Peptides: Chemistry, structure and biology

ChemInform, 2009

The most popular way to synthesize peptides is via the solidphase approach, mostly on a research scale, although progress is being made in large-scale production. The most evident example is Fuzeon, a commercial anti-HIV peptide, which is produced in multi-kilograms using a solid support for the synthesis of the fragments. Success in solid-phase peptide synthesis is heavily determined by the solid support. In this review we focus on the evolution of the solid support from the totally polystyrene-based resin used by Merrifield to the most sophisticated ones currently available on the market. These new resins offer access to previously inaccessible compounds as well as the possibility to be used in diverse applications but without losing stability. Moreover, these new supports are easy to handle. The final chapter of the review highlights the complex sequences that are difficult to achieve and the reasons for this. It then concludes by explaining the approaches that have been followed to synthesize such "difficult" peptides.

Tetrahedron, 1989

Journal of Combinatorial Chemistry, 2000

A method for solid-phase peptide synthesis in the N-to C-direction that delivers good coupling yields and a low degree of epimerization is reported. The optimized method involves the coupling, without preactivation, of the resin-bound C-terminal amino acid with excess amounts of amino acid tri-tert-butoxysilyl (Sil) esters, using HATU as coupling reagent and 2,4,6-trimethylpyridine (TMP, collidine) as a base. For the amino acids investigated, the degree of epimerization was typically 5%, except for Ser(t-Bu) which was more easily epimerized (ca. 20%). Five tripeptides (AA 1 -AA 2 -AA 3 ) with different properties were used as representative model peptides in the development of the synthetic method: Asp-Leu-Glu, Leu-Ala-Phe, Glu-Asp-Val, Asp-Ser-Ile, and Asp-D-Glu-Leu. The study used different combinations of HATU and TBTU as activating agents, N,N-diisopropylethylamine (DIEA) and TMP as bases, DMF and dichloromethane as solvents, and cupric chloride as an epimerization suppressant. The epimerization of AA 2 in the coupling of AA 3 was further reduced in the presence of cupric chloride. However, the use of this reagent also resulted in a decrease in loading onto the resin and significant cleavage between AA 1 and AA 2 . Experiments indicated that the observed suppressing effect of cupric chloride on epimerization in the present system merely seemed to be a result of a base-induced cleavage of the oxazolone system, the key intermediate in the epimerization process. Consequently, the cleavages were most pronounced in slow couplings. An improved synthesis of fully characterized amino acid tri-tert-butoxysilyl (Sil) ester hydrochloride building blocks is presented. The amino acid Sil esters were found to be stable as hydrochlorides but not as free bases. Although only a few peptides have been used in this study, we believe that the facile procedure devised herein should provide an attractive alternative for the solid-phase synthesis of short (six residues or less) C-terminally modified peptides, e.g., in library format.

Tetrahedron Letters, 1992

N-[9-(hydroxymethyl).2.tluorenyl] succinamic acid may be used as an anchoring linkage for the preparation of protected peptide segments in combination with Boc/Bzl' protection scheme. The new handle proved to be stable to the usual conditions of solid-phase peptide synthesis and gave the protected peptide in high yields and purities by neatment with piperidine or morpholine. Convergent solid-phase peptide synthesis appears to be the most plausible strategy for the synthesis of large peptides and proteins. 2 This strategy involves the preparation by solid-phase methodology of fully protected peptide segments, their purification in solution followed by their assembly on a new solid support and finally, the simultaneous cleavage of the side chain blocking groups and detachment of the target peptide from the resin. Ideally, preparation of protected peptide fragments requires a three-dimensional orthogonal scheme of protection involving both temporal and semipermanent blocking groups as well as a bifunctional linkage agent, handle which serves to attach the growing peptide to the resin. 3 Detachment of the peptide from the resin under sufficiently mild conditions leaves protecting groups unaffected and affords a fully protected intermediate suitable for later segment condensation. Up to now, several handles have been designed for this convergent strategy using the Boc/Bzl and Fmoc/r-Bu peptide synthesis chemistries. As far as the Boc/Bzl scheme of protection is concerned, protected peptides can be prepared by use of the photolabile ortho-nitrobenzyl4 and a-methylphenacyl5 handles, allyl-derived anchoring linkages [cleaved with Pd(0) in the presence of nucleophiles16 and nucleophile-and base-labile handles.7 These last ones offer the advantage that no special equipment is required (e. g. photolysis reactor for photolabile handles) and the use of sensitive reaction conditions is avoided (e.g. as those described for the cleavage of allyl-type handles). 6d Furthermore, the scale up should not represent any inconvenience. Our aim concentrates on the development of a new base-labile fluorene-derived handle which is easy to synthesize, stable to solid-phase peptide synthesis conditions, and capable of yielding the protected peptide quantitatively at the cleavage step.

The Journal of Organic Chemistry, 1991

ChemInform, 2006

The purpose of this article is to delineate strategic considerations and provide practical procedures to enable non-experts to synthesize peptides with a reasonable chance of success. This article is not encyclopedic but rather devoted to the Fmoc/tBu approach of solid phase peptide synthesis (SPPS), which is now the most commonly used methodology for the production of peptides. The principles of SPPS with a review of linkers and supports currently employed are presented. Basic concepts for the different steps of SPPS such as anchoring, deprotection, coupling reaction and cleavage are all discussed along with the possible problem of aggregation and side-reactions. Essential protocols for the synthesis of fully deprotected peptides are presented including resin handling, coupling, capping, Fmoc-deprotection, final cleavage and disulfide bridge formation. Index Entries: Solid phase peptide synthesis (SPPS); resin; Fmoc SPPS; coupling reagents; protecting groups; anchoring; side reaction.

Amino Acids, 2014

Here we review the strategies for the solidphase synthesis of peptides starting from the side chain of the C-terminal amino acid. Furthermore, we provide experimental data to support that C-terminal and side-chain syntheses give similar results in terms of purity. However, the stability of the two bonds that anchor the peptide to the polymer may determine the overall yield and this should be considered for the large-scale production of peptides. In addition, resins/linkers which do not subject to side reactions can be preferred for some peptides.

Journal of the American Chemical Society, 1998

Peptide targets for synthesis are often desired with C-terminal end groups other than the more usual acid and amide functionalities. Relatively few routes exist for synthesis of C-terminal-modified peptidessincluding cyclic peptidessby either solution or solid-phase methods, and known routes are often limited in terms of ease and generality. We describe here a novel Backbone Amide Linker (BAL) approach, whereby the growing peptide is anchored through a backbone nitrogen, thus allowing considerable flexibility in management of the termini. Initial efforts on BAL have adapted the chemistry of the tris(alkoxy)benzylamide system exploited previously with PAL anchors. Aldehyde precursors to PAL, e.g. 5-(4-formyl-3,5-dimethoxyphenoxy)valeric acid, were reductively coupled to the R-amine of the prospective C-terminal amino acid, which was blocked as a tert-butyl, allyl, or methyl ester, or to the appropriately protected C-terminal-modified amino acid derivative. These reductive aminations were carried out either in solution or on the solid phase, and occurred without racemization. The secondary amine intermediates resulting from solution amination were converted to the 9-fluorenylmethoxycarbonyl (Fmoc)-protected preformed handle derivatives, which were then attached to poly-(ethylene glycol)-polystyrene (PEG-PS) graft or copoly(styrene-1% divinylbenzene) (PS) supports and used to assemble peptides by standard Fmoc solid-phase chemistry. Alternatively, BAL anchors formed by onresin reductive amination were applied directly. Conditions were optimized to achieve near-quantitative acylation at the difficult step to introduce the penultimate residue, and a side reaction involving diketopiperazine formation under some circumstances was prevented by a modified protocol for N R-protection of the second residue/ introduction of the third residue. Examples are provided for the syntheses in high yields and purities of representative peptide acids, alcohols, N,N-dialkylamides, aldehydes, esters, and head-to-tail cyclic peptides. These methodologies avoid postsynthetic solution-phase transformations and are ripe for further extension.

Journal of the American Chemical Society, 1996

Cross-Linked Ethoxylate Acrylate Resin (CLEAR) supports were prepared by radical copolymerization, either in the bulk or suspension mode, of the branched cross-linker trimethylolpropane ethoxylate (14/3 EO/OH) triacrylate (1) with one or more of allylamine (2), 2-aminoethyl methacrylate‚HCl (3), poly(ethylene glycol-400) dimethacrylate (4), poly(ethylene glycol) ethyl ether methacrylate (5), and trimethylolpropane trimethacrylate (6). The resultant highly cross-linked copolymers by the bulk procedures were ground and sieved to particles, whereas the suspension polymerization procedure gave highly cross-linked spherical beaded supports. CLEAR polymeric supports showed excellent swelling properties in an unusually broad range of solvents, including water, alcohols, tetrahydrofuran, dichloromethane, and N,N-dimethylformamide. To demonstrate their usefulness for peptide synthesis, CLEAR supports were derivatized with an "internal reference" amino acid [norleucine] and a handle [5-(4-Fmocaminomethyl-3,5-dimethoxyphenoxy)valeric acid] and were tested for both batchwise and continuous-flow solidphase syntheses of challenging peptides such as acyl carrier protein (65-74), retro-acyl carrier protein (74-65), and the 17-peptide human gastrin-I. Comparisons to commercially available supports, e.g., polystyrene, Pepsyn K, Polyhipe, PEG-PS, TentaGel, and PEGA were also carried out. CLEAR supports are entirely stable under standard conditions of peptide synthesis but are in some cases labile to certain strong bases.

2020

In the frame of the present work, an efficient and sustainable aqueous solid-phase peptide synthesis was developed based on a novel sulfonated derivative of fluorenyl protecting group. The viability of this approach and its application range was demonstrated upon the assembly of 22 biologically active peptides. To make access to aqueous peptide synthesis, coupling efficency was assessed in water-based systems applying respective Nα-Smoc amino acids and using different activation approaches. In our hands, several water-compatible activating additives were found appropriate, with EDC-Cl, Oxima and HOPO being the most efficient ones. Our experiments showed that although coupling of amino acids in water gave reasonable yields and purity of peptides, the addition of organic co-solvents enhanced coupling performance significantly. Additional studies on enantiomeric composition showed no increased racemization levels during the ASPPS process. Ionic properties of the Smoc protecting group g...