P-Nitrophenyl alanine

The rates of reaction of both enantiomers of amino-acid esters in the presence of (S)-[324] are the same, but with (S)-[323] they are in most cases different. The reactions of L-amino acid esters in the presence of (S)-[323] are faster than those in the presence of (R)-[323] by factors of 9.2 (R = i-Pr), 8.2 (R = C6H5CH2) and 6.0 (R = i-Bu). No difference in rates is observed for L-alanine p-nitrophenyl ester. The results were explained in terms of the formation of diastereomeric tetrahedral intermediates [325] and [326]. The bulk of the group R will determine how much the complex stability of the (D)-complex decreases relative to that of the (L)-complex, which difference is reflected in the activation energy of the rate-determining step. 

Enantiomeric differentiation during the thiolysis of a-amino acid ester salts by two thiol-bearing 18-crown-6 derivatives prepared from (1/ , 2/ , 35, 45)- and R, 2S, 3R, 45)-camphane-2,3-diols has also been demonstrated [74]. Discrimination by factors of 1.7-1.9 in the rates of p-nitrophenol release from the enantiomers of alanine-p-nitrophenyl ester salts has been observed. By contrast, the tetrakis-L-cysteinyl methyl ester receptor molecule l,l-l,l,l,l-(60) exhibits [75] extremely high... 

Equimolar amounts of N-phthaloyl-j -alanine and p-nitrophenol refluxed 0.5 hr. or stored 24 hrs. at room temp, with polyphosphoric acid ester prepared from P2O5 and ethyl ether in chloroform N-phthaloyl-j -alanine p-nitrophenyl ester. Y 87%. F. e. s. Y. Kanaoka et al., Ghem. Ind. 196A, 2102. 

Condensation with N-t-Butoxycarbonyl a-Alanine p-Nitrophenyl Ester and N-t-Butoxycarbonyl -Alanine p-Nitrophenyl Ester... 

An additional method attempted for the synthesis of diazo derivatives of ATP was via the condensation of diazotized a-alanine p-nitrophenyl ester with ATP under imidazole catalysis. The N-protecting group from A -t-butoxycarbonyl a-alanine p-nitrophenyl ester was removed by acid and the product diazotized prior to attempted condensation with ATP. 

One of the most investigated type of reaction in the field of catalytic imprinted polymers, as indicated by the large number of publications available, is certainly ester hydrolysis. In particular, a great deal of work has been carried out on systems inspired by hydrolytic enzymes since 1987. In 2000, Shea et al. [37] reported the preparation of enantioselective imprinted polymers for the hydrolysis of N-tert-butoxycarbonyl phenylalanine-p-nitrophenyl ester (55), using a system already developed by the same group in 1994 [19]. The system was inspired by the natural hydrolytic enzyme chymotrypsin and polymerisable imidazole units (27) were used as functional monomers coupled via ester linkages to a chiral phosphonate (56), analogue of (d)- or (L)-phenyl-alanine. After template removal, the imprinted polymers showed selectivity towards the hydrolysis of the enantiomer with which they were imprinted. The ratio of the rate constants, k /k, was 1.9 for the polymer imprinted with the D-enantiomer and kjku was 1.2 for that imprinted with the L-enantiomer. Moreover, the imprinted polymer showed a 2.5-fold increase in the rate of the reaction when compared with the control polymer, imprinted with a... 

The obtained L-a-alanine grafted polymer 49 was further reacted with p-nitrophenyl ester-containing bases, according to the procedure mentioned earlier. From the NMR and UV spectra, the polymers obtained were found to contain about 98% adenine units 50 (A-Ala-PEI) and about 100% thymine units for polymer 51 (T-Ala-PEI). 

The successful separation of dipeptide diastereomers has been reported by Wieland and Bende (14), Taschner et al. (15), and Pravada et al. (16) either as the free peptides or as the N-protected methyl esters. Hubert and Dellacherie (5) separated diastereomeric p-nitrophenyl (Np) esters of N-protected di- and tripeptides starting from pure L-methionine and DL-alanine, they synthesized Np-S-L-Met-DL-Ala-O-Np and Np-S-L-Met-L-Met-DL-Ala-O-Np. The separation was achieved on silica gel F254 precoated (Merck) plates. TLC separation of diastereomeric dipeptides has been well documented by Arendt et al. (17) and Lepri et al. (18). 

Methyl carbobenzoxy-DL-alaninate heated 2-4 hrs. with fer -butyl glycinate at 80° in molten imidazole, which acts as a catalyst ferf-butyl carbobenzoxy-alanylglycinate. Y 78%. F. e. s. T. Wieland and K. Vogeler, Ang. Gh. 74, 904 (1962) from thiolic acid esters (cf. Synth. Meth. 8, 528) and free amino acids in the presence of water at 40° s. Ang. Gh. 75, 209 (1963) acceleration of p-nitrophenyl ester peptide synthesis (cf. Synth. Meth. 14, 450 75, 343) s. R. H. Mazur, J. Org. Ghem. 28, 2498 (1963) f. bifunctional catalysts s. H. G. Beyerman and W. Maassen van den Brink, Proc. Ghem. Soc. 7905, 266. 

N-Carbobenzoxy-L-alanine-/>-nitrophenyl ester is a specific substrate for elastase in which the rate-limiting step is deacylation, that is, hydrolysis of the acyl-enzyme intermediate. In 70% methanol over a reasonable temperature range the energy of activation of the turnover reaction, that is, deacylation, is 15.4 kcal mol. In the pH 6-7 region in this cryoprotective solvent, the turnover reacdon can be made negligibly slow at temperatures of -50 C or below. Under such conditions/i-nitro-phenol is released concurrent to acyl enzyme formation in a 1 1 stoichiometry with active enzyme in the presence of excess substrate. In other words, even at low temperatures, the acylation rate is much faster than deacylation and the acyl enzyme will accumulate on the enzyme. The rate of acyl-enzyme formation can be monitored by following the rate of p-nitrophenol release, and thus the concentration of trapped acyl enzyme may be determined. This calculadon has been carried out and... 

To 5.4 ml of an aqueous solution of )8-alanine (534 mg, 6 mmoles) and sodium carbonate (1.08 g, 10 mmole) is added 4-fluoro-3-nitrophenyl azide (900 mg, 4.9 mmoles). Ethanol (6.75 ml), water (5.4 ml), and another portion of ethanol (13.5 ml) are added subsequently to enhance the homogeneity of the reaction mixture. The reaction mixture suspension is stirred at 52° overnight with an attached cooling condenser. The resulting dark red mixture is first concentrated under reduced pressure to about one-third of its volume and then diluted with 18 ml of water. Two extractions with 45 ml of ether remove all the excess starting azide. The aqueous layer is acidified with 3 N HCl to pH 2 and extracted with three 90-ml portions of ether. The combined ether extract is washed three times, each with 50 ml of saturated NaCl solution, and is dried over sodium sulfate and then evaporated to dryness. The residue is recrystallized from hot ethanol. Yield 736 mg (59%) m.p. 142.5°-145° MS m/e 251 UV 260 (molar extinction coefficient 27.2 X... 

Tritium-labeled aryIazido-j8-alanine ATP (1.6 X 10 cpm//xmole) is prepared by condensing 3-[vV-(4 azido-2-nitrophenyl) Jaminopropionic acid with [2,8- H] adenosine 5-triphosphate tetrasodium salt (1 mCi) obtained from New England Nuclear. The P-labeled ATP analog is prepared in the identical manner utilizing y-labeled [ P]ATP. The synthesis of a number of labeled arylazido-j8-alanine nucleotides is schematically outlined in Fig. 1,... 

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