UCLA

The vast applications realized through polymer chemistry are in part due to the numerous possible polymeric architectures that contribute to distinct structure-property relationships. Despite the utility of designed polymeric scaffolds, their synthesis can pose a significant challenge. In the case of macromolecular targets not polymerizable by similar methods, post-polymerization conjugation is required. This synthetic strategy necessitates a highly efficient conjugation due to the low concentration of reactive units and the steric hindrance caused by polymer chains. The Maynard and Spokoyny labs have developed isolable and bench-stable (Me-DalPhos)Au(III)Aryl (Me-DalPhos = (Ad2P(o-C6H4)NMe2) reagents for the application of cysteine S-arylation. This S-arylation chemistry is highly chemoselective, pH tolerant (0.5-14), and rapid at room temperature. These Au(III)-oxidative addition complexes were hypothesized to be excellent facilitators of complex polymer architecture synthesis via ligand exchange and subsequent reductive elimination with a thiol-containing macromolecular coupling partner. The selectivity of (Me-DalPhos)Au(I)Cl for aryl iodide oxidative addition and the thiophilicty of Au(III) permits the use of many desirable side-chain functional groups without concern of cross-reactivity. Furthermore, the efficiency of this reaction was hypothesized to obviate the necessity of large excess equivalents needed for polymer conjugations. First, polymer functionalization was achieved via Au(III)-mediated direct conjugation of thiol-containing small molecule and polymer coupling partners (Chapter 2). Controlled synthesis of both thiol- and aryl iodide-capped polymers was achieved by synthetically modifying small molecule initiators and termination moieties for polymers prepared by reversible addition fragmentation chain-transfer (RAFT) polymerization, ring opening polymerization (ROP), ring opening metathesis polymerization (ROMP), and atom transfer radical polymerization (ATRP). All aryl iodide polymers underwent oxidative addition with (Me-DalPhos)Au(I)Cl at room temperature under ambient conditions to afford Au(III)-polymer precursors. Complete conversion was observed by 1H NMR. Reductive elimination reactions between thiol- and Au(III)-capped polymers occurred in one hour, in open air, and using an equimolar ratio of polymer precursors. Complete conversion to block copolymer products was observed by size exclusion chromatography (SEC), 1H NMR, and 2D Diffusion Ordered Spectroscopy (DOSY) NMR. Next, cyclic polymer-protein conjugates were prepared using Au(III)-chemistry and compared to linear polymer-protein counterparts (Chapter 3). Cyclic polymers were synthesized via a Williamson etherification bimolecular ring closure strategy. This was followed by oxidative addition with Au(I) to yield a cyclic Au(III)-PEG reagent with minimal linear contaminants. Cyclic Au(III) PEG was conjugated to a model protein containing one thiol, DARPin. For direct comparison, a linear Au(III) PEG reagent of the same molecular weight also underwent DARPin reductive elimination. We compared activity, thermal stability, secondary structure via circular dichroism (CD), and hydrodynamic radii via SDS-PAGE and FPLC for cyclic polymer-DARPin conjugates with their linear polymer counterparts. While biophysical differences were minimal for these bioconjugates, the hydrodynamic radius was smaller for that of the cyclic polymer conjugate which may be useful for drug formulations. Furthermore, molecular dynamics calculations demonstrated that the cyclic polymer interacted less frequently with the protein active site. This work adds to the scientific understanding of the effect of polymer architecture on protein-polymer conjugate properties. Then, polymeric Au(III) reagents mediated the regioselective formation of block copolymer proteins and protein heterodimers (Chapter 4). Small molecule competition studies via LCMS and buried volume calculations were used to determine aryl-iodide substrates that could impart S-arylation regioselectivity for Au(III) reagents. A meta-xylene derivative was determined to be the optimal substrate, as it provided steric hindrance that slowed the kinetic rate of S-arylation. Subsequently, a heterotelechelic PEG reagent (2 kDa) was synthesized, where one terminus contained a para aryl-iodide and the remaining termini contained a meta-xylene aryl-iodide. Oxidative addition yielded a regioselective and bifunctional S-arylation PEG reagent. This PEG reagent underwent reductive elimination with DARPin to produce a monopegylated product, with no observable formation of protein homodimer via SDS-PAGE and LCMS. Without further purification, a second reductive elimination with a thiol-terminated pNIPAM and a thiolated glucagon was performed, highlighting the practicality of this one-pot method. Finally, electrospun polymer fibers were functionalized using Au(III) organometallic complexes (Chapter 5). Polyesters were prepared with aryl-iodide end-groups and electrospun into fiber mats under positive voltage. Upon discovery that the polyester fiber morphology was not maintained during oxidative addition due to solubility in DCM, a copolymer of norbornene imide derivatives containing hydrophilic amines and aryl iodides for conjugation was prepared by ROMP. However, gold nanoparticles were observed during oxidative addition of these polyimide fibers in DCM, despite a more compatible solubility relationship. As an alternative, a copolymer of norbornene imide derivatives containing thiols and hydrophobic butyl groups was synthesized for reductive elimination with pre-made Au(III) oxidative addition complexes in water. Surprisingly, fiber morphology was disturbed as observed by SEM, and successful conjugation could not be verified when compared to negative controls.