The applications of block copolymers are myriad, ranging from electronics to functionalized resins to therapeutics. The ring-opening metathesis polymerization (ROMP) is an especially valuable reaction for block copolymer assembly because each block can be generated with length control. We sought to use this polymerization to expand the repertoire of block copolymers by implementing a strategy that involves post-polymerization modification of a backbone bearing selectively reactive groups. To this end, we demonstrate that ROMP can be used to synthesize a block copolymer scaffold that possesses three types of functional groups – a succinimidyl ester, an α-chloroacetamide group, and a ketone – each of which can be modified independently. Thus, a single scaffold can be elaborated to afford a wide range of block copolymers. Exploiting this synthetic approach and the length control offered by ROMP, we assemble block copolymers capable of traversing the membrane and entering mammalian cells.

Because of the central role of Concanavalin A (Con A) in the study of protein-carbohydrate interactions, a thorough understanding of the multivalent functions of Con A is imperative. Here, the association of monomeric and dimeric derivatives of Con A with mannose-functionalized generation two through six PAMAM dendrimers is reported. Hemagglutination assay results indicate relatively low activity of the dendrimers for monomeric Con A, with small increases as the dendrimer generation increases. Isothermal titration microcalorimetry experiments indicate monovalent binding by the dendrimers with monomeric Con A and divalent binding by the dendrimers with dimeric Con A. Continuous (and comparable) but narrowing increases in enthalpy and entropy and the slight increase in association constants with monomeric Con A as the dendrimer generation increases suggest favorable proximity effects on binding. Both the hemagglutination assay and the calorimetry experiments suggest that statistical binding enhancements can be observed with monomeric Con A. The results described here should allow for a more quantitative evaluation of the enhancements that are often observed in protein-carbohydrate interactions for glycosylated frameworks binding to Con A.

Olefin metathesis has emerged as a promising strategy for modulating the stability and activity of biologically relevant compounds; however, the ability to control olefin geometry in the product remains a challenge. Recent advances in the design of cyclometalated ruthenium catalysts has led to new strategies for achieving such control with high fidelity and Z selectivity, but the scope and limitations of these catalysts on substrates bearing multiple functionalities, including peptides, remained unexplored. Herein, we report an assessment of various factors that contribute to both productive and nonproductive Z-selective metathesis on peptides. The influence of sterics, side-chain identity, and preorganization through peptide secondary structure are explored by homodimerization, cross metathesis, and ring-closing metathesis. Our results indicate that the amino acid side chain and identity of the olefin profoundly influence the activity of cyclometalated ruthenium catalysts in Z-selective metathesis. The criteria set forth for achieving high conversion and Z selectivity are highlighted by cross metathesis and ring-closing metathesis on diverse peptide substrates. The principles outlined in this report are important not only for expanding the scope of Z-selective olefin metathesis to peptides but also for applying stereoselective olefin metathesis in general synthetic endeavors.

The C-type lectin dendritic cell-specific intercellular adhesion molecule 3–grabbing nonintegrin (DC-SIGN) can serve as a docking site for pathogens on the surface of dendritic cells. Pathogen binding to DC-SIGN can have diverse consequences for the host. DC-SIGN can facilitate HIV-1 dissemination, but the interaction of Mycobacterium tuberculosis with DC-SIGN is important for host immunity. The ability of pathogens to target DC-SIGN provides impetus to identify ligands that can perturb these interactions. Here, we describe the first stable small molecule inhibitors of DC-SIGN. These inhibitors were derived from a collection of quinoxalinones, which were assembled using a tandem cross metathesis-hydrogenation sequence. To assess the ability of these small molecules to block DC-SIGN-mediated glycan adhesion and internalization, we developed a sensitive flow cytometry assay. Our results reveal that the quinoxalinones are effective inhibitors of DC-SIGN–glycan interactions. These compounds block both glycan binding to cells and glycan internalization. We anticipate that these non-carbohydrate inhibitors can be used to elucidate the role of DC-SIGN in pathogenesis and immune function.

The binding of a polymeric ligand to a cell surface receptor can promote its internalization. Methods to track and visualize multivalent ligands within a cell can give rise to new therapeutic strategies and illuminate signaling processes. We have used the features of the ring-opening metathesis polymerization (ROMP) to develop a general strategy for synthesizing multivalent ligands equipped with a latent fluorophore. The utility of ligands of this type is highlighted by visualizing multivalent antigen internalization in live B cells.Advances in organic and polymer chemistry are providing access to new classes of bioactive polymers. 1 With the ability to generate synthetic macromolecules that vary in structure and physical properties, the applications of polymers have expanded rapidly. Some uses include as substrates for cell growth and differentiation, 2 vehicles for drug delivery, 3 therapeutics, 4 and molecules for studying cell signaling. 5 For some biological applications, bioactive polymers must be taken up into cells. Still, little is known about the cellular internalization and trafficking of polymers. Here, we present an approach for following these processes.The bioactive polymers that we focused upon were those generated by ruthenium carbeneinitiated ring-opening metathesis polymerization (ROMP). It was shown that ROMP could be used to generate biologically-active polymers over 10 years ago. 6 Since that time, ROMP has been used produce materials with a variety of biological activities. 7 Continuous advances in catalyst development and polymerization techniques have provided methods to control key features of polymer structure, including their length and the functional groups they present. 8 Ruthenium carbene initiators tolerate a diverse array of functional groups; therefore, they can be used synthesize highly functionalized polymers with tailored biological activities. ROMP initially was used to generate polymers that act on the outside of the cell, but more recently, it has been employed to assemble compounds that can be internalized by cells. Our interest in polymer uptake was prompted by our studies of B cell signaling. 9 For example, polymers generated by ROMP that display antigenic epitopes can promote antibody production in vivo. The ability of these polymers to activate this process depends upon their interactions with the antigen-specific B cell receptor (BCR), a membrane-bound immunoglobulin on the surface of B cells. These polymers bind to the specific B cell receptor to activate signaling but they also promote its internalization. We therefore anticipated that, like other antigens, these polymers would be taken up by endocytosis. To investigate polymer internalization, we envisioned using antigenic polymers equipped with a group that would report directly on internalization.Most approaches to following ligand internalization rely on appending a fluorescent dye to the molecule of interest. Uptake is detected using a discontinuous assay (typically fluorescence microscopy). Becaus...