Utilization of the Heavy Atom Effect for the Development of a Photosensitive 8-Azacoumarin-Type Photo labile Protecting Group

A remarkable improvement of the photochemical properties of coumarin-type photolabile protecting groups was achieved by iodine substitution. The newly identified 7-hydroxy-6-iodo-8-azacoumarin (8-aza-Ihc)-caged acetate showed excellent photolytic efficiency, significantly higher than that of the corresponding bromine-containing coumarin- and azacoumarin-type caging groups. The results provide a solid approach to improving the photosensitivity of photolabile protecting groups.