Applications of reversible covalent bonding within the context of spin trapping, boronate ester formation, conjugate addition of amines and thiols, and the synthesis of natural product analogues

Reversible covalent bonding is an essential chemical tool that incorporates the strength of covalent bonds and the dynamism of intermolecular interactions. This type of bonding has found applications across fields of chemistry, including sensing of small molecules, screening against target for the design of host/guest systems, and enzyme inhibition. Herein are discussed examples of reversible covalent bonding. A three-component assembly incorporating 2-formylphenyl boronic acid, N-alkylhydroxylamine, and catechol was synthesized with the intention of acting as a reversible spin trap for nitric oxide detection. This assembly was further studied as a potential bioorthogonal method for specific chemical modification of amino acids within a peptide or protein. This system is amenable to a variety of substrates, including L-DOPA, a catechol-containing amino acid, which can readily be incorporated into proteins. This assembly is also compatible with existing bioorthogonal reactions, allowing for multiple labeling reactions to be conducted simultaneously. The ability to reversibly crosslink two substrates under mild conditions has the potential for wide application. Our group has previously developed a conjugate acceptor, derived from Meldrum’s acid, that sequentially crosslinks an amine and a thiol under aqueous conditions at neutral pH. This crosslinking can be decoupled with a chemical trigger to regenerate the original species. We have since expanded this system to include the addition of aniline derivatives. We have further optimized this conjugate acceptor and studied the pK [subscript a] ’s and reaction rates of the decoupling using different substrates. The natural product piperlongumine has been found to induce apoptosis in cancer cells with little effect on normal cells and is thought to act through increasing the level of reactive oxygen species (ROS). This increase in ROS is proposed to occur through the reversible addition of glutathione into the more reactive Michael acceptor, followed by the addition of a glutathione-binding protein to the second Michael acceptor. We have synthesized piperlongumine using a route that can be easily modified to access derivatives with various substituents in order to study the potency of analogs and to test the proposed mechanism