Total Synthesis of Glycosylated Human Interferon-γ

Recent Progress in Synthetic and Biological Application of Diorganyl Diselenides

Diorganyl diselenides have emerged as privileged structures because they are easy to prepare, have distinct reactivity, and have broad biological activity. They have also been used in the synthesis of natural products as an electrophile in the organoselenylation of aromatic systems and peptides, reductions of alkenes, and nucleophilic substitution. This review summarizes the advancements in methods for the transformations promoted by diorganyl diselenides in the main functions of organic chemistry. Parallel, it will also describe the main findings on pharmacology and toxicology of diorganyl diselenides, emphasizing anti-inflammatory, hypoglycemic, chemotherapeutic, and antimicrobial activities. Therefore, an examination detailing the reactivity and biological characteristics of diorganyl diselenides provides valuable insights for academic researchers and industrial professionals.

Investigation of N-Glycan Functions in Receptor for Advanced Glycation End Products V Domain through Chemical Glycoprotein Synthesis

The receptor for advanced glycation end products (RAGE) plays a crucial role in inflammation-related pathways and various chronic diseases. Despite the recognized significance of N-glycosylation in the ligand-binding V domain (VD) of RAGE, a comprehensive understanding of the site-activity and structure-activity relationships is lacking due to the challenges in obtaining homogeneous glycoprotein samples through biological expression. Here, we combined chemical and chemoenzymatic approaches to synthesize RAGE-VD and its congeners with Asn3-glycosylation by incorporating precise N-glycan structures. Evaluation of these samples revealed that, in comparison to other RAGE-VD forms, α2,6-sialylated N-glycosylation at the Asn3 site results in more potent inhibition of HMGB1-induced nuclear factor-κB (NF-κB) expression in RAGE-overexpressing cells. Hydrogen/deuterium exchange-mass spectrum analysis revealed a sialylated RAGE-VD-induced interaction region within HMGB1. Conversely, Asn3 N-glycosylation in VD has negligible effects on RAGE-VD/S100B interactions. This study established an approach for accessing homogeneously glycosylated RAGE-VD and explored the modulatory effects of N-glycosylation on the interactions between RAGE-VD and its ligand proteins.

Deselenylative Acylation and Nitration of Monoselenides

A deselenylative protocol that enables the construction of the C-C and C-N bonds has been disclosed. By using acyl chloride/AgOTf as an efficient acylation reagent, diarylselenides smoothly undergo deselenylative acylation to produce a series of aroyl compounds. In addition, deselenylative nitration can be enabled by a mild nitration reagent consisting of TsCl and AgNO3, furnishing a diverse array of nitroaromatic compounds.

Total Chemical Synthesis of Glycosylated TREM2 Ectodomain

Mutations in a microglia-associated gene TREM2 increase the risk of Alzheimer's disease. Currently, structural and functional studies of TREM2 mainly rely on recombinant TREM2 proteins expressed from mammalian cells. However, using this method, it is difficult to achieve site-specific labeling. Here, we present the total chemical synthesis of the 116 amino acid TREM2 ectodomain. Rigorous structural analysis ensured correct structural fold after refolding. Treating microglial cells with refolded synthetic TREM2 enhanced microglial phagocytosis, proliferation, and survival. We also prepared TREM2 constructs with defined glycosylation patterns and found that glycosylation at N79 is critical to the thermal stability of TREM2. This method will provide access to TREM2 constructs with site-specific labeling, such as fluorescent labeling, reactive chemical handles, and enrichment handles, to further advance our understanding of TREM2 in Alzheimer's disease.

Recent advances on the synthesis of N-linked glycoprotein for the elucidation of glycan functions

Glycoproteins play roles in many biological events, while, the glycan structure-function relationship has remained to be studied. In order to understand glycan function, homogeneous glycoproteins have been synthesized. This review introduced recent progress of their synthetic approaches.

Stereoselective synthesis of glycosyl azides from anomeric hydroxides via protecting group manipulations

Herein, we report the direct conversion of anomeric hydroxides to glycosyl azides in one step using diphenylphosphoryl azide. Protecting group manipulations on the hexose sugars have enabled the stereoselective synthesis of either the α-glycosyl azides or the β-anomeric azides in moderate to very good yields. The reaction has also been successfully used to enable the synthesis of β-2-deoxy-2-aminoglucosyl azides.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Ligation Embedding Aggregation Disruptor Strategy Enables the Chemical Synthesis of PD-1 Immunoglobulin and Extracellular Domains

Chemical synthesis of proteins with aggregable or colloidal peptide segments presents a formidable task, as such peptides prove to be difficult for both solid-phase peptide synthesis and peptide ligation. To address this issue, we have developed ligation embedding aggregation disruptor (LEAD) as an effective strategy for the chemical synthesis of difficult-to-obtain proteins. The N,O/S-benzylidene acetals generated from Ser/Thr ligation and Cys/Pen ligation are found to effectively disrupt peptide aggregation, and they can be carried for sequential ligations toward protein synthesis. The effectiveness and generality of this strategy have been demonstrated with total syntheses of programmed cell death protein 1 immunoglobulin like V-type domain and extracellular domain.

Design and Synthesis of Glycosylated Cholera Toxin B Subunit as a Tracer of Glycoprotein Trafficking in Organelles of Living Cells

Glycosylation of proteins is known to be essential for changing biological activity and stability of glycoproteins on the cell surfaces and in body fluids. Delivering of homogeneous glycoproteins into the endoplasmic reticulum (ER) and the Golgi apparatus would enable us to investigate the function of asparagine-linked (N-) glycans in the organelles. In this work, we designed and synthesized an intentionally glycosylated cholera toxin B-subunit (CTB) to be transported to the organelles of mammalian cells. The heptasaccharide, the intermediate structure of various complex-type N-glycans, was introduced to the CTB. The synthesized monomeric glycosyl-CTB successfully entered mammalian cells and was transported to the Golgi and the ER, suggesting the potential use of synthetic CTB to deliver and investigate the functions of homogeneous N-glycans in specific organelles of living cells.

Automated Peptide Synthesizers and Glycoprotein Synthesis

The development and application of commercially available automated peptide synthesizers has played an essential role in almost all areas of peptide and protein research. Recent advances in peptide synthesis method and solid-phase chemistry provide new opportunities for optimizing synthetic efficiency of peptide synthesizers. The efforts in this direction have led to the successful preparation of peptides up to more than 150 amino acid residues in length. Such success is particularly useful for addressing the challenges associated with the chemical synthesis of glycoproteins. The purpose of this review is to provide a brief overview of the evolution of peptide synthesizer and glycoprotein synthesis. The discussions in this article include the principles underlying the representative synthesizers, the strengths and weaknesses of different synthesizers in light of their principles, and how to further improve the applicability of peptide synthesizers in glycoprotein synthesis.

Types of Interferons and Their Expression in Plant Systems

Interferons (IFNs) are divided into 3 types (type I, type II, and type III) on the basis of sequence homology and functional properties. Recombinant IFNs have been approved by regulatory agencies in many countries for clinical treatment of hepatitis B, hepatitis C, and other diseases; these IFNs are mainly produced in microorganisms and mammalian cell systems. However, there are serious obstacles to the production of recombinant IFNs in microorganism systems; for example, the recombinant IFN may have different glycosylation patterns from the native protein, be present in insoluble inclusion bodies, be contaminated with impurities such as endotoxins and nucleic acids, have a short half-life in human blood, and incur high production costs. Some medicinal proteins have been successfully expressed in plants and used in clinical applications, suggesting that plants may also be a good system for IFN expression. However, there are still many technical problems that need to be addressed before the clinical application of plant-expressed IFNs, such as increasing the amount of recombinant protein expression and ensuring that the IFN is modified with the correct type of glycosylation. In this article, we review the classification of IFNs, their roles in antiviral signal transduction pathways, their clinical applications, and their expression in plant systems.

Synthetic Thiol and Selenol Derived Amino Acids for Expanding the Scope of Chemical Protein Synthesis

Cells employ post-translational modifications (PTMs) as key mechanisms to expand proteome diversity beyond the inherent limitations of a concise genome. The ability to incorporate post-translationally modified amino acids into protein targets via chemical ligation of peptide fragments has enabled the access to homogeneous proteins bearing discrete PTM patterns and empowered functional elucidation of individual modification sites. Native chemical ligation (NCL) represents a powerful and robust means for convergent assembly of two homogeneous, unprotected peptides bearing an N-terminal cysteine residue and a C-terminal thioester, respectively. The subsequent discovery that protein cysteine residues can be chemoselectively desulfurized to alanine has ignited tremendous interest in preparing unnatural thiol-derived variants of proteogenic amino acids for chemical protein synthesis following the ligation-desulfurization logic. Recently, the 21st amino acid selenocysteine, together with other selenyl derivatives of amino acids, have been shown to facilitate ultrafast ligation with peptidyl selenoesters, while the advancement in deselenization chemistry has provided reliable bio-orthogonality to PTMs and other amino acids. The combination of these ligation techniques and desulfurization/deselenization chemistries has led to streamlined synthesis of multiple structurally-complex, post-translationally modified proteins. In this review, we aim to summarize the latest chemical synthesis of thiolated and selenylated amino-acid building blocks and exemplify their important roles in conquering challenging protein targets with distinct PTM patterns.

Diselenide-selenoester ligation in the chemical synthesis of proteins

Peptides and proteins represent an important class of biomolecules responsible for a plethora of structural and functional roles in vivo. Following their translation on the ribosome, the majority of eukaryotic proteins are post-translationally modified, leading to a proteome that is much larger than the number of genes present in a given organism. In order to understand the functional role of a given protein modification, it is necessary to access peptides and proteins bearing homogeneous and site-specific modifications. Accordingly, there has been significant research effort centered on the development of peptide ligation methodologies for the chemical synthesis of modified proteins. In this chapter we outline the discovery and development of a contemporary methodology called the diselenide-selenoester ligation (DSL) that enables the rapid and efficient fusion of peptide fragments to generate synthetic proteins. The practical aspects of using DSL for the preparation of chemically modified peptides and proteins in the laboratory is described. In addition, recent advances in the application of the methodology are outlined, exemplified by the synthesis and biological evaluation of a number of complex protein targets.

Sulfated Glycoprotein Synthesis

Chemical protein synthesis has achieved tremendous progress in the past decades. With the development of chemical ligation as powerful tools, the scope of synthetic protein is greatly expanded. Proteoglycans are a class of sulfated glycoproteins widely distributed on the cell surface and in the extracellular matrix, which are extensively engaged in cellular communication events. Consisting of protein backbone and glycosaminoglycan(s) side chain, proteoglycans are highly complex and heterogeneous in nature. Chemical synthesis provides facile and reliable approach to these molecules, with defined glycan structure and sulfation pattern. One remaining problem is that the acid-labile sulfates could hardly survive during the typical solid phase peptide synthesis (SPPS) process. In this chapter, strategic design of a "glycopeptide cassette" for the preparation of sulfated glycoprotein is described. In particular, we provide protocols for the chemical synthesis of ectodomain fragment (23-120) of sulfated glycoprotein syndecan-1.

Rapid one-pot iterative diselenide-selenoester ligation using a novel coumarin-based photolabile protecting group

The development of an iterative one-pot peptide ligation strategy is described that capitalises on the rapid and efficient nature of the diselenide–selenoester ligation reaction, together with photodeselenisation chemistry. This ligation strategy hinged on the development of a novel photolabile protecting group for the side chain of selenocysteine, namely the 7-diethylamino-3-methyl coumarin (DEAMC) moiety. Deprotection of this DEAMC group can be effected in a mild, reagent-free manner using visible light (λ = 450 nm) without deleterious deselenisation of selenocysteine residues, thus enabling a subsequent ligation reaction without purification. The use of this DEAMC-protected selenocysteine in iterative DSL chemistry is highlighted through the efficient one-pot syntheses of 60- and 80-residue fragments of mucin-1 as well as apolipoprotein CIII in just 2–4 hours.

A method for the rapid one-pot iterative assembly of proteins via diselenide–selenoester ligation (DSL) chemistry is described that capitalises on a novel coumarin-based photolabile protecting group for selenocysteine.

Chemical (neo)glycosylation of biological drugs

Biological drugs, specifically proteins and peptides, are a privileged class of medicinal agents and are characterized with high specificity and high potency of therapeutic activity. However, biologics are fragile and require special care during storage, and are often modified to optimize their pharmacokinetics in terms of proteolytic stability and blood residence half-life. In this review, we showcase glycosylation as a method to optimize biologics for storage and application. Specifically, we focus on chemical glycosylation as an approach to modify biological drugs. We present case studies that illustrate the success of this methodology and specifically address the highly important question: does connectivity within the glycoconjugate have to be native or not? We then present the innovative methods of chemical glycosylation of biologics and specifically highlight the emerging and established protecting group-free methodologies of glycosylation. We discuss thermodynamic origins of protein stabilization via glycosylation, and analyze in detail stabilization in terms of proteolytic stability, aggregation upon storage and/or heat treatment. Finally, we present a case study of protein modification using sialic acid-containing glycans to avoid hepatic clearance of biological drugs. This review aims to spur interest in chemical glycosylation as a facile, powerful tool to optimize proteins and peptides as medicinal agents.