Diels-Alder adducts of 3-N-substituted derivatives of (−)-Cytisine as influenza A/H1N1 virus inhibitors; stereodifferentiation of antiviral properties and preliminary assessment of action mechanism

Assessing the inhibitory effects of some secondary amines, thioureas and 1,3-dimethyluracil conjugates of (-)-cytisine and thermopsine on the RNA-dependent RNA polymerase of SARS-CoV-1 and SARS-CoV-2

SARS-CoV-2 causes COVID-19, with symptoms ranging from mild to severe, including pneumonia and death. This beta coronavirus has a 30-kilobase RNA genome and shares about 80 % of its nucleotide sequence with SARS-CoV-1. The replication/transcription complex, essential for viral RNA synthesis, includes RNA-dependent RNA polymerase (RdRp, nsp12) enhanced by nsp7 and nsp8. Antivirals like molnupiravir and remdesivir, which are RdRp inhibitors, treat severe COVID-19 but have limitations, highlighting the need for new therapies. This study assessed (-)-cytisine, methylcytisine, and thermopsine derivatives against SARS-CoV-1 and SARS-CoV-2 in vitro, focusing on their RdRp inhibition. Selected compounds from a previous study were evaluated using a SARS-CoV-2 RNA polymerase assay kit to investigate their structure-activity relationships. Compound 17 (1,3-dimethyluracil conjugate with (-)-cytisine and thermopsine) emerged as a potent inhibitor of SARS-CoV-1 and SARS-CoV-2 RdRp, with an IC50 value of 7.8 μM against SARS-CoV-2 RdRp. It showed a dose-dependent reduction in cytopathic effects in cells infected with SARS-CoV-1 and SARS-CoV-2 replicon-based single-round infectious particles (SRIPs) and significantly inhibited SARS-CoV N protein expression, with EC50 values of 0.12 µM for SARS-CoV-1 and 1.47 µM for SARS-CoV-2 SRIPs. Additionally, compound 17 reduced viral subgenomic RNA levels in a concentration-dependent manner in SRIP-infected cells. The structure-activity relationships of compound 17 with SARS-CoV-1 and SARS-CoV-2 RdRp were also investigated, highlighting it as a promising lead for developing antiviral agents against SARS and COVID-19.

Inhibition of dengue viruses by N-methylcytisine thio derivatives through targeting viral envelope protein and NS2B-NS3 protease

Dengue virus (DENV) is a significant global health threat, causing millions of cases worldwide each year. Developing antiviral drugs for DENV has been a challenging endeavor. Our previous study identified anti-DENV properties of two (-)-cytisine derivatives contained substitutions within the 2-pyridone core from a pool of 19 (-)-cytisine derivatives. This study aimed to expand on the previous research by investigating the antiviral potential of N-methylcytisine thio (mCy thio) derivatives against DENV, understanding the molecular mechanisms of antiviral activity for the active thio derivatives. The inhibitory assays on DENV-2-induced cytopathic effect and infectivity revealed that mCy thio derivatives 3 ((1R,5S)-3-methyl-1,2,3,4,5,6-hexahydro-8H-1,5-methanopyrido[1,2-a][1,5]diazocine-8-thione) and 6 ((1S,5R)-3-methyl-2-thioxo-1,2,3,4,5,6-hexahydro-8H-1,5-methanopyrido[1,2-a][1,5]diazocin-8-one) were identified as the active compounds against both DENV-1 and DENV-2. Derivative 6 displayed robust antiviral activity against DENV-2, with EC50 values ranging from 0.002 to 0.005 μM in different cell lines. Derivative 3 also exhibited significant antiviral activity against DENV-2. The study found that these compounds are effective at inhibiting DENV-2 at both the entry stage (including virus attachment) and post-entry stages of the viral life cycle. The study also investigated the inhibition of the DENV-2 NS2B-NS3 protease activity by these compounds. Derivative 6 demonstrated notably stronger inhibition compared to mCy thio 3, revealing its dual antiviral action at both the entry and post-entry stages. Molecular docking simulations indicated that mCy thio derivatives 3 and 6 bind to the domain I and III of the DENV E protein, as well as the active of NS2B-NS3 protease, suggesting their molecular interactions with the virus. The study demonstrates the antiviral efficacy of N-methylcytisine thio derivatives against DENV. It provides valuable insights into the potential interactions between these compounds and viral target proteins, which could be useful in the development of antiviral drugs for DENV.

Recent Advances in the Chemistry of Saturated Annulated Nitrogen-Containing Polycyclic Compounds

This review is devoted to the analysis of works published over the past 20 years on the chemistry of saturated annulated nitrogen-containing polycyclic compounds, the molecules of which consist of four, five, six, and seven cycles, and contain from one to eight endocyclic nitrogen atoms.

Catalytic Enantioselective Diels Alder Reaction: Application in the Synthesis of Antiviral Agents

The Diels–Alder reaction (DAR) is one of the most effective and reliable strategies for the construction of six-membered carbocyclic and heterocyclic rings, and it is widely used in the synthesis of organic molecules and drugs. Due to the high regio- and stereo-selectivity and its versatility, DARs have represented a powerful tool for organic chemistry for many years. In addition, the asymmetric DAR has become a fundamental synthetic approach in the preparation of optically active six-membered rings and natural compounds. The COVID-19-related pandemic requires continuous research; DAR represents an useful method to obtain optically active intermediates for the synthesis of antiviral agents under different catalytic conditions. We would like to highlight an intriguing synthetic procedure applied to the development of novel synthetic protocols that are potentially useful against a large panel of viruses and other unmet diseases.

Synthesis and antiviral evaluation of cytisine derivatives against dengue virus types 1 and 2

Dengue virus (DENV) causes about 50-100 million cases per year worldwide. However, there is still a big challenge in developing antiviral drugs against DENV infection. Some derivatives of alkaloid (-)-cytisine, like other alkaloid analogs, have been proposed for their antiviral potential. This study investigated antiviral activity and mechanisms of the cytisine derivatives, and discovered the structure-activity relationship against DENV. The antiviral assays were performed using one strain of DENV1 and DENV2, and two cell lines Vero E6 and A549. The structure-activity relationship of the effective compounds was also evaluated using combination of time-of-addition/removal assay and molecular docking. Compounds 3, 4, 12 (N-allylcytisine-3-thiocarbamide), 16, and 20 exhibited the high antiviral activity with IC₅₀ values of lower than 3 μM against DENV1 and DENV2. Of them, the derivative 12 showed the highest antiviral activities against DENV1 (IC₅₀ = 0.14 μM) and DENV-2 (IC₅₀ = <0.1 μM), exhibiting the potent inhibition on virus attachment and entry stages. Meanwhile, the compounds 4 and 20 had a strong inhibition at the post-entry stage (IC₅₀ = <0.1 μM). A correlation between the experimental pIC₅₀ values and predicted pKi calculated by docking of compounds into DENV E protein was significant, correlating with the impact of compound 12 on the attachment stage, but compounds 4, and 20 on post-entry stage. The results provided the insight into the directions of synthetic modifications of starting (-)-cytisine as the inhibitors of DENV E protein at attachment and entry stages of DENV life cycle.

Antiviral activity of amides and carboxamides of quinolizidine alkaloid (-)-cytisine against human influenza virus A (H1N1) and parainfluenza virus type 3

Novel derivatives of quinolizidine alkaloid (-)-cytisine were synthesised. ADME properties, cytotoxicity against HEK293 cells and activity against viruses of influenza A/California/07/09(H1N1)pdm09 virus (IAV) and human parainfluenza virus type 3 (HPIV3) were evaluated. It was shown, that 9-carboxamides of methylcytisine (with phenyl and allyl urea's fragments) are most active compounds against IAV probably due to predicted in silico peculiarity of their interactions with the 4R7B active site of IAV neuraminidase. Indexes of selectivity (SI) calculated as ratio of CC₅₀/IC₅₀ of these ureas are 47 and 59 correspondingly. It was also found, that derivatives obtained from allyl isocyanate and (-)-cytisine or 9,11-dibromocytisine are able to inhibit a reproduction of HPIV3 with SI = 58 and 95. Moreover, last compound - (1 R,5R)-N-allyl-9,11-dibromo-8-oxo-1,5,6,8-tetrahydro-2H-1,5-methanopyrido[1,2-a][1,5]diazocine-3(4H)-carboxamide with two bromine atom in 2-pyridone core of starting (-)-cytisine molecule, demonstrated high activity against HPIV3 (SI = 95) and moderate activity against IAV (SI = 16).

Synthesis of Camphecene and Cytisine Conjugates Using Click Chemistry Methodology and Study of Their Antiviral Activity

A series of camphecene and quinolizidine alkaloid (-)-cytisine conjugates has been obtained for the first time using 'click' chemistry methodology. The cytotoxicity and virus-inhibiting activity of compounds were determined against MDCK cells and influenza virus A/Puerto Rico/8/34 (H1N1), correspondingly, in in vitro tests. Based on the results obtained, values of 50 % cytotoxic dose (CC₅₀ ), 50 % inhibition dose (IC₅₀ ) and selectivity index (SI) were determined for each compound. It has been shown that the antiviral activity is affected by the length and nature of linkers between cytisine and camphor units. Conjugate 13 ((1R,5S)-3-(6-{4-[(2-{(E)-[(1R,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene]amino}ethoxy)methyl]-1H-1,2,3-triazol-1-yl}hexyl)-1,2,3,4,5,6-hexahydro-8H-1,5-methanopyrido[1,2-a][1,5]diazocin-8-one), which contains cytisine fragment separated from triazole ring by -C₆ H₁₂ - aliphatic linker, showed the highest activity at relatively low toxicity (CC₅₀ =168 μmol, IC₅₀ =8 μmol, SI=20). Its selectivity index appeared higher than that of reference compound, rimantadine. According to theoretical calculations, the antiviral activity of the lead compound 13 can be explained by its influence on the functioning of neuraminidase.