Synthesis of Neoglycopolymers by a Combination of “Click Chemistry” and Living Radical Polymerization

Preparation of a new electro-optic polymer cross-linkable via copper-free thermal Huisgen cyclo-addition and fabrication of optical waveguides by Reactive Ion Etching

High-quality trails of ridge waveguides were successfully fabricated using a new cross-linkable polymer (PCC01) by UV photolithography followed by Reactive-Ion Etching (RIE) process. The cross-linking reaction of PCC01 is based on the copper-free Huisgen cyclo-addition between an azide and an acetylene group. The new cross-linkable polymer (PCC01) consists of a structural modification of the previously described materials (Scarpaci et al. Polym. Chem.2011, 2, 157), because the ethynyl group is functionalized by a methyl group instead of the TMS protecting group. This feature prevents the formation of silica (SiO(2)) generated by trimethylsilyl groups and which was stopping the engraving process before completion. Herein, we describe the synthesis, the NLO characterizations, and the fabrication of a high-quality ridge waveguide with PCC01. The new cross-linkable polymer PCC01 not only solves the problems encountered with our previously described polymers, but also presents an enhancement of the electro-optic stability, because d(33) coefficients up to 30 pm/V stable at 150 °C were recorded.

Biotinylated thermoresponsive core cross-linked nanoparticles via RAFT polymerization and "click" chemistry

A straightforward approach to the synthesis of "clickable" thermoresponsive core cross-linked (CCL) nanoparticles was developed. This approach was based on reversible addition-fragmentation chain transfer (RAFT) radical cross-linking polymerization of styrene and divinylbenzene with azide-functionalized poly(N-isopropylacrylamide) (PNIPAM-N(3)) as macro chain transfer agent in a selective solvent. Spherical nanoparticles with a diameter of 12nm were obtained after 24h polymerization. When the lyophilized CCL nanoparticles were dispersed in THF, spherical nanoparticles were observed, confirming the stability of CCL nanoparticles. The transmission electron microscopy (TEM) studies demonstrated that spherical nanoparticles and wormlike structure coexisted in the aqueous solution. The CCL nanoparticles have a lower critical solution temperature (LCST) at about 29.6°C, a little lower than that of PNIPAM homopolymer. Biotin molecules were conjugated to the surface of CCL nanoparticles via "click" chemistry in aqueous media. After bioconjugation, the LCST shifted to 28.3°C. The bioavailability of biotin to protein avidin was evaluated by a 4'-hydroxyazobenzene-2-carboxylic acid/avidin (HABA/avidin) binding assay and TEM.

Synthesis of glycopolymers for microarray applications via ligation of reducing sugars to a poly(acryloyl hydrazide) scaffold

In this paper, we report on a general synthetic strategy for the assembly of glycopolymers that capitalizes on the intrinsic reactivity of reducing glycans toward hydrazides to form stable cyclic N-glycosides. We developed a poly(acryloyl hydrazide) (PAH) scaffold to which we conjugated a variety of reducing glycans ranging in structure from simple mono- and disaccharides to considerably more complex human milk and blood oligosaccharides. The conjugation proceeds under mild conditions with excellent ligation efficiencies and in a stereoselective manner, providing glycopolymers with pendant glycans accommodated mostly in their cyclic β-glycosidic form. Utilizing a biotin-terminated PAH scaffold prepared via RAFT polymerization, we quickly assembled a panel of glycopolymers that we microarrayed on streptavidin-coated glass. We then demonstrated that in these microarrays, the glycopolymer ligands bind lectins according to the structures of their pendant glycans. Importantly, glycopolymers containing biologically relevant branched oligosaccharides, such as sialyl Lewis^x, as well as sulfated glycosaminoglycan-like epitopes can be readily prepared using our methodology.

Convergent assembly and surface modification of multifunctional dendrimers by three consecutive click reactions

Multifunctional dendrimers bearing two or more surface functionalities have the promise to provide smart drug delivery devices that can for example combine tissue targeting and imaging or be directed more precisely to a specific tissue or cell type. We have developed a concise synthetic methodology for efficient dendrimer assembly and heterobifunctionalization based on three sequential azide-alkyne cycloadditions. The methodology is compatible with biologically important compounds rich in chemical functionalities such as peptides, carbohydrates, and fluorescent tags. In the approach, a strain-promoted azide-alkyne cycloaddition (SPAAC) between polyester dendrons modified at the focal point with an azido and 4-dibenzocyclooctynol (DIBO) moiety provided dendrimers bearing terminal and TMS-protected (TMS=trimethylsilyl) alkynes at the periphery. The terminal alkynes were outfitted with azido-modified polyethylene glycol (PEG) chains or galactosyl residues by using Cu(I) -catalyzed azide-alkyne cycloadditions (CuAAC). Next, a one-pot TMS deprotection and second click reaction of the resulting terminal alkyne with azido-containing compounds gave multifunctional dendrimers bearing complex biologically active moieties at the periphery.

High-affinity glycopolymer binding to human DC-SIGN and disruption of DC-SIGN interactions with HIV envelope glycoprotein

Noncovalent interactions between complex carbohydrates and proteins drive many fundamental processes within biological systems, including human immunity. In this report we aimed to investigate the potential of mannose-containing glycopolymers to interact with human DC-SIGN and the ability of these glycopolymers to inhibit the interactions between DC-SIGN and the HIV envelope glycoprotein gp120. We used a library of glycopolymers that are prepared via combination of copper-mediated living radical polymerization and azide-alkyne [3+2] Huisgen cycloaddition reaction. We demonstrate that a relatively simple glycopolymer can effectively prevent the interactions between a human dendritic cell associated lectin (DC-SIGN) and the viral envelope glycoprotein gp120. This approach may give rise to novel insights into the mechanisms of HIV infection and provide potential new therapeutics.

"Clickable" polymer nanoparticles: a modular scaffold for surface functionalization

The versatility of copper-catalyzed alkyne-azide coupling (CuAAC) in functionalizing drug-loaded polymer nanoparticles is demonstrated via the modification of surfaces of acetylene-functionalized PNPs with folate, biotin, and gold nanoparticles.

New amphiphilic glycopolymers by click functionalization of random copolymers - application to the colloidal stabilisation of polymer nanoparticles and their interaction with concanavalin A lectin

Glycopolymers with mannose units were readily prepared by click chemistry of an azido mannopyranoside derivative and a poly(propargyl acrylate-co-N-vinyl pyrrolidone). These glycopolymers were used as polymer surfactants, in order to obtain glycosylated polycaprolactone nanoparticles. Optimum stabilization for long time storage was achieved by using a mixture of glycopolymers and the non-ionic triblock copolymer Pluronic^® F-68. The mannose moieties are accessible at the surface of nanoparticles and available for molecular recognition by concanavalin A lectin. Interaction of mannose units with the lectin were evaluated by measuring the changes in nanoparticles size by dynamic light scattering in dilute media.

Polymeric phosphorylcholine-camptothecin conjugates prepared by controlled free radical polymerization and click chemistry

Novel polymer-drug conjugates, consisting of zwitterionic poly(methacryloyloxyethyl phosphorylcholine) (polyMPC) as the polymer component, and camptothecin (CPT) as the drug, were prepared by two methods. In one case, CPT was transformed by acylation into a functional initiator for copper catalyzed atom transfer radical polymerization (ATRP), and polyMPC was grown from this therapeutic initiator. In the other case, a one-pot ATRP-"click" conjugation strategy was employed to synthesize novel polyMPC structures containing multiple copies of the drug pendant to the zwitterionic polymer chain. The latter method allows polyMPC-graft-CPT conjugates to be prepared with a high weight percent drug loading (up to 14% CPT) with excellent solubility in pure water (>250 mg/mL). The linkage chemistry chosen between the polyMPC backbone and the pendant drugs proved critically important for assuring drug release within a time frame reasonable to consider these structures as a platform for injectable cancer therapeutics. Liberation of the drug from the polymer backbone was monitored by high-performance liquid chromatography, using size-exclusion and reverse-phase columns, and the toxicity of the polymer-drug conjugates was examined in cell culture against breast (MCF7), ovarian (OVCAR-3), and colorectal (COLO 205) cancer cell lines.