Advancing Photo-Click Chemistry towards Macrocyclization and Sequence-defined Oligomers

Nature uses sequence-defined (having a precise sequence of units) monodisperse (same molecular weight) polymers for the data storage and transfer (DNA, RNA), for the control of properties and structure (proteins), for the efficient catalysis of various reactions (enzymes), and many more. However, these bio-macromolecules have limited stability and lack chemical and structural diversity. Current methods for the preparation of sequence-defined monodisperse polymers are usually based on solid support synthesis. This allows for the use of the large excess of reagents to drive reactions to completion and for the efficient purification at each step. Unfortunately, solid support methods limit the amount of polymer production to milligram quantities. We have developed photo-SPAAC ligation approach to the bulk synthesis of sequence-defined polymers. The trifunctional monomer, containing photo-caged cyclooctyne, azide group, and a moiety allowing the attachment of various functionalities (e.g., dye, catalysts, enzymes, etc.). Photoactivation of the cyclooctyne at the terminus of the growing chain allows for the attachment of the next monomer via quantitative and fast SPAAC reaction. The excess of the monomer has been shown to quench itself thus preventing the formation of mismatched sequences. We have demonstrated the purification-free synthesis of two pentamers sequences.