A new photoremovable protecting group : synthesis and reaction mechanism

A new photoremovable protecting group, allowing for irradiation up to 400 nm, is introduced. A simple synthetic route to three derivatives was described and their photochemistry in aqueous solutions and acetonitrile was investigated. Quantum yields of substrate deprotection Фdep (HBr, CH3COOH and HOPO(OEt)2) were measured spectrophotometrically and by HPLC and were found to be satisfactory (Φ = 0.3 – 0.7). Nucleofugacity of the leaving group, the nature of solvent, and the pH determine the reaction mechanism. A reactive intermediate, expelling the protected substrate, was detected by laser flash photolysis (LFP) and by time-resolved infrared spectroscopy (TRFTIR), and the release rate constants of substrates were found to be in the microsecond time-domain. A mechanistic scheme rationalizing our observation is proposed.