of three ions in living cells and zebrafishes.