A mild capping method for SPPS on the N-methyl diaminobenzoyl linker: Synthesis of an N-acyl urea appended C. elegans neuropeptide

Review on the o-Aminoaniline Moiety in Peptide and Protein Chemistry

Peptides and proteins are important functional biomolecules both inside and outside of living organisms. The ability to prepare various types of functionalized peptides and proteins is essential for understanding fundamental biological processes, such as protein folding and post-translational modifications (PTMs), and for developing new therapeutics for many diseases, such as cancers and neurodegenerative diseases. The o-aminoaniline moiety was first proposed for activation to a thioester precursor and used for native chemical ligation to prepare large peptides and proteins. In the past decade, the function of o-aminoaniline has been greatly expanded to facilitate the preparation of homogeneously modified peptide and protein samples, where the modifications can include cyclization, C-terminus diversification, etc. Many o-aminoaniline derivatives have also been developed to overcome the inherent limitations of previous versions. In this review, we attempt to summarize the recent developments of different o-aminoaniline derivatives, focusing on their application to the preparation of functional peptide and protein molecules.

Solid-Phase Synthesis of Peptide Hydrazides: Moving Toward Green Chemistry

Peptide hydrazides are widely applied as precursors of peptide thioesters, valuable building blocks for the synthesis of proteins by native chemical ligation. In addition, they can be applied for the selective modification of cargo or carrier molecules using hydrazone ligation technique. In this work, we describe key aspects of solid phase synthesis of peptide hydrazides on hydrazine 2CT and hydrazone resin. Special attention is paid to the optimization of synthetic procedures using "preferred" and "usable" organic solvents. Thus, optimization of 2-CTC resin loading with Fmoc-hydrazine permits to reduce reagents consumption and avoid DMF and DCM application. The final products can be released from the polymer support with simultaneous BOC removal with 5% HCl (aq) in acetone. Although this protocol demands subsequent peptide deprotection to remove other protecting groups, it benefits of significantly reduced TFA consumption. Because of improved stability in acidic conditions and the possibility of selective Mtt removal and peptide cleavage in green solvents, hydrazone resin can be considered as a useful alternative for peptide hydrazides synthesis. Obtained results can simplify the synthesis of peptide building blocks for native chemical ligation using CMR-free reagents and solvents.

Synthesis of the l- and d-SH2 domain of the leukaemia oncogene Bcr-Abl

The d- and l-versions of the Bcr-Abl SH2 domain (12.7 kDa) were synthesized. Key optimizations included pseudoproline incorporation, N-terminal hydrophilic tail addition and mild N-acetoxy succinimide acetylation. Their folding and activity are as for the recombinant protein. Our results will enable engineering of mirror-image monobody antagonists of the central oncoprotein Bcr-Abl.

The d- and l-versions of the Bcr-Abl SH2 domain (12.7 kDa) were synthesized successfully and show similar folding as compared to a recombinantly expressed version.

Safety-catch linkers for Fmoc solid-phase synthesis of peptide thioesters and hydrazides by amide-to-imide activation

The use of C-terminal peptide thioesters and hydrazides in synthetic protein chemistry has inspired the search for optimal solid-phase peptide synthesis (SPPS) strategies for their assembly. However, peptide thioesters are not directly accessible by conventional Fmoc-SPPS owing to the nucleophilicity of the secondary amine required for Fmoc removal. Here, we report the mild and effective activation of the pGlu linker and a new safety-catch linker that was used for the convenient synthesis of peptide thioesters and hydrazides via efficient amide-to-imide activation followed by nucleophilic displacement.

Recent advances in the synthesis of C-terminally modified peptides

C-Terminally modified peptides are important for the development and delivery of peptide-based pharmaceuticals because they impact peptide activity, stability, hydrophobicity, and membrane permeability. Additionally, the vulnerability of C-terminal esters to cleavage by endogenous esterases makes them excellent pro-drugs. Methods for post-SPPS C-terminal functionalization potentially enable access to libraries of modified peptides, facilitating tailoring of their solubility, potency, toxicity, and uptake pathway. Apparently minor structural changes can significantly impact the binding, folding, and pharmacokinetics of the peptide. This review summarizes developments in chemical methods for C-terminal modification of peptides published since the last review on this topic in 2003.