Pd(II)-mediated C-H activation for cysteine bioconjugation

Ultrafast Au(III)-Mediated Arylation of Cysteine

Through mechanistic work and rational design, we have developed the fastest organometallic abiotic Cys bioconjugation. As a result, the developed organometallic Au(III) bioconjugation reagents enable selective labeling of Cys moieties down to picomolar concentrations and allow for the rapid construction of complex heterostructures from peptides, proteins, and oligonucleotides. This work showcases how organometallic chemistry can be interfaced with biomolecules and lead to a range of reactivities that are largely unmatched by classical organic chemistry tools.

Efficient end-group functionalization and diblock copolymer synthesis via Au(III) polymer reagents

Herein, we describe the synthesis of bench-stable organometallic Au(III) terminated polymer reagents. These reagents mediate the chemoselective S-arylation of thiol-containing small molecules and polymers to yield functionalized mono-telechelic polymers and diblock copolymers, respectively. These transformations proceed rapidly within minutes and produce conjugates in quantitative conversion, making this strategy a robust addition to the polymer functionalization toolbox.

Nickel-Catalyzed Antibody Bioconjugation

New biocompatible methods for post-translational protein modification are challenging to develop but crucial to create improved chemical probes and optimize next-generation biologic therapies such as antibody-drug conjugates (ADCs). Herein, we describe the bottom-up construction of an aqueous nickel-catalyzed cross-coupling for the chemospecific arylation of cysteine residues on peptides and proteins and its use for the preparation of ADCs. A variety of arene linkages are exemplified, enabling the incorporation of small molecules, probes, and cytotoxic payloads. The utility of this new bioconjugation platform in a drug discovery setting is highlighted by the construction of novel ADCs with target-mediated in vitro cytotoxic activity.

Isoindolium-Based Allenes: Reactivity Studies and Applications in Fluorescence Temperature Sensing and Cysteine Bioconjugation

The reaction of a series of electron-deficient isoindolium-based allenes with sulfhydryl compounds has been studied, leading to the formation of isoindolium-based vinyl sulfides. The vinyl sulfides generated could be readily converted into the corresponding indanones and amines upon heating at 30-70 °C with good yields up to 61 %. The thermal cleavage reaction of vinyl sulfides was further studied for developing temperature-sensitive systems. Notably, a novel FRET-based fluorescent temperature sensor was designed and synthesized for temperature sensing at 50 °C, giving a 6.5-fold blue fluorescence enhancement. Moreover, chemoselective bioconjugation of cysteine-containing peptides with the isoindolium-based allenes for the construction of multifunctional peptide bioconjugates was investigated. Thermal cleavage of isoindoliums on the modified peptides at 35-70 °C gave indanone bioconjugates with up to >99 % conversion. These results indicated the biocompatibility of this novel temperature-sensitive reaction.

Organometallic S-arylation Reagents for Rapid PEGylation of Biomolecules

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 poly(ethylene glycol) monomethyl ether (mPEG)-protein conjugates with high efficiency. 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.