- Mechanistic insight into the lability of the benzyloxycarbonyl (Z) group in N-protected peptides under mild basic conditions
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An unexpected lability of the benzyloxycarbonyl (Z) protecting group under mild basic conditions at room temperature is explained by a mechanism based on anchimeric assistance. It is found that the vicinal amide group stabilises the tetrahedral intermediate formed after nucleophilic addition of hydroxide to the carbonyl of the Z group. This effect operates in N-protected tripeptides and tetrapeptides but Z-protected dipeptides are stable under the same conditions due to blockage of the vicinal amide NH by intramolecular H-bonding with the terminal carboxylate moiety. Copyright
- Tena-Solsona, Marta,Angulo-Pachon, Cesar A.,Escuder, Beatriu,Miravet, Juan F.
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p. 3372 - 3378
(2014/06/09)
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- Deprotection of t-butyl esters of amino acid derivatives by nitric acid in dichloromethane
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The extension of the deprotection procedure of t-butylated carboxyl function using HNO3 in CH2Cl2 to a number of appropriately selected N-Z- derivatives of natural amino acid esters was investigated. The method was found to work effectively with alanine, phenylalanine, serine and the dipeptide aspartame, but the reagent brought about a number of unwanted transformations with tyrosine, methionine and tryptophan. Suitable protection of functions present in the latter ones allowed selective ester dealkylation, but tyrosine underwent unavoidable fast preliminary ring nitration. 2000 Elsevier Science Ltd.
- Strazzolini, Paolo,Scuccato, Massimo,Giumanini, Angelo G.
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p. 3625 - 3633
(2007/10/03)
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- SYNTHESIS OF THE HEXAPEPTIDE 11-16 OF THE NATURAL SEQUENCE OF HUMAN CALCITONIN
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A new variant of the preparative synthesis of hexapeptide 11-16 of the natural sequence of human calcitonin is described.In several of the stages 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline was used successfully as the condensing agent.The final and in
- Karel'skii, V. N.,Krysin, E. P.,Rostovskaya, G. E.,Antonov, A. A.,Smirnov, M. B.
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p. 520 - 523
(2007/10/02)
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- STUDIES ON AMINO ACIDS AND PEPTIDES - VII SYNTHESES OF ASPARTAME AND THIOASPARTAME
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The protected aspartame, 4, has been prepared from the benzyl ester of N-benzyloxycarbonyl-S-aspartic acid, 1, and the methyl S-phenylalanate, 3, using 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide, LR, as a coupling reagent.Another protected aspartame, 7, has been prepared from the tert-butyl ester of 1--succinimide, 6, and methyl S-phenylalanate, 3.Thiations of 4/7 by LR produces a protected thioaspartame, 5/9.Deprotection of 7 and 9 gives aspartame, 8, and the slightly sweet thioaspartame, 10, in high yields.
- Yde, B.,Thomsen, I.,Thorsen, M.,Clausen,K.,Lawesson, S.-O.
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p. 4121 - 4126
(2007/10/02)
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