Protein and peptide therapeutics represent a large class of treatments for a plethora of diseases, with more than 100 therapeutics garnering approval by the Food and Drug Administration (FDA) for clinical use. Conjugation of synthetic polymers to these biomacromolecule therapeutics significantly increases both the stability and in vivo lifetime of the drug, making the application of proteins and peptides as disease treatments more feasible and effective. Bioconjugation techniques for biomolecule–polymer conjugation are numerous; however, slow kinetics and steric challenges generally necessitate excess reagents or long reaction times. Organometallic transformations are known to circumvent these issues; yet, harsh reaction conditions, incompatibility in aqueous media, and substrate promiscuity often limit their use in a biological context. The work reported herein demonstrates a facile and benign organometallic Au(III) S-arylation approach that enables the synthesis of biomolecule-polymer conjugates rapidly and at low concentrations and temperatures with near equimolar amounts of polymer reagent.
First, poly(ethylene glycol) monomethyl ether (mPEG)-protein conjugates were synthesized with high efficiency (Chapter 2). Isolable and bench-stable 2, 5, and 10 kDa mPEG-Au(III) reagents were synthesized via oxidative addition into terminal aryl iodide substituents installed on mPEG substrates with a (Me-DalPhos)Au(I)Cl precursor. Reaction of the isolable mPEG-Au(III) oxidative addition complexes with a cysteine thiol on a biomolecule resulted in facile and selective cysteine arylation chemistry, forging covalent S-aryl linkages and affording the mPEG-biomolecule conjugates. Notably, low polymer reagent loadings were used to achieve near quantitative conversion at room temperature in 1 min due to the rapid kinetics and high chemoselectivity of this Au-based bioconjugation approach. Therefore, this work represents an important addition to the protein–polymer conjugation chemical toolbox.
Next, atom transfer radical polymerization (ATRP) is utilized to synthesize controlled polymers which subsequently undergo oxidative addition to form Au(III) polymer reagents (Chapter 3). These reagents are then reacted with biomolecules with low reagent loading and under mild conditions to form biomolecule polymer conjugates via the grafting to approach. In a complementary approach, Au(III) ATRP initiator reagents are synthesized for subsequent bioconjugation to form biomacroinitators. These macroinitiators are then subjected to polymerization conditions to form conjugates via the grafting from approach. The tolerance of both the oxidative addition and bioconjugation reactions to various chemical functionalities is explored, and the kinetics of the bioconjugation are challenged with a particularly bulky branched polymer substrate.Then, a detailed kinetic analysis was performed on this Au(III) system, with the goal of creating design principles for precise control over the reactivity. This work led to the discovery of a Au(III) OA complex which exhibits the fastest rate of abiotic bioconjugation to a native amino acid residue. In order to study the kinetic limits of these new, faster reagents, we sought to perform these reactions at as low concentration as possible (Chapter 4). Conjugates were analyzed using LC-MS and SDS-PAGE down to nM concentrations. A fluorescent Au(III) reagent was also synthesized to test the conjugation down to the pM range. This ability to modulate the kinetics of these reactions to be either faster or slower also allowed for the development of a range of Au(III) OA complexes with various rates for tunable bioconjugation and this was utilized to generate bifunctional linkers to synthesize a range of biomolecular heterostructures in a controlled and selective fashion (Chapter 4).
Finally, my work as a leader in the Organization for Cultural Diversity in Science (OCDS) at UCLA will be discussed (Chapter 5). This student led organization is tasked with the challenge to promote diversity, equity and inclusion (DEI) in UCLA’s Division of Physical Sciences, and has several modes by which they work to achieve this goal. The organization focuses on outreach, professional development, and provides a safe social environment in which DEI matters can be explored. Over several years of involvement, I have witnessed successes and identified ongoing challenges, all which will be discussed herein.
