Synthesis of carbohydrate-functionalised sequence-defined oligo(amidoamine)s by photochemical thiol-ene coupling in a continuous flow reactor

Synthetic Chemistry in Flow: From Photolysis & Homogeneous Photocatalysis to Heterogeneous Photocatalysis

Photocatalytic synthesis of value-added chemicals has gained increasing attention in recent years owing to its versatility in driving many important reactions under ambient conditions. Selective hydrogenation, oxidation, coupling, and halogenation with a high conversion of the reactants have been realized using designed photocatalysts in batch reactors with small volumes at a laboratory scale; however, scaling-up remains a critical challenge due to inefficient utilization of incident light and active sites of the photocatalysts, resulting in poor catalytic performance that hinders its practical applications. Flow systems are considered one of the solutions for practical applications of light-driven reactions and have experienced great success in photolytic and homogeneous photocatalysis, yet their applications in heterogeneous photocatalysis are still under development. In this perspective, we have summarized recent progress in photolytic and photocatalytic synthetic chemistry performed in flow systems from the view of reactor design with a special focus on heterogeneous photocatalysis. The advantages and limitations of different flow systems, as well as some practical considerations of design strategies are discussed.

Sweet Janus Particles: Multifunctional Inhibitors of Carbohydrate-Based Bacterial Adhesion

Escherichia coli and other bacteria use adhesion receptors, such as FimH, to attach to carbohydrates on the cell surface as the first step of colonization and infection. Efficient inhibitors that block these interactions for infection treatment are multivalent carbohydrate-functionalized scaffolds. However, these multivalent systems often lead to the formation of large clusters of bacteria, which may pose problems for clearing bacteria from the infected site. Here, we present Man-containing Janus particles (JPs) decorated on one side with glycomacromolecules to target Man-specific adhesion receptors of E. coli. On the other side, poly(N-isopropylacrylamide) is attached to the particle hemisphere, providing temperature-dependent sterical shielding against binding and cluster formation. While homogeneously functionalized particles cluster with multiple bacteria to form large aggregates, glycofunctionalized JPs are able to form aggregates only with individual bacteria. The formation of large aggregates from the JP-decorated single bacteria can still be induced in a second step by increasing the temperature and making use of the collapse of the PNIPAM hemisphere. This is the first time that carbohydrate-functionalized JPs have been derived and used as inhibitors of bacterial adhesion. Furthermore, the developed JPs offer well-controlled single bacterial inhibition in combination with cluster formation upon an external stimulus, which is not achievable with conventional carbohydrate-functionalized particles.

A thiol-ene mediated approach for peptide bioconjugation using 'green' solvents under continuous flow

Flow chemistry has emerged as an integral process within the chemical sector permitting energy efficient synthetic scale-up while improving safety and minimising solvent usage. Herein, we report the first applications of the photoactivated, radical-mediated thiol-ene reaction for peptide bioconjugation under continuous flow. Bioconjugation reactions employing deep eutectic solvents, bio-based solvents and fully aqueous systems are reported here for a range of biologically relevant peptide substrates. The use of a water soluble photoinitiator, Irgacure 2959, permitted synthesis of glycosylated peptides in fully aqueous conditions, obviating the need for addition of organic solvents and enhancing the green credentials of these rapid, photoactivated, bioconjugation reactions.

Small tools for sweet challenges: advances in microfluidic technologies for glycan synthesis

Glycans, including oligosaccharides and glycoconjugates, play an integral role in modulating the biological functions of macromolecules. Many physiological and pathological processes are mediated by interactions between glycans, which has led to the use of glycans as biosensors for pathogen and biomarker detection. Elucidating the relationship between glycan structure and biological function is critical for advancing our understanding of the impact glycans have on human health and disease and for expanding the repertoire of glycans available for bioanalysis, especially for diagnostics. Such efforts have been limited by the difficulty in obtaining sufficient quantities of homogenous glycan samples needed to resolve the exact relationships between glycan structure and their structural or modulatory functions on a given glycoconjugate. Synthetic strategies offer a viable route for overcoming these technical hurdles. In recent years, microfluidics have emerged as powerful tools for realizing high-throughput and reproducible syntheses of homogenous glycans for the potential use in functional studies. This critical review provides readers with an overview of the microfluidic technologies that have been developed for chemical and enzymatic glycan synthesis. The advantages and limitations associated with using microreactor platforms to improve the scalability, productivity, and selectivity of glycosylation reactions will be discussed, as well as suggested future work that can address certain pitfalls.

Metal-free bioorthogonal click chemistry in cancer theranostics

Bioorthogonal chemistry is a powerful tool to site-specifically activate drugs in living systems. Bioorthogonal reactions between a pair of biologically reactive groups can rapidly and specifically take place in a mild physiological milieu without perturbing inherent biochemical processes. Attributed to their high selectivity and efficiency, bioorthogonal reactions can significantly decrease background signals in bioimaging. Compared with metal-catalyzed bioorthogonal click reactions, metal-free click reactions are more biocompatible without the metal catalyst-induced cytotoxicity. Although a great number of bioorthogonal chemistry-based strategies have been reported for cancer theranostics, a comprehensive review is scarce to highlight the advantages of these strategies. In this review, recent progress in cancer theranostics guided by metal-free bioorthogonal click chemistry will be depicted in detail. The elaborate design as well as the advantages of bioorthogonal chemistry in tumor theranostics are summarized and future prospects in this emerging field are emphasized.

Synthesis of Glycodendrimers with Antiviral and Antibacterial Activity

Glycodendrimers are an important class of synthetic macromolecules that can be used to mimic many structural and functional features of cell-surface glycoconjugates. Their carbohydrate moieties perform key important functions in bacterial and viral infections, often regulated by carbohydrate-protein interactions. Several studies have shown that the molecular structure, valency and spatial organisation of carbohydrate epitopes in glycoconjugates are key factors in the specificity and avidity of carbohydrate-protein interactions. Choosing the right glycodendrimers almost always helps to interfere with such interactions and blocks bacterial or viral adhesion and entry into host cells as an effective strategy to inhibit bacterial or viral infections. Herein, the state of the art in the design and synthesis of glycodendrimers employed for the development of anti-adhesion therapy against bacterial and viral infections is described.

Sequence-defined positioning of amine and amide residues to control catechol driven wet adhesion

Catechol and amine residues, both abundantly present in mussel adhesion proteins, are known to act cooperatively by displacing hydration barriers before binding to mineral surfaces. In spite of synthetic efforts toward mussel-inspired adhesives, the effect of positioning of the involved functional groups along a polymer chain is not well understood. By using sequence-defined oligomers grafted to soft hydrogel particles as adhesion probes, we study the effect of catechol-amine spacing, as well as positioning relative to the oligomer terminus. We demonstrate that the catechol-amine spacing has a significant effect on adhesion, while shifting their position has a small effect. Notably, combinations of non-charged amides and catechols can achieve similar cooperative effects on adhesion when compared to amine and catechol residues. Thus, these findings provide a blueprint for the design of next generation mussel-inspired adhesives.

On-Chip Neo-Glycopeptide Synthesis for Multivalent Glycan Presentation

Single glycan-protein interactions are often weak, such that glycan binding partners commonly utilize multiple, spatially defined binding sites to enhance binding avidity and specificity. Current array technologies usually neglect defined multivalent display. Laser-based array synthesis technology allows for flexible and rapid on-surface synthesis of different peptides. By combining this technique with click chemistry, neo-glycopeptides were produced directly on a functionalized glass slide in the microarray format. Density and spatial distribution of carbohydrates can be tuned, resulting in well-defined glycan structures for multivalent display. The two lectins concanavalin A and langerin were probed with different glycans on multivalent scaffolds, revealing strong spacing-, density-, and ligand-dependent binding. In addition, we could also measure the surface dissociation constant. This approach allows for a rapid generation, screening, and optimization of a multitude of multivalent scaffolds for glycan binding.

Immunological Evaluation of Synthetic Glycosylphosphatidylinositol Glycoconjugates as Vaccine Candidates against Malaria

Glycosylphosphatidylinositols (GPIs) are complex glycolipids present on the surfaces of Plasmodium parasites that may act as toxins during the progression of malaria. GPIs can activate the immune system during infection and induce the formation of anti-GPI antibodies that neutralize their activity. Therefore, an antitoxic vaccine based on GPI glycoconjugates may prevent malaria pathogenesis. To evaluate the role of three key modifications on Plasmodium GPI glycan in the activity of these glycolipids, we synthesized and investigated six structurally distinct GPI fragments from Plasmodium falciparum. The synthetic glycans were conjugated to the CRM197 carrier protein and were tested for immunogenicity and efficacy as antimalarial vaccine candidates in an experimental cerebral malaria model using C57BL/6JRj mice. Protection may be dependent on both the antibody and the cellular immune response to GPIs, and the elicited immune response depends on the orientation of the glycan, the number of mannoses in the structure, and the presence of the phosphoethanolamine and inositol units. This study provides insights into the epitopes in GPIs and contributes to the development of GPI-based antitoxin vaccine candidates against cerebral malaria.

Asymmetrically Branched Precision Glycooligomers Targeting Langerin

Asymmetrically branched precision glycooligomers are synthesized by solid-phase polymer synthesis for studying multivalent carbohydrate-protein interactions. Through the stepwise assembly of Fmoc-protected oligo(amidoamine) building blocks and Fmoc/Dde-protected lysine, straightforward variation of structural parameters such as the number and length of arms, as well as the number and position of carbohydrate ligands, is achieved. Binding of 1-arm and 3-arm glycooligomers toward lectin receptors langerin and concanavalin A (ConA) was evaluated where the smallest 3-arm glycooligomer shows the highest binding toward langerin, and stepwise elongation of one, two, or all three arms leads to decreased binding. When directly comparing binding toward langerin and ConA, we find that structural variation of the scaffold affects glycomimetic ligand binding differently for the different targets, indicating the potential to tune such ligands not only for their avidity but also for their selectivity toward different lectins.

A Malonyl-Based Scaffold for Conjugatable Multivalent Carbohydrate-BODIPY Presentations

A concise synthetic route from methylmalonate to a tetravalent aliphatic scaffold has been developed. The ensuing tetra-tethered derivative is equipped with two hydroxyl groups, as well as orthogonal alkene and alkyne functionalities. The usefulness of the scaffold has been demonstrated with the preparation of two representative multivalent derivatives: (i) a tetravalent compound containing two D-mannose units, one fluorescent boron-dipyrromethene (BODIPY) dye and a suitably functionalized amino acid and (ii) by way of dimerization and saponification, a water-soluble tetramannan derivative containing two fluorescent BODIPY units. Additionally, photophysical measurements conducted on these derivatives support the viability of the herein designed single and double BODIPY-labeled carbohydrate-based clusters as fluorescent markers.

Tunable biomaterials from synthetic, sequence-controlled polymers

Polymeric biomaterials have many applications including therapeutic delivery vehicles, medical implants and devices, and tissue engineering scaffolds. Both naturally-derived and synthetic materials have successfully been used for these applications in the clinic. However, the increasing complexity of these applications requires materials with advanced properties, especially customizable or tunable materials with bioactivity. To address this issue, there have been recent efforts to better recapitulate the properties of natural materials using synthetic biomaterials composed of sequence-controlled polymers. Sequence control mimics the primary structure found in biopolymers, and in many cases, provides an extra handle for functionality in synthetic polymers. Here, we first review the advances in synthetic methods that have enabled sequence-controlled biomaterials on a relevant scale, and discuss strategies for choosing functional sequences from a biomaterials engineering context. Then, we highlight several recent studies that show strong impact of sequence control on biomaterial properties, including in vitro and in vivo behavior, in the areas of hydrogels, therapeutic materials, and novel applications such as molecular barcodes for medical devices. The role of sequence control in biomaterials properties is an emerging research area, and there remain many opportunities for investigation. Further study of this topic may significantly advance our understanding of bioactive or smart materials, as well as contribute design rules to guide the development of synthetic biomaterials for future applications in tissue engineering and regenerative medicine.

Heteromultivalent Glycooligomers as Mimetics of Blood Group Antigens

Precision glycomacromolecules have proven to be important tools for the investigation of multivalent carbohydrate-lectin interactions by presenting multiple glycan epitopes on a highly-defined synthetic scaffold. Herein, we present a new strategy for the versatile assembly of heteromultivalent glycomacromolecules that contain different carbohydrate motifs in proximity within the side chains. A new building block suitable for the solid-phase polymer synthesis of precision glycomacromolecules was developed with a branching point in the side chain that bears a free alkyne and a TIPS-protected alkyne moiety, which enables the subsequent attachment of different carbohydrate motifs by on-resin copper-mediated azide-alkyne cycloaddition reactions. Applying this synthetic strategy, heteromultivalent glycooligomers presenting fragments of histo-blood group antigens and human milk oligosaccharides were synthesized and tested for their binding behavior towards bacterial lectin LecB.

Sequence-Defined Introduction of Hydrophobic Motifs and Effects in Lectin Binding of Precision Glycomacromolecules

This study investigates the influence of an increasingly hydrophobic backbone of multivalent glycomimetics based on sequence-defined oligo(amidoamines) on their resulting affinity toward bacterial lectins. Glycomacromolecules are obtained by stepwise assembly of tailor-made building blocks on solid support, using both hydrophobic aliphatic and aromatic building blocks to enable a gradual change in hydrophobicity of the backbone. Their binding behavior toward model lectin Concanavalin A (ConA) is evaluated using isothermal titration calorimetry (ITC) and surface plasmon resonance (SPR) showing higher affinities for glycomacromolecules with higher content of hydrophobic and aromatic moieties in the backbone. Finally, glycomacromolecules are tested in a bacterial adhesion inhibition study against Escherichia coli where more hydrophobic backbones yield higher inhibitory potentials most likely due to additional secondary interactions with hydrophobic regions of the protein receptor as well as a change in conformation exposing carbohydrate ligands for increased binding. Overall, the results highlight the influence and thereby importance of the polymer backbone itself on the resulting properties of polymeric biomimetics.

Recent Developments in Solid-Phase Strategies towards Synthetic, Sequence-Defined Macromolecules

Sequence-control in synthetic polymers is an important contemporary research area because it provides the opportunity to create completely novel materials for structure-function studies. This is especially relevant for biomimetic polymers, bioactive and information security materials. The level of control is strongly dependent and inherent upon the polymerization technique utilized. Today, the most established method yielding monodispersity and monomer sequence-definition is solid-phase synthesis. This Focus Review highlights recent advances in solid-phase strategies to access synthetic, sequence-defined macromolecules. Alternatives strategies towards sequence-defined macromolecules are also briefly summarized.

Recent Advances in the Synthesis of Glycoconjugates for Vaccine Development

During the last decade there has been a growing interest in glycoimmunology, a relatively new research field dealing with the specific interactions of carbohydrates with the immune system. Pathogens’ cell surfaces are covered by a thick layer of oligo- and polysaccharides that are crucial virulence factors, as they mediate receptors binding on host cells for initial adhesion and organism invasion. Since in most cases these saccharide structures are uniquely exposed on the pathogen surface, they represent attractive targets for vaccine design. Polysaccharides isolated from cell walls of microorganisms and chemically conjugated to immunogenic proteins have been used as antigens for vaccine development for a range of infectious diseases. However, several challenges are associated with carbohydrate antigens purified from natural sources, such as their difficult characterization and heterogeneous composition. Consequently, glycoconjugates with chemically well-defined structures, that are able to confer highly reproducible biological properties and a better safety profile, are at the forefront of vaccine development. Following on from our previous review on the subject, in the present account we specifically focus on the most recent advances in the synthesis and preliminary immunological evaluation of next generation glycoconjugate vaccines designed to target bacterial and fungal infections that have been reported in the literature since 2011.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Presenting Precision Glycomacromolecules on Gold Nanoparticles for Increased Lectin Binding

Glyco-functionalized gold nanoparticles have great potential as biosensors and as inhibitors due to their increased binding to carbohydrate-recognizing receptors such as the lectins. Here we apply previously developed solid phase polymer synthesis to obtain a series of precision glycomacromolecules that allows for straightforward variation of their chemical structure as well as functionalization of gold nanoparticles by ligand exchange. A novel building block is introduced allowing for the change of spacer building blocks within the macromolecular scaffold going from an ethylene glycol unit to an aliphatic spacer. Furthermore, the valency and overall length of the glycomacromolecule is varied. All glyco-functionalized gold nanoparticles show high degree of functionalization along with high stability in buffer solution. Therefore, a series of measurements applying UV-Vis spectroscopy, dynamic light scattering (DLS) and surface plasmon resonance (SPR) were performed studying the aggregation behavior of the glyco-functionalized gold nanoparticles in presence of model lectin Concanavalin A. While the multivalent presentation of glycomacromolecules on gold nanoparticles (AuNPs) showed a strong increase in binding compared to the free ligands, we also observed an influence of the chemical structure of the ligand such as its valency or hydrophobicity on the resulting lectin interactions. The straightforward variation of the chemical structure of the precision glycomacromolecule thus gives access to tailor-made glyco-gold nanoparticles (glyco-AuNPs) and fine-tuning of their lectin binding properties.

Click and Click-Inspired Chemistry for the Design of Sequence-Controlled Polymers

During the previous decade, many popular chemical reactions used in the area of "click" chemistry and similarly efficient "click-inspired" reactions have been applied for the design of sequence-defined and, more generally, sequence-controlled structures. This combination of topics has already made quite a significant impact on scientific research to date and has enabled the synthesis of highly functionalized and complex oligomeric and polymeric structures, which offer the prospect of many exciting further developments and applications in the near future. This minireview highlights the fruitful combination of these two topics for the preparation of sequence-controlled oligomeric and macromolecular structures and showcases the vast number of publications in this field within a relatively short span of time. It is divided into three sections according to the click-(inspired) reaction that has been applied: copper-catalyzed azide-alkyne cycloaddition, thiol-X, and related thiolactone-based reactions, and finally Diels-Alder-chemistry-based routes are outlined, respectively.

Sequence-Controlled Glycopolymers via Step-Growth Polymerization of Precision Glycomacromolecules for Lectin Receptor Clustering

A versatile approach for the synthesis of sequence-controlled multiblock copolymers, using a combination of solid phase synthesis and step-growth polymerization by photoinduced thiol-ene coupling (TEC) is presented. Following this strategy, a series of sequence-controlled glycopolymers is derived from the polymerization of a hydrophilic spacer macromonomer and different glycomacromonomers bearing between one to five α-d-Mannose (Man) ligands. Through the solid phase assembly of the macromonomers, the number and positioning of spacer and sugar moieties is controlled and translates into the sequence-control of the final polymer. A maximum M̅_n of 16 kDa, corresponding to a X̅_n of 10, for the applied macromonomers is accessible with optimized polymerization conditions. The binding behavior of the resulting multiblock glycopolymers toward the model lectin Concanavalin A (ConA) is studied via turbidity assays and surface plasmon resonance (SPR) measurements, comparing the ability of precision glycomacromolecules and glycopolymers to bind to and cross-link ConA in dependence of the number of sugar moieties and overall molecular weight. The results show that there is a clear correlation between number of Man ligands and Con A binding and clustering, whereas the length of the glycooligomer- or polymer backbone seems to have no effect.

Recent advances in photoinduced glycosylation: oligosaccharides, glycoconjugates and their synthetic applications

Carbohydrates have been demonstrated to perform imperative act in biological processes. This review highlights recent uses of photoinduced glycosylation in carbohydrate chemistry for the synthesis of oligosaccharides, thiosugars, glycoconjugates and glycoprotein.

Multivalent display of minimal Clostridium difficile glycan epitopes mimics antigenic properties of larger glycans

Synthetic cell-surface glycans are promising vaccine candidates against Clostridium difficile. The complexity of large, highly antigenic and immunogenic glycans is a synthetic challenge. Less complex antigens providing similar immune responses are desirable for vaccine development. Based on molecular-level glycan–antibody interaction analyses, we here demonstrate that the C. difficile surface polysaccharide-I (PS-I) can be resembled by multivalent display of minimal disaccharide epitopes on a synthetic scaffold that does not participate in binding. We show that antibody avidity as a measure of antigenicity increases by about five orders of magnitude when disaccharides are compared with constructs containing five disaccharides. The synthetic, pentavalent vaccine candidate containing a peptide T-cell epitope elicits weak but highly specific antibody responses to larger PS-I glycans in mice. This study highlights the potential of multivalently displaying small oligosaccharides to achieve antigenicity characteristic of larger glycans. The approach may result in more cost-efficient carbohydrate vaccines with reduced synthetic effort.

Immunologically-active glycans are promising vaccine candidates but can be difficult to synthesize. Here, the authors show that pentavalent display of a minimal disaccharde epitope on a chemical scaffold can mimic a native C. difficile glycan antigen, representing a simple approach to synthetic vaccine production.

Applications of Continuous-Flow Photochemistry in Organic Synthesis, Material Science, and Water Treatment

Continuous-flow photochemistry in microreactors receives a lot of attention from researchers in academia and industry as this technology provides reduced reaction times, higher selectivities, straightforward scalability, and the possibility to safely use hazardous intermediates and gaseous reactants. In this review, an up-to-date overview is given of photochemical transformations in continuous-flow reactors, including applications in organic synthesis, material science, and water treatment. In addition, the advantages of continuous-flow photochemistry are pointed out and a thorough comparison with batch processing is presented.

Selective and Efficient Generation of ortho-Brominated para-Substituted Phenols in ACS-Grade Methanol

The mono ortho-bromination of phenolic building blocks by NBS has been achieved in short reaction times (15-20 min) using ACS-grade methanol as a solvent. The reactions can be conducted on phenol, naphthol and biphenol substrates, giving yields of >86% on gram scale. Excellent selectivity for the desired mono ortho-brominated products is achieved in the presence of 10 mol % para-TsOH, and the reaction is shown to be tolerant of a range of substituents, including CH3, F, and NHBoc.

Biodegradable poly(amidoamine)s with uniform degradation fragments via sequence-controlled macromonomers

This work presents the translation of sequence-controlled synthesis of macromonomers into sequence-defined and selectively degradable precision polymers.

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.

Investigation of the protective properties of glycosylphosphatidylinositol-based vaccine candidates in a Toxoplasma gondii mouse challenge model

Vaccination against the ubiquitous parasite Toxoplasma gondii would provide the most efficient prevention against toxoplasmosis-related congenital, brain and eye diseases in humans. We investigated the immune response elicited by pathogen-specific glycosylphosphatidylinositol (GPI) glycoconjugates using carbohydrate microarrays in a BALB/c mouse model. We further examined the protective properties of the glycoconjugates in a lethal challenge model using the virulent T. gondii RH strain. Upon immunization, mice raised antibodies that bind to the respective GPIs on carbohydrate microarrays, but were mainly directed against an unspecific GPI epitope including the linker. The observed immune response, though robust, was unable to provide protection in mice when challenged with a lethal dose of viable tachyzoites. We demonstrate that anti-GPI antibodies raised against the here described semi-synthetic glycoconjugates do not confer protective immunity against T. gondii in BALB/c mice.

Multivalent thioglycopeptoids via photoclick chemistry: potent affinities towards LecA and BC2L-A lectins

The straightforward access to peptoid-based multivalent thioglycoclusters displaying 1-thio-β-d-galactose or 1-thio-α/β-d-mannose and their evaluation towards two bacterial lectins are described.

Synthesis of non-linear protein dimers through a genetically encoded Thiol-ene reaction

Site-specific incorporation of bioorthogonal unnatural amino acids into proteins provides a useful tool for the installation of specific functionalities that will allow for the labeling of proteins with virtually any probe. We demonstrate the genetic encoding of a set of alkene lysines using the orthogonal PylRS/PylTCUA pair in Escherichia coli. The installed double bond functionality was then applied in a photoinitiated thiol-ene reaction of the protein with a fluorescent thiol-bearing probe, as well as a cysteine residue of a second protein, showing the applicability of this approach in the formation of heterogeneous non-linear fused proteins.

Photochemical transformations accelerated in continuous-flow reactors: basic concepts and applications

Continuous-flow photochemistry is used increasingly by researchers in academia and industry to facilitate photochemical processes and their subsequent scale-up. However, without detailed knowledge concerning the engineering aspects of photochemistry, it can be quite challenging to develop a suitable photochemical microreactor for a given reaction. In this review, we provide an up-to-date overview of both technological and chemical aspects associated with photochemical processes in microreactors. Important design considerations, such as light sources, material selection, and solvent constraints are discussed. In addition, a detailed description of photon and mass-transfer phenomena in microreactors is made and fundamental principles are deduced for making a judicious choice for a suitable photomicroreactor. The advantages of microreactor technology for photochemistry are described for UV and visible-light driven photochemical processes and are compared with their batch counterparts. In addition, different scale-up strategies and limitations of continuous-flow microreactors are discussed.