| http://www.w3.org/ns/prov#value | - A preferred class of photoremovable protecting groups has the general formula: ##STR3## where R1, R2, R3, and R4 independently are a hydrogen atom, a lower alkyl, aryl, benzyl, halogen, hydroxyl, alkoxyl, thiol, thioether, amino, nitro, carboxyl, formate, formamido or phosphido group, or adjacent substituents (i.e., R1 -R2, R2 -R3, R3 -R4) are substituted oxygen groups that together form an cyclic
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