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2- -5-nitrophenyl ester protect acids

In the second major method of peptide synthesis the carboxyl group is activated by converting it to an active ester, usually a p-nitrophenyl ester. Recall from Section 20.12 that esters react with ammonia and amines to give fflnides. p-Nitrophenyl esters are much more reactive than methyl and ethyl esters in these reactions because p-nitrophenoxide is a better (less basic) leaving group than methoxide and ethoxide. Simply allowing the active ester and a C-protected amino acid to stand in a suitable solvent is sufficient to bring about peptide bond formation by nucleophilic acyl substitution. [Pg.1139]

For the elongation of the chain starting from 11 toward the N-terminal group, direct condensation of the activated p-nitrophenyl esters of such amino acids as N-protected L-cysteine, L-glutamic acid, glycine, L-leu-cine, L-proline, L-serine, L-tyrosine, andL-valine with 2-acetamido-3,4,6-... [Pg.153]

Nitrophenyl esters of amino acids, which are important for peptide syntheses, have been obtained in a one-pot reaction from TV-protected amino acids, CDI, and /j-nitro-phenol at room temperature however, better yields of these esters could be achieved by use of TV-trifluoroacetylimidazole. In this reaction a mixed anhydride is presumably formed as an intermediate, which then acylates the alcohol component [17]... [Pg.41]

The amino acid attached to a polymer is treated with an vV-protected, carboxyl-activated amino acid to give the supported peptide. In the following reaction the triazolide was formed in situ from the p-nitrophenyl ester and 1,2,4-triazole 1341... [Pg.155]

The first successful synthesis of a biologically active cyclic peptide, gramicidin S, was accomplished by Schwyzer and Sieber[6,7l via the 4-nitrophenyl ester. The fact that -protected peptide esters can be deprotected to give the peptide active ester salts has made this approach popular not only in the synthesis of sequential polypeptides but also of cyclic peptides. Among the various active esters examined for this purpose, the pentafluorophenyl esters have emerged as the most reactive ones, although a high risk of epimerization is encountered when C-terminal chiral amino acids are involved. [Pg.470]

The reagents sketched in Figure 13.2 are stable and can be prepared either in solution or on insoluble supports. Activated Boc- or Fmoc-protected amino acid derivatives that are sufficiently stable to be isolated, some of which are commercially available, include acyl chlorides [9,13], fluorides [10,14,15], symmetric anhydrides [16], pentafluorophenyl esters, Af-hydroxysuccinimidyl esters, and 4-nitrophenyl esters [17,18],... [Pg.326]

This O-acylisourea is attacked by p-nitrophenol to give the p-nitrophenyl ester of the Z-protected amino acid. [Pg.760]

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]. [Pg.90]

The dipeptide is now coupled—but is still protected. Deprotection (HBr/AcOH) gave the HC1 salt of LeuGly ethyl ester for further reaction. The rest of the peptide was built up in much the same way—each amino acid being introduced as the Cbz-protected p-nitrophenyl ester before being deprotected ready for the next coupling, until all nine of oxytocin s amino acids had been introduced. [Pg.654]

Conversion of a Boc-protected amino acid to a p-nitrophenyl ester. [Pg.1114]

Leonhardt and Mosbach prepared metal-complexing imprinted polymers by polymerising Co " complexes of N-vinyl imidazole and A-protected amino acids [14]. After work-up of the polymer and removal of the amino acid templates, the catalytic activities of the resulting imprinted metal-complexing polymers were evaluated by following the hydrolysis of the p-nitrophenyl esters of various amino acids. Assessment of the rate of hydrolysis revealed a clear preference for the substrates used as the templates. The polymers could be used several times without any deterioration of the catalytic activities and true turnover was observed. [Pg.197]

Methylenedioxy)benzyl esters (piperonyl esters) are cleaved more readily than the 4-methoxybenzyl ester by acid hydrolysis with 2 M HBr/AcOH or TFA at room temperature within 5 minutes.3,4-(Methylenedioxy)benzyl esters are readily prepared either by transesterification of anoino acid 4-nitrophenyl esters with 3,4-(methylenedioxy)benzyl alcohol in imidazole/dioxane (rt, 12 h) or from Nps-protected amino acids with 3,4-(methyl-enedioxy)benzyl chloride/TEA in DMF at room temperature. [Pg.216]

The 4-methoxybenzyl esters are prepared by transesterification of N-protected amino acid nitrophenyl esters with 4-methoxybenzyl alcohol in the presence of several equivalents of imidazole, followed by subsequent acidolytic cleavage of the N-protecting group.Alternatively, reaction of N-protected amino acids silver(I) salts with 4-methoxybenzyl halides (TEA/CHCI3, rt, 24 h, 60% yield) or treatment of N-protected amino acids with 4-meth-... [Pg.217]

Compounds such as 4-nitrophenyl and 2,4,5-trichlorophenyl esters of N-protected amino acids were originally prepared also by reaction of the N-protected acids with di- or trisub-stituted esters of carbonic,sulfinic,f l or phosphinic acids l in, or with addition of, pyridine. This was followed by the use of mixed carbonates 54 that served both for acylation of amino acid 53 to N-protected acid 55 and subsequent esterification to 56 using carbodiimide (Scheme 13).A variant of this was the preparation of the unusual l,l,4-trioxo-2,5-di-phenyl-4,5-dihydro-3-thienyl 57 esters of Boc amino acids 56c, which avoided the use of carbodiimide since esterification proceeds in the presence of tetramethylguanidine.P l... [Pg.456]

See the discussion in Section 3.2.2 Scheme 21 shows the synthesis of the protected tripeptide 76 from the amino acid nitrophenyl ester, followed by aminolysis. ... [Pg.462]

In the absence of base, active esters of both N-alkoxycarbonyl amino acids and N -protected peptides undergo anninolysis with preservation of chiral integrity. There is ample evidence to substantiate this statementP d and no evidence to the contrary. But there is a wealth of accumulated evidence that active esters undergo isomerization when left in the presence of tertiary annine.t In this regard, 4-nitrophenyl esters are much more sensitive than trichlorophenyl esters and piperidino esters are exceptions in that they are unaffected by tertiary anoine.W The isomerization recently observed in the TBTU-mediated couplings of Fmoc-Cys(R )-OH in the presence of 1,2,3-benzotriazol-l-ol in continuous flow solid-phase synthesis is a further example of this phenomenon. The result can be attributed to the effect of tertiary amine on the benzotriazolyl ester that is formed by capture of the acyluronium intermediate before it has time to be aminolyzed. [Pg.463]

Aminolysis of active ester 91 can be effected by the amino group of an amino acid or peptide that is not protected at the terminal carboxy group (Scheme 27). Zwitterionic amino acid 92 or peptide is deprotonated by the addition of a base that generates the anionic form of the reactant. A partially aqueous milieu containing a water-miscible solvent such as acetone, dioxane, or acetonitrile is best for solubilizing the reactants. Esters that are hydrolyzed slowly or not at all are preferred because the acid produced is not readily separated from target molecule 66 (obtained from anion 93) because of their similar properties. Piperidino esters do not undergo hydrolysis but their aminolysis is slow.bl 4-Nitrophenyl esters react efficiently but the nitrophenol is difficult to remove. Succinimido esters are employed most frequently and are particularly useful in the preparation of N -protected dipeptides. Use of an excess of amino acid 92 favors complete consumption of active ester 91 by aminolysis before any of it can hydrolyze. [Pg.467]


See other pages where 2- -5-nitrophenyl ester protect acids is mentioned: [Pg.112]    [Pg.234]    [Pg.1139]    [Pg.1141]    [Pg.1141]    [Pg.33]    [Pg.137]    [Pg.126]    [Pg.395]    [Pg.14]    [Pg.81]    [Pg.320]    [Pg.295]    [Pg.1148]    [Pg.309]    [Pg.331]    [Pg.234]    [Pg.167]    [Pg.51]    [Pg.136]    [Pg.295]    [Pg.2186]    [Pg.2191]    [Pg.2195]    [Pg.2205]    [Pg.447]    [Pg.450]    [Pg.465]   
See also in sourсe #XX -- [ Pg.598 ]




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Esters, protection

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