Direct 3-Acylation of Indolizines by Carboxylic Acids for the Practical Synthesis of Red Light-Releasable Caged Carboxylic Acids.

To enhance the practicality of photouncaging system using 3-acyl-2-methoxyindolizines, direct acylation of indolizines with carboxylic acids was developed using condensation reagents, generally used for peptide coupling. This method allowed for caging a broad range of carboxylic acids with indolizines. The method enabled a facile synthesis of water-soluble caged bioactive carboxylic acids having an intramolecular photosensitizer. The efficient release of carboxylic acids from the synthesized caged compounds upon red light irradiation was confirmed in neutral buffered solutions.

Indolizines Enabling Rapid Uncaging of Alcohols and Carboxylic Acids by Red Light-Induced Photooxidation.

The irradiation of red light-emitting-diode light (λ = 660 nm) to 3-acyl-2-methoxyindolizines in the presence of a catalytic amount of methylene blue triggered the photooxidation of the indolizine ring, resulting in a nearly quantitative release of alcohols or carboxylic acids within a few minutes. The method was applicable for photouncaging various functional molecules such as a carboxylic anticancer drug and a phenolic fluorescent dye from the corresponding indolizine conjugates, including an insulin-indolizine-dye conjugate.