Reactifs de couplage peptidique I (1) - l'hexafluorophosphate de benzotriazolyl N-oxytrisdimethylamino phosphonium (B.O.P.)

TiF4-catalyzed direct amidation of carboxylic acids and amino acids with amines

Unlike other metal fluorides, catalytic titanium tetrafluoride enhances the direct amidation of aromatic and aliphatic carboxylic acids and N-protected amino acids in refluxing toluene. While aromatic acids were converted to amides with 10 mol% of the catalyst within 24 h, aliphatic acids underwent a faster reaction (12 h), with lower catalyst loading (5 mol%). This protocol is equally efficient with alkyl and aryl amines providing a variety of carboxamides and peptides in 60-99% yields.

Design of Potent and Salt-Insensitive Antimicrobial Branched Peptides

Dendrimeric and branched peptides are polypeptides formed by diverse types of scaffolds to give them different forms. Previously, we reported a cascade-type, Lys-scaffolded antimicrobial peptide dendrimer D4R tethered with four RLYR tetrapeptides. Antimicrobial D4R is broad-spectrum, salt insensitive, and as potent as the natural-occurring tachyplesins, displaying minimum inhibitory concentrations (MIC) < 1 μM. However, the relationships between scaffolds and antimicrobial potency remain undefined. Here, we report the design of four novel types of peptide antimicrobials whose scaffolded backbones are lysine (Lys), iso-Lys, ornithine (Orn), or iso-Orn tethered with RLYR on their α- or sidechain-amines to give ε-, δ-, and their α-branched peptides. When assayed against ten microorganisms, the Lys-scaffolded α- and ε-branched peptides are broadly active, salt insensitive, and as potent as D4R and tachyplesins, whereas the corresponding Orn-scaffolded α- and δ-branched peptides are salt sensitive and much less potent, displaying MICs ranging from 1 to >500 μM. Structure-activity relationship studies suggested that Lys-scaffolds, but not Orn-scaffolds, can support a reverse turn to organize RLYR tetrapeptides as parallel β-strands to form an amphipathic structure with Leu-Tyr as a hydrophobic core. Together, these results provide a structural approach for designing potent and salt-insensitive dendrimeric or branched peptide antimicrobials.

Friedel-Crafts-Type Acylation and Amidation Reactions in Strong Brønsted Acid: Taming Superelectrophiles

In this review, we discuss Friedel-Crafts-type aromatic amidation and acylation reactions, not exhaustively, but mainly based on our research results. The electrophilic species involved are isocyanate cation and acylium cation, respectively, and both have a common ⁺C=O structure, which can be generated from carboxylic acid functionalities in a strong Brønsted acid. Carbamates substituted with methyl salicylate can be easily ionized to the isocyanate cation upon (di)protonation of the salicylate. Carboxylic acids can be used directly as a source of acylium cations. However, aminocarboxylic acids are inert in acidic media because two positively charged sites, ammonium and acylium cation, will be generated, resulting in energetically unfavorable charge-charge repulsion. Nevertheless, the aromatic acylation of aminocarboxylic acids can be achieved by using tailored phosphoric acid esters as Lewis bases to abrogate the charge-charge repulsion. Both examples tame the superelectrophilic character.

Acid catalysis through N-protonation in undistorted carboxamides: improvement of amide proton sponge acylating ability

Acid catalysis of weakly distorted or undistorted carboxamides in acyl-migration reactions proceeding through N-protonation is the process with low probability in contrast to O-protonation. This circumstance made the experimental study...

Generation of Oxyphosphonium Ions by Photoredox/Cobaloxime Catalysis for Scalable Amide and Peptide Synthesis in Batch and Continuous-Flow

Phosphine-mediated deoxygenative nucleophilic substitutions, such as the Mitsunobu reaction, are of great importance in organic synthesis. However, the conventional protocols require stoichiometric oxidants to trigger the formation of the oxyphosphonium intermediates for the subsequent nucleophilic additions. Through dual catalysis of photoredox and cobaloxime, we realized a radical strategy for the catalytic formation of acyloxyphosphonium ions that enables direct amidation. The deoxygenative protocol exhibits a broad scope and has been used in the late-stage amidation of drug molecules. In addition to batch reactions, a continuous-flow reactor was developed, enabling rapid peptide synthesis on gram scale. The successful assembly of a tetrapeptide on the solid support further demonstrated the versatility of this photocatalytic system. Moreover, experimental and computational studies are consistent with the hypothesis of acyloxyphosphonium ions being formed as the key intermediates.

Post-Synthetic Macrocyclization of Rotaxane Building Blocks

Although not often encountered, cyclic interlocked molecules are appealing molecular targets because of their restrained tridimensional structure which is related to both the cyclic and interlocked shapes. Interlocked molecules such as rotaxane building blocks may be good candidates for post-synthetic intramolecular cyclization if the preservation of the mechanical bond ensures the interlocked architecture throughout the reaction. This is obviously the case if the modification does not involve the cleavage of either the macrocycle's main chain or the encircled part of the axle. However, among the post-synthetic reactions, the chemical linkage between two reactive sites belonging to embedded elements of rotaxanes still consists of an underexploited route to interlocked cyclic molecules. This Review lists the rare examples of macrocyclization through chemical connection between reactive sites belonging to a surrounding macrocycle and/or an encircled axle of interlocked rotaxanes.

Synthesis of α-Amino Acid N-Carboxyanhydrides

A simple phosgene- and halogen-free method for synthesizing α-amino acid N-carboxyanhydrides (NCAs) is described. The reaction between Boc-protected α-amino acids and T3P reagent gave the corresponding NCA derivatives in good yield and purity with no detectable epimerization. The process is safe, is easy-to-operate, and does not require any specific installation. It generates nontoxic, easy to remove byproducts. It can apply to the preparation of NCAs for the on-demand on-site production of either little or large quantities.

Synthetic and computational efforts towards the development of peptidomimetics and small-molecule SARS-CoV 3CLpro inhibitors

Severe Acute Respiratory Syndrome (SARS) is a severe febrile respiratory disease caused by the beta genus of human coronavirus, known as SARS-CoV. Last year, 2019-n-CoV (COVID-19) was a global threat for everyone caused by the outbreak of SARS-CoV-2. 3CLpro, chymotrypsin-like protease, is a major cysteine protease that substantially contributes throughout the viral life cycle of SARS-CoV and SARS-CoV-2. It is a prospective target for the development of SARS-CoV inhibitors by applying a repurposing strategy. This review focuses on a detailed overview of the chemical synthesis and computational chemistry perspectives of peptidomimetic inhibitors (PIs) and small-molecule inhibitors (SMIs) targeting viral proteinase discovered from 2004 to 2020. The PIs and SMIs are one of the primary therapeutic inventions for SARS-CoV. The journey of different analogues towards the evolution of SARS-CoV 3CLpro inhibitors and complete synthetic preparation of nineteen derivatives of PIs and ten derivatives of SMIs and their computational chemistry perspectives were reviewed. From each class of derivatives, we have identified and highlighted the most compelling PIs and SMIs for SARS-CoV 3CLpro. The protein-ligand interaction of 29 inhibitors were also studied that involved with the 3CLpro inhibition, and the frequent amino acid residues of the protease were also analyzed that are responsible for the interactions with the inhibitors. This work will provide an initiative to encourage further research for the development of effective and drug-like 3CLpro inhibitors against coronaviruses in the near future.

Exploring Cyclic Sulfamidate Building Blocks for the Synthesis of Sequence-Defined Macromolecules

The preparation of sequence-defined macromolecules using cyclic sulfamidates on solid-phase is outlined. The challenges surrounding an AB+CD approach are described with focus on understanding the formation of ring-opened side products when using amide coupling reagents. To avoid undesired side product formation, a strategy of iterative ring-openings of cyclic sulfamidates on solid-phase is explored. Ring-opening on primary and secondary amines is successfully reported, generating both linear and branched chain growth. However, attempts to selectively cleave N-sulfate bearing sp³ -hybridized groups cannot be demonstrated, limiting the overall building block scope for this methodology. Consequently, the active ring-opening of cyclic sulfamidates on amine-functionalized oligo(amidoamine) backbones is successfully applied to produce sequence-defined, N-sulfated macromolecules.

Ammonia-borane as a Catalyst for the Direct Amidation of Carboxylic Acids

Ammonia-borane serves as an efficient substoichiometric (10%) precatalyst for the direct amidation of both aromatic and aliphatic carboxylic acids. In situ generation of amine-boranes precedes the amidation and, unlike the amidation with stoichiometric amine-boranes, this process is facile with 1 equiv of the acid. This methodology has high functional group tolerance and chromatography-free purification but is not amenable for esterification. The latter feature has been exploited to prepare hydroxyl- and thiol-containing amides.

Crystal structure of 1-(2,4,6-trichlorobenzoyloxy) benzotriazole (TCB-OBt): observation of uncommon intermolecular oxygen–oxygen interaction and synthetic application in amidation

A simple active ester (TCB-OBt) has a significant hallmark in synthetic organic chemistry and materials science.

Gram-Scale Preparation of C-Terminal-Modified Enkephalin Analogues by Typical Liquid-Phase Peptide Synthesis

This article describes the gram-scale liquid-phase peptide synthesis of C-terminal-modified enkephalin analogues that possess high analgesic efficacy in animals, high potency for mu and delta opioid receptors, and high metabolic stability and potential blood-brain barrier permeability. Despite the long cycle time and tedious purification steps, liquid-phase synthesis is still a preferred method for large-scale peptide synthesis due to its cost effectiveness (i.e., amount of amino acids and reagents required), easy detection, and isolation of impurities compared with solid-phase synthesis. A robust liquid-phase synthesis protocol is described, involving BOP-assisted coupling and Boc deprotection, which has been well established in the laboratory and is a useful synthetic protocol for cost-effective production of peptide drugs. © 2019 by John Wiley & Sons, Inc.

[MeArg1, NLe10]-apelin-12: Optimization of solid-phase synthesis and evaluation of biological properties in vitro and in vivo

Chemically modified peptide apelin-12 ([MeArg¹, NLe¹⁰]-apelin12, peptide M) is able to reduce reactive oxygen species (ROS) formation, cell death, and metabolic and ionic homeostasis disorders in experimental myocardial ischemia-reperfusion injury. These beneficial effects indicate the therapeutic potential of this compound in cardiovascular diseases. The goals of this work were to optimize the synthesis of peptide M, and to study its proteolytic stability and effect on the heart function of rabbits with doxorubicin (Dox) cardiomyopathy. We have developed a rational method of solid-phase synthesis of peptide M using the Fmoc methodology in combination with the temporary protection of the guanidine function of arginine residues by protonation (salt formation) during the formation of the amide bond. It avoids the formation of by-products, and simplifies the post-synthetic procedures, providing an increase in the yield of the final product of higher purity. Comparative evaluation of the proteolytic stability of peptide M and apelin-12 in human blood plasma was carried out using ¹H NMR spectroscopy. It was shown that the half-life of peptide M in plasma is approximately three times longer than that of apelin-12. Intravenous infusion of increasing doses of peptide M caused a gradual increase in left ventricular (LV) fractional shortening and ejection fraction in rabbits after 8 weeks of Dox administration (2 mg/kg weekly). The effect of the modified peptide on LV systolic dysfunction was significantly more pronounced than the effect of apelin-12, which suggests the promise of using this pharmacological agonist of the APJ receptor in patients with heart failure.

Amide Synthesis through the In Situ Generation of Chloro- and Imido-Phosphonium Salts

We describe a methodology for the amidation of carboxylic acids by generating phosphonium salts in situ from N-chlorophthalimide and triphenylphosphine. Aliphatic, benzylic, and aromatic carboxylic acids can be transformed into their amide counter parts using primary and secondary amines. This functional group interconversion is achieved at room temperature in good to excellent yields. Mechanistic work shows the in situ formation of chloro- and imido-phosphonium salts that react as activating agents for carboxylic acids and generate an acyloxy-phosphonium species.

An expeditious synthesis of thiazolidinones and tetathiazanones

In the present study, 4-thiazolidinones have been assembled by HBTU mediated three-component reaction of amine, aldehyde and mercapto acid derivatives at room temperature. The final compounds are obtained in excellent yields within 30 minutes.

Solid Phase synthesis of Amides Using Mukaiyama'S Reagent

A new solid-phase synthetic method using Mukaiyama's reagent under mild conditions is reported to prepare amides in high purity without purification after cleavage from the resins.

A Facile Synthesis of Acylhydrazines from Acylbenzotriazoles

Acylbenzotriazoles were found to react with substituted hydrazines and aqueous hydrazine under very mild conditions, thus affording a facile synthesis of three types of acylhydrazines in moderate to excellent yields.

Evaluation of a non-prime site substituent and warheads combined with a decahydroisoquinolin scaffold as a SARS 3CL protease inhibitor

A non-prime site substituent and warheads combined with a decahydroisoquinolin scaffold was evaluated as a novel inhibitor for severe acute respiratory syndrome (SARS) chymotrypsin-like protease (3CL^pro). The decahydroisoquinolin scaffold has been demonstrated to be an effective hydrophobic center to interact with S2 site of SARS 3CL^pro, but the lack of interactions at S3 to S4 site is thought to be a major reason for the moderate inhibitory activity. In this study, the effects of an additional non-prime site substituent on the scaffold as well as effects of several warheads are evaluated. For the introduction of a desired non-prime site substituent, amino functionality was introduced on the decahydroisoquinolin scaffold, and the scaffold was constructed by Pd(II) catalyzed diastereoselective ring formation. The synthesized decahydroisoquinolin inhibitors showed about 2.4 times potent inhibitory activities for SARS 3CL^pro when combined with a non-prime site substituent. The present results indicated not only the expected additional interactions with the SARS 3CL^pro but also the possibility of new inhibitors containing a fused-ring system as a hydrophobic scaffold and a new warhead such as thioacetal.

Acetylcholinesterase Inhibition and Antioxidant Activity of N-trans-Caffeoyldopamine and N-trans-Feruloyldopamine

Phenolic acids and their derivatives found in nature are well-known for their potential biological activity. In this study, two amides derived from trans-caffeic/ferulic acid and dopamine were synthesized and characterized by Fourier-transform infrared spectroscopy (FTIR), mass spectrometry, proton and carbon-13 nuclear magnetic resonance spectroscopy. The compounds were tested for the inhibition of acetylcholinesterase (AChE) from Electrophorus electricus and for antioxidant activity by scavenging 2,2-diphenyl-1-pycrylhydrazyl free radical (DPPH^•) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS^•+), reducing ferric ions, and ferrous ions chelation. N-trans-Feruloyldopamine displayed the highest inhibitory effect on AChE with half-maximal inhibitory concentration (IC₅₀) values of 8.52 μM. In addition, an in silico study was done to determine the most favorable AChE cluster with the synthesized compounds. Further, these clusters were investigated for binding positions at the lowest free binding energy. Both synthesized hydroxycinnamates were found to be better antioxidants than the parent acids in in vitro tests applied. N-trans-Caffeoyldopamine showed the best antioxidant activity in the three tested methods—against non-biological stable free radicals IC₅₀ 5.95 μM for DPPH^•, 0.24 μM for the ABTS^•+ method, and for reducing power (ascorbic acid equivalent (AAE) 822.45 μmol/mmol)—while for chelation activity against Fe²⁺ ions N-trans-feruloyldopamine had slightly better antioxidant activity (IC₅₀ 3.17 mM).

Thirteen decades of peptide synthesis: key developments in solid phase peptide synthesis and amide bond formation utilized in peptide ligation

A historical overview of peptide chemistry from T. Curtius to E. Fischer to M. Bergmann and L. Zervas is first presented. Next, the fundamentals of peptide synthesis with a focus on solid phase peptide synthesis by R. B. Merrifield are described. Immobilization strategies to attach the first amino acid to the resin, coupling strategies in stepwise peptide chain elongation, and approaches to synthesize difficult peptide sequences are also shown. A brief comparison between tert-butyloxycarbonyl (Boc)/benzyl (Bzl) strategy and 9-fluorenylmethoxycarbonyl (Fmoc)/tert-butyl (t -Bu) strategy utilized in solid phase peptide synthesis is given with an emphasis on the latter. Finally, the review focuses on the discovery and development of peptide ligation and the latest advances in this field including native amide bond formation strategies, these include the native chemical ligation, α-ketoacid-hydroxylamine ligation, and serine/threonine ligation which are the most commonly used chemoselective ligation methods that provide amide bond at the ligation site. This review provides an overview of the literature concerning the most important advances in the chemical synthesis of proteins and peptides covering the period from 1882 to 2017.

Chemoselective generation of acyl phosphates, acylium ion equivalents, from carboxylic acids and an organophosphate ester in the presence of a Brønsted acid

Reactions of an organophosphate ester with carboxylic acids proceeded smoothly and chemoselectively in the presence of a Brønsted acid, affording acyl phosphate intermediates, leading to formation of various functional aromatic ketones.

Chemical Synthesis of Antimicrobial Peptides

Solid-phase peptide synthesis (SPPS) is the method of choice for chemical synthesis of peptides. In this nonspecialist review, we describe commonly used resins, linkers, protecting groups, and coupling reagents in 9-fluorenylmethyloxycarbonyl (Fmoc) SPPS. Finally, a detailed protocol for manual Fmoc SPPS is presented.

Studies of Azetidin-2-one as a Reactive Enolate Synthon of β-Alanine for Condensations with Aldehydes and Ketones

Studies describe formation of the lithium enolate of N-(4-methoxybenzyloxy)azetidin-2-one (1) and characterization of representative aldol reactions with aldehydes and ketones. Diastereoselectivity features the production of anti-aldol adducts from α,β-unsaturated ketones and α-branched aliphatic aldehydes. The stereoselectivity is rationalized via closed, six-membered transition-state arrangements leading to the formation of Felkin-Anh and anti-Felkin products. Examples illustrate the direct incorporation of monocyclic β-lactams into a variety of molecular architectures. The utility of 1 as an enolate synthon of homoglycine (β-alanine) is illustrated by the efficient synthesis of novel β-amino acid derivatives, including complex 4-hydroxy-2-pyridinones.

Design of peptidase-resistant peptide inhibitors of myosin light chain kinase

Myosin light chain kinase (MLCK) is a key regulator of various forms of cell motility including smooth muscle contraction, cell migration, cytokinesis, receptor capping, secretion, etc. Inhibition of MLCK activity in endothelial and epithelial monolayers using cell-permeant peptide Arg-Lys-Lys-Tyr-Lys-Tyr-Arg-Arg-Lys (PIK, Peptide Inhibitor of Kinase) allows protecting the barrier capacity, suggesting a potential medical use of PIK. However, low stability of L-PIK in a biological milieu prompts for development of more stable L-PIK analogues for use as experimental tools in basic and drug-oriented biomedical research. Previously, we designed PIK1, H-(N^α Me)Arg-Lys-Lys-Tyr-Lys-Tyr-Arg-Arg-Lys-NH₂ , that was 2.5-fold more resistant to peptidases in human plasma in vitro than L-PIK and equal to it as MLCK inhibitor. In order to further enhance proteolytic stability of PIK inhibitor, we designed the set of six site-protected peptides based on L-PIK and PIK1 degradation patterns in human plasma as revealed by ¹ H-NMR analysis. Implemented modifications increased half-live of the PIK-related peptides in plasma about 10-fold, and these compounds retained 25-100% of L-PIK inhibitory activity toward MLCK in vitro. Based on stability and functional activity ranking, PIK2, H-(N^α Me)Arg-Lys-Lys-Tyr-Lys-Tyr-Arg-D-Arg-Lys-NH₂ , was identified as the most stable and effective L-PIK analogue. PIK2 was able to decrease myosin light chain phosphorylation in endothelial cells stimulated with thrombin, and this effect correlated with the inhibition by PIK2 of thrombin-induced endothelial hyperpermeability in vitro. Therefore, PIK2 could be used as novel alternative to other cell-permeant inhibitors of MLCK in cell culture-based and in vivo studies where MLCK catalytic activity inhibition is required. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

Synthesis and Evaluation of a Library of Fluorescent Dipeptidomimetic Analogues as Substrates for Modified Bacterial Ribosomes

Described herein are the synthesis and photophysical characterization of a library of aryl-substituted oxazole- and thiazole-based dipeptidomimetic analogues, and their incorporation into position 66 of green fluorescent protein (GFP) in lieu of the natural fluorophore. These fluorescent analogues resemble the fluorophore formed naturally by GFP. As anticipated, the photophysical properties of the analogues varied as a function of the substituents at the para position of the phenyl ring. The fluorescence emission wavelength maxima of compounds in the library varied from ∼365 nm (near-UV region) to ∼490 nm (visible region). The compounds also exhibited a large range of quantum yields (0.01-0.92). The analogues were used to activate a suppressor tRNACUA and were incorporated into position 66 of GFP using an in vitro protein biosynthesizing system that employed engineered ribosomes selected for their ability to incorporate dipeptides. Four analogues with interesting photophysical properties and reasonable suppression yields were chosen, and the fluorescent proteins (FPs) containing these fluorophores were prepared on a larger scale for more detailed study. When the FPs were compared with the respective aminoacyl-tRNAs and the actual dipeptide analogues, the FPs exhibited significantly enhanced fluorescence intensities at the same concentrations. Part of this was shown to be due to the presence of the fluorophores as an intrinsic element of the protein backbone. There were also characteristic shifts in the emission maxima, indicating the environmental sensitivity of these probes. Acridon-2-ylalanine and oxazole 1a were incorporated into positions 39 and 66 of GFP, respectively, and were shown to form an efficient Förster resonance energy transfer (FRET) pair, demonstrating that the analogues can be used as FRET probes.

O-Glycosylation methods in the total synthesis of complex natural glycosides

We highlight the total syntheses of 33 complex natural O-glycosides, with a particular focus on the O-glycosylation methods that enable the connection of the saccharides and aglycones.

A novel synthetic luteinizing hormone-releasing hormone (LHRH) analogue coupled with modified β-cyclodextrin: insight into its intramolecular interactions

BACKGROUND

Cyclodextrins (CDs) in combination with therapeutic proteins and other bioactive compounds have been proposed as candidates that show enhanced chemical and enzymatic stability, better absorption, slower plasma clearance and improved dose-response curves or immunogenicity. As a result, an important number of therapeutic complexes between cyclodextrins and bioactive compounds capable to control several diseases have been developed.

RESULTS

In this article, the synthesis and the structural study of a conjugate between a luteinizing hormone-releasing hormone (LHRH) analogue, related to the treatment of hormone dependent cancer and fertility, and modified β-cyclodextrin residue are presented. The results show that both the phenyl group of tyrosine (Tyr) as well as the indole group of tryptophan (Trp) can be encapsulated inside the cyclodextrin cavity. Solution NMR experiments provide evidence that these interactions take place intramolecularly and not intermolecularly.

CONCLUSIONS

The study of a LHRH analogue conjugated with modified β-cyclodextrin via high field NMR and MD experiments revealed the existence of intramolecular interactions that could lead to an improved drug delivery.

GENERAL SIGNIFICANCE

NMR in combination with MD simulation is of great value for a successful rational design of peptide-cyclodextrin conjugates showing stability against enzymatic proteolysis and a better pharmacological profile.

Design, Synthesis, and Optimization of Balanced Dual NK1/NK3 Receptor Antagonists

In connection with a program directed at potent and balanced dual NK1/NK3 receptor ligands, a focused exploration of an original class of peptidomimetic derivatives was performed. The rational design and molecular hybridization of a novel phenylalanine core series was achieved to maximize the in vitro affinity and antagonism at both human NK1 and NK3 receptors. This study led to the identification of a new potent dual NK1/NK3 antagonist with pK i values of 8.6 and 8.1, respectively.

Total synthesis of nucleoside antibiotic A201A

A201A, a unique nucleoside antibiotic with potent antibacterial activities, has been synthesized for the first time in a total of 47 steps in a highly modular and linear manner, highlighting the elaboration/incorporation of an unprecedented hexofuranoside unit bearing an exocyclic enol ether moiety.

Solid phase protein chemical synthesis

The chemical synthesis of peptides or small proteins is often an important step in many research projects and has stimulated the development of numerous chemical methodologies. The aim of this review is to give a substantial overview of the solid phase methods developed for the production or purification of polypeptides. The solid phase peptide synthesis (SPPS) technique has facilitated considerably the access to short peptides (<50 amino acids). However, its limitations for producing large homogeneous peptides have stimulated the development of solid phase covalent or non-covalent capture purification methods. The power of the native chemical ligation (NCL) reaction for protein synthesis in aqueous solution has also been adapted to the solid phase by the combination of novel linker technologies, cysteine protection strategies and thioester or N,S-acyl shift thioester surrogate chemistries. This review details pioneering studies and the most recent publications related to the solid phase chemical synthesis of large peptides and proteins.