Synthesis of azapeptides by the Fmoc/tert-butyl/polyamide technique
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Abstract:
A new synthesis of azapeptides for use in the study of a proteolytic enzyme associated with Alzheimer's disease is described. The method utilizes fluoren-9-ylmethoxycarbonyl (Fmoc) amino acid carbazates and hydrazides in the Fmoc/tert-butyl/polyamide technique. The preparation of these compounds is presented. Reaction of Fmoc-amino acid hydrazides with an appropriate aldehyde, followed by reduction, gave fully protected amino acid carbazate dipeptide synthon. These derivatives were used to prepare aza amino acid peptide analogues by reaction with a resin-bound amino group, activated with bis-2,4-dinitrophenyl carbonate in the presence of a base. With this activation of the amino group, hydantoin is formed in a major side-reaction, but the cyclisation could be virtually eliminated by omission of the base from the activation procedure. Upon final trifluoroacetic acid-mediated cleavage of the azapeptide, trifluoroacetylation of the N-terminal serine residue was observed.Keywords:
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Trifluoroacetic acid
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Peptide Synthesis
A series of Tfa-Leu-Y-Z-OMe and Tfa-X-Ala-Z-OMe, in which X, Y and Z are Gly, Ala, Val, Leu, Pro or Phe, were prepared from the corresponding Cbo-tripeptide methyl esters, respectively, and separation of these tripeptide derivatives by gas chromatography (GLC) was studied. It was found that the relationship between the amino acid composition of the tripeptides and their qi-values (relative retention values) analogous to the case of the dipeptides could be detectable, although there were some marked exceptions within our limited experiments.
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Abstract Organometallic dipeptide ester complexes of the general formula [(L)M(Cl)( K 2 ‐NH 2 CH 2 CONCH 2 CO 2 R)] ( 1 : LCp*, MRh, 2 : LCp*, MIr, 3 : Lη 6 ‐C 6 Me 6 , MRu) react smoothly with various α‐L‐amino acid esters in the presence of NEt 3 to yield the tripeptide ester complexes [(L)M(Cl)( K 2 ‐NH 2 CHR'CONCH 2 CONHCH 2 CO 2 R)] ( 5–7 ). In the same fashion chloro K 2 ‐tetrapeptide ester complexes 10 and 11 are obtained either from tripeptide ester complexes or by subsequent addition of two equivalents of amino acid ester to a dipeptide ester complex. When the strong base NaOMe is used in the reaction of the diglycine ester compounds with amino acid esters. K 3 ‐tripeptide ester complexes 12 and 13 are produced, in which one of the two coordinated peptide nitrogen atoms is pyramidal. The hexamethylbenzene ruthenium complexes 13 with tripeptide ligands are formed with very high diastereoselectivity. A plausible reaction mechanism for the metal‐promoted peptide synthesis is presented. Synthesis and isolation of the peptide esters proceeds without racemization.
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In this work, we describe the development of a computational screening approach for tripeptide-dipeptide co-assembly. Studies are carried out both in water and in oil–water mixtures, to evaluate possible candidates that give rise to hydrogels or more stable emulsions, respectively, through nanofibre formation. The results give rise to design rules for the identification of promising systems for numerous types of soft materials. The possibility of achieving innovative functional materials through the co-assembly of tripeptides and dipeptides is studied. In particular, coarse-grained simulations allowed for the extraction of some promising dipeptides that, together with H-aspartyl-phenylalanyl-phenylalanine-OH (DFF), are able to act as hydrogelators or emulsifiers with superior characteristics relative to DFF on its own.
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We have prepared a series of N-TFA-glycyl and N-TFA-l-prolyl dipeptide methyl ester from the corresponding dipeptide methyl esters by treating them with (TFA-Gly)2O and TFA-l-Pro-Cl, respectively. Separation of these tripeptide derivatives by G.L.C. was studied and a relationship between the amino acid compositions of the tripeptides and their qi-values (relative retention values) was observed, analogous to the case of the dipeptides previously reported.
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We have prepared a series of N-TFA-glycyl and N-TFA-L-prolyl dipeptide methyl ester from the corresponding dipeptide methyl esters by treating them with (TFA-Gly)2O and TFA-L-Pro-Cl, respectively. Separation of these tripeptide derivatives by G. L. C. was studied and a relationship between the amino acid compositions of the tripeptides and their qi-values (relative retention values) was observed, analogous to the case of the dipeptides previously reported.2)
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The creation of antagonists of substance P (SP) has been the focus of intensive research because of their potential as therapeutic agents. A conventional for an SP antagonist is the synthesis of SP analogs in which amino acids are substituted or some peptide bonds are modified. Another useful method is the screening of compounds from a sample file. This method, called random screening, led to the discovery of novel and potent non-peptide antagonists. Apart from these two strategies, we were able to design low-molecular weight antagonists from a known peptide lead. The search for the essential part for receptor binding, improvement of the stability against enzymatic metabolism, and chemical modifications led to a potent tripeptide (4, FR 113680). The molecular size of this tripeptide was reduced to a dipeptide structure such as 13, through newly designed branched tripeptides (510). Further optimization of the lysine part of 13 into (2 S, 4 R) Hyp and subsequent modification of the side chain parts culminated in the potent dipeptide antagonist (15, FK 888). The pharmacological profile of 15 as an antiasthma agent is also presented.
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A model tripeptide, Gly-L-Leu-L-Phe, was immobilized with activated aminomethyl polystyrene, and its C-terminal was reduced to an alcohol. This peptidyl alcohol was selectively hydrolyzed at the C-terminal amide bond to afford a polymer-supported dipeptide (Gly-L-Leu) and amino alcohol (Phe-OH). The amino alcohol, including its absolute configuration, was determined by labelling with (+)-MNB-COOH, and the dipeptide was reused for a determination of its C-terminal amino acids. The d, l-amino acids of the tripeptide were sequentially determined from the C-terminus.
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At present, most investigations involving the Maillard reaction models have focused on free amino acids (FAAs), whereas the effects of peptides on volatile products are poorly understood. In our study, the formation mechanism of pyrazines, which were detected as characteristic volatiles in sunflower seed oil, from the reaction system of glucose and lysine-containing dipeptides and tripeptides was studied. The effect of the amino acid sequences of the dipeptides and tripeptides on pyrazine formation was further highlighted. Four different dipeptides and six tripeptides were selected. The results showed that the production of pyrazines in the lysine-containing dipeptide models was higher than that in the tripeptide and control models. Compounds 2,5(6)-Dimethylpyrazine and 2,3,5-trimethylpyrazine were the main pyrazine compounds in the dipeptide models. Furthermore, the C- or N-terminal amino acids of lysine-containing dipeptides can exert an important effect on the formation of pyrazines. In dipeptide models with lysine at the C-terminus, the content of total pyrazines followed the order of Arg−Lys > His−Lys; the order of the total pyrazine content was Lys−His > Lys−Arg in dipeptide models with N-terminal lysine. Additionally, for the tripeptide models with different amino acid sequences, more pyrazines and a greater variety of pyrazines were detected in the tripeptide models with N-terminal lysine/arginine than in the tripeptide models with N-terminal histidine. However, the total pyrazine content and the percentage of pyrazines in the total volatiles were similar in the tripeptide models with the same amino acids at the N-terminus. This study clearly illustrates the ability of dipeptides and tripeptides containing lysine, arginine and histidine to form pyrazines, improving volatile formation during sunflower seed oil processing.
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