P-Nitrophenyl trifluoroacetate

Kinetic studies of the reaction of Z-phenyl cyclopropanecarboxylates (1) with X-benzylamines (2) in acetonitrile at 55 °C have been carried out. The reaction proceeds by a stepwise mechanism in which the rate-determining step is the breakdown of the zwitterionic tetrahedral intermediate, T, with a hydrogen-bonded four-centre type transition state (3). The results of studies of the aminolysis reactions of ethyl Z-phenyl carbonates (4) with benzylamines (2) in acetonitrile at 25 °C were consistent with a four- (5) and a six-centred transition state (6) for the uncatalysed and catalysed path, respectively. The neutral hydrolysis of p-nitrophenyl trifluoroacetate in acetonitrile solvent has been studied by varying the molarities of water from 1.0 to 5.0 at 25 °C. The reaction was found to be third order in water. The kinetic solvent isotope effect was (A h2o/ D2o) = 2.90 0.12. Proton inventories at each molarity of water studied were consistent with an eight-membered cyclic transition state (7) model. 

This is also a traditional peptide synthesis procedure. Joullie and coworkers [79] used it in the synthesis of the cyclopeptide alkaloid dihydromauritine A (142). As shown in Scheme 47, the linear precursor 140 was treated with p-nitrophenyl trifluoroacetate in pyridine to give the p-nitrophenyl ester. After cleavage of the Boc group, the amino ester was subjected to cyclization in dilute DMF in the presence of hydroxybenztriazole (HOBt) and diisopropylethylamine at 25 °C for 5 days. The cyclic product 141 v/as obtained in 10% yield only. 

Coupling, active ester Bis-(2,4-dinitrophenyl)carbonate. Chloroacetonitrile. Di(p-nitrophenyl)carbonate. 2-Ethoxypyridine-l-oxide. p-Nitrobenzyl tosylate. p-Nitrophenol. p-Nitrophenyl trifluoroacetate. Pentachlorophenol. Phenyltrimethylammonium ethoxide. Phosgene. Pyrazole. Sulfur dioxide-Dimethylformamide. Tetraethyl pyrophosphite. N,N -Thionyldiimidazole. 2,4,S-Trichlorophenol. 

FIGURE 11.11 Derivatives used in HPLC 1, fluorescamine 2, fluorenylmethoxycarbonyl 3, FMOC 4, Dansyl chloride 5, 8-quinolinesulfonyl chloride 6, NPA-Osu 7, SIFA 8, CENU 9, OPA 10, NITC 11, 2,3,4,5,6-pentafluorobenzylaldehyde (PFBAY) 12, p-nitrophenyl trifluoroacetate (NPTFA). 

A soln. of carbobenzoxy-L-phenylalanine in dry pyridine treated at room temp, with p-nitrophenyl trifluoroacetate, and the product isolated after 10 min. 

Many of these reactions are not observed at all when the relevant groups are allowed to come together in bimolecular processes in aqueous solution. For mechanistic work involving intermolecular reactions, therefore, it is necessary to use activated substrates. Much of what we know about the relevant reactions of esters, for example, comes from studies using aryl esters like p-nitrophenyl acetate, or acyl-activated compounds like ethyl trifluoroacetate (Bruice and Benkovic, 1966 Jencks, 1969 Bender, 1971). 

Poly( L-lysine trifluoroacetate )(4) was prepared according to the method of Sela ( 5 ). The p-nitrophenyl esters ( 1, 2, 3 )... 

Synthesis of these dendrimers is performed by condensation of the amino acid lysine, whose amino functions have previously been protected with tert-bu-tyloxycarbonyl groups (Boc), onto an (activated) L-lysine p-nitrophenyl ester. The resulting coupling product (Fig. 4.11) is then deprotected with trifluoroacetic acid and thus activated for renewed reaction. Iteration of the assembly and activation step ultimately led to a polylysine dendrimer with 1024 terminal butyloxycarbonyl groups [21]. 

Prepared in quantitative yield by refluxing p-nitrophenol with trifluoroacetic anhydride, the reagent reacts rapidly with a carbobenzoxyamino acid at room Icmperature to give the p-nitrophenyl ester. The reaction with a carbobenzoxy peptide is slower and requires heat or a long reaction period. p-Nitrophenyl trichloro-ncetate is active only in refluxing pyridine and gives p-nitrophenyl esters in poor yield. 

Peptide synthesis /-Amyl chloroformate. Bis-(2,4-dinitrophenyl)carbonate. Bis-o-phenylene pyrophosphite. i-Butyl chloroformate. sec-Butyl chloroformate. /-Butyl chloroformate. /-Butyl 2,4,5-trichlorophenyl carbonate. CopoIy(ethylene-N-hydroxymaleimide). N,N-Diethyl-I-propynylamine. Di-(p-nitrophenyl)sulfate. Ethoxyacetylene. N-Ethoxycarbonyl-2-ethoxy-l,2-dihydroquinoline. N-Ethylbenzisoxazolium fluoroborate. Ethyl chloroformate. N-Ethyl-5-phenylisoxazolium-3 -sulfonate. N-Hydroxysuccinimide trifluoroacetate. Methyl-morpholine. 4-Methylthiophenol. p-Nitrophenol. Oxalylchloride. Pentachlorophenol. Pentamethylbenzyl chloride. /-Pentyl chloroformate. Phenacyl bromide. Polyhexamethylene carbodiimide. Tetraethyl pyrophosphite. 1,2,4-Triazole. 

Carboxylic acid aryl esters from carboxylic acids and aryl trifluoroacetates Carboxylic acid p-nitrophenyl esters Retention of optical activity... 

The mechanism of activation of deoxyribonucleoside phosphoramidites by IH-tetrazole has recently attracted considerable attention. It has been argued that the protonation of the phosphoramidite function by l f-tet azole was rapid and followed by the reversible and slower formation of a phosphorotetrazolide intermediate (39). It is to be noted that relative to 5-(p-nitrophenyl)- IH-tetrazole (55), 1 -hydroxy-benzotriazole (24), / /-methylanilinium trifluoroacetate (40), iV-methyl-anilinium trichloroacetate (41), 5-trifluoromethyl-l//-tetrazole (23), A-methylimidazole hydrochloride (23), and )V-methylimidazole-trifluoromethane sulfonate (42), which have also been tested as activators, l/f-tetrazole still remained the most commonly used reagent for the activation of deoxyribonucleoside phosphoramidites. 

Stearic acid shaken 30 min. at 25° with excess trifluoroacetic anhydride, then chloramphenicol added portionwise, the resulting soln. allowed to stand 45 min. at 25°, warmed 5 min. at 50°, poured into ice and neutralized with NaHCOg after a few min.crude d(—)-fhreo-l-(p-nitrophenyl)-l-stearoyl-2-dichloracet-amido-1,3-propanediol. Y 82.5%.—This method cannot he used for the acylation with strong acids such as formic, chloracetic, or dichloracetic acids. F. e. s. L. Almirante and G. Tosolini, J. Org. Chem. 26, 111 (1961). 

IV-Phenylimidazolium triflate IV-Phenylimidazolium perchlorate 2-(Bromo)-4,5-(dicyano)imidazole IV-Methylbenzimidazolium triflate Pyridinium tetrafluoroborate IV-Methylanilinium trifluoroacetate lV-(p-Acetylphenyl)imidazolium triflate IV-Phenylimidazolium tetrafluoroborate ImidazoUum perchlorate 5-(/t-Nitrophenyl)-l//-tetrazole 4,5- (Dicy ano)imidazDle 4-(Phenyl)imidazDlium triflate Benzimidazolium tetrafluoroborate Imidazolium tetrafluoroborate Imidazolium triflate Benzimidazolium triflate 2-(Phenyl)imidazolium triflate A-Methylimidazolium triflate 4-(Methyl)imidazolium triflate l//-Tetrazole... 

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