New phototriggers: Extending the p-hydroxyphenacyl pi-pi* absorption range

[GRAPHICS] Introducing 3-methoxy or 3,5-dimethoxy substituents on the 4-hydroxyphenacy l (pHP) photoremovable protecting group has been explored with two excitato ry gamma-amino acids, L-glutamic acid and gamma-amino butyric acid (GABA)., These substituents significantly extend the absorption range of the pHP ch romophore, e.g., the tail of absorption bands of 2a,b extend above 400 nm, well beyond the absorptions of aromatic amino acids and nucleotides. Irradi ation releases the amino acids with rate constants of similar to 10(7) s(-1 ) and appearance efficiencies (Phi(app)) of 0.03-0.04. The photoproducts ar e formed through the pHP excited triplet and are primarily products of phot oreduction and photohydrolysis, 1a,b also rearranged to the phenylacetic ac id 3.