Templating and Catalyzing [2+2] Photocycloaddition in Solution Using a Dynamic G-Quadruplex

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Nucleic Acid Chemistry

Background:

• G-quadruplex DNA structures offer unique scaffolds for molecular assembly.
• Photochemical [2+2] cycloaddition is a powerful tool for forming cyclobutane rings.
• Controlling reactivity within noncovalent assemblies remains a challenge.

Purpose of the Study:

• To develop a templating strategy for photochemical cyclobutane formation.
• To enable the synthesis of multiple cyclobutanes within a single noncovalent assembly.
• To investigate the mechanism and efficiency of this novel reaction.

Main Methods:

• Utilized a G-quadruplex formed by 5'-cinnamate guanosine units and potassium ions (K+).
• Employed photochemical [2+2] cycloaddition to induce cyclobutane formation.
• Characterized the reaction using experimental methods and quantum mechanical/molecular mechanics (ONIOM) calculations.

Main Results:

• Achieved the formation of 8 cyclobutanes in one noncovalent assembly.
• The reaction proceeded with high yields (>90%).
• Demonstrated high regio- and diastereoselectivity in the cyclobutane formation.

Conclusions:

• The templating/covalent capture strategy enables efficient photochemical synthesis of cyclobutanes.
• The G-quadruplex acts as a precise scaffold, positioning reactive groups for selective cycloaddition.
• The catalytic nature of the reaction in K+ highlights the dynamic and reversible aspects of the assembly.