Synthesis of glycoproteins

Development of Supramolecular Saccharide Sensors Based on Cyclodextrin Complexes and Self-assembling Systems

Cyclodextrins (CDs) are water-soluble host compounds having nano-size hydrophobic cavities that enable them to incorporate organic molecules in water. Optically inert CDs can be efficiently combined with various types of chromoionophores and fluoroionophores. In this study, using diverse combinations of phenylboronic acid fluorescent sensors and azoprobes with CDs, the unique saccharide recognition functions of CD, chemically modified CD, and CD gel complexes based on their synergistic function are clarified, thereby confirming their use as supramolecular saccharide sensors. To realize novel supramolecular chirality, the twisted structure of two ditopic azoprobes inside the γ-CD chiral cavity is controlled by multi-point recognition of guest ions in water. As different types of supramolecular saccharide sensors, phenylboronic acid-based self-assembling systems are also reviewed.

A palladium and gold catalytic system enables direct access to O- and S-linked non-natural glyco-conjugates

Here we report a straightforward cross-coupling method for the synthesis of non-natural glycoamino acids from alkyne-bearing monosaccharides and p-iodophenylalanine. Pd/Au-catalyzed Sonogashira coupling is tolerant to both O- and S-glycosides without any epimerization. In addition, no racemization of the amino acid was observed allowing direct access to the homogeneous glyco-conjugate in a single step. Notably, this Pd/Au catalytic system presents enhanced catalytic activity than conventional Pd/Cu and Pd-only platforms, and it further enables the convergent synthesis of glycodipeptides.

Synthesis of rhamnosylated arginine glycopeptides and determination of the glycosidic linkage in bacterial elongation factor P

We describe the synthesis and incorporation of α- and β-configured rhamnosyl arginine cassettes into Pseudomonas aeruginosa elongation factor P-derived glycopeptides. These were used to unequivocally determine the native anomeric configuration of the rhamnose moiety in EF-P.

A new class of N-linked protein glycosylation – arginine rhamnosylation – has recently been discovered as a critical modification for the function of bacterial elongation factor P (EF-P). Herein, we describe the synthesis of suitably protected α- and β-rhamnosylated arginine amino acid “cassettes” that can be directly installed into rhamnosylated peptides. Preparation of a proteolytic fragment of Pseudomonas aeruginosa EF-P bearing both α- and β-rhamnosylated arginine enabled the unequivocal determination of the native glycosidic linkage to be α through 2D NMR and nano-UHPLC-tandem mass spectrometry studies.

Chemical Methods for Encoding and Decoding of Posttranslational Modifications

A large array of posttranslational modifications can dramatically change the properties of proteins and influence different aspects of their biological function such as enzymatic activity, binding interactions, and proteostasis. Despite the significant knowledge that has been gained about the function of posttranslational modifications using traditional biological techniques, the analysis of the site-specific effects of a particular modification, the identification of the full complement of modified proteins in the proteome, and the detection of new types of modifications remains challenging. Over the years, chemical methods have contributed significantly in both of these areas of research. This review highlights several posttranslational modifications where chemistry-based approaches have made significant contributions to our ability to both prepare homogeneously modified proteins and identify and characterize particular modifications in complex biological settings. As the number and chemical diversity of documented posttranslational modifications continues to rise, we believe that chemical strategies will be essential to advance the field in years to come.

Chemical O-Glycosylations: An Overview

The development of glycobiology relies on the sources of particular oligosaccharides in their purest forms. As the isolation of the oligosaccharide structures from natural sources is not a reliable option for providing samples with homogeneity, chemical means become pertinent. The growing demand for diverse oligosaccharide structures has prompted the advancement of chemical strategies to stitch sugar molecules with precise stereo- and regioselectivity through the formation of glycosidic bonds. This Review will focus on the key developments towards chemical O-glycosylations in the current century. Synthesis of novel glycosyl donors and acceptors and their unique activation for successful glycosylation are discussed. This Review concludes with a summary of recent developments and comments on future prospects.

Synthesis of Glycosyl Amides Using Selenocarboxylates as Traceless Reagents for Amide Bond Formation

Carbohydrate-derived amides were successfully prepared in good yields from a broad range of substrates, including furanosyl and pyranosyl derivatives. The methodology successfully relied on the in situ generation of lithium selenocarboxylates from Se/LiEt3BH and acyl chlorides or carboxylic acids and their reaction with sugar azides. A key aspect of the present protocol is that we start from elemental selenium; isolation and handling of all reactive and sensitive selenium-containing intermediates is avoided, therefore providing the selenocarboxylate the status of a traceless reagent.

Cu-Catalyzed Click Reaction in Carbohydrate Chemistry

Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), popularly known as the "click reaction", serves as the most potent and highly dependable tool for facile construction of simple to complex architectures at the molecular level. Click-knitted threads of two exclusively different molecular entities have created some really interesting structures for more than 15 years with a broad spectrum of applicability, including in the fascinating fields of synthetic chemistry, medicinal science, biochemistry, pharmacology, material science, and catalysis. The unique properties of the carbohydrate moiety and the advantages of highly chemo- and regioselective click chemistry, such as mild reaction conditions, efficient performance with a wide range of solvents, and compatibility with different functionalities, together produce miraculous neoglycoconjugates and neoglycopolymers with various synthetic, biological, and pharmaceutical applications. In this review we highlight the successful advancement of Cu(I)-catalyzed click chemistry in glycoscience and its applications as well as future scope in different streams of applied sciences.

Efficient one-pot per-O-acetylation–thioglycosidation of native sugars, 4,6-O-arylidenation and one-pot 4,6-O-benzylidenation–acetylation of S-/O-glycosides catalyzed by Mg(OTf)2

Sequential one-pot per-O-acetylation–S-/O-glycosidation under neat condition, regioselective 4,6-O-arylidenation and sequential one-pot benzylidenation–acetylation of Mg(OTf)₂as non-hygroscopic, recyclable catalyst are reported.

Synthesis, evaluation and molecular docking studies of amino acid derived N-glycoconjugates as antibacterial agents

Six amino acid derived N-glycoconjugates of d-glucose were synthesized, characterized and tested for antibacterial activity against G(+)ve (Bacillus cereus) as well as G(-)ve (Escherichia coli and Klebsiella pneumoniae) bacterial strains. All the tested compounds exhibited moderate to good antibacterial activity against these bacterial strains. The results were compared with the antibacterial activity of standard drug Chloramphenicol, where results of A5 (Tryptophan derived glycoconjugates) against E. coli and A4 (Isoleucine derived glycoconjugates) against K. pneumoniae bacterial strains are comparable with the standard drug molecule. In silico docking studies were also performed in order to understand the mode of action and binding interactions of these molecules. The docking studies revealed that, occupation of compound A5 at the ATP binding site of subunit GyrB (DNA gyrase, PDB ID: 3TTZ) via hydrophobic and hydrogen bonding interactions may be the reason for its significant in vitro antibacterial activity.

A PEGylated photocleavable auxiliary mediates the sequential enzymatic glycosylation and native chemical ligation of peptides

Research aimed at understanding the specific role of glycosylation patterns in protein function would greatly benefit from additional approaches allowing direct access to homogeneous glycoproteins. Herein the development and application of an efficient approach for the synthesis of complex homogenously glycosylated peptides based on a multifunctional photocleavable auxiliary is described. The presence of a PEG polymer within the auxiliary enables sequential enzymatic glycosylation and straightforward isolation in excellent yields. The auxiliary-modified peptides can be directly used in native chemical ligations with peptide thioesters easily obtained by direct hydrazinolysis of the respective glycosylated peptidyl resins and subsequent oxidation. The ligated glycopeptides can be smoothly deprotected by UV irradiation. We apply this approach to the preparation of variants of the epithelial tumor marker MUC1 carrying one or more Tn, T, or sialyl-T antigens.

Highly transparent and stretchable field-effect transistor sensors using graphene-nanowire hybrid nanostructures

Transparent and stretchable electronics with remarkable bendability, conformability, and lightness are the key attributes for sensing or wearable devices. Transparent and stretchable field-effect transistor sensors using graphene-metal nanowire hybrid nanostructures have high mobility (≈3000 cm(2) V(-1) s(-1) ) with low contact resistance, and they are transferrable onto a variety of substrates. The integration of these sensors for RLC circuits enables wireless monitoring.

Applications of Chemical Ligation in Peptide Synthesis via Acyl Transfer

The utility of native chemical ligation (NCL) in the solution or solid phase synthesis of peptides, cyclic peptides, glycopeptides, and neoglycoconjugates is reviewed. In addition, the mechanistic details of inter- or intra-molecular NCLs are discussed from experimental and computational points of view.

Synthesis and biological activity of small peptides as NOP and opioid receptors' ligands: view on current developments

The heptadecapeptide nociceptin, also called orphanin FQ (N/OFQ), is the endogenous agonist of the N/OFQ peptide receptor (NOP receptor) and is involved in several central nervous system pathways, such as nociception, reward, tolerance, and feeding. The discovery of small molecule ligands for NOP is being actively pursued for several therapeutic applications. This review presents overview of the several recently reported NOP ligands (agonists and antagonists), with an emphasis of the structural features that may be important for modulating the intrinsic activity of these ligands. In addition, a brief account on the characterization of newly synthesized ligands of NOP receptor with aminophosphonate moiety and β-tryptophan analogues will be presented.

Protein–polymer therapeutics: a macromolecular perspective

The development of protein–polymer hybrids emerged several decades ago with the vision that their synergistic combination will offer macromolecular hybrids with manifold features to succeed as the next generation therapeutics.

Diastereoselective recognition of α-mannoside by hemicryptophane receptors

The synthesis and assignment of the absolute configuration of enantiopure hemicryptophane hosts are reported. The new hosts are able to recognize selectively mannoside guests compared to other sugar derivatives such as glucoside or galactoside.

The design of phenylboronic acid azoprobe–polyamidoamine dendrimer complexes as supramolecular sensors for saccharide recognition in water

Phenylboronic acid azoprobe–PAMAM dendrimer complex responded to saccharides and exhibited selective aggregation particularly with glucose at neutral pH.

Post-polymerization modification of poly(L-glutamic acid) with D-(+)-glucosamine

Carboxyl functional groups of poly(L-glutamic acid) (PGlu) were modified with a D-(+)-glucosamine (GlcN) by amidation using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) as a coupling reagent. The coupling reaction was performed in aqueous medium without protection of hydroxyl functional groups of D-(+)-glucosamine. Poly(L-glutamic acid) and GlcN functionalized polyglutamates (P(Glu-GlcN)) were thoroughly characterized by 1D and 2D NMR spectroscopy and SEC-MALS to gain detailed information on their structure, composition and molar mass characteristics. The results reveal successful functionalization with GlcN through the amide bond and also to a minor extent through ester bond formation in position 1 of GlcN. In addition, a ratio between the α- and β-form of glucosamine substituent coupled to polyglutamate repeating units as well as the content of residual dimethoxy triazinyl active ester moiety in the samples were evaluated.

Asymmetric disulfonimide-catalyzed synthesis of δ-amino-β-ketoester derivatives by vinylogous Mukaiyama-Mannich reactions

An organocatalytic asymmetric synthesis of δ-amino-β-ketoester derivatives has been developed. A chiral disulfonimide (DSI) serves as a highly efficient precatalyst for a vinylogous Mukaiyama-Mannich reaction of readily available dioxinone-derived silyloxydienes with N-Boc-protected imines, delivering products in excellent yields and enantioselectivities. The synthetic utility of this reaction is illustrated in various transformations, including a new CC bond-forming reaction, which provide useful enantioenriched building blocks. The methodology is applied in a formal synthesis of (-)-lasubin.

Modulating glycosylation with exogenous nucleophiles: an overview

The major challenge in carbohydrate synthesis is stereochemical control of glycosidic bond formation. Different glycosylation methods have been developed that are based on the modulation effect of external nucleophiles. This review highlights the development, synthetic application, challenges and outlook of the modulated glycosylation methods.

Native chemical ligation: a boon to peptide chemistry

The use of chemical ligation within the realm of peptide chemistry has opened various opportunities to expand the applications of peptides/proteins in biological sciences. Expansion and refinement of ligation chemistry has made it possible for the entry of peptides into the world of viable oral therapeutic drugs through peptide backbone cyclization. This progression has been a journey of chemical exploration and transition, leading to the dominance of native chemical ligation in the present advances of peptide/protein applications. Here we illustrate and explore the historical and current nature of peptide ligation, providing a clear indication to the possibilities and use of these novel methods to take peptides outside their typically defined boundaries.

Chemical synthesis of syndecan-3 glycopeptides bearing two heparan sulfate glycan chains

Despite the ubiquitous presence of proteoglycans in mammalian systems, methodologies to synthesize this class of glycopeptides with homogeneous glycans are not well developed. Herein, we report the first synthesis of a glycosaminoglycan family glycopeptide containing two different heparan sulfate chains, namely the extracellular domain of syndecan-3. With the large size and tremendous structural complexity of these molecules, multiple unexpected obstacles were encountered during the synthesis, including high sensitivity to base treatment and the instability of glycopeptides with two glycan chains towards catalytic hydrogenation conditions. A successful strategy was established by constructing the partially deprotected single glycan chain containing glycopeptides first, followed by union of the glycan-bearing fragments and cleavage of the ester-type protecting groups. This work lays the foundation for preparing other members of this important class of molecules.

Trifluoroethanethiol: an additive for efficient one-pot peptide ligation-desulfurization chemistry

Native chemical ligation followed by desulfurization is a powerful strategy for the assembly of proteins. Here we describe the development of a high-yielding, one-pot ligation-desulfurization protocol that uses trifluoroethanethiol (TFET) as a novel thiol additive. The synthetic utility of this TFET-enabled methodology is demonstrated by the efficient multi-step one-pot syntheses of two tick-derived proteins, chimadanin and madanin-1, without the need for any intermediary purification.

Chemical synthesis of asparagine-linked archaeal N-glycan from Methanothermus fervidus

Several N-linked glycoproteins have been identified in archaea and there is growing evidence that the N-glycan is involved in survival and functioning of archaea in extreme conditions. Chemical synthesis of the archaeal N-glycans represents a crucial step towards understanding the putative function of protein glycosylation in archaea. Herein the first total synthesis of the archaeal L-asparagine linked hexasaccharide from Methanothermus fervidus is reported using a highly convergent [3+3] glycosylation approach in high overall yields. The synthesis relies on efficient preparation of regioselectively protected thioglycoside building blocks for orthogonal glycosylations and late stage N-aspartylation.

S-Michael additions to chiral dehydroalanines as an entry to glycosylated cysteines and a sulfa-Tn antigen mimic

Stereoselective sulfa-Michael addition of appropriately protected thiocarbohydrates to chiral dehydroalanines has been developed as a key step in the synthesis of biologically important cysteine derivatives, such as S-(β-D-glucopyranosyl)-D-cysteine, which has not been synthesized to date, and S-(2-acetamido-2-deoxy-α-D-galactopyranosyl)-L-cysteine, which could be considered as a mimic of Tn antigen. The corresponding diamide derivative was also synthesized and analyzed from a conformational viewpoint, and its bound state with a lectin was studied.