Sequence-Defined Glycopolymer Segments Presenting Mannose: Synthesis and Lectin Binding Affinity

Synthesis of Dual-Responsive Amphiphilic Glycomacromolecules: Controlled Release of Glycan Ligands via pH and UV Stimuli

This work presents a versatile strategy for the synthesis of dual stimuli-responsive amphiphilic glycomacromolecules with tailored release properties. Amphiphilic precision glycomacromolecules (APGs) derived from tailor-made building blocks using solid phase polymer synthesis form glycofunctionalized micelles, a versatile class of materials with applications in drug delivery, as antiinfection agents as well as simple cell mimetics. In this work, this concept is extended by integrating cleavable building blocks into APGs now allowing stimuli-responsive release of glycan ligands or destruction of the micelles. This study incorporates a newly designed acid-labile building block, 4-(4-(((((9H-fluoren-9-yl)methoxy)carbonyl)amino)methyl)-1,3-dioxolan-2-yl)benzoic acid (DBA), suitable also for other types of solid phase or amide chemistry, and an established UV-cleavable 2-nitrobenzyl linker (PL). The results demonstrate that both linkers can be cleaved independently and thus allow dual stimuli-responsive release from the APG micelles. By choosing the APG design e.g., placing the cleavable linkers between glycomacromolecular blocks presenting different types of carbohydrates, they can tune APG and micellar stability as well as the interaction and cluster formation with a carbohydrate-recognizing lectin. Such dual-responsive glycofunctionalized micelles have wide potential for use in drug delivery applications or for the development as anti-adhesion agents in antiviral and antibacterial treatments.

GalNAc- or Mannose-PEG-Functionalized Polyplexes Enable Effective Lectin-Mediated DNA Delivery

A cationic, dendrimer-like oligo(aminoamide) carrier with four-arm topology based on succinoyl tetraethylene pentamine and histidines, cysteines, and N-terminal azido-lysines was screened for plasmid DNA delivery on various cell lines. The incorporated azides allow modification with various shielding agents of different polyethylene glycol (PEG) lengths and/or different ligands by copper-free click reaction, either before or after polyplex formation. Prefunctionalization was found to be advantageous over postfunctionalization in terms of nanoparticle formation, stability, and efficacy. A length of 24 ethylene oxide repetition units and prefunctionalization of ≥50% of azides per carrier promoted optimal polyplex shielding. PEG shielding resulted in drastically reduced DNA transfer, which could be successfully restored by active lectin targeting via novel GalNAc or mannose ligands, enabling enhanced receptor-mediated endocytosis of the carrier system. The involvement of the asialoglycoprotein receptor (ASGPR) in the uptake of GalNAc-functionalized polyplexes was confirmed in the ASGPR-positive hepatocarcinoma cell lines HepG2 and Huh7. Mannose-modified polyplexes showed superior cellular uptake and transfection efficacy compared to unmodified and shielded polyplexes in mannose-receptor-expressing dendritic cell-like DC2.4 cells.

Telechelic sequence-defined oligoamides: their step-economical synthesis, depolymerization and use in polymer networks

The application of sequence-defined macromolecules in material science remains largely unexplored due to their challenging, low yielding and time-consuming synthesis. This work first describes a step-economical method for synthesizing unnatural sequence-defined oligoamides through fluorenylmethyloxycarbonyl chemistry. The use of a monodisperse soluble support enables homogeneous reactions at elevated temperature (up to 65 °C), leading to rapid coupling times (<10 min) and improved synthesis protocols. Moreover, a one-pot procedure for the two involved iterative steps is demonstrated via an intermediate quenching step, eliminating the need for in-between purification. The protocol is optimized using γ-aminobutyric acid (GABA) as initial amino acid, and the unique ability of the resulting oligomers to depolymerize, with the formation of cyclic γ-butyrolactame, is evidenced. Furthermore, in order to demonstrate the versatility of the present protocol, a library of 17 unnatural amino acid monomers is synthesized, starting from the readily available GABA-derivative 4-amino-2-hydroxybutanoic acid, and then used to create multifunctional tetramers. Notably, the obtained tetramers show higher thermal stability than a similar thiolactone-based sequence-defined macromolecule, which enables its exploration within a material context. To that end, a bidirectional growth approach is proposed as a greener alternative that reduces the number of synthetic steps to obtain telechelic sequence-defined oligoamides. The latter are finally used as macromers for the preparation of polymer networks. We expect this strategy to pave the way for the further exploration of sequence-defined macromolecules in material science.

Potentiating Tweezer Affinity to a Protein Interface with Sequence-Defined Macromolecules on Nanoparticles

Survivin, a well-known member of the inhibitor of apoptosis protein family, is upregulated in many cancer cells, which is associated with resistance to chemotherapy. To circumvent this, inhibitors are currently being developed to interfere with the nuclear export of survivin by targeting its protein-protein interaction (PPI) with the export receptor CRM1. Here, we combine for the first time a supramolecular tweezer motif, sequence-defined macromolecular scaffolds, and ultrasmall Au nanoparticles (us-AuNPs) to tailor a high avidity inhibitor targeting the survivin-CRM1 interaction. A series of biophysical and biochemical experiments, including surface plasmon resonance measurements and their multivalent evaluation by EVILFIT, reveal that for divalent macromolecular constructs with increasing linker distance, the longest linkers show superior affinity, slower dissociation, as well as more efficient PPI inhibition. As a drawback, these macromolecular tweezer conjugates do not enter cells, a critical feature for potential applications. The problem is solved by immobilizing the tweezer conjugates onto us-AuNPs, which enables efficient transport into HeLa cells. On the nanoparticles, the tweezer valency rises from 2 to 16 and produces a 100-fold avidity increase. The hierarchical combination of different scaffolds and controlled multivalent presentation of supramolecular binders was the key to the development of highly efficient survivin-CRM1 competitors. This concept may also be useful for other PPIs.

Molecular Recognition of Glycan-Bearing Glycomacromolecules Presented at Membrane Surfaces by Lectins: An NMR View

Lectin-glycan interactions are at the heart of a multitude of biological events. Glycans are usually presented in a multivalent manner on the cell surface as part of the so-called glycocalyx, where they interact with other entities. This multivalent presentation allows us to overcome the typical low affinities found for individual glycan-lectin interactions. Indeed, the presentation of glycans may drastically impact their binding by lectins, highly affecting the corresponding binding affinity and even selectivity. In this context, we herein present the study of the interaction of a variety of homo- and heteromultivalent lactose-functionalized glycomacromolecules and their lipid conjugates with two human galectins. We have employed as ligands the glycomacromolecules, as well as liposomes decorated with those structures, to evaluate their interactions in a cell-mimicking environment. Key details of the interaction have been unravelled by NMR experiments, both from the ligand and receptor perspectives, complemented by cryo-electron microscopy methods and molecular dynamics simulations.

Glycan-Presenting Coacervates Derived from Charged Poly(active esters): Preparation, Phase Behavior, and Lectin Capture

This study presents the preparation and phase behavior of glycan-functionalized polyelectrolytes for capturing carbohydrate-binding proteins and bacteria in liquid condensate droplets. The droplets are formed by complex coacervation of poly(active ester)-derived polyanions and polycations. This approach allows for a straightforward modular introduction of charged motifs and specifically interacting units; mannose and galactose oligomers are used here as first examples. The introduction of carbohydrates has a notable effect on the phase separation and the critical salt concentration, potentially by reducing the charge density. Two mannose binding species, concanavalin A (ConA) and Escherichia coli, are shown to not only specifically bind to mannose-functionalized coacervates but also to some degree to unfunctionalized, carbohydrate-free coacervates. This suggests non-carbohydrate-specific charge-charge interactions between the protein/bacteria and the droplets. However, when mannose interactions are inhibited or when non-binding galactose-functionalized polymers are used, interactions are significantly weakened. This confirms specific mannose-mediated binding functionalization and suggests that introducing carbohydrates reduces non-specific charge-charge interactions by a so far unidentified mechanism. Overall, the presented route toward glycan-presenting polyelectrolytes enables new functional liquid condensate droplets with specific biomolecular interactions.

Synthesis of Homo- and Heteromultivalent Fucosylated and Sialylated Oligosaccharide Conjugates via Preactivated N-Methyloxyamine Precision Macromolecules and Their Binding to Polyomavirus Capsid Proteins

Glycoconjugates are a versatile class of bioactive molecules that have found application as vaccines and antivirals and in cancer therapy. Their synthesis typically involves elaborate functionalization and use of protecting groups on the carbohydrate component in order to ensure efficient and selective conjugation. Alternatively, non-functionalized, non-protected carbohydrates isolated from biological sources or derived through biotechnological methods can be directly conjugated via N-methyloxyamine groups. In this study, we introduce such N-methyloxyamine groups into a variety of multivalent scaffolds─from small to oligomeric to polymeric scaffolds─making use of solid-phase polymer synthesis to assemble monodisperse sequence-defined macromolecules. These scaffolds are then successfully functionalized with different types of human milk oligosaccharides deriving a library of homo- and heteromultivalent glycoconjugates. Glycomacromolecules presenting oligosaccharide side chains with either α2,3- or α2,6-linked terminal sialic acid are used in a binding study with two types of polyomavirus capsid proteins showing that the multivalent presentation through the N-methyloxyamine-derived scaffolds increases the number of contacts with the protein. Overall, a straightforward route to derive glycoconjugates from complex oligosaccharides with high variability yet control in the multivalent scaffold is presented, and applicability of the derived structures is demonstrated.

Enzymatic Sialylation of Synthetic Multivalent Scaffolds: From 3'-Sialyllactose Glycomacromolecules to Novel Neoglycosides

Sialoglycans play a key role in many biological recognition processes and sialylated conjugates of various types have successfully been applied, e.g., as antivirals or in antitumor therapy. A key feature for high affinity binding of such conjugates is the multivalent presentation of sialoglycans which often possess synthetic challenges. Here, the combination is described of solid phase polymer synthesis and enzymatic sialylation yielding 3'-sialyllactose-presenting precision glycomacromolecules. CMP-Neu5Ac synthetase from Neisseria meningitidis (NmCSS) and sialyltransferase from Pasteurella multocida (PmST1) are combined in a one-pot reaction giving access to sequence-defined sialylated macromolecules. Surprisingly, when employing Tris(hydroxymethyl)aminomethane (Tris) as a buffer, formation of significant amounts of α-linked Tris-sialoside is observed as a side reaction. Further exploring and exploiting this unusual sialylation reaction, different neoglycosidic structures are synthesized showing that PmST1 can be used to derive both, sialylation on natural carbohydrates as well as on synthetic hydroxylated scaffolds.

Glycosaminoglycan Mimetic Precision Glycomacromolecules with Sequence-Defined Sulfation and Rigidity Patterns

Sulfated glycosaminoglycans (sGAGs) such as heparan sulfate (HS) are structurally diverse linear polysaccharides that are involved in many biological processes and have gained interest as antiviral compounds. Their recognition is driven by a complex orchestra of structural parameters that are still under intense investigation. One distinct characteristic is the incorporation of sulfation patterns including highly sulfated and non-sulfated sequences that provide variations in flexibility and conformation, which in turn impact the biological function of sGAGs. However, these distinct features have not yet been fully realized in the synthetic preparation of sGAG mimetics. Here, we present the synthesis of three groups of sulfated glycomacromolecules as sGAG mimetics: (i) globally sulfated glycooligomers, (ii) glycooligomers with sequence-defined sulfation patterns, and (iii) a globally sulfated glycooligomer-oligo-L-proline hybrid structure. The complete synthesis, including chemical sulfation, was conducted on solid support, enabled by the introduction of a commercially available photocleavable linker allowing for the preservation of sensitive sulfates during cleavage of the products. Structures were obtained in good purity and with high degrees of sulfation demonstrating the wide applicability of this methodology to prepare tailor-made sulfated glycomacromolecules and similar sGAG mimetics. Structures were tested for their anticoagulant properties showing activity similar to their natural HS counterpart and significantly lower than HP.

Hierarchy of Complex Glycomacromolecules: From Controlled Topologies to Biomedical Applications

Carbohydrates bearing a distinct complexity use a special code (Glycocode) to communicate with carbohydrate-binding proteins at a high precision to manipulate biological activities in complex biological environments. The level of complexity in carbohydrate-containing macromolecules controls the amount and specificity of information that can be stored in biomacromolecules. Therefore, a better understanding of the glycocode is crucial to open new areas of biomedical applications by controlling or manipulating the interaction between immune cells and pathogens in terms of trafficking and signaling, which would become a powerful tool to prevent infectious diseases. Even though a certain level of progress has been achieved over the past decade, synthetic glycomacromolecules are still lagging far behind naturally existing glycans in terms of complexity and precision because of insufficient and inefficient synthetic techniques. Currently, specific targeting at a cellular level using synthetic glycomacromolecules is still challenging. It is obvious that multidisciplinary collaborations are essential between different specialized disciplines to enhance the carbohydrate receptor-targeting paradigm for new biomedical applications. In this Perspective, recent developments in the synthesis of sophisticated glycomacromolecules are highlighted, and their biological and biomedical applications are also discussed in detail.

Using precision polymer chemistry for plastics traceability and governance

Resolving the anonymity of plastic materials is critical for safeguarding the well-being of our natural environments and human health.

Bioactive Synthetic Polymers

Synthetic polymers are omnipresent in society as textiles and packaging materials, in construction and medicine, among many other important applications. Alternatively, natural polymers play a crucial role in sustaining life and allowing organisms to adapt to their environments by performing key biological functions such as molecular recognition and transmission of genetic information. In general, the synthetic and natural polymer worlds are completely separated due to the inability for synthetic polymers to perform specific biological functions; in some cases, synthetic polymers cause uncontrolled and unwanted biological responses. However, owing to the advancement of synthetic polymerization techniques in recent years, new synthetic polymers have emerged that provide specific biological functions such as targeted molecular recognition of peptides, or present antiviral, anticancer, and antimicrobial activities. In this review, the emergence of this generation of bioactive synthetic polymers and their bioapplications are summarized. Finally, the future opportunities in this area are discussed.

Synthetic Glycomacromolecules of Defined Valency, Absolute Configuration, and Topology Distinguish between Human Lectins

Carbohydrate-binding proteins (lectins) play vital roles in cell recognition and signaling, including pathogen binding and innate immunity. Thus, targeting lectins, especially those on the surface of immune cells, could advance immunology and drug discovery. Lectins are typically oligomeric; therefore, many of the most potent ligands are multivalent. An effective strategy for lectin targeting is to display multiple copies of a single glycan epitope on a polymer backbone; however, a drawback to such multivalent ligands is they cannot distinguish between lectins that share monosaccharide binding selectivity (e.g., mannose-binding lectins) as they often lack molecular precision. Here, we describe the development of an iterative exponential growth (IEG) synthetic strategy that enables facile access to synthetic glycomacromolecules with precisely defined and tunable sizes up to 22.5 kDa, compositions, topologies, and absolute configurations. Twelve discrete mannosylated "glyco-IEGmers" are synthesized and screened for binding to a panel of mannoside-binding immune lectins (DC-SIGN, DC-SIGNR, MBL, SP-D, langerin, dectin-2, mincle, and DEC-205). In many cases, the glyco-IEGmers had distinct length, stereochemistry, and topology-dependent lectin-binding preferences. To understand these differences, we used molecular dynamics and density functional theory simulations of octameric glyco-IEGmers, which revealed dramatic effects of glyco-IEGmer stereochemistry and topology on solution structure and reveal an interplay between conformational diversity and chiral recognition in selective lectin binding. Ligand function also could be controlled by chemical substitution: by tuning the side chains of glyco-IEGmers that bind DC-SIGN, we could alter their cellular trafficking through alteration of their aggregation state. These results highlight the power of precision synthetic oligomer/polymer synthesis for selective biological targeting, motivating the development of next-generation glycomacromolecules tailored for specific immunological or other therapeutic applications.

Take your Positions and Shine: Effects of Positioning Aggregation-Induced Emission Luminophores within Sequence-Defined Macromolecules

A luminophore with aggregation‐induced emission (AIE) is employed for the conjugation onto supramolecular ligands to allow for detection of ligand binding. Supramolecular ligands are based on the combination of sequence‐defined oligo(amidoamine) scaffolds and guanidiniocarbonyl‐pyrrole (GCP) as binding motif. We hypothesize that AIE properties are strongly affected by positioning of the luminophore within the ligand scaffold. Therefore, we systematically investigate the effects placing the AIE luminophore at different positions within the overall construct, for example, in the main or side chain of the olig(amidoamine). Indeed, we can show that the position within the ligand structure strongly affects AIE, both for the ligand itself as well as when applying the ligand for the detection of different biological and synthetic polyanions.

Exploring Cyclic Sulfamidate Building Blocks for the Synthesis of Sequence-Defined Macromolecules

The preparation of sequence-defined macromolecules using cyclic sulfamidates on solid-phase is outlined. The challenges surrounding an AB+CD approach are described with focus on understanding the formation of ring-opened side products when using amide coupling reagents. To avoid undesired side product formation, a strategy of iterative ring-openings of cyclic sulfamidates on solid-phase is explored. Ring-opening on primary and secondary amines is successfully reported, generating both linear and branched chain growth. However, attempts to selectively cleave N-sulfate bearing sp³ -hybridized groups cannot be demonstrated, limiting the overall building block scope for this methodology. Consequently, the active ring-opening of cyclic sulfamidates on amine-functionalized oligo(amidoamine) backbones is successfully applied to produce sequence-defined, N-sulfated macromolecules.

Discovery of Semi- and Fully-Synthetic Carbohydrate Vaccines Against Bacterial Infections Using a Medicinal Chemistry Approach

The glycocalyx, a thick layer of carbohydrates, surrounds the cell wall of most bacterial and parasitic pathogens. Recognition of these unique glycans by the human immune system results in destruction of the invaders. To elicit a protective immune response, polysaccharides either isolated from the bacterial cell surface or conjugated with a carrier protein, for T-cell help, are administered. Conjugate vaccines based on isolated carbohydrates currently protect millions of people against Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitides infections. Active pharmaceutical ingredients (APIs) are increasingly discovered by medicinal chemistry and synthetic in origin, rather than isolated from natural sources. Converting vaccines from biologicals to pharmaceuticals requires a fundamental understanding of how the human immune system recognizes carbohydrates and could now be realized. To illustrate the chemistry-based approach to vaccine discovery, I summarize efforts focusing on synthetic glycan-based medicinal chemistry to understand the mammalian antiglycan immune response and define glycan epitopes for novel synthetic glycoconjugate vaccines against Streptococcus pneumoniae, Clostridium difficile, Klebsiella pneumoniae, and other bacteria. The chemical tools described here help us gain fundamental insights into how the human system recognizes carbohydrates and drive the discovery of carbohydrate vaccines.

Hyaluronan (HA)-inspired glycopolymers as molecular tools for studying HA functions

Hyaluronic acid (HA), the only non-sulphated glycosaminoglycan, serves numerous structural and biological functions in the human body, from providing viscoelasticity in tissues to creating hydrated environments for cell migration and proliferation. HA is also involved in the regulation of morphogenesis, inflammation and tumorigenesis through interactions with specific HA-binding proteins. Whilst the physicochemical and biological properties of HA have been widely studied for decades, the exact mechanisms by which HA exerts its multiple functions are not completely understood. Glycopolymers offer a simple and precise synthetic platform for the preparation of glycan analogues, being an alternative to the demanding synthetic chemical glycosylation. A library of homo, statistical and alternating HA glycopolymers were synthesised by reversible addition-fragmentation chain transfer polymerisation and post-modification utilising copper alkyne-azide cycloaddition to graft orthogonal pendant HA monosaccharides (N-acetyl glucosamine: GlcNAc and glucuronic acid: GlcA) onto the polymer. Using surface plasmon resonance, the binding of the glycopolymers to known HA-binding peptides and proteins (CD44, hyaluronidase) was assessed and compared to carbohydrate-binding proteins (lectins). These studies revealed potential structure-binding relationships between HA monosaccharides and HA receptors and novel HA binders, such as Dectin-1 and DEC-205 lectins. The inhibitory effect of HA glycopolymers on hyaluronidase (HAase) activity was also investigated suggesting GlcNAc- and GlcA-based glycopolymers as potential HAase inhibitors.

PEGylated sequence-controlled macromolecules using supramolecular binding to target the Taspase1/Importin α interaction

A novel strategy to inhibit the oncologically relevant protease Taspase1 is explored by developing PEGylated macromolecular ligands presenting the supramolecular binding motif guanidiniocarbonylpyrrole (GCP). Taspase1 requires interaction of its nuclear localization signal (NLS) with import receptor Importin α. We show the synthesis and effective interference of PEGylated multivalent macromolecular ligands with Taspase1-Importin α-complex formation.

Applications of Discrete Synthetic Macromolecules in Life and Materials Science: Recent and Future Trends

In the last decade, the field of sequence-defined polymers and related ultraprecise, monodisperse synthetic macromolecules has grown exponentially. In the early stage, mainly articles or reviews dedicated to the development of synthetic routes toward their preparation have been published. Nowadays, those synthetic methodologies, combined with the elucidation of the structure-property relationships, allow envisioning many promising applications. Consequently, in the past 3 years, application-oriented papers based on discrete synthetic macromolecules emerged. Hence, material science applications such as macromolecular data storage and encryption, self-assembly of discrete structures and foldamers have been the object of many fascinating studies. Moreover, in the area of life sciences, such structures have also been the focus of numerous research studies. Here, it is aimed to highlight these recent applications and to give the reader a critical overview of the future trends in this area of research.

Geared Toward Applications: A Perspective on Functional Sequence-Controlled Polymers

Sequence-controlled polymers are an emerging class of synthetic polymers with a regulated sequence of monomers. In the past decade, tremendous progress has been made in the synthesis of polymers with the sophisticated sequence control approaching the level manifested in biopolymers. In contrast, the exploration of novel functions that can be achieved by controlling synthetic polymer sequences represents an emerging focus in polymer science. This Viewpoint will survey recent advances in the functional applications of sequence-controlled polymers and provide a perspective on the challenges and outlook for pursuing future applications of this fascinating class of macromolecules.

Controlling the Surface Functionalization of Ultrasmall Gold Nanoparticles by Sequence-Defined Macromolecules

Ultrasmall gold nanoparticles (diameter about 2 nm) were surface-functionalized with cysteine-carrying precision macromolecules. These consisted of sequence-defined oligo(amidoamine)s (OAAs) with either two or six cysteine molecules for binding to the gold surface and either with or without a PEG chain (3400 Da). They were characterized by 1 H NMR spectroscopy, 1 H NMR diffusion-ordered spectroscopy (DOSY), small-angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy. The number of precision macromolecules per nanoparticle was determined after fluorescent labeling by UV spectroscopy and also by quantitative 1 H NMR spectroscopy. Each nanoparticle carried between 40 and 100 OAA ligands, depending on the number of cysteine units per OAA. The footprint of each ligand was about 0.074 nm2 per cysteine molecule. OAAs are well suited to stabilize ultrasmall gold nanoparticles by selective surface conjugation and can be used to selectively cover their surface. The presence of the PEG chain considerably increased the hydrodynamic diameter of both dissolved macromolecules and macromolecule-conjugated gold nanoparticles.

Synthesis and self-assembly of amphiphilic precision glycomacromolecules

Amphiphilic precision glycomacromolecules (APG) are synthesized using solid-phase synthesis and studied for their self-assembly behavior and as inhibitors of bacterial adhesion.

Concise and Reliable Syntheses of Glycodendrimers via Self-Activating Click Chemistry: A Robust Strategy for Mimicking Multivalent Glycan-Pathogen Interactions

Individual interactions between glycans and their receptors are usually weak, although these weak interactions can combine to realize a strong interaction (multivalency). Such multivalency plays a crucial role in the recognition of host cells by pathogens. Glycodendrimers are useful materials for the reconstruction of this multivalent interaction. However, the introduction of a large number of glycans to a dendrimer core is fraught with difficulties. We herein synthesized antipathogenic glycodendrimers using the self-activating click chemistry (SACC) method developed by our group. The excellent reactivity of SACC enabled the efficient preparation of sialyl glycan and Gb3 glycan dendrimers, which exhibited strong avidity toward hemagglutinin on influenza virus and Shiga toxin B subunit produced by Escherichia coli, respectively. We demonstrated the usefulness of SACC-based glycodendrimers as antipathogenic compounds.

Effect of PEGylation on Receptor Anchoring and Steric Shielding at Interfaces: An Adhesion and Surface Plasmon Resonance Study with Precision Polymers

This study aims at quantifying the steric shielding effect of multivalent glycoconjugates targeting pathogens by blocking their carbohydrate binding sites. Specifically, PEGylated and non-PEGylated glycoconjugates are studied as inhibitors of lectins and bacterial adhesins evaluating the steric repulsion effect of the nonbinding PEG chains. We use the soft colloidal probe (SCP) adhesion assay to monitor the change in the adhesion energy of mannose (Man)-decorated hydrogel particles on a layer of concanavalin A (ConA) in the presence of sequence-defined multivalent glycoconjugate inhibitors over time. The results show that PEGylated glycoconjugates achieve a stronger adhesion inhibition when compared to non-PEGylated glycoconjugates although the dissociation constants (K_D) of the PEGgylated compounds to ConA were larger. These results appear in line with Escherichia coli adhesion inhibition assays showing a small increase of bacteria detachment by PEGgylated glycoconjugates compared to non-PEGylated compounds. This suggests that an increase of sterical shielding via PEGylation may help reduce the invasiveness of pathogens even after they have adhered. Adhesion studies based on electrostatic interactions using amine-linked PEG of varying molecular weight confirm that such sterical shielding effect is not limited to carbohydrate-mediated adhesion.

Sequence-Defined Heteromultivalent Precision Glycomacromolecules Bearing Sulfonated/Sulfated Nonglycosidic Moieties Preferentially Bind Galectin-3 and Delay Wound Healing of a Galectin-3 Positive Tumor Cell Line in an In Vitro Wound Scratch Assay

Within this work, a new class of sequence-defined heteromultivalent glycomacromolecules bearing lactose residues and nonglycosidic motifs for probing glycoconjugate recognition in carbohydrate recognition domain (CRD) of galectin-3 is presented. Galectins, a family of β-galactoside-binding proteins, are known to play crucial roles in different signaling pathways involved in tumor biology. Thus, research has focused on the design and synthesis of galectin-targeting ligands for use as diagnostic markers or potential therapeutics. Heteromultivalent precision glycomacromolecules have the potential to serve as ligands for galectins. In this work, multivalency and the introduction of nonglycosidic motifs bearing either neutral, amine, or sulfonated/sulfated groups are used to better understand binding in the galectin-3 CRD. Enzyme-linked immunosorbent assays and surface plasmon resonance studies are performed, revealing a positive impact of the sulfonated/sulfated nonglycosidic motifs on galectin-3 binding but not on galectin-1 binding. Selected compounds are then tested with galectin-3 positive MCF 7 breast cancer cells using an in vitro would scratch assay. Preliminary results demonstrate a differential biological effect on MCF 7 cells with high galectin-3 expression in comparison to an HEK 293 control with low galectin-3 expression, indicating the potential for sulfonated/sulfated heteromultivalent glycomacromolecules to serve as preferential ligands for galectin-3 targeting.

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.

Functional Nanoassemblies of Cyclic Polymers Show Amplified Responsiveness and Enhanced Protein-Binding Ability

The physicochemical properties of cyclic polymer adsorbates are significantly influenced by the steric and conformational constraints introduced during their cyclization. These translate into a marked difference in interfacial properties between cyclic polymers and their linear counterparts when they are grafted onto surfaces yielding nanoassemblies or polymer brushes. This difference is particularly clear in the case of cyclic polymer brushes that are designed to chemically interact with the surrounding environment, for instance, by associating with biological components present in the medium, or, alternatively, through a response to a chemical stimulus by a significant change in their properties. The intrinsic architecture characterizing cyclic poly(2-oxazoline)-based polyacid brushes leads to a broad variation in swelling and nanomechanical properties in response to pH change, in comparison with their linear analogues of identical composition and molecular weight. In addition, cyclic glycopolymer brushes derived from polyacids reveal an enhanced exposure of galactose units at the surface, due to their expanded topology, and thus display an increased lectin-binding ability with respect to their linear counterparts. This combination of amplified responsiveness and augmented protein-binding capacity renders cyclic brushes invaluable building blocks for the design of "smart" materials and functional biointerfaces.

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.

Multivalent glycan arrays

Glycan microarrays have become a powerful technology to study biological processes, such as cell-cell interaction, inflammation, and infections. Yet, several challenges, especially in multivalent display, remain. In this introductory lecture we discuss the state-of-the-art glycan microarray technology, with emphasis on novel approaches to access collections of pure glycans and their immobilization on surfaces. Future directions to mimic the natural glycan presentation on an array format, as well as in situ generation of combinatorial glycan collections, are discussed.

Bottlebrush Glycopolymers from 2-Oxazolines and Acrylamides for Targeting Dendritic Cell-Specific Intercellular Adhesion Molecule-3-Grabbing Nonintegrin and Mannose-Binding Lectin

Lectins are omnipresent carbohydrate binding proteins that are involved in a multitude of biological processes. Unearthing their binding properties is a powerful tool toward the understanding and modification of their functions in biological applications. Herein, we present the synthesis of glycopolymers with a brush architecture via a "grafting from" methodology. The use of a versatile 2-oxazoline inimer was demonstrated to open avenues for a wide range of 2-oxazoline/acrylamide bottle brush polymers utilizing aqueous Cu-mediated reversible deactivation radical polymerization (Cu-RDRP). The polymers in the obtained library were assessed for their thermal properties in aqueous solution and their binding toward the C-type animal lectins dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) and mannose-binding lectin (MBL) via surface plasmon resonance spectrometry. The encapsulation properties of a hydrophobic drug-mimicking compound demonstrated the potential use of glyco brush copolymers in biological applications.

Polymer-Stabilized Sialylated Nanoparticles: Synthesis, Optimization, and Differential Binding to Influenza Hemagglutinins

During influenza infection, hemagglutinins (HAs) on the viral surface bind to sialic acids on the host cell's surface. While all HAs bind sialic acids, human influenza targets terminal α2,6 sialic acids and avian influenza targets α2,3 sialic acids. For interspecies transmission (zoonosis), HA must mutate to adapt to these differences. Here, multivalent gold nanoparticles bearing either α2,6- or α2,3-sialyllactosamine have been developed to interrogate a panel of HAs from pathogenic human, low pathogenic avian, and other species' influenza. This method exploits the benefits of multivalent glycan presentation compared to monovalent presentation to increase affinity and investigate how multivalency affects selectivity. Using a library-orientated approach, parameters including polymer coating and core diameter were optimized for maximal binding and specificity were probed using galactosylated particles and a panel of biophysical techniques [ultraviolet-visible spectroscopy, dynamic light scattering, and biolayer interferometry]. The optimized particles were then functionalized with sialyllactosamine and their binding analyzed against a panel of HAs derived from pathogenic influenza strains including low pathogenic avian strains. This showed significant specificity crossover, which is not observed in monovalent formats, with binding of avian HAs to human sialic acids and vice versa in agreement with alternate assay formats. These results demonstrate that precise multivalent presentation is essential to dissect the interactions of HAs and may aid the discovery of tools for disease and zoonosis transmission.

Prophylactic Antiviral Activity of Sulfated Glycomimetic Oligomers and Polymers

In this work, we investigate the potential of highly sulfated synthetic glycomimetics to act as inhibitors of viral binding/infection. Our results indicate that both long-chain glycopolymers and short-chain glycooligomers are capable of preventing viral infection. Notably, glycopolymers efficiently inhibit Human Papillomavirus (HPV16) infection in vitro and maintain their antiviral activity in vivo, while the glycooligomers exert their inhibitory function post attachment of viruses to cells. Moreover, when we tested the potential for broader activity against several other human pathogenic viruses, we observed broad-spectrum antiviral activity of these compounds beyond our initial assumptions. While the compounds tested displayed a range of antiviral efficacies, viruses with rather diverse glycan specificities such as Herpes Simplex Virus (HSV), Influenza A Virus (IAV), and Merkel Cell Polyomavirus (MCPyV) could be targeted. This opens new opportunities to develop broadly active glycomimetic inhibitors of viral entry and infection.

Catechol-functionalized sequence-defined glycomacromolecules as covalent inhibitors of bacterial adhesion

Herein, we present the synthesis of catechol functionalized sequence-defined glycomacromolecules that can covalently block the binding site of lectins and bacterial adhesins.

Stereocontrolled, multi-functional sequence-defined oligomers through automated synthesis

In this work, stereocontrolled sequence-defined oligomers were prepared using an automated thiolactone-based platform that allows post-synthesis functionalisation.

Recovery, Purification, and Reusability of Building Blocks for Solid Phase Synthesis

Solid phase synthesis (SPS) is well established for the synthesis of biomacromolecules such as peptides, oligonucelotides, and oligosaccharides, and today is also used for the synthesis of synthetic macromolecules and polymers. The key feature of this approach is the stepwise assembly of building blocks on solid support, enabling monodispersity and monomer sequence control. However, in order to achieve such control, a high excess of building blocks is required during the reaction. Herein, the recovery, purification, and reusability of building blocks used in SPS, including representative examples of tailor-made building blocks, Fmoc-protected amino acids, and functionalized carbohydrate ligands, are reported for the first time. Results demonstrate the general applicability with recovery in high yields and high purity. Furthermore, the described recovery process can be applied in both manual and automated synthesis using a standard peptide synthesizer. Overall, this process is envisioned to be applicable for a large variety of building blocks used in the SPS of different types of molecules, and to contribute to more resourceful SPS syntheses.

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.

Synthesis of Porphyrin and Bacteriochlorin Glycoconjugates through CuAAC Reaction Tuning

Rapid and reproducible access to a series of unique porphyrin and bacteriochlorin glycoconjugates, including meso-glycosylated porphyrins and bacteriochlorins, and beta-glycosylated porphyrins, via copper catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) is reported for the first time. The work presented highlights the system-dependent reaction conditions required for glycosylation to porphyrins and bacteriochlorins based on the unique electronic properties of each ring system. Attenuated reaction conditions were used to synthesize fifteen new glycosylated porphyrin and bacteriochlorin analogs in 74 - 99% yield, and were extended to solid support to produce the first oligo(amidoamine)-based porphyrin glycoconjugate. These compounds hold significant potential as next generation water soluble catalysts and photodynamic therapy/photodynamic inactivation (PDT/PDI) agents.

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.

Divalent Sialylated Precision Glycooligomers Binding to Polyomaviruses and the Effect of Different Linkers

Divalent precision glycooligomers terminating in N-acetylneuraminic acid (Neu5Ac) or 3'-sialyllactose (3'-SL) with varying linkers between scaffold and the glycan portions are synthesized via solid phase synthesis for co-crystallization studies with the sialic acid-binding major capsid protein VP1 of human Trichodysplasia spinulosa-associated Polyomavirus. High-resolution crystal structures of complexes demonstrate that the compounds bind to VP1 depending on the favorable combination of carbohydrate ligand and linker. It is found that artificial linkers can replace portions of natural carbohydrate linkers as long as they meet certain requirements such as size or flexibility to optimize contact area between ligand and receptor binding sites. The obtained results will influence the design of future high affinity ligands based on the structures presented here, and they can serve as a blueprint to develop multivalent glycooligomers as inhibitors of viral adhesion.

Evaluation of hetero-multivalent lectin binding using a turbidity-based emulsion agglutination assay

Lectin hetero-multivalency, binding to two or more different types of ligands, has been demonstrated to play a role in case of both LecA (a Pseudomonas aeruginosa adhesin) and Cholera Toxin subunit B (a Vibrio cholerae toxin). In order to screen the ligand candidates that involve in hetero-multivalent binding from large molecular libraries, we present a turbidity-based emulsion agglutination (TEA) assay that can be conducted in a high-throughput format using the standard laboratory instruments and reagents. The benefit of this assay is that it relies on the use of emulsions that can be formed using ultrasonication, minimizing the bottleneck of substrate surface functionalization. By measuring the change in turbidity, we could quantify the lectin-induced aggregation rate of oil droplets to determine the relative binding strength between different ligand combinations. The TEA results are consistent with our prior binding results using a nanocube sensor. The developed TEA assay can serve as a high-throughput and customizable tool to screen the potential ligands involved in hetero-multivalent binding.

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.

Effects of linker and liposome anchoring on lactose-functionalized glycomacromolecules as multivalent ligands for binding galectin-3

We combine multivalent presentation of glycan ligands on sequence-defined oligo(amidoamines) and liposomes to achieve high avidity ligands targeting galectin-3.