The Facile Solid-Phase Synthesis of Thiazolo-Pyrimidinone Derivatives

A thiazolo-pyrimidinone derivative library was developed through a facile solid-phase synthesis method. For the reaction, the thiazolo[4,5-d]pyrimidin-7(6H)-one structure was synthesized through efficient Thorpe-Ziegler and cyclization reactions. The thiazolo[4,5-d]pyrimidin-7(6H)-one derivative library with a diversity of three had a total of four synthesis steps and 57 compounds. In addition, the yield per synthesis step was 65-97%, which was very high. The developed synthesis method and compounds will be used to find compounds with biological activity through the thiazole derivative structure-activity relationship.

Cysteinylprolyl imide (CPI) peptide: a highly reactive and easily accessible crypto-thioester for chemical protein synthesis

A new crypto-thioester, cysteinylprolyl imide (CPI) peptide, offers a practical synthetic pathway and reliable reaction rate to be successfully applied to chemical protein synthesis.

Native chemical ligation (NCL) between the C-terminal peptide thioester and the N-terminal cysteinyl-peptide revolutionized the field of chemical protein synthesis. The difficulty of direct synthesis of the peptide thioester in the Fmoc method has prompted the development of crypto-thioesters that can be efficiently converted into thioesters. Cysteinylprolyl ester (CPE), which is an N–S acyl shift-driven crypto-thioester that relies on an intramolecular O–N acyl shift to displace the amide-thioester equilibrium, enabled trans-thioesterification and subsequent NCL in one pot. However, the utility of CPE is limited because of the moderate thioesterification rates and the synthetic complexity introduced by the ester group. Herein, we develop a new crypto-thioester, cysteinylprolyl imide (CPI), which replaces the alcohol leaving group of CPE with other leaving groups such as benzimidazolidinone, oxazolidinone, and pyrrolidinone. CPI peptides were efficiently synthesized by using standard Fmoc solid-phase peptide synthesis (SPPS) and subsequent on-resin imide formation. Screening of the several imide structures indicated that methyloxazolidinone-t-leucine (MeOxd-Tle) showed faster conversion into thioester and higher stability against hydrolysis under NCL conditions. Finally, by using CPMeOxd-Tle peptides, we demonstrated the chemical synthesis of affibody via N-to-C sequential, three-segment ligation and histone H2A.Z via convergent four-segment ligation. This facile and straightforward method is expected to be broadly applicable to chemical protein synthesis.

Oxazolidinone-Mediated Sequence Determination of One-Bead One-Compound Cyclic Peptide Libraries

A novel one-bead one-compound (OBOC) dual ring-opening/cleavage approach for cyclic peptide sequencing was developed. The method selectively modifies serine, cysteine, threonine, and/or glutamic acid to an oxazolidinone-derived moiety, thereby increasing the susceptibility of the modified peptide backbone toward hydrolysis. The resulting linear peptide was then sequenced in 1 min by tandem mass spectrometry on a quadrupole time-of-flight instrument incorporating two-dimensional liquid chromatography and ion mobility spectrometry separation. To evaluate this approach, a library of cyclic peptides was successfully sequenced with 98% overall accuracy, demonstrating its robustness and broad substrate scope.

Tryptophan-Containing Non-Cationizable Opioid Peptides - a new chemotype with unusual structure and in vivo activity

Recently, a new family of opioid peptides containing tryptophan came to the spotlight for the absence of the fundamental protonable tyramine 'message' pharmacophore. Structure-activity relationship investigations led to diverse compounds, characterized by different selectivity profiles and agonist or antagonist effects. Substitution at the indole of Trp clearly impacted peripheral/central antinociceptivity. These peculiarities prompted to gather all the compounds in a new class, and to coin the definition 'Tryptophan-Containing Non-Cationizable Opioid Peptides', in short 'TryCoNCOPs'. Molecular docking analysis suggested that the TryCoNCOPs can still interact with the receptors in an agonist-like fashion. However, most TryCoNCOPs showed significant differences between the in vitro and in vivo activities, suggesting that opioid activity may be elicited also via alternative mechanisms.

Modern tools for the chemical ligation and synthesis of modified peptides and proteins

The ability to improve nature's capacity by introducing modification of biological interest in proteins and peptides (P&P) is one of the modern challenges in synthetic chemistry. Due to the unfavorable pharmacokinetic properties, many native P&P are of little use as therapeutic agents. Today, few methods for the preparation of modified proteins are available. Initially introduced to realize the ligation between two standard peptidic sequences, and hence to afford native proteins, the modern chemical methodologies, in other words native chemical ligation, expressed ligation, Staudinger ligation, auxiliary mediated ligation, aldehyde capture, etc., can be virtually utilized to ligate a variety of peptidomimetic partners, allowing a systematic access to modified, unnatural large P&P.

Serine promoted synthesis of peptide thioester-precursor on solid support for native chemical ligation

Fmoc solid phase peptide synthesis of peptide thioesters by displacement of the cyclic urethane moiety obtained by the selective activation of C-terminal serine.

Fmoc solid phase peptide synthesis of thioesters for the chemical synthesis of proteins via native chemical ligation is a challenge. We have developed a versatile approach for direct synthesis of peptide thioesters from a solid support utilizing Fmoc chemistry. Peptide thioester synthesis is performed by the formation of a cyclic urethane moiety via a selective reaction of the backbone amide chain with the side group of serine. The activated cyclic urethane moiety undergoes displacement by a thiol to generate the thioester directly from the solid support. Importantly, the method activates the serine residue for the synthesis of peptide thioesters; thus it is fully automated and free of the types of resins, linkers, handles, and unnatural amino acids typically needed for the synthesis of peptide thioesters using Fmoc chemistry. The resulting thioester is free of epimerization and is successfully applied for the synthesis of longer peptides using NCL.

5-aminomethyloxazolidine-2,4-dione hybrid α/β-dipeptide scaffolds as inductors of constrained conformations: Applications to the synthesis of integrin antagonists

Peptidomimetics represent an attractive starting point for drug discovery programs; in particular, peptidomimetics that result from the incorporation of a heterocycle may take advantage of increased enzymatic stability and higher ability to reproduce the bioactive conformations of the parent peptides, resulting in enhanced therapeutic potential. Herein, we present mimetics of the α4β1 integrin antagonist BIO1211 (MPUPA-Leu-Asp-Val-Pro-OH), containing a aminomethyloxazolidine-2,4-dione scaffold (Amo). Interestingly, the retro-sequences PhCOAsp(OH)-Amo-APUMP including either (S)- or (R)-configured Amo displayed significant ability to inhibit the adhesion of α4β1 integrin expressing cells, and remarkable stability in mouse serum. Possibly, the conformational bias exerted by the Amo scaffold determined the affinity for the receptors. These peptidomimetics could be of interest for the development of small-molecule agents effective against inflammatory processes and correlated autoimmune diseases.

Site-selective chemical cleavage of peptide bonds

Site-selective cleavage of extremely unreactive peptide bonds is a very important chemical modification that provides invaluable information regarding protein sequence, and it acts as a modulator of protein structure and function for therapeutic applications. For controlled and selective cleavage, a daunting task, chemical reagents must selectively recognize or bind to one or more amino acid residues in the peptide chain and selectively cleave a peptide bond. Building on this principle, we have developed an approach that utilizes a chemical reagent to selectively modify the serine residue in a peptide chain and leads to the cleavage of a peptide backbone at the N-terminus of the serine residue. After cleavage, modified residues can be converted back to the original fragments. This method exhibits broad substrate scope and selectively cleaves various bioactive peptides with post-translational modifications (e.g. N-acetylation and -methylation) and mutations (d- and β-amino acids), which are a known cause of age related diseases.

Integrin Ligands with α/β-Hybrid Peptide Structure: Design, Bioactivity, and Conformational Aspects

Integrins are cell surface receptors for proteins of the extracellular matrix and plasma-borne adhesive proteins. Their involvement in diverse pathologies prompted medicinal chemists to develop small-molecule antagonists, and very often such molecules are peptidomimetics designed on the basis of the short native ligand-integrin recognition motifs. This review deals with peptidomimetic integrin ligands composed of α- and β-amino acids. The roles exerted by the β-amino acid components are discussed in terms of biological activity, bioavailability, and selectivity. Special attention is paid to the synthetic accessibility and efficiency of conformationally constrained heterocyclic scaffolds incorporating α/β-amino acid span.

Fmoc solid-phase synthesis of C-terminal modified peptides by formation of a backbone cyclic urethane moiety

A universal strategy for solid phase synthesis of various C-terminal modified peptides independent of type of resins, unnatural linkers, and handles is developed. Semi-permanent protection at the C-termini of peptides is also afforded by the method described.

Linear and cyclic hybrids of alternating thiophene-amino acid units: synthesis and effects of chirality on conformation and molecular packing

The dipeptide isostere 5-aminothiophene carboxylic acid has been combined with L-phenylalanine moieties to provide linear and cyclic hybrid oligopeptides. A suitable protecting group strategy and appropriate coupling methods have been developed to guarantee a high degree of enantiopurity of the resulting amides. Cyclic tetraamides have been efficiently obtained by macrocyclization of the linear derivatives. In the case of racemized cyclization precursors, two diastereomeric macrocycles (S,S/R,R and meso) have been isolated. Their crystal structures show clear effects of the stereogenic centers on the ring conformations and molecular packing.