Category: 550-33-4

Exploiting Protein Conformational Change to Optimize Adenosine-Derived Inhibitors of HSP70 was written by Cheeseman, Matthew D.; Westwood, Isaac M.; Barbeau, Olivier; Rowlands, Martin; Dobson, Sarah; Jones, Alan M.; Jeganathan, Fiona; Burke, Rosemary; Kadi, Nadia; Workman, Paul; Collins, Ian; van Montfort, Rob L. M.; Jones, Keith. And the article was included in Journal of Medicinal Chemistry on May 26,2016.Recommanded Product: 550-33-4 The following contents are mentioned in the article:

HSP70 is a mol. chaperone and a key component of the heat-shock response. Because of its proposed importance in oncol., this protein has become a popular target for drug discovery, efforts which have as yet brought little success. This study demonstrates that adenosine-derived HSP70 inhibitors potentially bind to the protein with a novel mechanism of action, the stabilization by desolvation of an intramol. salt-bridge which induces a conformational change in the protein, leading to high affinity ligands. We also demonstrate that through the application of this mechanism, adenosine-derived HSP70 inhibitors can be optimized in a rational manner. This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4Recommanded Product: 550-33-4).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives. THF (Tetrahydrofuran) is water-miscible and has a low viscosity making it a highly versatile solvent used in a variety of industries. Tetrahydrofuran can also be produced, or synthesised, via catalytic hydrogenation of furan. This process involves converting certain sugars into THF by digesting to furfural. An alternative to this method is the catalytic hydrogenation of furan with a nickel catalyst.Recommanded Product: 550-33-4

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4

Coumarin-purine ribofuranoside conjugates as new agents against hepatitis C virus was written by Hwu, Jih Ru; Lin, Shu-Yu; Tsay, Shwu-Chen; De Clercq, Erik; Leyssen, Pieter; Neyts, Johan. And the article was included in Journal of Medicinal Chemistry on April 14,2011.Safety of (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol The following contents are mentioned in the article:

About 3% of world’s population is infected by the hepatitis C virus (HCV), for which prophylactic vaccine is not available yet. Nowadays, pegylated interferon-α and ribavirin are commonly used to treat HCV; unfortunately these drugs often produce significant side effects. Upon the desperate need of anti-HCV drugs, a plan to establish a new compound library was set that included leads with high antiviral activity, good hydrophilicity, yet low toxicity. Accordingly, 26 new conjugated nsds, e.g. I, were synthesized through the chem. coupling of various 9-(β-D-ribofuranosyl)purine-8-thiones with 3-(chloromethyl)coumarins bearing various substituents. A -SCH2- unit was used to link the coumarin and the purine moieties. The three hydroxyl groups at the 2′-, 3′-, and 5′-positions were selectively protected with an acyl or acetal group in these coumarin-purine ribofuranosides. Their anti-HCV and cytostatic determination assays were performed, and the structure-activity relationship was established. Three conjugates in the family of 8-(coumarin-3′-yl)methylthio-9-(β-D-ribofuranos-1”-yl)purine possessed an appealing ability to inhibit HCV replication with EC50 between 5.5 and 6.6 μM and EC90 of ∼20 μM. These data in the new compound library provide clues for the future in the development of anti-HCV leads for viral eradication. This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4Safety of (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives. Tetrahydrofuran (THF) is a Lewis base that bonds to a variety of Lewis acids such as I2, phenols, triethylaluminum and bis(hexafluoroacetylacetonato)copper(II). It is more basic than diethyl ether and forms stronger complexes with Li+, Mg2+, and boranes. It is a popular solvent for hydroboration reactions and for organometallic compounds such as organolithium and Grignard reagents.Safety of (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4

The terpene limonene induced the green mold of citrus fruit through regulation of reactive oxygen species (ROS) homeostasis in Penicillium digitatum spores was written by Tao, Nengguo; Chen, Yue; Wu, Yalan; Wang, Xiao; Li, Lu; Zhu, Andan. And the article was included in Food Chemistry on March 30,2019.Safety of (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol The following contents are mentioned in the article:

Herein, the dosage effect of limonene on the P. digitatum spore germination and its regulatory mechanisms were investigated. Results showed that limonene only at low concentrations displayed a stimulatory role, with the optimal concentration being 0.25 μL/mL. GC-MS and GC anal. revealed that limonene contents remained relative stable and no evidence of transformation was observed at stimulatory concentrations Metabolomics anal. showed that 61 metabolites including organic acids, amino acids, sugars, nucleosides, fatty acids, and their derivatives, were significantly changed (P < 0.05), suggesting the transitions between soluble sugars and energy-related metabolisms Proteomic anal. demonstrated that proteins in energy-related pathways and ROS homeostasis were also influenced. These were further confirmed by the activities of catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST), the contents of reactive oxygen species (ROS), hydrogen peroxide (H2O2), and glutathione (GSH). Our present research indicates that ROS homeostasis is involved in the limonene induced spore germination of P. digitatum. This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4Safety of (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives. Solid acid catalysis, and the advantages often associated with their use, have been proved equally efficient for the synthesis of tetrahydrofurans or furans. Tetrahydrofuran can also be produced, or synthesised, via catalytic hydrogenation of furan. This process involves converting certain sugars into THF by digesting to furfural. An alternative to this method is the catalytic hydrogenation of furan with a nickel catalyst.Safety of (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4

Biocatalytic synthesis of seleno-, thio- and chloro-nucleobase modified nucleosides by thermostable nucleoside phosphorylases was written by Zhou, Xinrui; Yan, Weizhu; Zhang, Chong; Yang, Zhaoyi; Neubauer, Peter; Mikhailopulo, Igor A.; Huang, Zhen. And the article was included in Catalysis Communications on March 5,2019.Formula: C10H12N4O4   The following contents are mentioned in the article:

Selenium-containing nucleosides are the building blocks of the Se-nucleic acids useful for structure-and-function study, drug discovery and for targeting nucleic acids and their protein complexes. However, chem. synthesis of these Se-containing nucleosides is labor-intensive and provides low overall yields. Thus, we decided to explore biocatalytic synthesis of the modified nucleosides (such as Se-nucleosides) by employing thermostable nucleoside phosphorylases from thermophilic microorganisms. We were surprised to discover that these enzymes can still recognize the nucleobases containing rather larger atoms, Se vs. O atom. These enzymes also showed excellent adaptability to some modified purines with high substrate conversion (up to 97%). This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4Formula: C10H12N4O4  ).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives.Tetrahydrofuran has many industry uses as a solvent including in natural and synthetic resins, high polymers, fat oils, rubber, polymer. It is more basic than diethyl ether and forms stronger complexes with Li+, Mg2+, and boranes. It is a popular solvent for hydroboration reactions and for organometallic compounds such as organolithium and Grignard reagents.Formula: C10H12N4O4  

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4

Organocatalyzed, Visible-Light Photoredox-Mediated, One-Pot Minisci Reaction Using Carboxylic Acids via N-(Acyloxy)phthalimides was written by Sherwood, Trevor C.; Li, Ning; Yazdani, Aliza N.; Dhar, T. G. Murali. And the article was included in Journal of Organic Chemistry on March 2,2018.Recommanded Product: 550-33-4 The following contents are mentioned in the article:

An improved, one-pot Minisci reaction has been developed using visible light, an organic photocatalyst, and carboxylic acids as radical precursors via the intermediacy of in situ-generated N-(acyloxy)phthalimides. The conditions employed are mild, demonstrate a high degree of functional group tolerance, and do not require a large excess of the carboxylic acid reactant. As a result, this reaction can be applied to drug-like scaffolds and mols. with sensitive functional groups, enabling late-stage functionalization, which is of high interest to medicinal chem. This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4Recommanded Product: 550-33-4).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives. Tetrahydrofuran (THF) is a Lewis base that bonds to a variety of Lewis acids such as I2, phenols, triethylaluminum and bis(hexafluoroacetylacetonato)copper(II). Tetrahydrofuran can also be produced, or synthesised, via catalytic hydrogenation of furan. This process involves converting certain sugars into THF by digesting to furfural. An alternative to this method is the catalytic hydrogenation of furan with a nickel catalyst.Recommanded Product: 550-33-4

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4

Megaspinoxide A: New Norterpene Cyclic Peroxide from the Sponge Diacarnus megaspinorhabdosa was written by Ibrahim, Sabrin R. M.; Al Haidari, Rwaida A.; Mohamed, Gamal A.. And the article was included in Natural Products Journal on March 31,2014.HPLC of Formula: 550-33-4 The following contents are mentioned in the article:

Re-investigation of the methanolic extract of the sponge Diacarnus megaspinorhabdosa afforded 1 new norsesterpene cyclic peroxide megaspinoxide A (I), together with 2 known compounds sigmosceptrellin B and nebularine. The structures of the isolated compounds were established on the basis of 1- and 2-dimensional NMR spectroscopic studies (1H, 13C, DEPT, COSY, HMQC, HMBC, and ROESY) as well as, mass spectral anal. The isolated compounds were evaluated for their cytotoxic and antimicrobial activities. This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4HPLC of Formula: 550-33-4).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives. Solid acid catalysis, and the advantages often associated with their use, have been proved equally efficient for the synthesis of tetrahydrofurans or furans. Oxidations have also proved to be valuable and efficient approaches to chiral tetrahydrofuran derivatives.HPLC of Formula: 550-33-4

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4

Microbial succession and metabolite changes during traditional serofluid dish fermentation was written by Li, Qianqian; Kang, Jiamu; Ma, Zhen; Li, Xiaoping; Liu, Liu; Hu, Xinzhong. And the article was included in LWT–Food Science and Technology on October 31,2017.Name: (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol The following contents are mentioned in the article:

Serofluid dish is a traditional Chinese salt-free fermented vegetable. In this study, the microbial succession and metabolite changes during celery serofluid dish fermentation were investigated using high-throughput sequencing and GC-TOFMS methods. The results showed that the leading genera of bacteria were Lactobacillus and Pediococcus in eight serofluid samples; Debaryomyces was the dominant fungal genus followed by Saccharomyces. A total of 182 metabolites were identified, mainly organic acids and amino acids. Correlation anal. revealed important links between microbial populations and metabolites. These results lend new insights into the fermentation process and provide a theor. basis for the economical production of safe, high-quality serofluid dish. This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4Name: (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives. Tetrahydrofuran (THF), or oxolane, is mainly used as a precursor to polymers. Being polar and having a wide liquid range, THF is a versatile solvent. Oxidations have also proved to be valuable and efficient approaches to chiral tetrahydrofuran derivatives.Name: (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4

Metabolomics insights into the mechanism by which Epichloe gansuensis endophyte increased Achnatherum inebrians tolerance to low nitrogen stress was written by Hou, Wenpeng; Wang, Jianfeng; Christensen, Michael J.; Liu, Jie; Zhang, Yongqiang; Liu, Yinglong; Cheng, Chen. And the article was included in Plant and Soil on June 30,2021.HPLC of Formula: 550-33-4 The following contents are mentioned in the article:

Epichloe gansuensis increases the tolerance of host plants to abiotic stress. However, little is known about the mechanism by which E. gansuensis improves grass growth under low nitrogen availability stress. Achnatherum inebrians with E. gansuensis (E+) and without E. gansuensis (E-) were treated with modified 1/2 Hoagland containing 0.01 mM (low N) or 7.5 mM N (normal level) for 18 wk. After 18 wk of treatment with N, the dry weight of E+ and E- plants were measured, and the metabolomics anal. of leaves and roots grown under two different N concentrations was conducted with GS-MS to determine differential metabolites and metabolic pathways. E+ A. inebrians had higher dry weight of leaves and roots compared to the E- A. inebrians under low N stress. E. gansuensis increased the tolerance of A. inebrians to low N stress by its capability to increase the content of organic acids (salicylic acid and 3-hydroxypropionic acid) and glucose-6-phosphate in leaves, and E. gansuensis increased the content of fatty acids (linolenic acid and oleic acid) and amino acids (glycine and 4-aminobutyric acid) in roots under low N stress. Finally, E. gansuensis reprogramed the metabolic pathway of amino acids of host grasses to adapt to the different N concentration Our results reveal the chem. mechanism by which E. gansuensis enhances the tolerance of host grasses to low N, and provide the theor. basis for utilizing E. gansuensis, improving of grasses and crops, and for developing new germplasm for low-N tolerant grasses. This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4HPLC of Formula: 550-33-4).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives.Tetrahydrofuran has many industry uses as a solvent including in natural and synthetic resins, high polymers, fat oils, rubber, polymer. It is more basic than diethyl ether and forms stronger complexes with Li+, Mg2+, and boranes. It is a popular solvent for hydroboration reactions and for organometallic compounds such as organolithium and Grignard reagents.HPLC of Formula: 550-33-4

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4

Metabolic networks and metabolites underlie associations between maternal glucose during pregnancy and newborn size at birth was written by Scholtens, Denise M.; Bain, James R.; Reisetter, Anna C.; Muehlbauer, Michael J.; Nodzenski, Michael; Stevens, Robert D.; Ilkayeva, Olga; Lowe, Lynn P.; Metzger, Boyd E.; Newgard, Christopher B.; Lowe, William L. Jr.; The HAPO Study Cooperative Research Group. And the article was included in Diabetes on July 31,2016.Electric Literature of C10H12N4O4   The following contents are mentioned in the article:

Maternal metabolites and metabolic networks underlying associations between maternal glucose during pregnancy and newborn birth weight and adiposity demand fuller characterization. We performed targeted and nontargeted gas chromatog./mass spectrometry metabolomics on maternal serum collected at fasting and 1 h following glucose beverage consumption during an oral glucose tolerance test (OGTT) for 400 northern European mothers at ∼28 wk’ gestation in the Hyperglycemia and Adverse Pregnancy Outcome Study. Amino acids, fatty acids, acylcarnitines, and products of lipid metabolism decreased and triglycerides increased during the OGTT. Analyses of individual metabolites indicated limited maternal glucose associations at fasting, but broader associations, including amino acids, fatty acids, carbohydrates, and lipids, were found at 1 h. Network analyses modeling metabolite correlations provided context for individual metabolite associations and elucidated collective associations of multiple classes of metabolic fuels with newborn size and adiposity, including acylcarnitines, fatty acids, carbohydrates, and organic acids. Random forest analyses indicated an improved ability to predict newborn size outcomes by using maternal metabolomics data beyond traditional risk factors, including maternal glucose. Broad-scale association of fuel metabolites with maternal glucose is evident during pregnancy, with unique maternal metabolites potentially contributing specifically to newborn birth weight and adiposity. This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4Electric Literature of C10H12N4O4  ).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives.Tetrahydrofuran has many industry uses as a solvent including in natural and synthetic resins, high polymers, fat oils, rubber, polymer. Commercial tetrahydrofuran contains substantial water that must be removed for sensitive operations, e.g. those involving organometallic compounds. Although tetrahydrofuran is traditionally dried by distillation from an aggressive desiccant, molecular sieves are superior.Electric Literature of C10H12N4O4  

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4

Metabolic profiles of flooding-tolerant mechanism in early-stage soybean responding to initial stress was written by Wang, Xin; Zhu, Wei; Hashiguchi, Akiko; Nishimura, Minoru; Tian, Jingkui; Komatsu, Setsuko. And the article was included in Plant Molecular Biology on August 31,2017.Computed Properties of C10H12N4O4   The following contents are mentioned in the article:

Key message: Metabolomic anal. of flooding-tolerant mutant and abscisic acid-treated soybeans suggests that accumulated fructose might play a role in initial flooding tolerance through regulation of hexokinase and phosphofructokinase. Abstract: Soybean is sensitive to flooding stress, which markedly reduces plant growth. To explore the mechanism underlying initial-flooding tolerance in soybean, mass spectrometry-based metabolomic anal. was performed using flooding-tolerant mutant and abscisic-acid treated soybeans. Among the commonly-identified metabolites in both flooding-tolerant materials, metabolites involved in carbohydrate and organic acid displayed same profile at initial-flooding stress. Sugar metabolism was highlighted in both flooding-tolerant materials with the decreased and increased accumulation of sucrose and fructose, resp., compared to flooded soybeans. Gene expression of hexokinase 1 was upregulated in flooded soybean; however, it was downregulated in both flooding-tolerant materials. Metabolites involved in carbohydrate/organic acid and proteins related to glycolysis/tricarboxylic acid cycle were integrated. Increased protein abundance of phosphofructokinase was identified in both flooding-tolerant materials, which was in agreement with its enzyme activity. Furthermore, sugar metabolism was pointed out as the tolerant-responsive process at initial-flooding stress with the integration of metabolomics, proteomics, and transcriptomics. Moreover, application of fructose declined the increased fresh weight of plant induced by flooding stress. These results suggest that fructose might be the critical metabolite through regulation of hexokinase and phosphofructokinase to confer initial-flooding stress in soybean. This study involved multiple reactions and reactants, such as (2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4Computed Properties of C10H12N4O4  ).

(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol (cas: 550-33-4) belongs to tetrahydrofuran derivatives. Solid acid catalysis, and the advantages often associated with their use, have been proved equally efficient for the synthesis of tetrahydrofurans or furans. Commercial tetrahydrofuran contains substantial water that must be removed for sensitive operations, e.g. those involving organometallic compounds. Although tetrahydrofuran is traditionally dried by distillation from an aggressive desiccant, molecular sieves are superior.Computed Properties of C10H12N4O4  

550-33-4;(2R,3S,4R,5R)-2-(Hydroxymethyl)-5-(9H-purin-9-yl)tetrahydrofuran-3,4-diol;The future of 550-33-4;New trend of C10H12N4O4  ;function of 550-33-4