Photolabile Protecting Groups Based on the Excited State Meta Effect: Development and Application

This review focuses on utilization of the excited state meta effect (ESME) in the development of photolabile protecting groups (PPGs). Structurally simple ESME-based PPGs for release of various functional groups (such as carbonyl, hydroxyl, carboxyl, amino, and thiol groups) are discussed. Examples that demonstrate the appealing advantages of these new PPGs are provided, including their efficient release of "poor" leaving groups such as hydroxyl or amino group directly instead of in their respective carbonate or carbamate form. Applications of these PPGs in synthesis, release of biologically important molecules, materials science, and biomedical engineering are also described.

Using the 3-Diethylaminobenzyl Group as a Photocage in Aqueous Solution

We have demonstrated that the 3-diethylaminobenzyl (DEABn) photolabile protecting group (PPG) is an effective and structurally simple PPG for releasing molecules in aqueous environment. In general, the photoreaction is clean, and the released substrate and the PPG product, i.e., 3-diethylaminobenzyl alcohol, are obtained in high yield. The clean photoreaction can also be achieved under mild ambient conditions with sunlight, while the reactant is stable under indoor lighting. Release of two substrates from one PPG chromophore in aqueous solution has been demonstrated to be feasible. We have also compared the uncaging properties of the DEABn and the widely used o-nitrobenzyl ( o-NB) group, given their comparable structural simplicity. With its clean and efficient photochemical reaction, DEABn should find wide applications, including in the basic and applied research areas where o-NB and its various derivatives are widely used.