Use In Peptide Synthesis Research Articles

Synthesis of (2S,3R,4R)-Dihydroxyisoleucine for Use in Amatoxin Synthesis.

We report a streamlined synthesis of (2S,3R,4R)-4,5-dihydroxy isoleucine (DHIle), an amino acid found in α-amanitin, which appears to be critical for toxicity. This synthetic route is transition metal-free and enables the production of significant quantities of DHIle with suitable protection for use in peptide synthesis. Its incorporation into a cytotoxic amatoxin analog is reported.

Exploring the Chemical Properties and Medicinal Applications of Tetramethylthiocycloheptyne Sulfoximine Used in Strain-Promoted Azide-Alkyne Cycloaddition Reactions.

The recently developed compound, tetramethylthiocycloheptyne sulfoximine (TMTHSI), has shown to be a promising strained alkyne for strain-promoted azide-alkyne cycloaddition (SPAAC), metal-free click chemistry. This research explores the properties of TMTHSI-based compounds via three aspects: (1) large-scale production, (2) unique stability in acidic conditions and its subsequent use in peptide synthesis, and (3) the functionalization of antibodies. Here, it is shown that (1) scale-up is achieved on a scale of up to 100 g. (2) TMTHSI is remarkably stable against TFA allowing for the site-specific functionalization of peptides on resin. Finally, (3) the functionalization of an antibody with a model payload is very efficient, with antibody conjugation demonstrating more beneficial features such as a high yield and limited hydrophobicity as compared to other alkyne reagent conjugates. These results illustrate the high potential of TMTHSI for diverse bioconjugation applications, with production already being GMP-compatible and a highly efficient conversion resulting in attractive costs of goods.

Negishi Cross-Coupling Provides Alkylated Tryptophans and Tryptophan Regioisomers.

Mild transition‐metal catalysed cross‐couplings enable direct functionalisation of biocatalytically halogenated tryptophans with alkyl iodides, representing a new alternative for late‐stage derivatisations of halogenated aromatic amino acids. Moreover, this strategy enables preparation of (homo)tryptophan regioisomers in a simple two‐step synthesis using a Pd‐catalysed Negishi cross coupling. This method provides access to non‐canonical constitutional surrogates of tryptophan, ready for use in peptide synthesis.

FeCl3‐Mediated Boc Deprotection: Mild Facile Boc‐Chemistry in Solution and on Resin

AbstractA mild, practical, and straight forward method for Boc deprotection and its use in peptide synthesis both in solution and on solid support is presented. Boc protecting group is removed from the N‐terminal amino acid of the amino acid and the peptide using environment‐friendly cost‐effective Lewis acid, FeCl3. The deprotected amino group undergoes C−N bond formation with the next Boc‐protected amino acid in the presence of a suitable coupling reagent and base. A library of di‐ to tetrapeptides is synthesized with moderate to good yield from standard and nonstandard Boc‐protected amino acids in solution. Most importantly, this protocol can be used for the solid‐phase peptide synthesis (SPPS) using Boc‐protected amino acids on the acid‐sensitive Rink amide resin, which is usually used for Fmoc chemistry. This protocol thus allows practicing Boc chemistry in a greener manner, and on‐demand switching from Fmoc to Boc chemistry and vice‐versa while synthesizing one oligopeptide on the same resin. The inherent orthogonality of Fmoc and Boc chemistry allows facile synthesis of branched and cyclized peptides on the resin as well.

Cover Feature: A Versatile Boc Solid Phase Synthesis of Daptomycin and Analogues Using Site Specific, On‐Resin Ozonolysis to Install the Kynurenine Residue (Chem. Eur. J. 62/2019)

Sub-zero amino acid transformation: The cover demonstrates the low temperature conversion of the amino acid l-tryptophan to the unnatural l-Kynurenine (Kyn) under a beam of ozone. Kyn is essential to the bioactivity of the FDA-approved, clinically-used peptide antibiotic Daptomycin (Cubicin) but its unique molecular structure prevents its use in peptide synthesis. The canonical amino acid tryptophan is readily incorporated into the peptide sequence of Daptomycin; under ozonolysis rapid conversion into Kyn realises a novel chemical synthesis of the frontline antibiotic Daptomyin. More information can be found in the Full Paper by P. W. R. Harris, M. A. Brimble, et al. on page 14101.

General, Mild, and Metal-Free Synthesis of Phenyl Selenoesters from Anhydrides and Their Use in Peptide Synthesis.

A mild, practical, and simple procedure for phenyl selenoesters synthesis from several anhydrides and diphenyl diselenide was developed. This transition-metal-free method provides a straightforward entry to storable Fmoc-amino acid selenoesters which are effective chemoselective acylating reagents. An application to oligopeptide synthesis was illustrated.

Oxyma-T, expanding the arsenal of coupling reagents

Herein, we report a new oxime-based additive (Oxyma-T) with a similar structure to HONM and Oxyma-B for use in peptide synthesis. Oxyma-T produces less racemization than HOBt, HOAt, OxymaPure, and Oxyma-B during the stepwise solution-phase synthesis of Z-Phg-Pro-NH2. Moreover, it exhibits superior coupling efficiency in comparison to HOBt during the SPPS of an Aib-enkephalin pentapeptide. Racemization during segment coupling follows the order: HOBt>Oxyma-T>OxymaPure>HOAt>Oxyma-B.

Synthesis of stable C-linked ferrocenyl amino acids and their use in solution-phase peptide synthesis.

Incorporation of ferrocenyl group to peptides is an efficient method to alter their hydrophobicity. Ferrocenyl group can also act as an electrochemical probe when incorporated onto functional peptides. Most often, ferrocene is incorporated onto peptides post-synthesis via amide, ester or triazole linkages. Stable amino acids containing ferrocene as a C-linked side chain are potentially useful building units for the synthesis of ferrocene-containing peptides. We report here an efficient route to synthesize ferrocene-containing amino acids that are stable and can be used in peptide synthesis. Coupling of 2-ferrocenyl-1,3-dithiane and iodides derived from aspartic acid or glutamic acid using n-butyllithium leads to the incorporation of a ferrocenyl unit to the δ-position or ε-position of an α-amino acid. The reduction or hydrolysis of the dithiane group yields an alkyl or an oxo derivative. The usability of the synthesized amino acids is demonstrated by incorporating one of the amino acids in both C-terminus and N-terminus of tripeptides in solution phase.

Novel copoly(styrene-divinylbenzene)-resins with different phenylmethylamine groups for use in Peptide synthesis method.

Differently than the 4-methylbenzhydrylamine-resin (MBHAR) which contains a methyl group coupled to the phenylmethylamine-functionalized copoly(styrene-divinilbenzene) structure, alternative resins containing the electron-donating 4-tert-butyl- (BUBHAR) or the electron-withdrawing 2-chloro- (ClBHAR) and 2,4-chloro- (diClBHAR) groups were developed as potential supports for α- carboxamide peptide synthesis. Initially, a time-course investigation of HF cleavage reaction (0 °C) with these resins bearing the vasoconstrictor angiotensin II (AngII, DRVYIHPF) or its Gly(8)-AngII analogue revealed that the peptide- BUBHAR linkage is much more labile than those with ClBHAR or diClBHAR. HF cleavage times of near 2 h or longer than 24 h were needed for complete removal of peptide chains from these two classes of resin, respectively. By including MBHAR and benzhydrylamine-resins (BHAR) in this comparative study, the decreasing order of acid stability of the peptidyl- resin linkage was diClBHAR > ClBHAR > BHAR > MBHAR ~ BUBHAR. The same stability order was observed for the HCl/propionic acid hydrolysis reaction (130°C) with the Phe- or Gly-resins. These findings thus suggest that ClBHAR and diClBHAR are not appropriate for use in peptide synthesis. Nevertheless, these supports could still be tested as stationary phases for affinity chromatography. When placed into more apolar solvents, the beads of all of these resins exhibited a greater swelling (as measured by a microscope) or higher mobility of the polymer matrix (as measured with EPR experiments using spin-labeled beads). Moreover, under the latter approach, BUBHAR displayed a comparatively higher solvation degree than did MBHAR (in DCM, DMF and NMP), with slightly higher peptide synthesis yields as well.

Efficient and Practical Procedure for the Esterification of the Free α-Carboxylic Acid of Amino Acid Residues with β-(Trimethylsilyl)ethoxymethyl Chloride and Triisopropylsilyl Chloride

An efficient and practical procedure for the free α-carboxylic acid esterification of amino acid residues with β-(trimethylsilyl)ethoxymethyl chloride and triisopropylsilyl chloride is described. The reaction takes place under mild conditions and the expected protected amino acids are obtained in good to excellent yields. Our method provides a useful alternative for the C-terminal carboxylic acid protection of amino acids and peptides. Moreover, the removal of such protection was also achieved under mild conditions, without affecting either the other protecting groups at the α-amino moiety and side chains or the optical integrity at the α-position of the amino acid residues. Examples of their use in peptide synthesis are also illustrated.

Synthesis of Well‐Defined Polystyrene Rink Amide Soluble Supports and Their Use in Peptide Synthesis

A soluble polystyrene‐based support bearing a cleavable Rink amide moiety is synthesized and utilized for the iterative synthesis of an oligopeptide. This soluble support is obtained in three steps. First, a well‐defined polystyrene segment is prepared by atom transfer radical polymerization (ATRP) using a fluorenylmethyloxycarbonyl (Fmoc)‐protected amino‐functional ATRP initiator. After polymerization, the Fmoc‐protecting group is cleaved and the obtained primary amine is coupled to a commercial Knorr linker (also known as Rink amide linker). The formed Rink amide soluble support is characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. As a proof of concept, this soluble support is used for the synthesis of a model tetrapeptide Glycine‐Lysine‐Serine‐Arginine. This peptide is also prepared on a commercial Rink amide resin, in order to compare the advantages and drawbacks of soluble and solid supports. It is found that the soluble support allows efficient synthesis of the model oligopeptide. Interestingly, it also allows a precise monitoring of the oligomer synthesis by SEC and NMR. image

Access to Enantiomerically Pure cis‐ and trans‐β‐Phenylproline by High‐Performance Liquid Chromatography Resolution

The preparation of all four stereoisomers of the proline analog that bears a phenyl group attached to the β carbon either cis or trans to the carboxylic acid (cis- and trans-β-phenylproline, respectively) has been addressed. The methodology developed allows access to multigram quantities of the target amino acids in enantiomerically pure form and suitably protected for use in peptide synthesis. Racemic precursors of cis-β-phenylproline and trans-β-phenylproline were prepared from easily available starting materials and subjected to high-performance liquid chromatography enantioseparation. Semipreparative columns (250 × 20 mm) containing chiral stationary phases based on amylose (Chiralpak IA) (Daicel-Chiral Technologies Europe, Illkirch, France) or cellulose (Chiralpak IC) were used respectively for the resolution of the cis- and trans-β-phenylproline precursors.

Click to Join Peptides/Proteins Together

Copper(I) is able to catalyze Huisgen 1,3-dipolar cycloaddition in a "click" fashion. This copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction presents excellent chemoselectivity and occurs over a wide-range of reaction conditions. It shows tolerance to variation in both pH and solvent polarity, thereby facilitating the ligation of peptides and proteins to produce peptidomimetics and synthetic proteins. In addition, the only product formed is a 1,4-disubstituted-1,2,3-triazole moiety, in many aspects resembling the natural peptide bond, including hydrogen-bonding capability, planarity, distance between the 1 and 4 substituents, and conformational restriction of the peptide backbone; thus the triazole-backbone-modified peptide, in which a triazole replaces the amide bond, may be anticipated to present a secondary structure similar to that of its natural counterpart. This Focus Review describes the scope and applications of copper(I)-catalyzed alkyne–azide cycloaddition in synthetic peptide/protein chemistry.

Synthesis of bioorthogonal and crosslinking amino acids for use in peptide synthesis

The ability to incorporate non-canonical amino acids into proteins by genetic or chemical methods allows one to introduce novel chemical properties into a protein at a defined residue. Such a residue may then be modified using common organic transformations. In this way, the structure or function of the peptide may be altered without perturbing any of the other neighbouring amino acids in the peptide chain. Here, we describe the syntheses and potential applications of multiple para-substituted phenylalanine derivatives comprising an isothiocyanate, α-diazoketone, or nitrone functionality. In all, three novel amino acids were synthesized in good overall yields. These non-canonical amino acids permit the further development of in vitro and in vivo chemoselective and regioselective bioconjugate reactions not possible with other reagents.

Synthesis and photophysical properties of a new amino acid possessing a BODIPY moiety

The synthesis of a new amino acid possessing a BODIPY fluorophore, which is of use in peptide synthesis, is described. The influence of the amino acid as well as of benzoxazole moieties on the BODIPY spectral and photophysical properties is discussed. The photophysical properties of this fluorophore were modified only to a small extent compared to those of the parent compound.

Synthesis of 1,1-Dioxobenzo[b]thiophene-2-ylmethyloxycarbonyl (Bsmoc) Protected N-Methyl Amino Acids by Reduction of Bsmoc-5-Oxazolidinones and Their Use in Peptide Synthesis

The synthesis of Bsmoc-N-methyl amino acids is presented. The first step involves p-toluenesulfonic acid (TsOH) catalysed condensation of a Bsmoc-amino acid with paraformaldehyde to furnish N-Bsmoc-5-oxazolidinone under MW irradiation. This intermediate is reduced to the corresponding N-methyl amino acid using triethylsilane (Et3SiH) and trifluoroacetic acid (TFA) at r.t. The N-methyl amino acids are converted into corresponding acid fluorides using diethylaminosulfur trifluoride (DAST) and employed as coupling agents in the synthesis of dipeptides. The peptide coupling was mediated by KOAt in CH2Cl2.

Straightforward Synthesis of Chiral Silylated Amino Acids through Hydrosilylation

AbstractA method using hydrosilylation of unsaturated amino acids was developed and optimised to obtain silylated amino acids. The platinum (Bu4N)2PtCl6 complex was identified as the best catalyst, and the procedure tolerated different unsaturated substrates, silane reagents and protecting groups. Seven silicon‐containing α‐amino acids were prepared in an enantiomerically pure form under mild conditions in good yields with orthogonal protections for versatile use in peptide synthesis.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Efficient access to N-protected derivatives of ( R, R, R)- and ( S, S, S)-octahydroindole-2-carboxylic acid by HPLC resolution

The preparation of the proline analogue (2 S,3a S,7a S)-octahydroindole-2-carboxylic acid (Oic) and its enantiomer, (2 R,3a R,7a R)-Oic, is described. A racemic precursor has been synthesized in good yield and subjected to HPLC resolution on a chiral column. The high efficiency of both the synthetic and chromatographic procedures has allowed the isolation of multigram quantities of each amino acid in enantiomerically pure form and suitably protected for use in peptide synthesis.

Synthesis of enantiomerically pure β,β-diphenylalanine (Dip) and fluorenylglycine (Flg)

A new strategy for the preparation of both enantiomers of two phenylalanine analogues, β,β-diphenylalanine and fluorenylglycine, has been developed. The combination of a high yielding racemic synthesis and a very efficient resolution procedure has provided significant amounts of each amino acid in enantiomerically pure form and suitably protected for use in peptide synthesis. This methodology can be easily applied to the preparation of larger quantities of enantiopure compounds.

Isosteric replacement of sulfur with other chalcogens in peptides and proteins

The review addresses the functional and structural properties of the two series of chalcogen analogues of amino acids in peptides and proteins, the methionine and the serine/cysteine series, and discusses the synthesis of the related selenium/tellurium analogues as well as their use in peptide synthesis and protein expression. Advances in synthetic methodologies and recombinant technologies and their combined applications in native and expressed protein ligation allows the isomorphous character of selenium- and tellurium-containing amino acids to be exploited for production of heavy metal mutants of proteins and thus to facilitate the phasing problem in x-ray crystallography. In addition, selenocysteine has been recognized as an ideal tool for the production of selenoenzymes with new catalytic activities. Moreover, the fully isomorphous character of disulfide replacement with diselenide is well suited to increase the robustness of cystine frameworks in cystine-rich peptides and proteins and for the de novo design of even non-native cystine frameworks by exploiting the highly negative redox potential of selenols.