- Characterization of a 5′-aldehyde terminus resulting from the oxidative attack at C5′ of a 2-deoxyribose on DNA
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The 5′-aldehyde terminus is a DNA oxidative damage resulting from attack at C5′ of 2-deoxyriboses by some potent natural or chemical DNA cleavers. To offer a fast and specific method for characterization of this type of damage, we used on-line electrospray ionization mass spectrometry (ESI-MS) detection during liquid chromatography analyses. The intrinsic reactivity of 5′-aldehyde terminus with nucleophiles (formation of hydrate with water, of a Tris adduct with Tris buffer) or through β-elimination reaction resulted in complex LC profiles and MS data. We showed that derivatization of the aldehyde function as an oxime ether gives a stable derivative easy to characterize during on-line ESI-MS analyses. Complete structural characterization of the Tris adduct and the oxime ether derivative were obtained from MS and detailed NMR studies performed on derivatized 5′-aldehyde thymidine models.
- Angeloff,Dubey,Pratviel,Bernadou,Meunier
-
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Read Online
- Efficient separation and purification method of 4,4'-dimethoxytrityl chloride and 4,4'-dimethoxytrityl alcohol
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The invention provides an efficient separation and purification method of 4,4'-dimethoxytrityl chloride and 4,4'-dimethoxytrityl alcohol. According to the method, a target product with high purity isprepared on the basis of ensuring high reaction yield, impurity components contained in the target product are clarified, the content of the impurity components is controlled, and particularly the content of hydroxyl impurities and the content of acetylated impurities are controlled to be 0.05% or less.
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Paragraph 0026-0027; 0029-0030; 0032-0042
(2021/03/03)
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- Synthesis method of high-purity 4, 4 '-dimethoxytriphenylchloromethane
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The invention provides a synthesis method of high-purity 4, 4 '-dimethoxytriphenylchloromethane, which comprises the following steps: by using anisole and trichlorotoluene as initial raw materials, carrying out F-C reaction, hydrochloric acid hydrolysis reaction and chlorination reaction to prepare a DMT-Cl crude product of which the purity is higher than 98.5%, and carrying out solvent crystallization to obtain a DMT-Cl finished product of which the purity is higher than 99.9%, thereby obtaining the DMT-Cl finished product yield higher than 98%. According to the method provided by the invention, on the basis of ensuring high reaction yield, the target product is prepared with high purity, impurity components contained in the target product are clear, the content of the impurity componentsis controlled, and particularly, hydroxyl impurities and acetylated impurities are controlled to be 0.05% or below.
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Paragraph 0009; 0027-0028; 0030-0031; 0033-0041
(2021/03/13)
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- Biomimetic 2-Imino-Nazarov Cyclizations via Eneallene Aziridination
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Amidoallyl cations are appealing three-carbon synthons for the preparation of complex amine-containing carbocycles; however, methods to generate and utilize these reactive species are limited and underexplored compared to those for oxallyl cations. Here we disclose a bioinspired strain-driven ring opening of bicyclic methyleneaziridines to 2-amidopentadienyl cation intermediates that readily engage in Nazarov cyclizations. Advantages of this strategy include ease of generation and improved reactivity compared to 3-pentadienyl cations, control over the ultimate position of the alkene, the potential for high dr between vicinal stereocenters, and the ability to further elaborate the products to fully substituted aminocyclopentanes. Experimental and computational studies support a dual role for the Rh2Ln complex as both a nitrene transfer catalyst and a Lewis acid promoter, insight that provides a framework for the future development of asymmetric 2-imino-Nazarov cyclizations.
- Corbin, Joshua R.,Fernández, Israel,Ketelboeter, Devin R.,Schomaker, Jennifer M.
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p. 5568 - 5573
(2020/04/09)
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- Copper(II)nitrate catalyzed regioselective protection of primary alcohols with 4,4′-dimethoxytrityl and 2,7-dimethyl-9-phenyl xanthen-9-yl groups in nucleosides and carbohydrates
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Regioselective protection of primary hydroxyl group in nucleoside and carbohydrate analogs was accomplished using dimethoxytrityl alcohol (DMTr-OH) or dimethylpixyl alcohol (DMPx-OH) in presence of copper(II)nitrate as a Lewis acid catalyst. Excellent selectivity was observed for the protection of primary hydroxyl group over secondary while glycosidic bond remain unaffected. Utility of this methodology was further exemplified via DMTr- and DMPx-protection of alipahtic acyclic and cyclic diols.
- Penjarla, Srishylam,Prasad, S. Rajendra,Reddy, Dhande Sudhakar,Banerjee, Shyamapada,Penta, Santhosh,Sanghvi, Yogesh S.
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p. 232 - 247
(2018/05/14)
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- Renewable amberlyst-15 catalyzed highly regioselective tritylation and deprotection of sugar-based diols
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Amberlyst-15 catalyzed highly regioselective tritylation of sugar-based diols was achieved under mild condition using 4,4′-dimethoxytrityl alcohol (DMTrOH). Deprotection of the corresponding DMTr group was also established by the variation to protic solvent. Meanwhile, the heterogeneous catalyst Amberlyst-15 was recycled 3 times with satisfactory retention of catalytic activity and proved its potential application in industry.
- Valeru, Anil,Luo, Zhibin,Penjarla, Srishylum,Khan, Imran,Liu, Bin,Sngepu, Bhavanarushi,Xu, Yin,Xie, Jimin
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p. 318 - 326
(2018/10/15)
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- Direct allylation of benzyl alcohols, diarylmethanols, and triarylmethanols mediated by XtalFluor-E
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We report the direct allylation of benzyl alcohols, diarylmethanols and triarylmethanols mediated by XtalFluor-E using allyltrimethylsilane. The resulting allylated products are obtained in moderate to high yield.
- Lebleu, Thomas,Paquin, Jean-Fran?ois
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supporting information
p. 442 - 444
(2017/01/10)
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- Hydride Reduction by a Sodium Hydride-Iodide Composite
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Sodium hydride (NaH) is widely used as a Br?nsted base in chemical synthesis and reacts with various Br?nsted acids, whereas it rarely behaves as a reducing reagent through delivery of the hydride to polar π electrophiles. This study presents a series of reduction reactions of nitriles, amides, and imines as enabled by NaH in the presence of LiI or NaI. This remarkably simple protocol endows NaH with unprecedented and unique hydride-donor chemical reactivity.
- Too, Pei Chui,Chan, Guo Hao,Tnay, Ya Lin,Hirao, Hajime,Chiba, Shunsuke
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supporting information
p. 3719 - 3723
(2016/03/26)
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- ORGANIC METAL COMPLEX, METHOD OF PRODUCING THE SAME AND CATALYST FOR TERTIARY ALCOHOL PRODUCTION
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PROBLEM TO BE SOLVED: To provide a novel organic palladium complex and a novel organic platinum complex and methods of producing them, and a catalyst for tertiary alcohol production from diarylketone and aryl boron compounds. SOLUTION: This invention provides an organic palladium complex represented by general formula (1). COPYRIGHT: (C)2015,JPOandINPIT
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Paragraph 0354 - 0356
(2016/11/07)
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- Synthesis of ketones via organolithium addition to acid chlorides using continuous flow chemistry
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An efficient method for the synthesis of ketones using organolithium and acid chlorides under continuous flow conditions has been developed. In contrast to standard batch chemistry, over-addition of the organolithium to the ketone for the formation of the undesired tertiary alcohol has been minimised representing a direct approach toward ketones.
- Moon, Soo-Yeon,Jung, Seo-Hee,Bin Kim,Kim, Won-Suk
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p. 79385 - 79390
(2015/10/06)
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- MELANIN PRODUCTION INHIBITOR
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Disclosed is a melanin production inhibitor which has an excellent inhibitory activity on the production of melanin and is highly safe. The melanin production inhibitor is represented by general formula (1) (excluding clotrimazole) and/or a pharmacologically acceptable salt thereof. In the formula, A1, A2 and A3 are independently selected from a hydrogen atom, an aryl group which may have a substituent, and an aromatic heterocyclic group which may have a substituent. At least one of A1, A2 and A3 is selected from the aryl group and the aromatic heterocyclic group, the total number of carbon atoms contained in A1, A2 and A3 is 6 to 50 and, when at least two of A1, A2 and A3 represent the aryl groups or the aromatic heterocyclic groups, the adjacent two aryl or aromatic heterocyclic groups may be bound to each other via an alkyl chain or an alkenyl chain to form a ring; m represents an integer of 0 to 2; X represents a hetero atom, a hydrogen atom, or a carbon atom; R1 and R2 are independently selected from a hydrogen atom and an oxo group. When one of R1 and R2 is an oxo group, the other is not present. R3 is selected from a hydrogen atom, and a C1-8 hydrocarbon group in which one or some of hydrogen atoms or carbon atoms may be substituted by a hetero atom or hetero atoms. The number of R3's present in the compound corresponds to X and, when two or more R3's are present, the R3's are independently present and the adjacent two R3's may be bound to each other to form, together with X, a ring, and the terminal of R3 may be bound to a carbon atom to which A1, A2 and A3 are bound, thereby forming a ring.
- -
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Paragraph 0230 - 0233; 0239 - 0242
(2015/12/17)
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- Acid-catalysed hydrolysis of trityl derivatives in strongly acidic aqueous media
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The kinetics of hydrolysis (deamination or dealcoholation) of tritylamines and 2,2,2-trifluoroethyl ethers and their corresponding 4-methoxy, 4,4′-dimethoxy-, and 4,4′,4″-trimethoxy-substituted analogues in aqueous solutions up to 3.5 mol · dm-3 in strong acid have been investigated at constant ionic strength. In all cases, acid-catalysed hydrolytic processes have been observed, with finite reactivity at [H 3O+] = 0. Strong upward curvature has been observed for kobs versus [HClO4]. Analysis of this dependence in terms of the HR acidity function and the X0 excess acidity scale allow explanation of the observed behaviour in terms of the increasing differences between concentrations and activities of the various species involved in the processes, including water, for which the activity coefficient strongly diverges from its standard state value as the acidity increases. This analysis has shown that, by taking account of the effect of the ionic strength, the same mechanistic models proposed for mildly acidic solutions are valid in more highly concentrated acid media. These comprise (i) protonation of the trityl ether followed by C-O bond heterolysis to give a carbenium ion-alcohol (ion-molecule) pair which can separate, and (ii) C-N bond heterolysis of the protonated tritylamine to give a carbenium ion-amine (ion-molecule) pair followed by separation of the fragments or protonation of the amine and subsequent separation of the ions. Each separated (substituted) trityl carbenium ion, regardless of its provenance, is invariably captured by a solvent molecule (water). Copyright 2013 John Wiley & Sons, Ltd. Strong upward curvatures observed for kobs versus [H3O+] kinetics results in the hydrolysis of tritylamines and trityl ethers in strongly acidic aqueous solutions are entirely understandable as medium effects and accurately described in terms of excess acidities. The mechanisms previously proposed for mild acidic conditions have been generalized to more strong acid media. Copyright
- Canle L., Moises,Maskill, Howard
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supporting information
p. 1016 - 1022
(2014/01/06)
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- Selective N-acylation and N-alkylation of biotin
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Simple and efficient methodology is presented for the selective acylation and alkylation of biotin at its 3′-nitrogen.
- Pehere, Ashok D.,Abell, Andrew D.
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experimental part
p. 9514 - 9518
(2012/01/06)
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- Improved synthesis of 5-hydroxymethyl-2′-deoxycytidine phosphoramidite using a 2′-deoxyuridine to 2′-deoxycytidine conversion without temporary protecting groups
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5-Hydroxymethylcytosine has recently been characterized as the 'sixth base' in human DNA. To enable research on this DNA modification, we report an improved method for the synthesis of 5-hydroxymethyl-2′-deoxycytidine (5-HOMedC) phosphoramidite for site-specific incorporation into oligonucleotides. To minimize manipulations we employed a temporary protecting group-free 2′-deoxyuridine to 2′-deoxycytidine conversion procedure that utilizes phase transfer catalysis. The desired 5-HOMedC phosphoramidite is obtained in six steps and 24% overall yield from 2′-deoxyuridine.
- Hansen, Anders S.,Thalhammer, Armin,El-Sagheer, Afaf H.,Brown, Tom,Schofield, Christopher J.
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supporting information; experimental part
p. 1181 - 1184
(2011/04/16)
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- Electrophilicity versus electrofugality of tritylium ions in aqueous acetonitrile
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First-order rate constants kw for the reactions of a series of donorsubstituted triphenylmethylium (tritylium) ions with water in aqueous acetonitrile have been determined photometrically at 20°C using stopped-flow and laser-flash techniques. T
- Horn, Markus,Mayr, Herbert
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supporting information; scheme or table
p. 7478 - 7487
(2010/08/20)
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- Stabilities of trityl-protected substrates: The wide mechanistic spectrum of trityl ester hydrolyses
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Ionization rates of para-substituted triphenylmethyl (trityl) acetates, benzoates, and para-nitrobenzoates have been determined in aqueous acetonitrile and aqueous acetone at 25 °C. Conventional and stoppedflow techniques have been used to evaluate rate constants ranging from 1.38 × 10-5 to 2.15 × 102S-1 by conductimetry and photospectrometry methods. The varying stabilities of the differently substituted tritylium ions account for a gradual change of reaction mechanism. Poorly stabilized carbocations are generated slowly by the ionization of their covalent precursors and trapped fast by water. Better stabilized carbocations are generated more rapidly and accumulate, so that ionization and trapping by water can be observed as separate steps in a single experiment. Finally, highly stabilized tritylium ions do not react with water, and only the rates of their formation could be measured. The ionization rate constants correlate linearly with Winstein's ionizing powers Y; the low slopes (0.17 + parameters is excellent for symmetrically substituted tritylium derivatives, deviations for unsymmetrically substituted systems are observed. The failing rate-equilibrium relationship between the rates of ionizations (log kion) and the stabilities of the carbocations in aqueous solution (pKR+) may be explained by the late " development of resonance between a p-amino group and the carbocationic center of the tritylium ion during the ionization process.
- Horn, Markus,Mayr, Herbert
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supporting information; experimental part
p. 7469 - 7477
(2010/09/11)
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- The kinetics and mechanism of the acid-catalysed detritylation of nucleotides in non-aqueous solution
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The kinetics and mechanism of the deprotection (detritylation) of 5′-O-(4,4′-dimethoxytrityl)-2′-deoxythymidine nucleoside catalysed by dichloroacetic acid to give a 4,4′-dimethoxytrityl carbocation have been studied in toluene, dichloromethane and acetonitrile. There is little or no effect of solvent polarity on the equilibrium and rate constants. Entropies of activation are highly negative ~-105 J K -1 mol-1 and similarly show little variation with solvent. Addition of small amounts of water to the reaction medium reduces the detritylation rate, presumably through its effect on the solution acidity. All observations are compatible with detritylation occurring through a concerted general acid-catalysed mechanism rather than a stepwise A1 process.
- Russell, Mark A.,Laws, Andrew P.,Atherton, John H.,Page, Michael I.
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experimental part
p. 52 - 57
(2009/04/10)
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- Nanostructured columnar and cubic liquid-crystalline assemblies consisting of unconventional rigid mesogens based on triphenylmethanes
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Liquid-crystalline (LC) molecules of unconventional shapes that form columnar and micellar cubic structures have been synthesized using triarylmethyl moieties as building blocks. The molecules have bowl- and dumbbell-shape. Despite the rigidity and bulkiness of the triarylmethyl moieties, the molecules form columnar and micellar cubic LC phases. The bowl-shaped molecules containing one triarylmethyl moiety show LC phases. The LC temperature ranges of the dumbbell-shaped molecules containing two triarylmethyl moieties connected by rigid rods are wider than those of bowl-shaped molecules containing one triarylmethyl moiety. The UV-vis spectroscopy of the dumbbell-shaped molecules having a terphenyl moiety reveals that the terphenyl moieties aggregate in the mesophase.
- Hatano, Tsukasa,Kato, Takashi
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p. 8368 - 8380
(2008/12/21)
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- N-tritylhydroxylamines: Preparations, structures, base strengths, and reactions with nitrous acid and perchloric acid
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N-Trityl, N-(4-methoxytrityl), N-(4,4′-dimethoxytrityl), and N-(4,4′,4″-trimethoxytrityl) derivatives of hydroxylamine, O-methylhydroxylamine, and O-benzylhydroxylamine have been prepared and characterised. Additionally, N,O-ditrityl- and N,O-bis(4,4′-dimethoxytrityl)-hydroxylamines have been made, and the X-ray crystal structure of the former has been determined. The pKa value of O-benzylhydroxylammonium in water (6.2) and of its N-trityl analogue in aqueous acetonitrile (7.5) have been measured. The N-tritylhydroxylamines all decompose under aqueous acidic conditions to give the corresponding trityl alcohols, and rate constants for uncatalysed and hydronium ion catalysed reactions of N-(4,4′-dimethoxytrityl)-O-methylhydroxylamine have been measured by stopped flow kinetics at 25 °C. This compound compares in reactivity with N-alkyl-N-(4,4′-dimethoxytrityl)amines rather than with 4,4′-dimethoxytritylamine. Attempted nitrosation of N-tritylhydroxylamine and its O-alkyl derivatives gave trityl alcohol, the intermediate N-nitroso compound being detectable but too unstable to isolate. From N-trityl-O-benzylhydroxylamine, attempted nitrosation led to the formation of triphenylmethane in addition to trityl alcohol, benzyl alcohol, and trityl benzyl ether. The mildly acidic conditions used for attempted nitrosation of methoxy-substituted N-tritylhydroxylamines led to deamination before addition of the nitrosating agent.
- Canle L, Moises,Clegg, William,Demirtas, Ibrahim,Elsegood, Mark R.J.,Haider, Johanna,Maskill, Howard,Miatt, Peter C.
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p. 1742 - 1747
(2007/10/03)
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- Substituent effects upon rates of deamination and base strengths of substituted N-tritylamines
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Substituted N-tritylamines undergo deamination in aqueous acidic solution containing organic cosolvents, and follow a pseudo first-order specific acid-catalysis rate law (kobs = k0 + kH[H3O+]); the products are the corresponding trityl alcohols in equilibrium with the trityl carbenium ions, and ammonium ions. The change from 4,4′-dimethoxy-to 4,4′,4″-trimethoxy-tritylamine increases reactivity by a factor of about 30 in both k0 and kH, but N-alkyl and N-aryl groups have much greater effects (ca. 106 for both k0 and kH for 4,4′-dimethoxytritylamine) which are largely independent of the nature of the N-alkyl and N-aryl groups. The anions of the catalytic strong acids (perchlorate, chloride, bromide, and nitrate) have only small effects as also does the concentration of acetonitrile as cosolvent; ethanoic acid as cosolvent is mildly rate-enhancing. Substituents in the aniline residue of N-(4,4′-dimethoxytrityl)-anilines have virtually no effect upon either k0 or kH (ρ = 0 for both). The results are interpreted by a mechanism involving a pre-equilibrium heterolysis of the (substituted) tritylammonium ion to give an ion-molecule pair which may undergo diffusional or acid-catalysed dissociation before the (substituted) trityl cation undergoes equilibrium nucleophilic capture by water. Base strengths of some substituted N-tritylamines have been measured; the substituted N-trityl group causes all amines (aliphatic and aromatic) to be comparably strongly basic (pKBH- ca. 9).
- Canle,Demirtas,Maskill
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p. 1748 - 1752
(2007/10/03)
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- Specific and chemoselective multi-α-arylation reaction of benzoylformic acid with or without decarbonylation in P2O5-MsOH and related acidic media
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In P2O5-MsOH, or related acidic media, benzoylformic acid (1) undergoes three types of di- or mono-α-arylation reactions with or without decarbonylation ((1) decarbonylative α,α-diarylation, yielding triarylmethanols 6, (2) decarbonylative α-monoarylation, giving benzophenone derivatives 7, and (3) α,α-diarylation without decarbonylation, affording diarylated carboxylic acids 5) and one simple decarbonylation, without arylation, to form benzoic acid (8), instead of the conventional Friedel- Crafts acylation type reaction. The product ratios are governed by the capability of the acidic medium to form mixed anhydrides with carboxylic acids and the ability of the arenes to accept electrophiles.
- Yonezawa, Noriyuki,Hino, Tetsuo,Matsuda, Kazuhisa,Matsuki, Toshiyuki,Narushima, Daisuke,Kobayashi, Masato,Ikeda, Tomiki
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p. 941 - 944
(2007/10/03)
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- The 4,4′-dimethoxytrityl carbenium ion by ionization of 4,4′-dimethoxytrityl alcohol in acetonitrile - Aqueous perchloric and nitric acids containing electrolytes: Kinetics, equilibria, and ion-pair formation
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We have studied the equilibration shown in eq. [3] of 4,4′-dimethoxytrityl alcohol in aqueous perchloric and nitric acids containing low proportions of acetonitrile using stopped-flow kinetics techniques. The rate constants for the overall progress to equilibrium, kobs, have been resolved into forward and reverse components using the equilibrium UV absorbance and a value for the molar absorptivity of the 4,4′-dimethoxytrityl carbenium ion determined in concentrated aqueous perchloric acid. The forward reaction (rate constant kf) is first order in both the alcohol and the acid concentrations; the reverse reaction (rate constant Kr) is pseudo first order with respect to the carbocation. At constant hydronium ion concentration, the forward rate constant increases linearly with the concentration of electrolyte, whereas the reverse rate constant decreases. These effects depend upon the nature of the anion, but not the cation, and are not ionic strength effects. At constant anion concentrations, kf in both acids, and kr in perchloric acid, are independent of hydronium ion concentration; however, kr decreases with increasing hydronium ion concentration at constant nitrate concentration. At nonconstant ionic strength, changes in kr and Kr observed in increasing concentrations of perchloric acid are attributable wholly to changes in perchlorate concentration. A mechanism is proposed which involves pre-equilibrium protonation of the alcohol, heterolysis of the protonated alcohol to give a 4,4′-dimethoxytrityl carbenium ion - water ion-molecule pair, then conversion of this into a dissociated carbenium ion in equilibrium with ion pairs. To account for the strong effects of perchlorate and nitrate upon the forward rate constants, it is proposed that these anions provide additional reaction channels from the ion-molecule pair. However, we find no evidence of acid catalysis in the reaction of the ion-molecule pair (in contrast to our finding for the reaction of the corresponding ion-molecule pair formed from dimethoxytritylamine in acidic media). Some of the elementary rate and equilibrium constants of the proposed mechanism have been evaluated.
- Crugeiras, Juan,Maskill, Howard
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p. 530 - 536
(2007/10/03)
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- The 4,4′-dimethoxytrityl carbenium ion by deamination of 4,4′-dimethoxytritylamine in acetonitrile-aqueous perchloric acid: Kinetics, equilibria, deuterium isotope effects, and possible ion-pair formation
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The rate of deamination of 4,4′-dimethoxytritylammonium cation, generated from the corresponding amine in aqueous perchloric acid containing a low proportion of acetonitrile at constant total perchlorate concentration, is first order in both dimethoxytritylammonium and hydronium ions. The specificity of the hydronium ion kinetic effect indicates acid catalysis with second-order rate constant, kH. There is also appreciable reactivity at [H3O+] = 0, i.e. an uncatalysed (solvent-induced) reaction channel from the substituted tritylammonium cation with first-order rate constant, ko. The deuterium solvent kinetic isotope effects upon uncatalysed and catalysed reaction channels have been measured [koH/koD = 1.51 (±0.03), kHH/kHD = 1.2 (±0.1), 25 °C and ionic strength = 1 mol dm-3]. The deuterium solvent isotope effect upon the subsequent equilibrium between 4,4′-dimethoxytrityl trityl cation and water (to give the substituted alcohol and hydronium ion) extrapolated to zero perchlorate concentration has also been determined, and the value (KR+)H/(KR+)D = 3.4 (±0.4) leads to a fractionation factor of ca. unity for the alcohol. The deamination is accelerated by increasing perchlorate concentrations at constant acidity; perchlorate also appears to have an appreciable effect upon the subsequent equilibrium involving the substituted trityl cation, water, hydronium ion, and the alcohol. Acetic acid, monochloroacetic acid, and trifluoroethanol also enhance the rate but not, apparently, by general acid catalysis, whereas the rate and final equilibrium are relatively insensitive to the proportion of the acetonitrile cosolvent. A mechanism for deamination is proposed which involves initial reversible heterolysis of the carbon-nitrogen bond of the tritylammonium cation followed by parallel diffusional separation and hydronium ion assisted separation. On the basis of the isotope effects, we conclude that the latter reaction channel involves either step-wise protonation of the ammonia molecule followed by rate-limiting separation of the cation-cation pair, or a strongly asynchronous (uncoupled) concerted process. Perchlorate may exert its appreciable kinetic and equilibrium effects simply by modifying the nature of the medium, i.e. by specific kinetic salt effects upon the various elementary steps in the overall reaction. Alternatively, the effect of perchlorate upon the final equilibrium may be explained by the reversible formation of specific ion-pairs between the extensively delocalised substituted trityl cation and the non-polarising perchlorate anion; we found no evidence of covalent dimethoxytrityl perchlorate. Correspondingly, the effect of perchlorate upon the observed pseudo first-order deamination rate constant could be due to its direct involvement in additional solvent-induced and hydronium ion-catalysed routes.
- Crugeiras, Juan,Maskill, Howard
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p. 1901 - 1907
(2007/10/03)
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- Triarylmethanes and 9-arylxanthenes as prototypes amphihydric compounds for relating the stabilities of cations, anions and radicals by C-H bond cleavage and electron transfer
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Thermodynamic stability properties of 11 p-substituted trityl and seven 9-phenylxanthyl carbocations are reported in sulfolane and of their conjugate carbanions in DMSO. The cations are compared by calorimetric heats of hydride transfer from cyanoborohydride ion, their first and second reduction potentials, their pK+Rs in aqueous sulfuric acid, 13C chemical shifts and free energies of methoxy exchange. Carbanions are compared by their heats and free energies (pKHA) of deprotonation and their first and second oxidation potentials. Radicals are compared by their oxidation and reduction potentials. Their bond dissociation energies are derived by alternative routes: from the carbocation and its reduction potential and from the carbanion and its oxidation potential. The various properties are correlated against each other and against appropriate Hammett-type substituent parameters. Correlations between the different measured properties reported here range from fair to excellent. Despite their importance as historic prototypes for the three trivalent oxidation states of carbon, trityl and xanthyl systems are atypical models for comparing transmission of electron demand in other series of carbocations, radicals or carbanions with significantly different structures. The 9-arylxanthyl series is especially poor because of its insensitivity to substituent effects. The effects of substituents on various properties which represent the stabilities of R+s correlate surprisingly well against those for corresponding R-s. Accordingly, compensating effects on the oxidation and reduction of a series of related R.s may lead to a nearly constant electron transfer energy and absolute hardness for the series. In contrast, the free energies for interconversion of the carbocations and carbanions which determine the gap between pKR+. and pKHA are very sensitive to structural change.
- Arnett, Edward M.,Flowers II, Robert A.,Ludwig, Richard T.,Meekhof, Alison E.,Walek, Stuart A.
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p. 499 - 513
(2007/10/03)
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- A new method for synthesis of 4,4'-dimethoxytrityl chloride
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The selection of appropriate protecting groups forms an essential part of oligonucleotide synthesis. 4,4'-Dimethoxytrityl group (DMT-), originally developed by Khorana at al., is still the most frequently used acid labile protecting group for selective blocking of 5'-hydroxyl function of the sugar moiety in the nucleosides or nucleotides.The conventional method of synthesis of 4,4'-dimethoxytrityl chloride (DMTCl, 7), involves the reaction of ethyl benzoate with anisyl magnesium bromide in dry benzene to give the crude product, di-p-anisylphenyl carbinol as a reddish oil which is subsequently converted into DMTCl on refluxing with acetyl chloride.
- Rathore, M.,Rani, P.,Mathur, N. K.,Narang, C. K.
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p. 634 - 635
(2007/10/03)
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- 1,1,1,3,3,3-Hexafluoro-2-propanol for the Removal of the 4,4'-Dimethoxytrityl Protecting Group from the 5'-Hydroxyl of Acid-Sensitive Nucleosides and Nucleotides
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1,1,1,3,3,3-Hexafluoro-2-propanol is introduced as a suitable reagent and solvent for the detritylation of 5'-O-(4,4'-dimethoxytrityl)-nucleosides and -deoxy- nucleosides, especially those that are susceptible to N-glycosyl cleavage under more strongly acidic conditions.
- Leonard, Nelson J.,Neelima
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p. 7833 - 7836
(2007/10/02)
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- Molar Absorptivity and pKR+ of the 4,4'-Dimethoxytrityl Carbenium Ion in Methanolic Water, and its Equilibrium with Chloride Ion
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The 4,4'-dimethoxytrityl carbenium ion has been generated in 80:20 (v/v) water-methanol containing perchloric acid in a rapid reaction from 4,4'-dimethoxytrityl alcohol and in a slower reaction from 4,4'-dimethoxytritylamine.The pK (-0.95; K=8.98) and molar absorptivity (ε=297 000) of the cation have been measured directly under equilibrium conditions in this highly aqueous medium at ionic strength = 1.0 mol dm-3 by a convenient spectrophotometric method at 25 deg C.In addition, the pK has been measured at other temperatures, which allows the determination of the standard enthalpy (ΔH = -11.4 kJ mol-1) and entropy (ΔS = -20 J K-1 mol-1) of the reaction of the cation with the solvent, and at other ionic strengths.The equilibrium constant for the formation of 4,4'-dimethoxytrityl chloride from the cation and chloride has also been measured in the same medium (KRCl = 8.20 at 25.0 deg C, ionic strength = 1.0 mol dm-3) by generating the cation from the alcohol and perchloric acid in the presence of 0.10 mol dm-3 sodium chloride.
- Lee, Won Heui,Maskill, H.
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p. 1463 - 1466
(2007/10/02)
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- The Mechanism of Deamination of Methoxy Substituted Tritylammonium Ions in Methanolic Aqueous Acid
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In methanolic aqueous acid, methoxy-substituted tritylammonium ions undergo heterolysis to give an equilibrium mixture of the substituted trityl cation, the corresponding alcohol (and methyl ether), and the ammonium cation via an SN1 mechanism; the detection of a reaction channel first order in hydronium ions may implicate substituted trityl cation-ammonia (ion-molecule) pairs as reactive intermediates.
- Bleasdale, Christine,Golding, Bernard T.,Lee, Won Heui,Maskill, H.,Riseborough, Jane,Smits, Elly
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- Efficient synthesis of azetidine through N-trityl- or N- dimethoxytritylazetidines starting from 3-amino-1-propanol or 3- halopropylamine hydrohalides
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Efficient synthetic routes for the preparation of azetidine starting from commercially available 3-amino-1-propanol or 3-halopropylamine hydrohalides are reported. First, the appropriate N-trityl- or N-dimethoxytrityl protected tosyloxy- or halopropylamines were prepared. These precursors were then cyclized into the N-trityl- or N-dimethoxytritylazetidines. The N-protecting groups were removed in the presence of perchloric acid giving the hydrogen perchlorate salt of azetidine. The latter compound was transformed into its free base using a strong base under anhydrous conditions. The relatively expensive 4,4'-dimethoxytrityl chloride and less expensive trityl chloride used in these synthetic procedures were recycled in good yields. Azetidine hydrogenperchlorate can be used to prepare N-substituted azetidines without the need to isolate the free azetidine.
- Huszthy,Bradshaw,Krakowiak,Wang,Dalley
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p. 1197 - 1207
(2007/10/02)
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- The stepwise synthesis of oligo(glycosyl phosphates) via glycosyl hydrogenphosphonates. The chemical synthesis of oligomeric fragments from Hansenula capsulata Y-1842 exophosphomannan and from Escherichia coli K51 capsular antigen
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A stepwise approach has been used in the syntheses of pentamannosyl tetraphosphate HO-4-6Man(α)-OMe and tetra(N-acetylglucosaminyl) triphosphate HO-3-3GlcNAc(β)-OC6H4NO2, which are fragments of the yeast and bacteria extracellular phosphoglycans.Elongation of the chain was performed with the use of suitably protected glycosyl hydrogenphosphonate derivatives for successive introduction of glycosyl phosphate residues.Partially protected monosaccharide derivatives and oligomeric blocks served as hydroxylic components.
- Nikolaev, Andrey V.,Ivanova, Irena A.,Shibaev, Vladimir N.
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- Reactivities of triarylmethyl and diarylmethyl cations with azide ion investigated by laser flash photolysis. Diffusion-controlled reactions
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By use of the technique of laser flash photolysis, rate constants kAz and ks have been directly measured for the reactions at 20 °C in acetonitrile-water (AN-W) solutions of varying composition of 18 triarylmethyl and 10 diarylmethyl cations with azide and solvent. The cations have ks that depend on substituent and vary from ~101 to ~107 s-1. For the more stable ions kAz also varies, increasing with decreased electron donation and also increasing by as much as 103 with increasing acetonitrile content. For less stable cations, however, the rate constant becomes independent of substituent. The break occurs when ks has reached ~105 s-1. The limiting rate constants have magnitudes in the vicinity of 1010 M-1 s-1; these do depend on solvent and type of cation, with diarylmethyl cations reacting at the limit 1.6 ± 0.2 times faster than triarylmethyl. The data can be fit by a model where there is diffusional encounter of the cation and azide to form an ion pair, with the combination within the ion pair rate-limiting for the more stable cations and the diffusion step rate-limiting for the less stable ones. The limiting rate constants represent the latter, diffusional encounter of the cation and azide. The Debye-Smoluchowski equation for diffusion-controlled reactions predicts rate constants that are larger than observed by factors of 2-2.5 for diarylmethyl and 4 for triarylmethyl. Deviations can be attributed to nonproductive encounters where the anion has approached the cation in the plane of one of the rings and thus cannot form a proper reacting configuration. The difference between the two types of cations is explained by the greater difficulty of achieving this configuration with the more sterically congested triarylmethyl cation. Ratios kAz/ks obtained from product analysis (competition kinetics) have previously been found to show adherence to the reactivity-selectivity principle. This has been interpreted (Rappoport, Jencks) in terms of the reaction with azide having reached the diffusion limit. The directly measured kAz establish that this is indeed the case. This study also validates the use of azide as a "clock" (Jencks, Richard) for converting such ratios to absolute rate constants through use of a value of 5 × 109 M-1 s-1 for kAz. The directly measured diffusion-limited kAz are somewhat larger than this, but the differences are small, at most a factor of 4.
- McClelland, Robert A.,Kanagasabapathy,Banait, Narinder S.,Steenken, Steen
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p. 1009 - 1014
(2007/10/02)
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- 4,4'-Dimethoxytrityl and 4-Monomethoxytrityl Tetrafluoroborate: Convenient Reagents for the Protection of Primary Alcohols Including Sugars
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In a non-donor solvent (e.g. acetonitrile) and in the presence of 2,6-di-t-butyl-4-methylpyridine, the readily prepared 4-methoxytrityl tetrafluoroborate (3) and 4,4'-dimethoxytrityl tetrafluoroborate (2) are highly effective reagents for the methoxytritylation and dimethoxytritylation, respectively, of primary alcohols including sugars.
- Bleasdale, Christine,Ellwood, Simon B.,Golding, Bernard T.
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p. 803 - 805
(2007/10/02)
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- Reactions of some p-Substituted Triphenylmethyl Chlorides with Alcohols, Alkali-metal Alcoholates, and Tributylamine
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The p-methoxylated triphenylmethyl chlorides (4a-c), when heated with alcohols, give mixtures of the corresponding triarylmethanes (5a-c) (via the hydride transfer to the corresponding triarylmethylium cations) and the alkyl (substituted triphenylmethyl) ethers (7a-c) (via polar susbtitution reactions).Part or all of the ether (7c) may be further converted into the substituted triphenylmethanol (6c).In the reaction of the mono-p-methoxylated halides (4a) and (4c) with methanol, the substitution products (7a) and (7c) are formed as the main products, while the main product of the reaction of the di-p-methoxylated halide (4b) with methanol is the substituted triphenylmethane (5b).When the methanol is replaced by 2H4> methanol, no reduction product is formed from the halide (4c).Reaction of halide (4c) with ethanol furnishes exclusively the substituted triphenylmethane (5c).The p-chlorophenyl(diphenyl)methyl chloride (4d) gives, with methanol, mainly or exclusively the ether (7d), and with ethanol, under mild conditions, gives the ether (9d).However, under vigorous conditions, the substituted triphenylmethane (5d) is formed.The reduction of the p-methoxylated triphenylmethyl chloride (4c) by alcohols as well as its conversion into alkyl (p-methoxylated triphenylmethyl) ethers are accompanied, to a certain degree, by exchange of the p-methoxy group of the substrate and the alkoxy group of the alcohol; no similar exchange of the p-chlorine atom of halide (4d) was observed.Explanations for all obsrved diferences are offered.The reactions of the substituted triphenylmethyl chlorides (4b-d) with alkoxides in the corresponding alcohols give the corresponding alkyl (substituted triphenylmethyl) ethers (7b), (7c), (9c), and (9d), respectively, in excellent yields.The reaction of the triarylmethyl chloride (4d) with potassiumt-butoxide in THF in the presence of acetone led, among other products, to the formation of oligomeric material which indicates the operation of single-electron-transfer induced processes.Reaction of the same chloride (4d) with tributylamine in refluxing cumene or t-butylbenzene led to the exclusive formation of a series of products all of which may be derived from the intermediacy of the substituted triphenylmethyl radical (18); the latter, in turn, is thought to arise as a result of dissociative electron transfer from tributylamine to chloride (4d).
- Izso, Gyoengyi,Huszthy, Peter,Lempert, Karoly,Fetter, Jozsef,Simig, Gyula,et al.
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p. 769 - 778
(2007/10/02)
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- One-electron Oxidation of Closed-shell Molecules. Part 4. Acid-induced Oxidative Cleavage of Substituted 1,2,2,2-Tetraphenylethanones (Benzpinacolones) with Diaroyl Peroxides
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The acid-induced oxidative cleavage of anispinacolone with diaroyl peroxides in 1,2-dichloroethane-trifluoroacetic acid (TFA) has been investigated.The principal two products after work-up are tris-(p-methoxyphenyl)methanol and p-methoxybenzoic acid; the latter was found as anhydrides in the reaction mixture.Free-radical formation in the course of the cleavage was verified by polymerization of added acrylonitrile in the oxidation by bis-(3,5-dinitrobenzoyl) peroxide.When the oxidation of anispinacolone (90percent (13)C) by dibenzoyl peroxide was carried out in a (13)C n.m.r. probe, an emission peak, assigned to p-methoxybenzoic trifluoroacetic anhydride, was observed.The logarithms of the rate constants for oxidation of p-substituted benzpinacolones by dibenzoyl peroxide were linearly correlated with the oxidation potentials of the benzpinacolones.These results are consistent with a single-electron transfer (s.e.t.) pathway from benzpinacolones to dibenzoyl peroxide.The oxidation is first-order in each reactant and is promoted by TFA.The effect of TFA is accounted for by two factors, (i) assisted O-O bond cleavage of the peroxide radical anion by TFA, and (ii) the formation of protonated peroxide, a more powerful oxidizing species.The former factor is dominant at lower TFA concentrations ( 0.05 M), the latter at higher concentrations.
- Kitagawa, Toshikazu,Takeuchi, Ken'ichi,Murai, Osamu,Matsui, Shin,Inoue, Takeshi,Nishimura, Makoto et al.
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p. 1987 - 1996
(2007/10/02)
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- A New Type of Protection Mode for the Guanine Residue by Using 1,2-Diisobutyryloxyethylene Group
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A new protecting group, 1,2-diisobutyryloxyethylene group, has successfully been used for protection of the guanine residue in the synthesis of oligodeoxyguanylates.
- Sekine, Mitsuo,Matsuzaki, Jun-ichi,Hata, Tsujiaki
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p. 5287 - 5290
(2007/10/02)
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