Development of a Photolabile Carbonyl-Protecting Group Toolbox

Abstract

New salicyl alcohol derived photolabile carbonyl protecting groups have been developed, and the effect of substituents on the photochemical properties of photolabile protecting groups (PPGs) has been studied. The 3-(dimethylamino)phenyl groups at the α position prove to be important to the efficiency of the deprotection reactions, as shown in the photo reactions of the acetal 9. On the other hand, expansion of the salicyl alcohol's benzene skeleton to naphthalene does not improve the photochemical properties of PPGs. A neutral protecting protocol has been generalized to new PPGs with α,α-diaryl salicyl alcohol backbone. Thus, installation of PPGs onto aldehydes is readily achieved at 140 °C without using any other chemical reagents. These PPGs are stable under acidic conditions typical for hydrolyzing acetals and constitute orthogonal protecting groups with traditional 1,3-dioxane/1,3-dioxolane for carbonyl compounds. Highly efficient release of carbohydrate molecules is demonstrated, which can be potentially useful in site-specific release and immobilization of carbohydrates for preparation of high-density microarrays. With the enriched PPG toolbox, PPGs are divided into three subgroups based on their UV absorption profiles. PPGs from different subgroups can be sequentially removed by using different UV irradiation wavelengths. For PPGs absorbing UVA (λ >315 nm), photochemical deprotection can be carried out with sunlight in high yields.