Secreted and surface-displayed carbohydrates are essential for virulence and viability of many parasites, including for immune system evasion. We have identified the α-Gal trisaccharide epitope on the surface of the protozoan parasites Leishmania infantum and Leishmania amazonensis, the etiological agents of visceral and cutaneous leishmaniasis, respectively, with the latter bearing larger amounts of α-Gal than the former. A polyvalent α-Gal conjugate on the immunogenic Qβ virus-like particle was tested as a vaccine against Leishmania infection in a C57BL/6 α-galactosyltransferase knockout mouse model, which mimics human hosts in producing high titers of anti-α-Gal antibodies. As expected, α-Gal-T knockout mice infected with promastigotes of both Leishmania species showed significantly lower parasite load in the liver and slightly decreased levels in the spleen, compared with wild-type mice. Vaccination with Qβ–α-Gal nanoparticles protected the knockout mice against Leishmania challenge, eliminating the infection and proliferation of parasites in the liver and spleen as probed by qPCR. The α-Gal epitope may therefore be considered as a vaccine candidate to block human cutaneous and visceral leishmaniasis.

Bicyclo[3.3.1]nonane (BCN) polycations were synthesized by the reaction of the bivalent electrophile thiabicyclo[3.3.1]nonane dinitrate with a series of simple bis(pyridine) nucleophiles. Oligomers of moderate chain length were formed in a modular approach that tolerated the inclusion of functionalized and variable-length linkers between the pyridine units. Post-polymerization modification via copper-catalyzed azide–alkyne cyloaddition was enabled by the inclusion of terminal alkyne groups in these monomers. Most of the resulting polymers, new members of the polyionene class, inhibited the growth of bacteria at the μg/mL level and killed static bacterial cells at polymer concentrations of tens of ng/mL, with moderate to good selectivity with respect to lysis of red blood cells. While resistance to the BCN polymers was developed only very slowly over multiple passages, a degradable version of the polycation was observed to make E. coli cells more susceptible to other quaternary ammonium based antimicrobials. Solid substrates (glass and crystalline silicon) covalently functionalized with a representative BCN polycation were also able to repetitively kill bacteria in solution at high rates and with cleaning by simple sonication between exposures.

A compact and stable bicyclic bridged ketal was developed as a ligand for the asialoglycoprotein receptor (ASGPR). This compound showed excellent ligand efficiency, and the molecular details of binding were revealed by the first X-ray crystal structures of ligand-bound ASGPR. This analogue was used to make potent di- and trivalent binders of ASGPR. Extensive characterization of the function of these compounds showed rapid ASGPR-dependent cellular uptake in vitro and high levels of liver/plasma selectivity in vivo. Assessment of the biodistribution in rodents of a prototypical Alexa647-labeled trivalent conjugate showed selective hepatocyte targeting with no detectable distribution in nonparenchymal cells. This molecule also exhibited increased ASGPR-directed hepatocellular uptake and prolonged retention compared to a similar GalNAc derived trimer conjugate. Selective release in the liver of a passively permeable small-molecule cargo was achieved by retro-Diels–Alder cleavage of an oxanorbornadiene linkage, presumably upon encountering intracellular thiol. Therefore, the multicomponent construct described here represents a highly efficient delivery vehicle to hepatocytes.

The copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction is a powerful tool for making connections in both organic reactions and biological systems. However, the use of this ligation process in living cells is limited by the toxicity associated with unbound copper ions. As an initial attempt to create peptide-based accelerating ligands capable of cellular expression, we performed synthesis and selection for such species on solid-phase synthesis beads bearing both candidate ligand and alkyne substrate. A simple histidine-containing motif (HXXH) was identified, and found after solution-phase optimization to produce single-turnover systems showing moderate rate acceleration over the ligand-free reaction. CuAAC reaction rates and yields for different alkynes were found to respond to the peptide ligands, demonstrating a substrate scope beyond what was used for the selection steps, but also illustrating the potential difficulty in evolving a general CuAAC catalyst.

Furfuryl carbamates are labile and require care to be accessed by activating furfuryl alcohols. An alternative oxanorbornadiene (OND)-based strategy is presented for the preparation of 5-R-substituted furfuryl carbamates via the reactions of amines with intermediate OND carbonates. The resulting OND carbamates, which are stable for several months, undergo thiol mediated retro-Diels–Alder reaction to deliver the desired furfuryl carbamates in a single flask. Conditions for the selective hydrolysis of furfuryl carbamates in the presence of tert-butyloxycarbonyl (Boc) groups were identified, and it was shown that furfuryl carbamates can be used as a prodrug handle.

A new family of modular, fragmentable oligo- and polycations has been developed based on the reactions of 9-thiabicyclo[3.3.1]dichloride and related compounds with substituted dipyridyl nucleophiles by an anchimeric assistance mechanism. Each bond-forming event in this condensation polymerization process generates a positive charge in the main chain. Product lengths were found to be dependent on the reactivity of the electrophile, which was tunable by changing the nature of the leaving group β to sulfur. The monomers were easily synthesized, and the resulting readily available polymers were found to be highly efficient binders of nucleic acid. They exhibited properties of cytotoxicity and DNA transfection expected of such polycationic materials, but with interesting structure–activity differences that remain to be explored. The polycations decomposed by hydrolysis at rates dependent on the leaving group ability of the pyridyl unit, which correlated roughly with the pKa of its conjugate acid. Polymer decomposition occurs simultaneously throughout the length of the chains, rather than from the ends; the decomposition products were tested and found to be only minimally toxic to cultured cells.

Oxanorbornadiene dicarboxylate (OND) reagents were explored for the purpose of binding and releasing chemical cargos from endogenous circulating serum albumins. ONDs bearing gadolinium chelates as model cargos exhibited variable conjugation efficiencies with albumin in rat subjects that are consistent with the observed reactivity of each linker and their observed stability toward serum hydrolases in vitro. The terminal elimination rate from circulation was dependent on the identity of the OND used, and increased circulation time of gadolinium cargo was achieved for linkers bearing electrophilic fragments designed to react with cysteine-34 of circulating serum albumin. This binding of and release from endogenous albumin highlights the potential of OND linkers in the context of optimizing the pharmacokinetic parameters of drugs or diagnostic agents.

The α-Gal antigen [Galα(1,3)Galβ(1,4)GlcNAcα] is an immunodominant epitope displayed by infective trypomastigote forms of Trypanosoma cruzi, the causative agent of Chagas disease. A virus-like particle displaying a high density of α-Gal was found to be a superior reagent for the ELISA-based serological diagnosis of Chagas disease and the assessment of treatment effectiveness. A panel of sera from patients chronically infected with T. cruzi, both untreated and benznidazole-treated, was compared with sera from patients with leishmaniasis and from healthy donors. The nanoparticle-α-Gal construct allowed for perfect discrimination between Chagas patients and the others, avoiding false negative and false positive results obtained with current state-of-the-art reagents. As previously reported with purified α-Gal-containing glycosylphosphatidylinositol-anchored mucins, the current study also showed concentrations of anti-α-Gal IgG to decrease substantially in patients receiving treatment with benznidazole, suggesting that the semiquantitative assessment of serum levels of this highly abundant type of antibody can report on disease status in individual patients.Keywords: anti-α-Gal antibodies; Chagas disease; diagnostics; ELISA; treatment assessment; Trypanosoma cruzi; α-Gal;

Oxanorbornadiene dicarboxylate (OND) reagents are potent Michael acceptors, the adducts of which undergo fragmentation by retro-Diels–Alder reaction at rates that vary with the substitution pattern on the OND moiety. Rapid conjugate addition between thiol-terminated tetravalent PEG and multivalent ONDs yielded self-supporting hydrogels within 1 min at physiological temperature and pH. Erosion of representative hydrogel formulations occurred with predictable and pH-independent rates on the order of minutes to weeks. These materials could be made non-degradable by epoxidation of the OND linkers without slowing gelation. Hydrogels prepared with OND linkers of equal valence had comparable physical properties, as determined by equilibrium swelling behavior, indicating similar internal network structure. Diffusion and release of entrained cargo varied with both the rate of degradation of PEG-OND hydrogels and the hydrodynamic radius of the entrained species. These results highlight the utility of OND linkers in the preparation of degradable network materials with potential applications in sustained release.

The in situ preparation and trapping of chlorine azide provided a versatile one-pot method for the azidochlorination of alkenes. Gaseous ClN3 generated from sodium azide, hypochlorite, and acetic acid can be explosive if isolation is attempted. Instead, we generated the reagent in biphasic media in the presence of olefinic compounds dissolved in the organic layer or evenly emulsified throughout the solution in the absence of organic solvent. Under these conditions, ClN3 is created slowly and trapped immediately at the aqueous–organic interface. The resulting safe and reliable procedure provided 1,2-azidochloride derivatives of a variety of substrates, with evidence for both polar and radical mechanisms. Minor impurities characterized in the product mixtures indicated the presence of alternative reaction pathways deriving primarily from radical intermediates.

The selective chemical modification of biological molecules drives a good portion of modern drug development and fundamental biological research. While a few early examples of reactions that engage amine and thiol groups on proteins helped establish the value of such processes, the development of reactions that avoid most biological molecules so as to achieve selectivity in desired bond-forming events has revolutionized the field. We provide an update on recent developments in bioorthogonal chemistry that highlights key advances in reaction rates, biocompatibility, and applications. While not exhaustive, we hope this summary allows the reader to appreciate the rich continuing development of good chemistry that operates in the biological setting.

A design for the selective release of drug molecules in the liver was tested, involving the attachment of a representative active agent by an ester linkage to various 2-substituted 5-aminovaleric acid carbamates. The anticipated pathway of carboxylesterase-1-mediated carbamate cleavage followed by lactamization and drug release was frustrated by unexpectedly high sensitivity of the ester linkage toward hydrolysis by carboxylesterase-2 and other microsomal components.

Virus-like particles (VLPs) are unique macromolecular structures that hold great promise in biomedical and biomaterial applications. The interior of the 30 nm-diameter Qβ VLP was functionalized by a three-step process: (1) hydrolytic removal of endogenously packaged RNA, (2) covalent attachment of initiator molecules to unnatural amino acid residues located on the interior capsid surface, and (3) atom-transfer radical polymerization of tertiary amine-bearing methacrylate monomers. The resulting polymer-containing particles were moderately expanded in size; however, biotin-derivatized polymer strands were only very weakly accessible to avidin, suggesting that most of the polymer was confined within the protein shell. The polymer-containing particles were also found to exhibit physical and chemical properties characteristic of positively charged nanostructures, including the ability to easily enter mammalian cells and deliver functional small interfering RNA.Keywords: ATRP; encapsulation; polymerization; unnatural amino acid; virus-like particle

Copper-catalyzed azide–alkyne cycloaddition (CuAAC) has found numerous applications in a variety of fields. We report here only modest differences in the reactivity of various classes of terminal alkynes under typical bioconjugative and preparative organic conditions. Propargyl compounds represent an excellent combination of azide reactivity, ease of installation, and cost. Electronically activated propiolamides are slightly more reactive, at the expense of increased propensity for Michael addition. Certain alkynes, including tertiary propargyl carbamates, are not suitable for bioconjugation due to copper-induced fragmentation. A fluorogenic probe based on such reactivity is available in one step from rhodamine 110 and can be useful for optimization of CuAAC conditions.