Competing pathways for photoremovable protecting groups: the effects of solvent, oxygen and encapsulation

Area of Science:

• Organic Chemistry
• Photochemistry
• Chemical Biology

Background:

• Photoremovable Protecting Groups (PPGs) are crucial for controlled release of molecules.
• Caging phenols with PPGs often leads to complex byproducts.
• Developing efficient PPGs for phenolics is an ongoing challenge.

Purpose of the Study:

• To evaluate the p-hydroxyphenacyl (pHP) cage for photodeprotection of simple and complex phenols.
• To investigate the byproduct formation pathways of the pHP cage.
• To explore the influence of reaction conditions on PPG byproduct profiles.

Main Methods:

• Photolysis of pHP-caged phenols under various conditions.
• Analysis of reaction products using spectroscopic and chromatographic techniques.
• Investigation of byproduct formation mechanisms, including the Favorskii rearrangement.

Main Results:

• The pHP cage successfully releases free phenols, including tyrosine.
• Phenol acidity dictates the primary reaction pathway and byproduct formation.
• More acidic phenols yield p-hydroxyphenylacetic acid via Favorskii rearrangement.
• Weaker phenols undergo reduction and hydrolysis.
• Using octa acid (OA) containers leads to non-Favorskii, unrearranged byproducts.

Conclusions:

• The pHP cage is a versatile tool for phenol photodeprotection.
• Byproduct profiles can be tuned by phenol structure and reaction environment.
• This work provides insights into controlling PPG byproduct formation for diverse applications.