A protective group represented by the following general formula, which is stable under the reaction conditions of the nucleic acid synthetic cycles and has little steric hindrance, and can be removed under mild conditions using fluoride ions as a base. This accelerates the removal of particles from the disc drive’s sealed chamber, reducing the likelihood of particle-induced data transfer errors or media damage. A method of preparing a printing plate is also disclosed, comprising imagewise exposure of the printing plate element and removing an unexposed area of the printing plate element with aqueous solution.