Racemization In Peptide Synthesis Research Articles

Suppression of alpha-carbon racemization in peptide synthesis based on a thiol-labile amino protecting group

In conventional solid-phase peptide synthesis (SPPS), α-amino groups are protected with alkoxycarbonyl groups (e.g., 9-fluorenylmethoxycarbonyl [Fmoc]). However, during SPPS, inherent side reactions of the protected amino acids (e.g., α-C racemization and aspartimide formation) generate by-products that are hard to remove. Herein, we report a thiol-labile amino protecting group for SPPS, the 2,4-dinitro-6-phenyl-benzene sulfenyl (DNPBS) group, which is attached to the α-amino group via a S–N bond and can be quantitatively removed in minutes under nearly neutral conditions (1 M p-toluenethiol/pyridine). The use of DNPBS greatly suppresses the main side reactions observed during conventional SPPS. Although DNPBS SPPS is not as efficient as Fmoc SPPS, especially for synthesis of long peptides, DNPBS and Fmoc are orthogonal protecting groups; and thus DNPBS SPPS and Fmoc SPPS can be combined to synthesize peptides that are otherwise difficult to obtain.

Cysteine racemization in peptide synthesis: a new and easy detection method.

A new method has been developed for the rapid determination of D-cysteine contents in synthetic peptides. It is based on the reduction of cystine residues, when present, with tris-alkylphosphines, selective derivatization of the cysteine residues with 4-vinylpyridine, followed by acid hydrolysis of the (4-pyridylethyl)cysteine-peptides. Baseline enantiomeric resolution of the D,L-S-beta-(4-pyridylethyl)cysteine, and thus quantification of D-enantiomer contents at levels < or = 1%, is easily achieved by capillary zone electrophoresis exploiting the host-guest complexation principle with crown ethers or by gas chromatography on chiral glass capillary columns upon conventional derivatization of the hydrolysate. The acid-stability of the (4-pyridylethyl)cysteine derivative prevents racemization via thiazoline intermediates and allows for standardization of the acid hydrolysis-dependent racemization.

Effect of copper(II) chloride on suppression of racemization in peptide synthesis by the mixed anhydride and related methods.

In segment couplings by the mixed anhydride method using isobutyloxycarbonyl chloride, the use of copper(II) chloride as an additive suppressed racemization completely in the same manner as in the carbodiimide method reported previously. This was confirmed by employing a number of couplings between Z-dipeptides and amino acid esters. The racemization-suppressing effect of other compounds were also evaluated by employing one of these model couplings to be at best only limitedly effective. Copper(II) chloride was effective also in the related method using EEDQ. Thus, in the couplings where a low level of racemization was observed without an additive, the addition of copper(II) chloride eliminated racemization even at ambient temperature where EEDQ is usually used. The effectiveness of copper(II) chloride was confirmed also in the BOP-Cl method. In the presence of HOBt racemization was reduced to a low but still detectable level, while it was suppressed completely by the addition of copper(II) chloride.

Effect of copper(II) chloride on suppression of racemization in peptide synthesis by the carbodiimide method.

Copper(II) chloride was found to be an extremely efficient racemization-suppressing additive in the DCC method as compared with the hitherto known ones, by employing the model coupling Z-Gly-L-Val-OH + H-L-Val-OMe in DMF. Although some other copper salts also had a profound effect, copper(II) chloride was the best from the viewpoint of both racemization suppression and coupling efficiency. The effectiveness of copper(II) chloride was further confirmed by employing the EDC-mediated couplings of Z-Gly-containing dipeptides with amino acid esters or dipeptide esters, and those of Z-L-Ala (or L-Val)-L-Val-OH with amino acid esters or dipeptide esters. In almost all the cases studied, no detectable amount (less than 0.1%) of epimer was observed by the HPLC analysis in the presence of copper(II) chloride. This was also the case even with an extremely stringent coupling system Z-L-Pro-L-Val-OH + H-L-Pro-OMe. With reference to the mechanism of racemization suppression, it was found that copper(II) chloride has a strong ability to suppress the racemization of the 5(4H)-oxazolone, which may be formed from an activated carboxyl component during the coupling.

Racemization studies in peptide synthesis through the separation of protected epimeric peptides by reversed-phase high performance liquid chromatography.

Separation of protected epimeric peptides, Z-Gly-Xaa-Xbb-OMe (where Xaa and Xbb = chiral amino acid residues), by reversed-phase HPLC was utilized for studying racemization in peptide synthesis. Thus, the following factors which might affect the extent of racemization during the coupling by the carbodiimide method were investigated: the combination of amino acid residues to be coupled, coexisting tertiary amine salts, and the relative configuration of the amino acid residues. The following points were revealed: the combination of bulky residues at the coupling site results in extensive racemization in a polar solvent such as DMF, the amine hydrochlorides cause less racemization than the p-toluene-sulfonates in DMF, and the influence of relative configuration differs depending on the solvent and the individuality of the amino components. Furthermore, the racemization-suppressing effect of some additives in the carbodiimide method was reevaluated by employing the same procedure.

An Improvement of the Anderson Test by the Use of High Performance Liquid Chromatography

Abstract The replacement of the N-benzyloxycarbonyl (Z) group in the Anderson peptide (Z–Gly–l/d–Phe–Gly–OEt) by Z–l-Ala and the subsequent separation of the diastereomers of the resulting tetrapeptide by reversed-phase HPLC offer a more convenient version with higher accuracy to the original Anderson test for studying racemization in peptide synthesis.

ChemInform Abstract: Effect of Tertiary Amines and Amine Salts on Racemization in Peptide Synthesis.

ChemInformVolume 18, Issue 17 Natural Products ChemInform Abstract: Effect of Tertiary Amines and Amine Salts on Racemization in Peptide Synthesis. A. M. KOLODZIEJCZYK, A. M. KOLODZIEJCZYK Dep. Org. Chem., Techn. Univ., Gdansk, PolandSearch for more papers by this authorM. SLEBIODA, M. SLEBIODA Dep. Org. Chem., Techn. Univ., Gdansk, PolandSearch for more papers by this author A. M. KOLODZIEJCZYK, A. M. KOLODZIEJCZYK Dep. Org. Chem., Techn. Univ., Gdansk, PolandSearch for more papers by this authorM. SLEBIODA, M. SLEBIODA Dep. Org. Chem., Techn. Univ., Gdansk, PolandSearch for more papers by this author First published: April 28, 1987 https://doi.org/10.1002/chin.198717330AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue17April 28, 1987 RelatedInformation

Effect of tertiary amines and amine salts on racemization in peptide synthesis

An effect of different tertiary amines, anions and cations on yield, product purity and reaction rate in DCC‐mediated Ac‐Phe‐Leu‐OMe synthesis was studied. Degree of racemization and side‐product yields down to 0.05% were readily determined by HPLC. The increasing effect of tertiary amino salts on degree of racemization was determined more precisely than previously and, more interestingly, their suppression of N‐acylurea formation was discovered. Unexpectedly, we found that the suppressing effect of the racemization of l‐hydroxybenztriazole was completely blocked by tribenzylamine. Furthermore, kinetic investigation showed that degree of racemization was not directly linked with 5(4H)‐oxazolone formation and aminolysis. The much greater racemization observed than calculated from the rate of formation and aminolysis of 5(4H)‐oxazolone led us to the conclusion that an activated form of Ac‐Phe other than 5(4H)‐oxazolone could be co‐responsible for racemization in the investigated reaction. An efficient method for preparation of N‐(acetyl‐DL‐phenylalanyl)‐dicyclohexylurea is described.

ChemInform Abstract: Influence of Additives on Suppression of Racemization in Peptide Syntheses.

AbstractThe effect of polymeric additives [polyacrylic acid (IVa) and its derivatives (IVb), (IVc)] on the suppression of racemization in peptide synthesis is investigated using the model reaction shown in the scheme.

ChemInform Abstract: Influence of Additives on Suppression of Racemization in Peptide Synthesis. Part 4. The Use of Additives for Suppression of Racemization in Peptide Synthesis by the Method of Mixed Anhydrides.

AbstractAnhand des Anderson‐Tests [Darstellung des Peptides (l)] wird die Wirkung verschiedener Zusätze auf die Unterdrückung der Racemisierung bei der Peptid‐Kondensation nach der Mischanhydrid‐Methode untersucht.

Studies on amino acids and peptides x : Hplc-mediated test of 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphos-phetane 2,4-disulfide (lawesson's reagent) as a racemization-free coupling reagent

The easily available 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadi-phosphetane 2,4-disulfide (Lawesson's Reagent), 1, has been tested as a coupling reagent for racemization in peptide synthesis. The assay procedure is separation of stereomeric products by HPLC. Z-S-Pro-S-Val-S-Pro-OtBu and Z-S-Leu-S-Phe-S-Val-OtBu have been used as test peptides in 2+1 segment couplings, and only a small amount of epimerization (0.5 and <0.1%, respectively) has been observed.

Determination of epimeric peptides for assessing enantiomeric purity of starting materials and studying racemization in peptide synthesis using high-performance liquid chromatography

Chromatography of the epimeric peptide pairs for the series Xxx-Lys, Lys-Yyy, Gly-Xxx-Lys, Gly-Lys-Yyy (Xxx is the activated residue during coupling, Yyy is the residue aminolysing the activated residue forming the peptide bond) and some neutral, acidic and N-methylated peptides on a μBondapak C1 8 column is described. Good resolution was achieved in most cases using isocratic elution with aqueous ammonium acetate, or buffers of lower pH. Observations on factors affecting retention of peptides are made, and the potential use of these model compounds for determining enantiomeric content in amino acid derivatives and studying racemization are discussed.

ChemInform Abstract: Quantitation and Sequence Dependence of Racemization in Peptide Synthesis

ChemInform Abstract: Quantitation and Sequence Dependence of Racemization in Peptide Synthesis

Copper(II) chloride as a new, efficient additive suppressing racemization in peptide synthesis by the carbodiimide method

Copper(II) chloride was found to be an extremely efficient additive suppressing racemization in the carbodiimide mediated couplings.

Influence of Additives on Suppression of Racemization in Peptide Synthesis. V. Additives Based on Liquid Crystal Forming Structure Elements for Suppressing Racemization in Reptide Synthesis by the DCC‐ and Mixed Anhydrides Methods

AbstractA new type of additives suppressing racemization during peptide synthesis by the DCC‐ and mixed anhydrides methods are liquid crystal forming organic molecules or similar compounds with a specific long chain structure. The suppressing effect of the new additives was followed by the Anderson test, the modified Young and n.m.r. tests. There was no racemization in a new Leu‐enkephalin synthesis by the mixed anhydrides method with azoxybenzene as additive.

ChemInform Abstract: RACEMIZATION IN PEPTIDE SYNTHESIS

Chemischer InformationsdienstVolume 11, Issue 5 Reviews ChemInform Abstract: RACEMIZATION IN PEPTIDE SYNTHESIS D. S. KEMP, D. S. KEMPSearch for more papers by this author D. S. KEMP, D. S. KEMPSearch for more papers by this author First published: February 5, 1980 https://doi.org/10.1002/chin.198005399AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue5February 5, 1980 RelatedInformation

RACEMIZATION IN PEPTIDE SYNTHESIS BY THE UGI REACTION

Abstract The Izumiya test for racemization in peptide synthesis was applied to examine the effect of solvent and temperature on racemization in the synthesis of a tripeptide derivative by the Ugi reaction (four-component condensation). Almost no racemization was observed under the reaction conditions using methanol and at low temperature.

A SERIES OF LYSYLDIPEPTIDE DERIVATIVES FOR RACEMIZATION STUDIES IN PEPTIDE SYNTHESIS

The series of diastereomeric peptide derivatives N-benzoyl-D,L-X-N epsilon-benzyloxycarbonyl-L-lysine methyl ester where X = alanyl, valyl, leucyl, phenylalanyl and isoleucyl are submitted as model systems for studying racemization in peptide synthesis. The diastereomers can be analyzed by quantitation of the separated ester methyl proton peaks of their nuclear magnetic resonance spectra. Data on the tendency to racemize of the different residues are presented. In polar solvents, valyl and isoleucyl residues racemize more readily than the other residues.

The dependence of racemization in peptide synthesis on the relative configuration of amino acids

The dependence of racemization in peptide synthesis on the relative configuration of amino acids

Amino-acids and peptides. 28. Determination of racemization in peptide synthesis by nuclear magnetic resonance spectroscopy.

Diastereoisomeric aromatic alanyl peptides possess different n.m.r. spectra owing to a diamagnetic shielding phenomenon. Observation of the shifted methyl resonance is an excellent procedure for the study of racemization in peptide synthesis. Eight alanyl dipeptides are available as models for the evaluation and testing of any N-acyl protecting group or coupling agent. The method is general, convenient, rapid, and sensitive.