Selenoimidazolium Salts as Supramolecular Reagents for Protein Alkylation

Chalcogen Bond-Driven Alkylations: Selenoxide-Pillar[5]arene as a Recyclable Catalyst for Displacement Reactions in Water

A novel strategy to catalyze alkylation reactions through chalcogen bond interaction using a supramolecular structure is presented herein. Utilizing just 1.0 mol % of selenoxide-pillar[5]arene (P[5]SeO) as the catalyst we achieved efficient catalysis in the cyanation of benzyl bromide in water. Our approach demonstrated high efficiency and effectiveness, with the results supported by designed control experiments and theoretical models, highlighting the catalytic effect of the pillar[5]arene through noncovalent interactions. Quantum-chemical calculations (ωB97X-D/def2-TZVP@SMD) pointed out that the catalyzed cyanation reaction followed an SN2-like mechanism, with energy barriers (ΔH≠) ranging from 16.7 to 18.2 kcal mol-1, exhibiting dissociative character depending on the para-substituent. 1H NMR analysis revealed that P[5]SeO acted as a catalyst through inclusion complex formation, facilitating the transfer of the electrophilic substrate to the aqueous solution for nucleophilic displacement. Our reaction protocol proved applicable to various substrates, including aromatic and alpha-carbonyl derivatives. The use of sodium azide as the nucleophile was also feasible. Importantly, our method allowed scalability, and the catalyst P[5]SeO could be recovered and reused effectively for multiple reaction cycles, showcasing sustainability.

Telluride-Based Pillar[5]arene: A Recyclable Catalyst for Alkylation Reactions in Aqueous Solution

The syntheses of previously unknown sulfide- and telluride-pillar[n]arenes are reported here. These macrocycles, among others, were tested as catalysts for alkylation reactions in aqueous solutions. Telluride-pillar[5]arene (P[5]-TePh) showed the best performance, emulating the behavior of the methyltransferase enzyme cofactor S-adenosyl-l-methionine. Using 1.0 mol % of P[5]-TePh, benzyl bromides reacted with NaCN/NaN3 in water, yielding organic nitriles/azides. The catalyst was recycled and efficiently reused for up to six cycles. 1H NMR experiments indicate a possible interaction between the substrate and P[5]-TePh's cavity.

Chemical modification of proteins - challenges and trends at the start of the 2020s

Ribosomally expressed proteins perform multiple, versatile, and specialized tasks throughout Nature. In modern times, chemically modified proteins, including improved hormones, enzymes, and antibody-drug-conjugates have become available and have found advanced industrial and pharmaceutical applications. Chemical modification of proteins is used to introduce new functionalities, improve stability or drugability. Undertaking chemical reactions with proteins without compromising their native function is still a core challenge as proteins are large conformation dependent multifunctional molecules. Methods for functionalization ideally should be chemo-selective, site-selective, and undertaken under biocompatible conditions in aqueous buffer to prevent denaturation of the protein. Here the present challenges in the field are discussed and methods for modification of the 20 encoded amino acids as well as the N-/C-termini and protein backbone are presented. For each amino acid, common and traditional modification methods are presented first, followed by more recent ones.

Development and Recent Advances in Lysine and N-Terminal Bioconjugation for Peptides and Proteins

The demand for creation of protein diversity and regulation of protein function through native protein modification and post-translational modification has ignited the development of selective chemical modification methods for peptides and proteins. Chemical bioconjugation offers selective functionalization providing bioconjugates with desired properties and functions for diverse applications in chemical biology, medicine, and biomaterials. The amino group existing at the lysine residue and N-terminus of peptides and proteins has been extensively studied in bioconjugation because of its good nucleophilicity and high surface exposure. Herein, we review the development of chemical methods for modification of the amino groups on lysine residue and N-terminus featuring excellent selectivity, mild reaction conditions, short reaction time, high conversion, biocompatibility, and preservation of protein integrity. This review is organized based on the chemoselectivity and site-selectivity of the chemical bioconjugation reagents to the amino acid residues aiming to provide guidance for the selection of appropriate bioconjugation methods.

Synthetic application of chalcogenonium salts: beyond sulfonium

The application of chalcogenonium salts in organic synthesis has grown enormously in the past decades since the discovery of the methyltransferase enzyme cofactor S-adenosyl-L-methionine (SAM), featuring a sulfonium center as the reactive functional group. Chalcogenonium salts can be employed as alkylating agents, sources of ylides and carbon-centered radicals, partners for metal-catalyzed cross-coupling reactions and organocatalysts. Herein, we will focus the discussion on heavier chalcogenonium salts (selenonium and telluronium), presenting their utility in synthetic organic transformations and, whenever possible, drawing comparisons in terms of reactivity and selectivity with the respective sulfonium analogues.

Chemical technologies for precise protein bioconjugation interfacing biology and medicine

Proteins provide an excellent means to monitor and regulate biological processes. Hence, a precise chemical toolbox for their modification becomes indispensable. In this perspective, this feature article outlines our efforts to establish the core principles of chemoselectivity, site-selectivity, site-specificity, site-modularity, residue-modularity, and protein-specificity. With the knowledge to systematically regulate these parameters, the field has access to technological platforms that can address multiple challenges at the interface of chemistry, biology, and medicine.