Structural biology of SARS-CoV-2: open the door for novel therapies.

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is the causative agent of the pandemic disease COVID-19, which is so far without efficacious treatment. The discovery of therapy reagents for treating COVID-19 are urgently needed, and the structures of the potential drug-target proteins in the viral life cycle are particularly important. SARS-CoV-2, a member of the Orthocoronavirinae subfamily containing the largest RNA genome, encodes 29 proteins including nonstructural, structural and accessory proteins which are involved in viral adsorption, entry and uncoating, nucleic acid replication and transcription, assembly and release, etc. These proteins individually act as a partner of the replication machinery or involved in forming the complexes with host cellular factors to participate in the essential physiological activities. This review summarizes the representative structures and typically potential therapy agents that target SARS-CoV-2 or some critical proteins for viral pathogenesis, providing insights into the mechanisms underlying viral infection, prevention of infection, and treatment. Indeed, these studies open the door for COVID therapies, leading to ways to prevent and treat COVID-19, especially, treatment of the disease caused by the viral variants are imperative.

Inhibition of the futalosine pathway for menaquinone biosynthesis suppresses Chlamydia trachomatis infection.

Chlamydia trachomatis, an obligate intracellular bacterium with limited metabolic capabilities, possesses the futalosine pathway for menaquinone biosynthesis. Futalosine pathway enzymes have promise as narrow-spectrum antibiotic targets, but the activity and essentiality of chlamydial menaquinone biosynthesis have yet to be established. In this work, menaquinone-7 (MK-7) was identified as a C. trachomatis-produced quinone through liquid chromatography-tandem mass spectrometry. An immunofluorescence-based assay revealed that treatment of C. trachomatis-infected HeLa cells with the futalosine pathway inhibitor docosahexaenoic acid (DHA) reduced inclusion number, inclusion size, and infectious progeny. Supplementation with MK-7 nanoparticles rescued the effect of DHA on inclusion number, indicating that the futalosine pathway is a target of DHA in this system. These results open the door for menaquinone biosynthesis inhibitors to be pursued in antichlamydial development.

Aminofutalosine Deaminase in the Menaquinone Pathway of Helicobacter pylori.

Helicobacter pylori is a Gram-negative bacterium that is responsible for gastric and duodenal ulcers. H. pylori uses the unusual mqn pathway with aminofutalosine (AFL) as an intermediate for menaquinone biosynthesis. Previous reports indicate that hydrolysis of AFL by 5'-methylthioadenosine nucleosidase (HpMTAN) is the direct path for producing downstream metabolites in the mqn pathway. However, genomic analysis indicates jhp0252 is a candidate for encoding AFL deaminase (AFLDA), an activity for deaminating aminofutolasine. The product, futalosine, is not a known substrate for bacterial MTANs. Recombinant jhp0252 was expressed and characterized as an AFL deaminase (HpAFLDA). Its catalytic specificity includes AFL, 5'-methylthioadenosine, 5'-deoxyadenosine, adenosine, and S-adenosylhomocysteine. The kcat/Km value for AFL is 6.8 × 104 M-1 s-1, 26-fold greater than that for adenosine. 5'-Methylthiocoformycin (MTCF) is a slow-onset inhibitor for HpAFLDA and demonstrated inhibitory effects on H. pylori growth. Supplementation with futalosine partially restored H. pylori growth under MTCF treatment, suggesting AFL deamination is significant for cell growth. The crystal structures of apo-HpAFLDA and with MTCF at the catalytic sites show a catalytic site Zn2+ or Fe2+ as the water-activating group. With bound MTCF, the metal ion is 2.0 Å from the sp3 hydroxyl group of the transition state analogue. Metabolomics analysis revealed that HpAFLDA has intracellular activity and is inhibited by MTCF. The mqn pathway in H. pylori bifurcates at aminofutalosine with HpMTAN producing adenine and depurinated futalosine and HpAFLDA producing futalosine. Inhibition of cellular HpMTAN or HpAFLDA decreased the cellular content of menaquinone-6, supporting roles for both enzymes in the pathway.

Mass spectrometry investigation of nucleoside adducts of fatty acid hydroperoxides from oxidation of linolenic and linoleic acids.

The widespread presence of lipid hydroperoxides in foodstuffs and biological samples has aroused great attentions in recent years, while it remains challenging for analysis of the fragility of O - O bond linkage of peroxides. In this present study, we explored the utility of electrospray ionization mass spectrometry (ESI-MS) for characterization of two fatty acid hydroperoxides from oxidation of linoleic acid and α-linolenic acid, which are the essential fatty acids abundant in many seeds and vegetable oils. The results indicated that in-source fragmentation occurred in the detection of the two fatty acid hydroperoxides in both positive and negative ion modes, which yielded characteristic fragments for ESI-MS analysis. In addition, the genotoxicity of fatty acid hydroperoxides for generation of nucleoside adducts was investigated. It was found that a variety of nucleoside adducts were formed from the reactions of fatty acid hydroperoxides and nucleosides. Furthermore, the decomposition products of the fatty acid hydroperoxides were determined, which provided evidence to elucidate the reaction mechanism for formation of nucleoside adducts.

Discovery of potential pharmacodynamic ingredients of Dang-Gui-Si-Ni decoction based on absorbed ingredients and molecular docking.

ETHNOPHARMACOLOGICAL RELEVANCE: The Dang-Gui-Si-Ni (DGSN) decoction as a classic prescription has been widely used for thousands of years in the clinical practice of traditional Chinese medicine (TCM). Especially in recent years, the potential efficacy of TCM for the treatment of Raynaud's syndrome has attracted great attention as there are still no specific remedies for this disease. However, the active constituents and underlying mechanisms responsible for the therapeutic benefits are not well understood, which makes it difficult to ensure quality control or to design research and drug development strategies. To identify the potential pharmacodynamic ingredients (PPIs) of TCM will help to achieve suitable process control procedures for industrial production and large-scale manufacturing. AIM OF THE STUDY: In the present study, we propose a multi-dimensional qualitative analysis method combining water-decoction spectra, in-vitro intestinal absorption spectra, in-vivo plasma spectra, and molecular docking of components to quickly identify the PPIs for the DGSN decoction of TCM. MATERIALS AND METHODS: Water-based decoctions of DGSN were prepared in accordance with the clinical use registered in ancient books. Ultra-high-performance liquid chromatography-quadrupole-time of flight mass spectrometry (UHPLC-Q/TOF-MS) coupled with computerized modelling activity screening was used to quickly identify the PPIs of the DGSN decoction. Bioactive compounds absorbed in vitro were identified using the everted intestinal sac model from rats and compounds absorbed in vivo were confirmed in portal vein blood samples obtained following oral administration in rats. Molecular docking validation experiments were adopted to predict the binding activity to coagulation factors I, II, VII, X, and IX. The active components were further confirmed by pharmacodynamics analysis. The anticoagulant activity of the DGSN decoction was verified using rat models. RESULTS: Thirty-one compounds were identified in the DGSN decoction. According to the in vivo experiments, 22 compounds that could be absorbed in vivo were detected by the everted intestinal sac model in rats. This model greatly reduces the scope of PPIs and is easy to perform. Ten compounds were detected in the portal vein blood in rats. The compounds detected in plasma provide stronger evidence supporting the PPIs. Molecular docking in vitro experiments indicated that 7 compounds exhibited better binding activity with coagulation factors I, II, VII, X, and IX. The animal experiments confirmed that the DGSN decoction could improve the microcirculation, providing indirect proof of anticoagulant activity suggested by the molecular docking studies. Finally, based on the multi-dimensional methods, 9 potential compounds present in the DGSN decoction were identified as PPIs (i.e., ferulic acid, paeoniflorin, albiflorin, chlorogenic acid, cryptochlorogenic acid, liquiritin, liquiritin apioside, cinnamaldehyde and glycyrrhizic acid). CONCLUSION: Overall, this study combined the water-decoction spectra, intestinal absorption spectra in vitro, plasma spectra in vivo, and molecular docking studies to establish a multi-dimensional qualitative analysis method of the DGSN decoction. Meanwhile, 9 compounds in DGSN decoction were identified as PPIs using this method, and are proposed for application as quality standards for complex TCM prescriptions.

Repurposing Nucleoside Analogs for Human Coronaviruses.

Coronavirus disease 2019 (COVID-19) is a serious illness caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 or CoV-2). Some reports claimed certain nucleoside analogs to be active against CoV-2 and thus needed confirmation. Here, we evaluated a panel of compounds and identified novel nucleoside analogs with antiviral activity against CoV-2 and HCoV-OC43 while ruling out others. Of significance, sofosbuvir demonstrated no antiviral effect against CoV-2, and its triphosphate did not inhibit CoV-2 RNA polymerase.

One-Pot Derivatization for Wide-Scope Detection of Nucleobases and Deoxyribosides in Natural Medicinal Foods with Liquid Chromatography-Tandem Mass Spectrometry.

A new chemical labeling-based LC-MS/MS approach was developed for quantitative profiling of nine canonical bases and deoxynucleosides (dNs) in natural products. Using 2-bromo-1-(4-dimethylamino-phenyl)-ethaone (BrDPE) as the tagging reagent, a previously unexploited N-alkylpyrimidine derivative (Nad) was created for one-pot labeling of widescope nucleobases via a flexible bromophilic substitution under mild conditions. The derivatization notably improved the LC-MS detection sensitivity by 31-107 fold, enabling a fast dilute-and-shoot analysis of highly diluted samples. The optimized and validated method demonstrated satisfactory accuracy (87-107%), precision (RSDs < 7.5%), and recovery (89-105%) for matrix-matched standard addition. The method was applied to simultaneously determine all target analytes and four uncanonical analogues and base-modified species in seven traditional health foods, which differ in contents by up to 600-fold for discrimination among samples. Further, the base-labeled Nads exhibit a unique fragmentation signature that could be used for untargeted screening of nucleobase-containing metabolites by simplified LC-MS/MS workflow to improve quality evaluation of natural medicinal products.

Honey as Source of Nitrogen Compounds: Aromatic Amino Acids, Free Nucleosides and Their Derivatives.

The content of selected major nitrogen compounds including nucleosides and their derivatives was evaluated in 75 samples of seven varieties of honey (heather, buckwheat, black locust, goldenrod, canola, fir, linden) by targeted ultra-high performance liquid chromatography-diode array detector - high-resolution quadrupole time-of-flight mass spectrometry (UHPLC-DAD-QqTOF-MS) and determined by UHPLC-DAD. The honey samples contained nucleosides, nucleobases and their derivatives (adenine: 8.9 to 18.4 mg/kg, xanthine: 1.2 to 3.3 mg/kg, uridine: 17.5 to 51.2 mg/kg, guanosine: 2.0 to 4.1 mg/kg; mean amounts), aromatic amino acids (tyrosine: 7.8 to 263.9 mg/kg, phenylalanine: 9.5 to 64.1 mg/kg; mean amounts). The amounts of compounds significantly differed between some honey types. For example, canola honey contained a much lower amount of uridine (17.5 ± 3.9 mg/kg) than black locust where it was most abundant (51.2 ± 7.8 mg/kg). The presence of free nucleosides and nucleobases in different honey varieties is reported first time and supports previous findings on medicinal activities of honey reported in the literature as well as traditional therapy and may contribute for their explanation. This applies, e.g., to the topical application of honey in herpes infections, as well as its beneficial activity on cognitive functions as nootropic and neuroprotective, in neuralgia and is also important for the understanding of nutritional values of honey.

Deploying Fluorescent Nucleoside Analogues for High-Throughput Inhibitor Screening.

High-throughput small-molecule screening in drug discovery processes commonly rely on fluorescence-based methods including fluorescent polarization and fluorescence/Förster resonance energy transfer. These techniques use highly accessible instrumentation; however, they can suffer from high false-negative rates and background signals, or might involve complex schemes for the introduction of fluorophore pairs. Herein we present the synthesis and application of fluorescent nucleoside analogues as the foundation for directed approaches for competitive binding analyses. The general approach describes selective fluorescent environment-sensitive (ES) nucleoside analogues that are adaptable to diverse enzymes that act on nucleoside-based substrates. We demonstrate screening a set of uridine analogues and development of an assay for fragment-based lead discovery with the TcdB glycosyltransferase (GT), an enzyme associated with virulence in Clostridium difficile. The uridine-based probe used for this high-throughput screen has a KD value of 7.2 µm with the TcdB GT and shows a >30-fold increase in fluorescence intensity upon binding. The ES-based probe assay is benchmarked against two other screening approaches.

Profiling and identification of aqueous extract of Cordyceps sinensis by ultra-high performance liquid chromatography tandem quadrupole-orbitrap mass spectrometry.

Characterization of aqueous extract in traditional Chinese medicine (TCM) is challenging due to the poor retention of the analytes on conventional C18 columns. This study presents a systematic characterization method based on a rapid chromatographic separation (8 min) on a polar-modified C18 (Waters Cortecs T3) column of aqueous extract of Cordyceps sinensis. UHPLC-HRMS method was used to profile components in both untargeted and targeted manners by full MS/PIL/dd-MS2 acquisition approach. The components were identified or tentatively identified by reference standards comparison, fragmentation rules elucidation and available databases search. A total of 91 components, including 10 nucleobases, 20 nucleosides, 39 dipeptides, 18 amino acids and derivatives and 4 other components, were characterized from the aqueous extract of C. sinensis. And this was the first time to systematically report the presence of nucleosides and dipeptides in C. sinensis, especially for modified nucleosides. The chemical basis inquiry of this work would be beneficial to mechanism exploration and quality control of C. sinensis and related products. Meanwhile, this work also provided an effective solution for characterization of aqueous extract in TCM.

A Stark Contrast to Modern Earth: Phosphate Mineral Transformation and Nucleoside Phosphorylation in an Iron- and Cyanide-Rich Early Earth Scenario.

Organophosphates were likely an important class of prebiotic molecules. However, their presence on the early Earth is strongly debated because the low availability of phosphate, which is generally assumed to have been sequestered in insoluble calcium and iron minerals, is widely viewed as a major barrier to organophosphate generation. Herein, we demonstrate that cyanide (an essential prebiotic precursor) and urea-based solvents could promote nucleoside phosphorylation by transforming insoluble phosphate minerals in a "warm little pond" scenario into more soluble and reactive species. Our results suggest that cyanide and its derivatives (metal cyanide complexes, urea, ammonium formate, and formamide) were key reagents for the participation of phosphorus in chemical evolution. These results allow us to propose a holistic scenario in which an evaporitic environment could concentrate abiotically formed organics and transform the underlying minerals, allowing significant organic phosphorylation under plausible prebiotic conditions.

Nucleoside Analogs with Selective Antiviral Activity against Dengue Fever and Japanese Encephalitis Viruses.

Dengue virus (DENV) and Japanese encephalitis virus (JEV) are important arthropod-borne viruses from the Flaviviridae family. DENV is a global public health problem with significant social and economic impacts, especially in tropical and subtropical areas. JEV is a neurotropic arbovirus endemic to east and southeast Asia. There are no U.S. FDA-approved antiviral drugs available to treat or to prevent DENV and JEV infections, leaving nearly one-third of the world's population at risk for infection. Therefore, it is crucial to discover potent antiviral agents against these viruses. Nucleoside analogs, as a class, are widely used for the treatment of viral infections. In this study, we discovered nucleoside analogs that possess potent and selective anti-JEV and anti-DENV activities across all serotypes in cell-based assay systems. Both viruses were susceptible to sugar-substituted 2'-C-methyl analogs with either cytosine or 7-deaza-7-fluoro-adenine nucleobases. Mouse studies confirmed the anti-DENV activity of these nucleoside analogs. Molecular models were assembled for DENV serotype 2 (DENV-2) and JEV RNA-dependent RNA polymerase replication complexes bound to nucleotide inhibitors. These models show similarities between JEV and DENV-2, which recognize the same nucleotide inhibitors. Collectively, our findings provide promising compounds and a structural rationale for the development of direct-acting antiviral agents with dual activity against JEV and DENV infections.

Comparative Analysis of Carbohydrates, Nucleosides and Amino Acids in Different Parts of Trichosanthes kirilowii Maxim. by (Ultra) High-Performance Liquid Chromatography Coupled with Tandem Mass Spectrometry and Evaporative Light Scattering Detector Methods.

Trichosanthes kirilowii Maxim. is one of the original plants for traditional Chinese medicines Trichosanthis Fructus, Trichosanthis Semen, Trichosanthis Pericarpium and Trichosanthis Radix. Amino acids, nucleosides and carbohydrates are usually considered to have nutritional value and health-care efficacy. In this study, methods involving high-performance liquid chromatography coupled with evaporative light scattering detector (HPLC-ELSD), UV-visible spectrophotometry and ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) were established for quantifying carbohydrates (fructose, glucose, stachyose, raffinose and polysaccharide), fourteen nucleosides and twenty one amino acids. Moreover, sixty-three samples from nine different parts, including pericarp, seed, fruit pulp, stem, leaf, main root, main root bark, lateral root and lateral root bark of T. kirilowii from different cultivated varieties were examined. The established methods were validated with good linearity, precision, repeatability, stability, and recovery. The results showed that the average content of total amino acids in roots (15.39 mg/g) and root barks (16.38 mg/g) were relatively higher than for others. Contents of nucleosides in all parts of T. kirilowii were below 1.5 mg/g. For carbohydrates, fruit pulp has a higher content than others for glucose (22.91%), fructose (20.63%) and polysaccharides (27.29%). By using partial least-squared discriminate analysis (PLS-DA), Variable importance in the projection (VIP) plots and analysis of variance (ANOVA) analysis, the characteristic components of the different organs (fruit, stems and leaves, roots) were found. This analysis suggested there were potential medicinal and nutritive health care values in various parts of the T. kirilowii, which provided valuable information for the development and utilization of T. kirilowii.

Comprehensive evaluation of wild Cordyceps cicadae from different geographical origins by TOPSIS method based on the macroscopic infrared spectroscopy (IR) fingerprint.

Cordyceps cicadae is an entomogenous fungus that has been used as a valuable traditional Chinese herbal tonic, however, it can be difficult to discern the false from the genuine. In this study, the macroscopic IR fingerprint methods containing Fourier transform infrared spectroscopy (FT-IR) and second derivative infrared spectroscopy (SD-IR) were used to elucidate wild C. cicadae. The TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method was used to comprehensively evaluate C. cicadae from different geographical origins based on the macroscopic infrared spectroscopy (IR) fingerprint. The FT-IR spectra of C. cicadae exhibited the major characteristics of the absorptive peaks of carbohydrates, lipids and nucleosides at the position of 3291, 2925, 2845, 1651, 1547, 1455, 1080 and 950 cm-1. The high resolution of SD-IR further amplified the difference and revealed the potentially characteristic IR absorption spectrum. TOPSIS evaluation showed that C. cicadae from Anhui possess the strongest intensity of absorption bands among all the samples. Notably, FT-IR combined with SD-IR can effectively reveal the overall chemical components without damaging medicinal materials, and TOPSIS methods can provide a novel scientific evidence for comprehensively assessing different origins of wild C. cicadae.

Determination and Quantitative Comparison of Nucleosides in two Cordyceps by HPLC-ESI-MS-MS.

A hybrid quadruple linear ion trap liquid chromatography-tandem mass spectrometry (LC-MS-MS) analytical method has been developed for simultaneous determination of 13 nucleosides from Cordyceps cicadae and Cordyceps sinensis for assessing whether C. cicadae can become a substitute for C. sinensis, based on that C. cicadae has in common with C. sinensis for treating chronic diseases. Among the 13 compounds, three compounds including cytidine, hypoxanthine and 2'-deoxyguanosine were firstly identified and quantified in C. cicadae. Ideal separation was achieved in one single LC-MS-MS run of 12 min by optimized chromatographic conditions. The identification and quantification analysis of target compounds were performed in electrospray ionization tandem mass spectrometry. The limit of detection and quantity for 13 compounds were <42.0 and 84.2 ng/mL, respectively. The determination results of 12 batches of C. sinensis and 20 batches of C. cicadae were then analyzed and classified by multivariate statistical analysis. C. cicadae contained a relatively higher level of three nucleosides (cytidine, uracil and 2'-deoxyuridine) than those in C. sinensis. The results of this study provided the theoretical basis for the substitution of C. sinensis with C. cicadae. The optimized method could be used for the quality control and investigate bioactive compound variation of Cordyceps.

Magnetic silica nanoparticles for use in matrix-assisted laser desorption ionization mass spectrometry of labile biomolecules such as oligosaccharides, amino acids, peptides and nucleosides.

Magnetic silica nanoparticles (MSNPs) were prepared and applied for the first time as a matrix in MALDI MS for analysis of small thermally labile biomolecules including oligosaccharides, amino acids, peptides, nucleosides, and ginsenosides. The matrix was characterized by scanning electron microscopy and UV-vis spectroscopy. It displays good performance in analyses of such biomolecules in the positive ion mode. In addition, the method generates significantly less energetic ions compared to the use of carbon nanotubes or graphene-assisted LDI MS and thus produces intact molecular ions with little or no fragmentation. In addition, the MSNPs have better surface homogeneity and better salt tolerance and cause lower noise. It is assumed that the soft ionization observed when using MSNPs as a matrix is due to the specific surface area and the homogenous surface without large clusters. The matrices were applied to the unambiguous identification and relative quantitation of the water extract of Panax ginseng roots. Any false-positive results as obtained when using graphene and carbon nanotubes as a matrix were not observed. Graphical abstract Schematic presentation of the application of magnetic silica nanoparticles in laser desorption ionization mass spectrometry. Their use results in little or no fragmentation during analysis of small labile biomolecules with some advantages such as better surface homogeneity, high salt tolerance, and lower noise.

Nucleoside and N-acetyldopamine derivatives from the insect Aspongopus chinensis.

Two new nucleoside derivatives, named asponguanosines A and B (1 and 2), three new N-acetyldopamine analogues, aspongamides C-E (3-5), one new sesquiterpene, aspongnoid D (6), and three known compounds were isolated from the medicinal insect Aspongopus chinensis. Their structures including absolute configurations were assigned by using spectroscopic methods and ECD and 13C NMR calculations. Biological activities of compounds 3-7 towards human cancer cells, COX-2, ROCK1, and JAK3 were evaluated.

A dilute-and-shoot multispectral integration approach towards nontargeted component profiling of traditional herbal Yin-zhi-huang using liquid chromatography-photodiode array-ion trap/time-of-flight characterization.

Ying-zhi-huang Injection (YZH-I) is a classic intravenous formulation of polyherbal Chinese medicine which has been prescribed to treat severe jaundice and acute hepatitis for nearly 50 years. Despite some published data on its major components in the constituent herbs, the overall chemical profile of the potentially bioactive ingredients in YZH-I formula remains largely unknown. Here we developed a multispectral integration approach towards nontargeted phytochemical profiling of YZH-I by liquid chromatography-ultraviolet diode array detector coupled to ion trap/time-of-flight multistage mass spectrometry (LC-DAD-IT(MSn)/TOF) with fast polarity-switching mode. A simple generic dilute-and-shoot procedure was introduced as a non-destructive pretreatment method for facile wide-scope component profiling of herbal injection samples. A total of 61 constituents were isolated and characterized by the multiplex data acquisition, among which 45 components were identified from YZH-I, including 21 organic acid derivatives, 8 iridoid glycosides, 15 flavones and adenosine. Of the 45 identified compounds, 8 were unequivocally confirmed by comparing authentic standards, and 37 were tentatively assigned by elucidating accurate MSn spectra and retrieving published data. It is the first report of systematic chemical profiling of YZH preparations with online integration of dilute-and-shoot LC-DAD and accurate multistage mass spectra. This study is expected to present an effective integrated strategy to comprehensive quality control of complex herbal injection formulas.

Quality Evaluation of Apocyni Veneti Folium from Different Habitats and Commercial Herbs Based on Simultaneous Determination of Multiple Bioactive Constituents Combined with Multivariate Statistical Analysis.

Apocyni Veneti Folium (AVF) is a kind of staple traditional Chinese medicine with vast clinical consumption because of its positive effects. However, due to the habitats and adulterants, its quality is uneven. To control the quality of this medicinal herb, in this study, the quality of AVF was evaluated based on simultaneous determination of multiple bioactive constituents combined with multivariate statistical analysis. A reliable method based on ultra-fast liquid chromatography tandem triple quadrupole mass spectrometry (UFLC-QTRAP-MS/MS) was developed for the simultaneous determination of a total of 43 constituents, including 15 flavonoids, 6 organic acids, 13 amino acids, and 9 nucleosides in 41 Luobumaye samples from different habitats and commercial herbs. Furthermore, according to the contents of these 43 constituents, principal component analysis (PCA) was employed to classify and distinguish between AVF and its adulterants, leaves of Poacynum hendersonii (PHF), and gray relational analysis (GRA) was performed to evaluate the quality of the samples. The proposed method was successfully applied to the comprehensive quality evaluation of AVF, and all results demonstrated that the quality of AVF was higher than the PHF. This study will provide comprehensive information necessary for the quality control of AVF.

Nucleosides for the treatment of respiratory RNA virus infections.

Influenza virus, respiratory syncytial virus, human metapneumovirus, parainfluenza virus, coronaviruses, and rhinoviruses are among the most common viruses causing mild seasonal colds. These RNA viruses can also cause lower respiratory tract infections leading to bronchiolitis and pneumonia. Young children, the elderly, and patients with compromised cardiac, pulmonary, or immune systems are at greatest risk for serious disease associated with these RNA virus respiratory infections. In addition, swine and avian influenza viruses, together with severe acute respiratory syndrome-associated and Middle Eastern respiratory syndrome coronaviruses, represent significant pandemic threats to the general population. In this review, we describe the current medical need resulting from respiratory infections caused by RNA viruses, which justifies drug discovery efforts to identify new therapeutic agents. The RNA polymerase of respiratory viruses represents an attractive target for nucleoside and nucleotide analogs acting as inhibitors of RNA chain synthesis. Here, we present the molecular, biochemical, and structural fundamentals of the polymerase of the four major families of RNA respiratory viruses: Orthomyxoviridae, Pneumoviridae/Paramyxoviridae, Coronaviridae, and Picornaviridae. We summarize past and current efforts to develop nucleoside and nucleotide analogs as antiviral agents against respiratory virus infections. This includes molecules with very broad antiviral spectrum such as ribavirin and T-705 (favipiravir), and others targeting more specifically one or a few virus families. Recent advances in our understanding of the structure(s) and function(s) of respiratory virus polymerases will likely support the discovery and development of novel nucleoside analogs.