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1. Chemoenzymatic Semi‐synthesis Enables Efficient Production of Isotopically Labeled α‐Synuclein with Site‐Specific Tyrosine Phosphorylation

   https://doi.org/10.1002/cbic.202000742  

   Pan, Buyan ; Park, Joo Hyung ; Ramlall, Trudy ; Eliezer, David ; Rhoades, Elizabeth ; Petersson, E. James ( January 2021 , ChemBioChem)

   Post‐translational modifications (PTMs) can affect the normal function and pathology of α‐synuclein (αS), an amyloid‐fibril‐forming protein linked to Parkinson's disease. Phosphorylation of αS Tyr39 has recently been found to display a dose‐dependent effect on fibril formation kinetics and to alter the morphology of the fibrils. Existing methods to access site‐specifically phosphorylated αS for biochemical studies include total or semi‐synthesis by native chemical ligation (NCL) as well as chemoenzymatic methods to phosphorylate peptides, followed by NCL. Here, we investigated a streamlined method to produce large quantities of phosphorylated αS by co‐expressing a kinase with a protein fragment inEscherichia coli. We also introduced the use of methyl thioglycolate (MTG) to enable one‐pot NCL and desulfurization. We compare our optimized methods to previous reports and show that we can achieve the highest yields of site‐specifically phosphorylated protein through chemoenzymatic methods using MTG, and that our strategy is uniquely well suited to producing¹⁵N‐labeled, phosphorylated protein for NMR studies.

    

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2. Coupling of sterically demanding peptides by β-thiolactone-mediated native chemical ligation

   https://doi.org/10.1039/c7sc04744d  

   Chen, Huan ; Xiao, Yunxian ; Yuan, Ning ; Weng, Jiaping ; Gao, Pengcheng ; Breindel, Leonard ; Shekhtman, Alexander ; Zhang, Qiang ( January 2018 , Chemical Science)

   The ligation of sterically demanding peptidyl sites such as those involving Val–Val and Val–Pro linkages has proven to be extremely challenging with conventional NCL methods that rely on exogenous thiol additives. Herein, we report an efficient β-thiolactone-mediated additive-free NCL protocol that enables the establishment of these connections in good yield. The rapid NCL was followed by in situ desulfurization. Reaction rates between β-thiolactones and conventional thioesters towards NCL were also investigated, and direct aminolysis was ruled out as a possible pathway. Finally, the potent cytotoxic cyclic-peptide axinastatin 1 has been prepared using the developed methodology. 

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3. Umpolung Ala B Reagents for the Synthesis of Non‐Proteogenic Amino Acids, Peptides and Proteins**

   https://doi.org/10.1002/ange.202207153  

   Zhu, Feng ; Miller, Eric ; Powell, Wyatt C. ; Johnson, Kelly ; Beggs, Alexander ; Evenson, Garrett E. ; Walczak, Maciej A. ( June 2022 , Angewandte Chemie)

   Non‐proteogenic amino acids and functionalized peptides are important motifs in modern drug discovery. Here we report that Ala^Bcan serve as universal building blocks in the synthesis of a diverse collection of modified amino acids, peptides, and proteins. First, we develop the synthesis of Ala^Bfrom redox‐active esters of aspartic acid resulting in a series of β‐boronoalanine derivatives. Next, we show that Ala^Bcan be integrated into automated oligopeptide solid‐phase synthesis. Ala^Bis compatible with common transformations used in preparative peptide chemistry such as native chemical ligation and radical desulfurization as showcased by total synthesis of Ala^B‐containing ubiquitin. Furthermore, Ala^Breagents participate in Pd‐catalyzed reactions, including C−C cross‐couplings and macrocyclizations. Taken together, Ala^Bsynthons are practical reagents to access modified peptides, proteins, and in the synthesis of cyclic/stapled peptides.

    

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4. Umpolung Ala B Reagents for the Synthesis of Non‐Proteogenic Amino Acids, Peptides and Proteins**

   https://doi.org/10.1002/anie.202207153  

   Zhu, Feng ; Miller, Eric ; Powell, Wyatt C. ; Johnson, Kelly ; Beggs, Alexander ; Evenson, Garrett E. ; Walczak, Maciej A. ( June 2022 , Angewandte Chemie International Edition)

   Non‐proteogenic amino acids and functionalized peptides are important motifs in modern drug discovery. Here we report that Ala^Bcan serve as universal building blocks in the synthesis of a diverse collection of modified amino acids, peptides, and proteins. First, we develop the synthesis of Ala^Bfrom redox‐active esters of aspartic acid resulting in a series of β‐boronoalanine derivatives. Next, we show that Ala^Bcan be integrated into automated oligopeptide solid‐phase synthesis. Ala^Bis compatible with common transformations used in preparative peptide chemistry such as native chemical ligation and radical desulfurization as showcased by total synthesis of Ala^B‐containing ubiquitin. Furthermore, Ala^Breagents participate in Pd‐catalyzed reactions, including C−C cross‐couplings and macrocyclizations. Taken together, Ala^Bsynthons are practical reagents to access modified peptides, proteins, and in the synthesis of cyclic/stapled peptides.

    

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5. CyClick Chemistry for the Synthesis of Cyclic Peptides

   https://doi.org/10.1002/anie.201911900  

   Adebomi, Victor ; Cohen, Ryan D. ; Wills, Rachel ; Chavers, Holland Andrew Hays ; Martin, Gary E. ; Raj, Monika ( November 2019 , Angewandte Chemie International Edition)

   Here, we report a novel “CyClick” strategy for the macrocyclization of peptides that works in an exclusively intramolecular fashion thereby precluding the formation of dimers and oligomers via intermolecular reactions. The CyClick chemistry is highly chemoselective for the N‐terminus of the peptide with a C‐terminal aldehyde. In this protocol, the peptide conformation internally directs activation of the backbone amide bond and thereby facilitates formation of a stable 4‐imidazolidinone‐fused cyclic peptide with high diastereoselectivity (>99 %). This method is tolerant to a variety of peptide aldehydes and has been applied for the synthesis of 12‐ to 23‐membered rings with varying amino acid compositions in one pot under mild reaction conditions. The reaction generated peptide macrocycles featuring a 4‐imidazolidinone in their scaffolds, which acts as an endocyclic control element that promotes intramolecular hydrogen bonding and leads to macrocycles with conformationally rigid turn structures.

    

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