Nucleoside and nucleotide HIV reverse transcriptase inhibitors: 25 years after zidovudine

Structure-Based Design of Novel Thiazolone[3,2-a]pyrimidine Derivatives as Potent RNase H Inhibitors for HIV Therapy

Ribonuclease H (RNase H) was identified as an important target for HIV therapy. Currently, no RNase H inhibitors have reached clinical status. Herein, a series of novel thiazolone[3,2-a]pyrimidine-containing RNase H inhibitors were developed, based on the hit compound 10i, identified from screening our in-house compound library. Some of these derivatives exhibited low micromolar inhibitory activity. Among them, compound 12b was identified as the most potent inhibitor of RNase H (IC50 = 2.98 μM). The experiment of magnesium ion coordination was performed to verify that this ligand could coordinate with magnesium ions, indicating its binding ability to the catalytic site of RNase H. Docking studies revealed the main interactions of this ligand with RNase H. A quantitative structure activity relationship (QSAR) was also conducted to disclose several predictive mathematic models. A molecular dynamics simulation was also conducted to determine the stability of the complex. Taken together, thiazolone[3,2-a]pyrimidine can be regarded as a potential scaffold for the further development of RNase H inhibitors.

4'-Ethynyl-2'-Deoxycytidine (EdC) Preferentially Targets Lymphoma and Leukemia Subtypes by Inducing Replicative Stress

Anticancer nucleosides are effective against solid tumors and hematologic malignancies, but typically are prone to nucleoside metabolism resistance mechanisms. Using a nucleoside-specific multiplexed high-throughput screening approach, we discovered 4'-ethynyl-2'-deoxycytidine (EdC) as a third-generation anticancer nucleoside prodrug with preferential activity against diffuse large B-cell lymphoma (DLBCL) and acute lymphoblastic leukemia (ALL). EdC requires deoxycytidine kinase (DCK) phosphorylation for its activity and induces replication fork arrest and accumulation of cells in S-phase, indicating it acts as a chain terminator. A 2.1Å cocrystal structure of DCK bound to EdC and UDP reveals how the rigid 4'-alkyne of EdC fits within the active site of DCK. Remarkably, EdC was resistant to cytidine deamination and SAMHD1 metabolism mechanisms and exhibited higher potency against ALL compared with FDA-approved nelarabine. Finally, EdC was highly effective against DLBCL tumors and B-ALL in vivo. These data characterize EdC as a preclinical nucleoside prodrug candidate for DLBCL and ALL.

A ProTide of AZT Shows Activity Against Human Papillomaviruses

Infection by human papillomaviruses (HPV) can cause warts and tumors. So far, no small molecule antiviral has been approved for the treatment of infections with this DNA virus, although preclinical studies show activity for nucleosidic compounds, such as 9-(2-phosphonylmethoxy)ethylguanine (PMEG) or cidofovir. This prompted us to test new prodrug versions of the nucleoside analog 3'-azido-2',3'-dideoxythymidine (AZT), known to be active against reverse transcriptases and approved for the treatment of HIV. Here we report the synthesis of an ethylbutyl alaninyl ester phosphosphoramidate prodrug of AZT, dubbed AZAEB, and its activity against HPV, a target not known to be sensitive to AZT. A methyl ester derivative was found to be inactive against this and three other DNA viruses, while the phosphoramidate prodrug AZAEB showed a modest inhibitory effect against HPV types 6, 11, 18 and 31. Our results open up new avenues of study for the treatment of diseases caused by members of the papillomaviridae family.

Antiviral Activity of Lipophilic Nucleoside Tetraphosphate Compounds

We report on the synthesis and characterization of three types of nucleoside tetraphosphate derivatives 4-9 acting as potential prodrugs of d4T nucleotides: (i) the δ-phosph(on)ate is modified by two hydrolytically stable alkyl residues 4 and 5; (ii) the δ-phosph(on)ate is esterified covalently by one biodegradable acyloxybenzyl moiety and a nonbioreversible moiety 6 and 7; or (iii) the δ-phosphate of nucleoside tetraphosphate is masked by two biodegradable prodrug groups 8 and 9. We were able to prove the efficient release of d4T triphosphate (d4TTP, (i)), δ-monoalkylated d4T tetraphosphates (20 and 24, (ii)), and d4T tetraphosphate (d4T4P, (iii)), respectively, by chemical or enzymatic processes. Surprisingly, δ-dialkylated d4T tetraphosphates, δ-monoalkylated d4T tetraphosphates, and d4T4P were substrates for HIV-RT. Remarkably, the antiviral activity of TetraPPPPro-prodrug 7 was improved by 7700-fold (SI 5700) as compared to the parent d4T in CEM/TK- cells, denoting a successful cell membrane passage of these lipophilic prodrugs and an intracellular delivery of the nucleotide metabolites.

Antiretroviral Therapy in Pregnancy: A 2023 Review of the Literature

PURPOSE OF REVIEW

Selection of antiretroviral therapy during pregnancy must consider maternal physiology and resulting pharmacokinetic changes in pregnancy, resistance and efficacy profiles, tolerability and frequency of adverse effects, teratogenicity, and maternal, neonatal, and pregnancy outcomes. The objective of this review is to summarize the underlying data that informs the current clinical perinatal guidelines in the USA.

RECENT FINDINGS

Data now supports the use of dolutegravir at all stages of pregnancy with no significant increase in neural tube defects. Safety and pharmacokinetic data on newer antiretroviral medications in pregnancy continue to lag behind the general population. While there are multiple safety and tolerability concerns with older regimens, there are now multiple options of regimens that are highly efficacious and have good safety data in pregnancy. Most pregnant patients who are virally suppressed on a well-tolerated regimen are able to safely continue those medications during pregnancy.

Membrane-permeable tenofovir-di- and monophosphate analogues

The development of new antiviral agents such as nucleoside analogues or acyclic nucleotide analogues (ANPs) and prodrugs thereof is an ongoing task. We report on the synthesis of three types of lipophilic triphosphate analogues of (R)-PMPA and dialkylated diphosphate analogues of (R)-PMPA. A highly selective release of the different nucleotide analogues ((R)-PMPA-DP, (R)-PMPA-MP, and (R)-PMPA) from these compounds was achieved. All dialkylated (R)-PMPA-prodrugs proved to be very stable in PBS as well as in CEM/0 cell extracts and human plasma. In primer extension assays, both the monoalkylated and the dialkylated (R)-PMPA-DP derivatives acted as (R)-PMPA-DP as a substrate for HIV-RT. In contrast, no incorporation events were observed using human polymerase γ. The dialkylated (R)-PMPA-compounds exhibited significant anti-HIV efficacy in HIV-1/2 infected cells (CEM/0 and CEM/TK-). Remarkably, the dialkylated (R)-PMPA-MP derivative 9a showed a 326-fold improved activity as compared to (R)-PMPA in HIV-2 infected CEM/TK- cells as well as a very high SI of 14,000. We are convinced that this study may significantly contribute to advancing antiviral agents developed based on nucleotide analogues in the future.

Lipophilic Nucleoside Triphosphate Prodrugs of Anti-HIV Active Nucleoside Analogs as Potential Antiviral Compounds

Nucleoside analogs require three phosphorylation steps catalyzed by cellular kinases to give their triphosphorylated metabolites. Herein, the synthesis of two types of triphosphate prodrugs of different nucleoside analogs is disclosed. Triphosphates comprising: i) a γ-phosphate or γ-phosphonate bearing a bioreversible acyloxybenzyl group and a long alkyl group and ii) γ-dialkyl phosphate/phosphonate modified nucleoside triphosphate analogs. Almost selective conversion of the former TriPPPro-compounds into the corresponding γ-alkylated nucleoside triphosphate derivatives is demonstrated in CEM/0 cell extracts that proved to be stable toward further hydrolysis. The latter γ-dialkylated triphosphate derivatives lead to the slow formation of the corresponding NDPs. Both types of TriPPPro-compounds are highly potent in wild-type CEM/0 cells and more importantly, they exhibit even better activities against HIV-2 replication in CEM/TK- cell cultures. A finding of major importance is that, in primer extension assays, γ-phosphate-modified-NTPs, γ-mono-alkylated-triphosphates, and NDPs prove to be substrates for HIV-RT but not for cellular DNA-polymerases α,γ.

Pronucleotides of 2',3'-Dideoxy-2',3'-Didehydrothymidine as Potent Anti-HIV Compounds

We report on the synthesis and evaluation of three different nucleotide prodrug systems: (i) nucleoside triphosphate analogues in which the γ-phosph(on)ate has two different lipophilic nonbioreversible alkyl residues with d4TDP as the released nucleotide analogue; (ii) nucleoside diphosphate analogues bearing a bioreversible and a stable β-alkyl group; or (iii) nucleoside diphosphate analogues bearing two nonhydrolysable lipophilic alkyl moieties. The delivery of d4TDP (for the triphosphate precursor) and d4TMP (for the diphosphate precursor) was demonstrated in CD4+ T-lymphocyte CEM cell extracts as well as in phosphate buffer saline (PBS). In primer extension assay, we found that γ-dialkylated d4TTP derivatives and d4TDP were accepted as substrates by HIV-RT. Several of these compounds were observed to be extremely active against HIV-1/2 replication in HIV-infected cells. A more than 45,000-fold increase in the anti-HIV activity was detected for compound 18a as compared to the parent d4T which results in a selectivity index value of 37,000.

Drug Reprofiling to Identify Potential HIV-1 Protease Inhibitors

The use of protease inhibitors in human immunodeficiency virus type 1 (HIV-1) treatment is limited by adverse effects, including metabolic complications. To address these challenges, efforts are underway in the pursuit of more potent and less toxic HIV-1 protease inhibitors. Repurposing existing drugs offers a promising avenue to expedite the drug discovery process, saving both time and costs compared to conventional de novo drug development. This study screened FDA-approved and investigational drugs in the DrugBank database for their potential as HIV-1 protease inhibitors. Molecular docking studies and cell-based assays, including anti-HIV-1 in vitro assays and XTT cell viability tests, were conducted to evaluate their efficacy. The study findings revealed that CBR003PS, an antibiotic currently in clinical use, and CBR013PS, an investigational drug for treating endometriosis and uterine fibroids, exhibited significant binding affinity to the HIV-1 protease with high stability. Their EC50 values, measured at 100% cell viability, were 9.4 nM and 36.6 nM, respectively. Furthermore, cell-based assays demonstrated that these two compounds showed promising results, with therapeutic indexes higher than 32. In summary, based on their favorable therapeutic indexes, CBR003PS and CBR013PS show potential for repurposing as HIV-1 protease inhibitors.

Nucleoside Analog Reverse-Transcriptase Inhibitors in Membrane Environment: Molecular Dynamics Simulations

The behavior of four drugs from the family of nucleoside analog reverse-transcriptase inhibitors (zalcitabine, stavudine, didanosine, and apricitabine) in a membrane environment was traced using molecular dynamics simulations. The simulation models included bilayers and monolayers composed of POPC and POPG phospholipids. It was demonstrated that the drugs have a higher affinity towards POPG membranes than POPC membranes due to attractive long-range electrostatic interactions. The results obtained for monolayers were consistent with those obtained for bilayers. The drugs accumulated in the phospholipid polar headgroup region. Two adsorption modes were distinguished. They differed in the degree of penetration of the hydrophilic headgroup region. Hydrogen bonds between drug molecules and phospholipid heads were responsible for adsorption. It was shown that apricitabine penetrated the hydrophilic part of the POPC and POPG membranes more effectively than the other drugs. Van der Waals interactions between S atoms and lipids were responsible for this.

N4 -Hydroxycytidine/Molnupiravir Inhibits RNA-Virus Induced Encephalitis by Producing Mutated Viruses with Reduced Fitness

A diverse group of RNA viruses including Rabies, Polio, La Crosse, West Nile, Zika, Nipah, Eastern and Western equine encephalitis, Venezuelan equine encephalitis, Japanese encephalitis, and tick-borne encephalitis viruses have the ability to gain access to and replicate in the central nervous system (CNS), causing severe neurological disease. Current treatment for these patients is generally limited to supportive care. To address the need for a generalizable antiviral, we utilized a strategy of mutagenesis to limit virus replication. We evaluated ribavirin (RBV), favipiravir (FAV) and N 4 -hydroxycytidine (NHC) against La Crosse virus (LACV) which is the primary cause of pediatric arboviral encephalitis cases in North America. NHC was more potent than RBV or FAV in neuronal cells. Oral administration of molnupiravir (MOV), the 5'-isobutyryl prodrug of NHC, decreased neurological disease development by 32% following intraperitoneal (IP) infection of LACV. MOV also reduced disease by 23% when virus was administered intranasally (IN). NHC and MOV produced less fit viruses by incorporating predominantly G-to-A or C-to-U mutations. Furthermore, NHC also inhibited two other orthobunyaviruses, Jamestown Canyon virus and Cache Valley virus. Collectively, these studies indicate that NHC/MOV has therapeutic potential to inhibit virus replication and subsequent neurological disease caused by this neurotropic RNA virus.

Efficacy of Zidovudine-Amikacin Combination Therapy In Vitro and in a Rat Tissue Cage Infection Model against Amikacin-Resistant, Multidrug-Resistant Enterobacteriales

Multidrug-resistant (MDR) Enterobacteriales infections have become an urgent global threat to public health. The aim of this study was to evaluate the efficacy of zidovudine-amikacin combination therapy in vitro and in vivo. Molecular characteristics and antibiotic resistance profiles of 53 amikacin-resistant MDR, extensively drug-resistant (XDR), or pan-drug-resistant (PDR) clinical isolates were examined via PCR and susceptibility testing. Checkerboard assays were performed for these 53 isolates to assess in vitro synergistic effects of the zidovudine-amikacin combination, and static time-kill experiments were performed for four XDR or PDR Enterobacteriales isolates. A Galleria mellonella model and a rat tissue cage infection model were established to assess in vivo synergistic effects. The aac(6')-Ib gene was detected in 25 (47.2%) isolates, followed by armA in 5 (9.4%) isolates, rmtB in 27 (50.9%) isolates, and rmtC in 3 (5.8%) isolates. Checkerboard assays showed the synergy of this combination against 38 (71.7%) isolates. The time-kill assays further confirmed that zidovudine strongly synergized with amikacin against four XDR or PDR Enterobacteriales isolates. The Galleria mellonella model study showed that the survival benefit of zidovudine-amikacin combination therapy was significantly better than that of monotherapy for those four Enterobacteriales isolates. Furthermore, the rat tissue cage infection model study showed that zidovudine-amikacin combination therapy displayed more potent bactericidal activity than monotherapy after 3 and 7 days of treatment for the above four isolates. Our data support the idea that the zidovudine-amikacin combination could be a plausible alternative therapy against infections with amikacin-resistant MDR Enterobacteriales, especially with XDR and PDR Enterobacteriales. IMPORTANCE Our study revealed for the first time that the zidovudine-amikacin combination shows a significant bactericidal effect against amikacin-resistant MDR, XDR, and PDR Enterobacteriales. Second, using in vitro and in vivo approaches, our study showed that zidovudine strongly synergized with amikacin against amikacin-resistant MDR Enterobacteriales isolates. Most importantly, with regard to survival benefit, pharmacokinetics, and bactericidal effects, our in vivo experiment demonstrated the effectiveness of zidovudine-amikacin.

Comparative application of derivative spectrophotometric and HPLC techniques for the simultaneous determination of lamivudine and tenofovir disoproxil fumarate in fixed-dose combined drugs

Background

Lamivudine (LAM) and tenofovir disoproxil fumarate (TDF) are part of a fixed-dose combination (FDC) therapy recommended by WHO. Both drugs exhibit similar solubility in many solvent systems and tend to have overlapping spectra with maxima at 260 and 270 nm, respectively, in the UV spectrum—thus making their spectrophotometric assay difficult in FDCs. A third-order derivative (D3, d3A/dλ3) spectrophotometric technique was applied to simultaneously evaluate TDF and LAM in FDC drugs, with amplitudes at 240 and 262.5 nm, respectively. Pharmacopoeia-recommended chromatographic method was also applied for comparative purpose.

Results

Method performance by the proposed D3 technique showed linearity for LAM and TDF from 2–10 µg mL−1 to 8–24 µg mL−1, respectively (R2 ≥ 0.998), while for HPLC method both drugs ranged from 0.25 to 5.0 µg mL−1 (R2 ≥ 0.999). The intercepts and slopes of the regression equations were ≤ 1.62 × 10−4 and ≤ 3.58 × 10−5, respectively, while calculated standard errors were ≤ 8.04 × 10−5. Limits of detection and quantification for both methods were ≤ 0.46 μg mL−1 and ≤ 1.40 μg mL−1, respectively, for LAM, while corresponding limits for TDF were ≤ 2.61 and ≤ 7.90 μg mL−1. The percentage recovery for both drugs and methods ranged from 94.80 to 100.33%. The amount of LAM and TDF in brands I and II was ≥ 99.59 ± 1.19% and ≥ 99.39 ± 0.63%, respectively, for the proposed D3 spectroscopic method, while corresponding values for the HPLC method were ≥ 99.86 ± 0.50 and ≥ 99.87 ± 0.32%. Statistically, both methods were adjudged to have no significant difference at 95% confidence level as the student’s t-test values; experimental paired t- and F-test values were found satisfactory.

Conclusion

The D3 spectrophotometric technique was time saving, cheap, simple and more environmental friendly and shows reliability, precision and accuracy and could be used for routine analysis of FDCs where HPLC is not available.

Graphical abstract

Anti-retroviral treatment with zidovudine alters pyrimidine metabolism, reduces translation, and extends healthy longevity via ATF-4

The human population is aging, and the need for interventions to slow progression of age-related diseases (geroprotective interventions) is growing. Repurposing compounds already used clinically, usually at modified doses, allows rapid implementation of geroprotective pharmaceuticals. Here we find the anti-retroviral nucleoside reverse transcriptase inhibitor (NRTI) zidovudine robustly extends lifespan and health span in C. elegans, independent of electron transport chain impairment or ROS accumulation. Rather, zidovudine treatment modifies pyrimidine metabolism and transcripts related to proteostasis. Testing regulators of mitochondrial stress and proteostasis shows that lifespan extension is dependent on activating transcription factor 4 (ATF-4). ATF-4 regulates longevity induced by mitochondrial stress, specifically communication between mitochondrial and cytosolic translation. Translation is reduced in zidovudine-treated worms, also dependent on ATF-4. Finally, we show ATF-4-dependent lifespan extension induced by didanosine, another NRTI. Altogether, our work elucidates the geroprotective effects of NRTIs such as zidovudine in vivo, via reduction of translation and ATF-4.

Rationally designed inhibitors of the Musashi protein-RNA interaction by hotspot mimicry

RNA-binding proteins (RBPs) are key post-transcriptional regulators of gene expression, and thus underlie many important biological processes. Here, we developed a strategy that entails extracting a "hotspot pharmacophore" from the structure of a protein-RNA complex, to create a template for designing small-molecule inhibitors and for exploring the selectivity of the resulting inhibitors. We demonstrate this approach by designing inhibitors of Musashi proteins MSI1 and MSI2, key regulators of mRNA stability and translation that are upregulated in many cancers. We report this novel series of MSI1/MSI2 inhibitors is specific and active in biochemical, biophysical, and cellular assays. This study extends the paradigm of "hotspots" from protein-protein complexes to protein-RNA complexes, supports the "druggability" of RNA-binding protein surfaces, and represents one of the first rationally-designed inhibitors of non-enzymatic RNA-binding proteins. Owing to its simplicity and generality, we anticipate that this approach may also be used to develop inhibitors of many other RNA-binding proteins; we also consider the prospects of identifying potential off-target interactions by searching for other RBPs that recognize their cognate RNAs using similar interaction geometries. Beyond inhibitors, we also expect that compounds designed using this approach can serve as warheads for new PROTACs that selectively degrade RNA-binding proteins.

An evaluation of postmarketing reports of hyperglycaemia associated with dolutegravir for treatment of HIV in Eswatini

BACKGROUND

Dolutegravir (DTG) is an Integrase Strand Transfer Inhibitor (INSTI) indicated in combination with other antiretroviral agents for the treatment of HIV infection. It is available in a number of pharmaceutical preparations including the fixed-dose combination (TLD) containing tenofovir (300 mg) + lamivudine (300 mg) + dolutegravir (50 mg). In 2018, Eswatini adopted TLD as the preferred first-line HIV treatment regimen for adults and adolescents as per WHO recommendations. From March 2019 to March 2020, the National Pharmacovigilance Center (NPC) in Eswatini received 8 reports of hyperglycaemia associated with the use of DTG. This study was conducted to investigate if Eswatini NPC database included cases suggestive of causality between dolutegravir and hyperglycaemia.

METHOD

A qualitative synthesis of information from the Eswatini national pharmacovigilance database from March 2019 to March 2020 was conducted to investigate a casual association between hyperglycaemia and dolutegravir.

RESULTS

All reports with dolutegravir containing regimen and suspected Adverse Event of hyperglycaemia in the period of March 2019 to March 2020 were included in the study. Seven of the reports were serious (resulted in hospitalization and one case concerned optic neuritis, leading to blindness). Two patients had a medical history of diabetes while the rest of the patients had never experienced hyperglycaemia before starting dolutegravir. For all the reports, the time to onset of hyperglycaemia ranges from 2-5 months after the initiation of DTG. None of the patients discontinued the use of DTG. All the patients were treated with oral hypoglycaemic medication. In severe cases, patients were treated with intravenous normal saline and ringer lactate as well as rapid-acting insulins. All patients are currently stable on oral hypoglycaemic drugs.

CONCLUSION

Cases that support causality between dolutegravir containing regimen and hyperglycaemia were found. These cases were mainly serious. Based on these findings it is recommended that healthcare professionals (HCPs) actively screen all patients for risk factors of hyperglycaemia before DTG initiation. In addition, it is important that HCPs are aware of the possible association between DTG and hyperglycaemia.

HIV nucleoside reverse transcriptase inhibitors

More than 40 years into the pandemic, HIV remains a global burden and as of now, there is no cure in sight. Fortunately, highly active antiretroviral therapy (HAART) has been developed to manage and suppress HIV infection. Combinations of two to three drugs targeting key viral proteins, including compounds inhibiting HIV reverse transcriptase (RT), have become the cornerstone of HIV treatment. This review discusses nucleoside reverse transcriptase inhibitors (NRTIs), including chain terminators, delayed chain terminators, nucleoside reverse transcriptase translocation inhibitors (NRTTIs), and nucleotide competing RT inhibitors (NcRTIs); focusing on their history, mechanism of action, resistance, and current clinical application, including long-acting regimens.

Effects of Two Antiretroviral Drugs on the Crustacean Daphnia magna in River Water

Antiretroviral (ARVs) drugs are used to manage the human immunodeficiency virus (HIV) disease and are increasingly being detected in the aquatic environment. However, little is known about their effects on non-target aquatic organisms. Here, Daphnia magna neonates were exposed to Efavirenz (EFV) and Tenofovir (TFV) ARVs at 62.5–1000 µg/L for 48 h in river water. The endpoints assessed were mortality, immobilization, and biochemical biomarkers (catalase (CAT), glutathione S-transferase (GST), and malondialdehyde (MDA)). No mortality was observed over 48 h. Concentration- and time-dependent immobilization was observed for both ARVs only at 250–1000 µg/L after 48 h, with significant immobilization observed for EFV compared to TFV. Results for biochemical responses demonstrated that both ARVs induced significant changes in CAT and GST activities, and MDA levels, with effects higher for EFV compared to TFV. Biochemical responses were indicative of oxidative stress alterations. Hence, both ARVs could potentially be toxic to D. magna.

Amplifying anti-flooding electrode to fabricate modular electro-fenton system for degradation of antiviral drug lamivudine in wastewater

The advanced oxidation based on in-situ hydrogen peroxide production using carbon air cathode is very potential for wastewater treatment. However, catalyst flooding and complex assembly patterns are the bottleneck limiting the air cathode to the long-term and large-scale application. In this work, a novel anti-flooding air-breathing cathode (ABC) was prepared by a simple rolling-spraying method with relatively low price commercial materials. The novel method changed the morphology of gas diffusion layer as well as adjusted the hydrophobicity of air side of the catalyst layer. As a result, water-air distribution management was achieved and TPI disequilibrium was prevented. Compare with traditional ABC, the H₂O₂ yield and current efficiency (CE) of optimized anti-flooding ABC (ABC_0.9) increased by 13.5% (941 ± 10 mg·L^-1·h^-1 with CE of 84% at 30 mA·cm^-2), the material cost and fabrication time decreased by 10.1% (2.32 ¥·dm^-2, ~0.36 $·dm^-2) and 40%. Amplified ABC coupled with Ti/IrO₂ anodes were integrated into a modular electrode used for H₂O₂generation. When the current density (j) increased from 10 to 30 mA·cm^-2, the energy cost increased from 0.19 to 0.43 ¥·mol^-1 H₂O₂ (from 0.03 to 0.07 $·mol^-1 H₂O₂). The modular electrode was utilized in a 2 L pre-pilot scale reactor for antiviral drug lamivudine degradation by electro-Fenton (EF) process. 100% of lamivudine and 78.1% of total organic carbon (TOC) were removed within 60 min at 20 mA·cm^-2. The susceptible sites on the lamivudine toward hydroxyl radicals were investigated and transformation products (TP) as well as degradation pathway were studied.

An Overview of Marketed Nucleoside and Nucleotide Analogs

Nucleos(t)ide chemistry has been the subject of intense research, mainly because of the promising antiviral and antitumoral activity associated with this compound class. Numerous analogs have been synthesized over the past decades, yielding a number of derivatives that have reached the status of marketed drugs. Herein, an overview of the nucleos(t)ide analogs that have received marketing approval is given. The review is divided into several sections, including antiviral and antitumoral nucleoside analogs as well as nucleoside analogs that have received marketing approval in other therapeutic areas. © 2022 Wiley Periodicals LLC.

Discordant Liver Fibrosis Predictors in Virologically Suppressed People Living with HIV without Hepatitis Virus Infection

Severe liver fibrosis (LF) is associated with poor long-term liver-related outcomes in people living with HIV (PLWH). The study aimed to explore the prevalence and predictors of LF and the concordance between different non-invasive methods for the estimation of LF in HIV-infected individuals without hepatitis virus infection. We enrolled PLWH with HIV-1-RNA <50 copies/mL for >12 months, excluding individuals with viral hepatitis. LF was assessed by transient elastography (TE) (significant >6.65 kPa), fibrosis-4 (FIB-4) (significant >2.67), and AST-to-platelet ratio index (APRI) (significant >1.5). We included 234 individuals (67% males, median age 49 years, median time from HIV diagnosis 11 years, 38% treated with integrase strand transfer inhibitors). In terms of the TE, 13% had ≥F2 stage; FIB-4 score was >1.5 in 7%; and APRI > 0.5 in 4%. Higher body mass index, diabetes mellitus, detectable baseline HIV-1 RNA and longer atazanavir exposure were associated with higher liver stiffness as per TE. Predictors of higher APRI score were CDC C stage and longer exposure to tenofovir alafenamide, while HBcAb positivity and longer exposure to tenofovir alafenamide were associated to higher FIB-4 scores. Qualitative agreement was poor between FIB-4/TE and between APRI/TE by non-parametric Spearman correlation and kappa statistic. In our study, in the group of PLWH without viral hepatitis, different non-invasive methods were discordant in predicting liver fibrosis.

Synthesis and antiviral activity of 2'-deoxy-6'-substituted carbocyclic nucleosides

A series of 2'-deoxy carbocyclic nucleosides characterized by various 6'-substitutions were synthesized and evaluated for their antiviral activities against three viruses, including hepatitis B virus (HBV), hepatitis C virus, and influenza virus. The in vitro antiviral assays indicated that these nucleosides only showed inhibitory activities against HBV, and the substituted groups at the 6' position significantly affected the activity. Among them, the guanosine analog 2b bearing a 6'-α-hydroxyl methyl group was the most potent compound with an EC₅₀ value of 80 nM. The present study provided useful information for the discovery of antiviral carbocyclic nucleosides.

Host Defence RNases as Antiviral Agents against Enveloped Single Stranded RNA Viruses

Owing to the recent outbreak of Coronavirus Disease of 2019 (COVID-19), it is urgent to develop effective and safe drugs to treat the present pandemic and prevent other viral infections that might come in the future. Proteins from our own innate immune system can serve as ideal sources of novel drug candidates thanks to their safety and immune regulation versatility. Some host defense RNases equipped with antiviral activity have been reported over time. Here, we try to summarize the currently available information on human RNases that can target viral pathogens, with special focus on enveloped single-stranded RNA (ssRNA) viruses. Overall, host RNases can fight viruses by a combined multifaceted strategy, including the enzymatic target of the viral genome, recognition of virus unique patterns, immune modulation, control of stress granule formation, and induction of autophagy/apoptosis pathways. The review also includes a detailed description of representative enveloped ssRNA viruses and their strategies to interact with the host and evade immune recognition. For comparative purposes, we also provide an exhaustive revision of the currently approved or experimental antiviral drugs. Finally, we sum up the current perspectives of drug development to achieve successful eradication of viral infections.

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

Sugar-modified nucleosides have gained considerable attention in the scientific community, either for use as molecular probes or as therapeutic agents. When the methylene group of the ribose ring is replaced with a sulfur atom at the 3’-position, these compounds have proved to be structurally potent nucleoside analogues, and the best example is BCH-189. The majority of methods traditionally involves the chemical modification of nucleoside structures. It requires the creation of artificial sugars, which is accompanied by coupling nucleobases via N-glycosylation. However, over the last three decades, efforts were made for the synthesis of 1,3-oxathiolane nucleosides by selective N-glycosylation of carbohydrate precursors at C-1, and this approach has emerged as a strong alternative that allows simple modification. This review aims to provide a comprehensive overview on the reported methods in the literature to access 1,3-oxathiolane nucleosides. The first focus of this review is the construction of the 1,3-oxathiolane ring from different starting materials. The second focus involves the coupling of the 1,3-oxathiolane ring with different nucleobases in a way that only one isomer is produced in a stereoselective manner via N-glycosylation. An emphasis has been placed on the C–N-glycosidic bond constructed during the formation of the nucleoside analogue. The third focus is on the separation of enantiomers of 1,3-oxathiolane nucleosides via resolution methods. The chemical as well as enzymatic procedures are reviewed and segregated in this review for effective synthesis of 1,3-oxathiolane nucleoside analogues.

HCV RdRp, sofosbuvir and beyond

The therapeutic targeting of the nonstructural protein 5B (NS5B) RNA-dependent RNA polymerase (RdRp) of the Hepatitis C Virus (HCV) with nucleotide analogs led to a deep understanding of this enzymes structure, function and substrate specificity. Unlike previously studied DNA polymerases including the reverse transcriptase of Human Immunodeficiency Virus, development of biochemical assays for HCV RdRp proved challenging due to low solubility of the full-length protein and inefficient acceptance of exogenous primer/templates. Despite the poor apparent specific activity, HCV RdRp was found to support rapid and processive transcription once elongation is initiated in vitro consistent with its high level of viral replication in the livers of patients. Understanding of the substrate specificity of HCV RdRp led to the discovery of the active triphosphate of sofosbuvir as a nonobligate chain-terminator of viral RNA transcripts. The ternary crystal structure of HCV RdRp, primer/template, and incoming nucleotide showed the interaction between the nucleotide analog and the 2'-hydroxyl binding pocket and how an unfit mutation of serine 282 to threonine results in resistance by interacting with the uracil base and modified 2'-position of the analog. Host polymerases mediate off-target toxicity of nucleotide analogs and the active metabolite of sofosbuvir was found to not be efficiently incorporated by host polymerases including the mitochondrial RNA polymerase (POLRMT). Knowledge from studying inhibitors of HCV RdRp serves to advance antiviral drug discovery for other emerging RNA viruses including the discovery of remdesivir as an inhibitor of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2), the virus that causes COVID-19.

Current Trends and Limitations in Dengue Antiviral Research

Dengue is the most prevalent arthropod-borne viral disease worldwide and affects approximately 2.5 billion people living in over 100 countries. Increasing geographic expansion of Aedes aegypti mosquitoes (which transmit the virus) has made dengue a global health concern. There are currently no approved antivirals available to treat dengue, and the only approved vaccine used in some countries is limited to seropositive patients. Treatment of dengue, therefore, remains largely supportive to date; hence, research efforts are being intensified for the development of antivirals. The nonstructural proteins, 3 and 5 (NS3 and NS5), have been the major targets for dengue antiviral development due to their indispensable enzymatic and biological functions in the viral replication process. NS5 is the largest and most conserved nonstructural protein encoded by flaviviruses. Its multifunctionality makes it an attractive target for antiviral development, but research efforts have, this far, not resulted in the successful development of an antiviral targeting NS5. Increase in structural insights into the dengue NS5 protein will accelerate drug discovery efforts focused on NS5 as an antiviral target. In this review, we will give an overview of the current state of therapeutic development, with a focus on NS5 as a therapeutic target against dengue.

DNA Polymerase θ: A Cancer Drug Target with Reverse Transcriptase Activity

The emergence of precision medicine from the development of Poly (ADP-ribose) polymerase (PARP) inhibitors that preferentially kill cells defective in homologous recombination has sparked wide interest in identifying and characterizing additional DNA repair enzymes that are synthetic lethal with HR factors. DNA polymerase theta (Polθ) is a validated anti-cancer drug target that is synthetic lethal with HR factors and other DNA repair proteins and confers cellular resistance to various genotoxic cancer therapies. Since its initial characterization as a helicase-polymerase fusion protein in 2003, many exciting and unexpected activities of Polθ in microhomology-mediated end-joining (MMEJ) and translesion synthesis (TLS) have been discovered. Here, we provide a short review of Polθ's DNA repair activities and its potential as a drug target and highlight a recent report that reveals Polθ as a naturally occurring reverse transcriptase (RT) in mammalian cells.

Liver Fibrosis during Antiretroviral Treatment in HIV-Infected Individuals. Truth or Tale?

After the introduction of antiretroviral treatment (ART) back in 1996, the lifespan of people living with HIV (PLWH) has been substantially increased, while the major causes of morbidity and mortality have switched from opportunistic infections and AIDS-related neoplasms to cardiovascular and liver diseases. HIV itself may lead to liver damage and subsequent liver fibrosis (LF) through multiple pathways. Apart from HIV, viral hepatitis, alcoholic and especially non-alcoholic liver diseases have been implicated in liver involvement among PLWH. Another well known cause of hepatotoxicity is ART, raising clinically significant concerns about LF in long-term treatment. In this review we present the existing data and analyze the association of LF with all ART drug classes. Published data derived from many studies are to some extent controversial and therefore remain inconclusive. Among all the antiretroviral drugs, nucleoside reverse transcriptase inhibitors, especially didanosine and zidovudine, seem to carry the greatest risk for LF, with integrase strand transfer inhibitors and entry inhibitors having minimal risk. Surprisingly, even though protease inhibitors often lead to insulin resistance, they do not seem to be associated with a significant risk of LF. In conclusion, most ART drugs are safe in long-term treatment and seldom lead to severe LF when no liver-related co-morbidities exist.

Nanotechnology-based approaches for emerging and re-emerging viruses: Special emphasis on COVID-19

In recent decades, the major concern of emerging and re-emerging viral diseases has become an increasingly important area of public health concern, and it is of significance to anticipate future pandemic that would inevitably threaten human lives. The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a newly emerged virus that causes mild to severe pneumonia. Coronavirus disease (COVID-19) became a very much concerned issue worldwide after its super-spread across the globe and emerging viral diseases have not got specific and reliable diagnostic and treatments. As the COVID-19 pandemic brings about a massive life-loss across the globe, there is an unmet need to discover a promising and typically effective diagnosis and treatment to prevent super-spreading and mortality from being decreased or even eliminated. This study was carried out to overview nanotechnology-based diagnostic and treatment approaches for emerging and re-emerging viruses with the current treatment of the disease and shed light on nanotechnology's remarkable potential to provide more effective treatment and prevention to a special focus on recently emerged coronavirus.

An original pronucleotide strategy for the simultaneous delivery of two bioactive drugs

The synthesis and in vitro anti-HIV activity of a novel series of phosphoramidate pronucleotides including a S-pivaloyl-2-thioethyl (tBuSATE) group as biolabile phosphate protecting group are reported. Such constructs, obtained through different phosphorus chemistries, are characterized by the association of two different anti-HIV nucleoside analogues linked to the phosphorus atom respectively by the sugar residue and the exocyclic amino function of the nucleobase. In vitro, comparative anti-HIV evaluation demonstrates that such original prodrugs are able to allow the efficient intracellular combination release of a 5'-mononucleotide as well as another nucleoside analogue. In human T4-lymphoblastoid cells, the pronucleotide 1 shows remarkable antiviral activity with an EC₅₀ in the nanomolar range (0.6 ηM) and without additional cytotoxicity. In addition, these two pronucleotide models exhibit higher selectivity index than the equimolar mixture of their constitutive nucleoside analogues opening the way to further studies with regard to the current use of drug combinations.

Voltammetric Methods Used in the Determination of Nucleoside Reverse Transcriptase Inhibitors

Background:

The Human Immunodeficiency Virus (HIV) has now been established as the causative agent of the Acquired Immunodeficiency Syndrome (AIDS) and exactly 25 antiretroviral drugs have been formally approved for clinical use in the treatment of AIDS. The life quality and duration of HIV-positive patients have increased with the usage of antiretroviral drugs in the treatment of AIDS. Nucleoside Reverse Transcriptase Inhibitors (NRTIs) are one of the subgroups of antiretroviral.

Objective:

The quantification of drugs is important, as they make positive contributions to dose adjustments in practice. Voltammetric methods are very powerful analytical methods used in the pharmaceutical industry because of the determination of therapeutic agents and/or their metabolites in clinical samples at extremely low concentrations (10-50 ng/ml).

Methods:

This review mainly includes the pharmacological properties and recent determination studies by voltammetric methods from pharmaceutical dosage forms and biological samples of eight NRTIs group antiretroviral drugs (zidovudine, abacavir, adefovir, entecavir, zalcitabine, didanosine, emtricitabine, lamivudine) that are used in the clinic and show electroactive properties, were performed.

Conclusion:

Due to the variety of working electrodes in voltammetric methods, it is possible to choose the electrode that best responds. In this way, the analysis of NRTIs was possible at lower concentrations in pharmaceuticals and biological samples with voltammetric methods in these studies without the necessity for the sample pre-treatment or time-consuming extraction steps. The voltammetric methods provide good stability, repeatability, reproducibility and high recovery for the analysis of the analyte. They could be used for the pharmacokinetic studies as well as for quality control laboratory studies.

An in-depth analysis of novel combinatorial drug therapy via nanocarriers against HIV/AIDS infection and their clinical perspectives: a systematic review

Introduction: Conventional antiretroviral therapy against HIV infections is threatening to become outdated due to the low chemical, physical, biological, and pharmacokinetic characteristics of therapeutic molecules, followed by the high chance of emergence of drug resistance. Considering the co-encapsulation of multi-infection agents in a single nanocarrier is emerging to offer various benefits such as synergistic action, improved therapeutic efficacy, reduced drug resistance development, patient compliance, and economical therapy.Areas covered: A systematic review of nano-based combinatorial drug therapy was performed using various databases including Scopus, PubMed, Google Scholar, and Science Direct between 2000 and 2020. The search set was screened as per the inclusion and exclusion criteria, followed by 46 scientific articles and seven clinical studies selected for in-depth analysis.Expert opinion: There has been an immense effort to analyze the mechanism of HIV infection to develop a promising therapeutic approach, although the aim of complete prevention has not been succeeded yet. The key finding is to overcome the challenges associated with conventional therapy by the combinatorial drug in a single nanoformulation, which holds great potential for impact in the management of HIV infection.

Nano Co-Crystal Embedded Stimuli-Responsive Hydrogels: A Potential Approach to Treat HIV/AIDS

Currently, the human immunodeficiency virus (HIV) that causes acquired immunodeficiency syndrome (AIDS) can only be treated successfully, using combination antiretroviral (ARV) therapy. Lamivudine (3TC) and zidovudine (AZT), two compounds used for the treatment of HIV and prevention of disease progression to AIDS are used in such combinations. Successful therapy with 3TC and AZT requires frequent dosing that may lead to reduced adherence, resistance and consequently treatment failure. Improved toxicity profiles of 3TC and AZT were observed when combined as a nano co-crystal (NCC). The use of stimuli-responsive delivery systems provides an opportunity to overcome the challenge of frequent dosing, by controlling and/or sustaining delivery of drugs. Preliminary studies undertaken to identify a suitable composition for a stimulus-responsive in situ forming hydrogel carrier for 3TC-AZT NCC were conducted, and the gelation and erosion time were determined. A 25% w/w Pluronic® F-127 thermoresponsive hydrogel was identified as a suitable carrier as it exhibited a gelation time of 5 min and an erosion time of 7 days. NCC-loaded hydrogels were evaluated using in vitro dissolution and cytotoxicity assays. In vitro dissolution undertaken using membrane-less diffusion over 168 h revealed that 3TC and AZT release from NCC-loaded hydrogels was complete and followed zero-order kinetic processes, whereas those loaded with the micro co-crystal and physical mixture were incomplete and best described using the Korsmeyer-Peppas kinetic model. The release of AZT and 3TC from the physical mixture and MCC-loaded gel exhibited a value for n of 0.595 for AZT release from the physical mixture and 0.540 for the MCC technology, whereas the release exponent for 3TC was 0.513 for the physical mixture and 0.557 for the MCC technology indicating that diffusion and erosion controlled 3TC and AZT release. In vitro cytotoxicity assay data revealed that the addition of NCC to the thermoresponsive hydrogel resulted in an improved cell viability of 88.0% ± 5.0% when compared to the cell viability of the NCC of 76.9% ± 5.0%. The results suggest that the use of a thermoresponsive nanosuspension may have the potential to be delivered as an intramuscular injection that can subsequently increase bioavailability and permit dose reduction and/or permit use of a longer dosing frequency.

Improving properties of the nucleobase analogs T-705/T-1105 as potential antiviral

In this minireview we describe our work on the improvement of the nucleobase analogs Favipiravir (T-705) und its non-fluorinated derivative T-1105 as influenza and SARS-CoV-2 active compounds. Both nucleobases were converted into nucleotides and then included in our nucleotide prodrugs technologies cycloSal-monophosphates, DiPPro-nucleoside diphosphates and TriPPPro-nucleoside triphosphates. Particularly the DiPPro-derivatives of T-1105-RDP proved to be very active against influenza viruses. T-1105-derivatives in general were found to be more antivirally active as compared to their T-705 counterpart. This may be due to the low chemical stability of all ribosylated derivatives of T-705. The ribosyltriphosphate derivative of T-1105 was studied for the potential to act as a inhibitor of the SARS-CoV-2 RdRp and was found to be an extremely potent compound causing lethal mutagenesis. The pronucleotide technologies, the chemical synthesis, the biophysical properties and the biological effects of the compounds will be addressed as well.

Top-Down Synthesis of a Lamivudine-Zidovudine Nano Co-Crystal

Lamivudine (3TC) and zidovudine (AZT) are antiretroviral agents used to manage HIV/AIDS infection. A wet media milling top-down approach was used to develop and produce nano co-crystals of 3TC and AZT. Micro co-crystals were prepared by solvent evaporation and subsequently milled in the presence of two surfactants, viz., sodium lauryl sulfate (SLS) and α-tocopheryl polyethylene glycol succinate 1000 (TPGS 1000). Optimisation was undertaken using design of experiments (DoE) and response surface methodology (RSM) to establish and identify parameters that may affect the manufacturing of nano co-crystals. The impact of SLS and TPGS 1000 concentration, milling time, and number of units of milling medium on the manufacturing of nano co-crystals, was investigated. The critical quality attributes (CQA) monitored were particle size (PS), Zeta potential (ZP), and polydispersity index (PDI). Powder X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, transmission electron microscopy, energy dispersive X-ray spectroscopy scanning electron microscopy, and cytotoxicity assays were used for additional characterization of the optimised nano co-crystal. The mean PS, PDI, and ZP of the optimised top-down nanocrystal were 271.0 ± 92.0 nm, 0.467 ± 0.073, and −41.9 ± 3.94 mV, respectively. In conclusion, a simple, inexpensive, rapid, and precise method of nano co-crystal manufacturing was developed, validated, and optimised using DoE and RSM, and the final product exhibited the target CQA.

Prodrugs of γ-Alkyl-Modified Nucleoside Triphosphates: Improved Inhibition of HIV Reverse Transcriptase

The development of nucleoside triphosphate prodrugs is one option to apply nucleoside reverse transcriptase inhibitors. Herein, we report the synthesis and evaluation of d4TTP analogues, in which the γ-phosphate was modified covalently by lipophilic alkyl residues, and acyloxybenzyl prodrugs of these γ-alkyl-modified d4TTPs, with the aim of delivering of γ-alkyl-d4TTP into cells. Selective formation of γ-alkyl-d4TTP was proven with esterase and in CD4+ -cell extracts. In contrast to d4TTP, γ-alkyl-d4TTPs proved highly stable against dephosphorylation. Primer extension assays with HIV reverse transcriptase (RT) and DNA-polymerases α, β or γ showed that γ-alkyl-d4TTPs were substrates for HIV-RT only. In antiviral assays, compounds were highly potent inhibitors of HIV-1 and HIV-2 also in thymidine-kinase-deficient T-cell cultures (CEM/TK- ). Thus, the intracellular delivery of such γ-alkyl-nucleoside triphosphates may potentially lead to nucleoside triphosphates with a higher selectivity towards the viral polymerase that can act in virus-infected cells.

Application of Molecular Dynamics Simulations to the Design of Nucleotide Inhibitors Binding to Norovirus Polymerase

The RNA-dependent RNA polymerase (RdRp) of norovirus is an attractive target of antiviral agents aimed at providing protection against norovirus-associated gastroenteritis. Here, we perform molecular dynamics simulations of the crystal structure of norovirus RdRp in complex with several known binders, as well as free-energy simulations by free-energy perturbation (FEP) to determine binding free energies of these molecules relative to the natural nucleotide substrates. We determine experimental EC₅₀ values and nucleotide incorporation efficiencies for several of these compounds. Moreover, we investigate the mechanism of inhibition of some of these ligands. Using FEP, we screened a virtual nucleotide library with 121 elements for binding to the polymerase and successfully identified two novel chain terminators.

γ-Ketobenzyl-Modified Nucleoside Triphosphate Prodrugs as Potential Antivirals

The antiviral activity of nucleoside reverse transcriptase inhibitors is often hampered by insufficient phosphorylation. Nucleoside triphosphate analogues are presented, in which the γ-phosphate was covalently modified by a non-bioreversible, lipophilic 4-alkylketobenzyl moiety. Interestingly, primer extension assays using human immunodeficiency virus reverse transcriptase (HIV-RT) and three DNA-polymerases showed a high selectivity of these γ-modified nucleoside triphosphates to act as substrates for HIV-RT, while they proved to be nonsubstrates for DNA-polymerases α, β, and γ. In contrast to d4TTP, the γ-modified d4TTPs showed a high resistance toward dephosphorylation in cell extracts. A series of acyloxybenzyl-prodrugs of these γ-ketobenzyl nucleoside triphosphates was prepared. The aim was the intracellular delivery of a stable γ-modified nucleoside triphosphate to increase the selectivity of such compounds to act in infected versus noninfected cells. Delivery of γ-ketobenzyl-d4TTPs was proven in T-lymphocyte cell extracts. The prodrugs were potent inhibitors of HIV-1/2 in cultures of infected CEM/0 cells and more importantly in thymidine kinase-deficient CD4⁺ T-cells.

γ-Non-Symmetrically Dimasked TriPPPro Prodrugs as Potential Antiviral Agents against HIV

Nucleoside analogue reverse transcriptase inhibitors (NRTI) and nucleoside analogue monophosphate prodrugs are used in combination antiretroviral therapy (cART). The design of antivirally active nucleoside triphosphate prodrugs is a recent and an important advancement in the field of nucleoside analogue drug development. Here, we report on TriPPPro‐derivatives of nucleoside analogue triphosphates (NTPs) that comprised two different acyloxybenzyl‐masks at the γ‐phosphate of the NTP aiming to achieve the metabolic bypass. Thus, γ‐non‐symmetrically dimasked TriPPPro‐compounds (γ‐(AB,ab)‐d4TTPs) were synthesized and they proved to be active against HIV‐1 and HIV‐2 in cultures of infected wild‐type human CD4⁺ T‐lymphocyte (CEM/0) cells and more importantly also in thymidine kinase‐deficient CD4⁺ T‐cells (CEM/TK‐). From hydrolysis studies both in phosphate buffer (PB, pH 7.3) and CEM cell extracts, there was surprisingly no differentiation in the cleavage of the two acyloxybenzyl prodrug‐masks. However, if within one of the two acyloxybenzyl groups a short PEG‐type methoxytriglycol group was introduced, the “standard” acyloxybenzyl‐mask was cleaved with high preference.

Membrane Permeable, Bioreversibly Modified Prodrugs of Nucleoside Diphosphate-γ-Phosphonates

Nucleoside reverse transcriptase inhibitors (NRTIs) are widely used as antiviral and anticancer agents, although they require intracellular phosphorylation into their antivirally active form, the triphosphorylated nucleoside analogue metabolites. We report on the synthesis and characterization of a new class of nucleoside triphosphate analogues comprising a C-alkyl-phosphonate moiety replacing the γ-phosphate. These compounds were converted into bioreversibly modified lipophilic prodrugs at the γ-phosphonate by the attachment of an acyloxybenzyl (ester) or an alkoxycarbonyloxybenzyl (carbonate) group. Such compounds formed γ-C-(alkyl)-nucleoside triphosphate analogues with high selectivity because of an enzyme-triggered delivery mechanism. The latter compounds were very stable in CD4⁺ T-lymphocyte (CEM cell) extracts, and they were substrates for HIV-reverse transcriptase without being substrates for DNA-polymerases α, β, and γ. In antiviral assays, the excellent antiviral activity of the prodrugs that was found in CEM/0 cells was completely kept in CEM/TK^- cells. The activity was improved by 3 logs as compared to the parent nucleoside d4T.

Synthesis of chiral pyrimidine-substituted diester D-A cyclopropanes via asymmetric cyclopropanation of phenyliodonium ylides

A highly enantioselective cyclopropanation to synthesize pyrimidine-substituted diester D-A cyclopropanes is reported. Various N1-vinylpyrimidines react well with phenyliodonium ylides, delivering chiral cyclopropanes in up to 97% yield with up to 99% ee. Through simple [3+2] annulation with benzaldehyde or ethyl glyoxylate, different chiral pyrimidine nucleoside analogues with a sugar ring could be obtained.

Overview of therapeutic drug research for COVID-19 in China

Since the outbreak of novel coronavirus pneumonia (COVID-19) in December 2019, more than 2,500,000 people worldwide have been diagnosed with SARS-CoV-2 as of April 22. In response to this epidemic, China has issued seven trial versions of diagnosis and treatment protocol for COVID-19. According to the information that we have collected so far, this article provides an overview of potential therapeutic drugs and compounds with much attention, including favipiravir and hydroxychloroquine, as well as traditional Chinese medicine, which have been reported with good clinical treatment effects. Moreover, with further understanding of SARS-CoV-2 virus, new drugs targeting specific SARS-CoV-2 viral components arise and investigations on these novel anti-SARS-CoV-2 agents are also reviewed.