Photorelease of Alcohols from 2-Nitrobenzyl Ethers Proceeds via Hemiacetals and May Be Further Retarded by Buffers Intercepting the Primary aci-Nitro Intermediates

Abstract

The mechanism for the photoinduced release of glycolic acid from its 2-nitrobenzyl ether was reinvestigated. The pH-dependent rate constants of the thermal reactions initiated by irradiation are similar to those reported previously for 2-nitrobenzyl methyl ether. A hemiacetal intermediate that limits the release rate of glycolic acid at pH values </=7 was identified by time-resolved IR and UV measurements. Furthermore, 2-(2'-nitrosophenyl)-1,3-dioxolan-4-one, a long-lived intermediate formed by intramolecular trapping of the aci-tautomer, was observed and characterized.

Applications of p-hydroxyphenacyl (pHP) and coumarin-4-ylmethyl photoremovable protecting groups

“…The rate of o NPE cage release is also many orders of magnitude slower than that of the p HP analogs: k rel = 1.0–10 s −1 ( o NPE) 2 vs. 10 8 –10 9 s −1 ( p HP). 8,17,22 The vital time frame required for RasGTP catalysis by TR-FTIR was too fast for o NPE GTP initiation.…”

“…o -Nitrobenzyl derivatives are by far the most commonly used photoremovable protecting groups (PPGs), 1 despite their known disadvantages: following electronic excitation, the caged compounds are released on a time scale of microseconds at best, 2 and o -nitroso aromatic ketones are produced as side products, which usually absorb more strongly than the parent PPG at the irradiation wavelengths and which may interfere with the effect of the released bioactive material under study, because of their toxic effect on biological tissues. 3 With the need for higher time resolution in studies of the leading events in biological processes, there is a demand for clean, rapidly released triggers or initiators of these processes.…”

Photolysis of ortho-nitrobenzylic derivatives: the importance of the leaving group

“…17 ln the growing family of PPGs, the o-nitrobenzyl group is one of the oldest, but still widely used groups, mainly due to its robustness and relative photophysical insensitivity to interfering influences. There have been many studies, both experimental and computational, on the mechanism of the photoinduced decomposition of this kind of PPGs [18][19][20][21][22][23][24][25][26] but many unanswered questions remain, such as the impact of substituents in various positions, and the origin of an intriguing kinetic isotope effect. 27,28 For example, it has been shown that the quantum yields ϕ for the disappearance of nitrobenzyl PPGs, or those for the release of the leaving groups, depend strongly on the chemical character of the leaving group (LG).…”

Micropatterning of polymethacrylates by single‐ or two‐photon irradiation using π‐conjugated o‐nitrobenzyl ester phototrigger as side chains

“…[2][3][4] Among the reported photoactivated groups, o-nitrobenzyl derivatives (ONB) have gained wide acceptance due to their versatile modification and well-known photorearrangement mechanism to generate o-nitrosobenzaldehyde. 3,[5][6][7] Besides its application as an orthogonal protecting group in organic synthesis, 8 it has been extensively used in the side chains of polymer as a photochemically labile group and also exhibited utility in photoresist [9][10][11][12][13] and photocontrolled release in light-dissociable block copolymer micelles. 14 In addition, a lot of caged biological active compounds have been prepared by using ONB phototrigger groups.…”