End-functionalized polymers by controlled/living radical polymerizations: synthesis and applications

This review focuses on end-functionalized polymers synthesized by controlled/living radical polymerizations and the applications in fields including bioconjugate formation, surface modification, topology construction, and self-assembly.

Degradable polymer prodrugs with adjustable activity from drug-initiated radical ring-opening copolymerization

Degradable polymer prodrugs based on gemcitabine (Gem) as an anticancer drug were synthesized by 'drug-initiated' nitroxide-mediated radical ring-opening copolymerization (NMrROP) of methacrylic esters and 2-methylene-4-phenyl-1,3-dioxolane (MPDL). Different structural parameters were varied to determine the best biological performances: the nature of the monomer [i.e., oligo(ethylene glycol) methacrylate (OEGMA) or methyl methacrylate (MMA)], the nature of the Gem-polymer linker (i.e., amide or amide and diglycolate) and the MPDL content in the copolymer. Depending on the nature of the methacrylate monomer, two small libraries of water-soluble copolymer prodrugs and nanoparticles were obtained (M n ∼10 000 g mol-1, Đ = 1.1-1.5), which exhibited tunable hydrolytic degradation under accelerated conditions governed by the MPDL content. Drug-release profiles in human serum and in vitro anticancer activity on different cell lines enabled preliminary structure-activity relationships to be established. The cytotoxicity was independently governed by: (i) the MPDL content - the lower the MPDL content, the greater the cytotoxicity; (ii) the nature of the linker - the presence of a labile diglycolate linker enabled a greater Gem release compared to a simple amide bond and (iii) the hydrophilicity of the methacrylate monomer-OEGMA enabled a greater anticancer activity to be obtained compared to MMA-based polymer prodrugs. Remarkably, the optimal structural parameters enabled reaching the cytotoxic activity of the parent (free) drug.

C-ON bond homolysis of alkoxyamines: when too high polarity is detrimental

Throughout the last decade, the effect of electron withdrawing groups (EWGs) has been known to play a role - minor or moderate depending on the nitroxyl fragment R₁R₂NO - in the change in the homolysis rate constant (k_d) for C-ON bond homolysis in alkoxyamines (R₁R₂NOR). It has been shown that the effect of EWGs on k_d is described by a linear relationship with the electrical Hammett constant σ_I. Since then, linear multi-parameter relationships f(σ_RS,ν,σ_I) have been developed to account for the effects involved in the changes in k_d, which are the stabilization of the released radical (σ_RS) and the bulkiness (ν) and polarity (σ_I) of the alkyl fragment. Since a decade ago, new results have been published highlighting the limits of such correlations. In this article, previous multi-parameter linear relationships are amended using a parabolic model, i.e. (σ_I,nitroxide - σ_I,alkyl)², to describe the effect of EWGs in the alkyl fragment on k_d. In contrast to previous studies, these improved linear multi-parameter relationships f(σ_RS,ν,Δσ_I²) are able to account for the presence of several EWGs on the alkyl fragment, R. An unexpectedly strong solvent effect - a ca. 1500-fold increase in k_d - from tert-butylbenzene to the water/methanol mixture is also observed for 3-((2,2,6,6-tetramethylpiperidin-1-yl)oxyl)pentane-2,4-dione 1b in comparison to a ca. 5-fold increase in k_d that is generally observed.

Responsive Hybrid (Poly)peptide-Polymer Conjugates

(Poly)peptide-polymer conjugates continue to garner significant interest in the production of functional materials given their composition of natural and synthetic building blocks that confer select and synergistic properties. Owing to opportunities to design predefined architectures and structures with different morphologies, these hybrid conjugates enable new approaches for producing micro- or nanomaterials. Their modular design enables the incorporation of multiple responsive properties into a single conjugate. This review presents recent advances in (poly)peptide-polymer conjugates for drug-delivery applications, with a specific focus on the utility of the (poly)peptide component in the assembly of particles and nanogels, as well as the role of the peptide in triggered drug release.

Structure–cytotoxicity relationship of drug-initiated polymer prodrug nanoparticles

Cladribine (CdA)-based polymer prodrug nanoparticles were obtained by “drug-initiated” RAFT polymerization of squalenyl methacrylate (SqMA) from two different CdA-bearing chain transfer agents (CTAs) to evaluate the influence of the nature of the linkage between CdA and the CTA, and the bulkiness of the polymer, on the drug release and the biological performance.

Dual-initiator alkoxyamines with an N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl) nitroxide moiety for preparation of block co-polymers

Novel SG1-based alkoxyamines were used as initiators for preparation of block-copolymers both, by sequential NMP and by graft-polymerization.