1-[2-(2-Hydroxyalkyl)phenyl]ethanone:  A New Photoremovable Protecting Group for Carboxylic Acids

Abstract

[reaction: see text] A new photoremovable protecting group for carboxylic acids is introduced. The protecting group 1-[2-(2-hydroxyalkyl)phenyl]ethanone, HAPE, is used to protect various carboxylic acids. When photolyzed, the protected compound releases the acid in 70-85% isolated yields. The synthesis and the results of photorelease of the protected acids are presented here.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

“…760 Solvent effects on the photoreduction 715 and cyclization 759 processes were observed as expected; in polar protic solvents, photoreduction was less efficient and cyclization was more efficient, whereas the opposite was true in non-polar aprotic solvents. 760 A different mechanism involving photoenolization 609,761 followed by heterolytic elimination 230,231,233,762 was demonstrated by Kamdzhilov and Wirz 232 for substituted 5-(ethylene-2-yl)-1,4-naphthoquinone 138 (Scheme 41), which absorbs below 405 nm. This compound released HBr and diethyl phosphate upon irradiation at 365 nm (Φ r = 0.35 and 0.70, respectively) in a neutral aqueous solution, but a poorer leaving group (acetic acid) was released less efficiently (Φ r < 0.01).…”

“…The 1-(2-nitrophenyl)­ethyloxycarbonyl (NPEOC) group 17 and its α-methyl analog , 18 (NPPOC; the “OC” stands for the −OC­(=O) group, which is typically a part of the LG) constitute a separate class of nitroaryl PPGs. Despite its close structural similarity to oNB ( 5a ), the proposed photoreaction mechanism of o -nitro-2-phenethyl derivatives is markedly different, involving a photoinduced elimination step (Scheme ) reminiscent of that reported for (2-hydroxyethyl)­benzophenone-type PPGs. ,− The quantum yields obtained for o -nitro-2-phenethyl derivatives exceed those for their oNB analogs , (for example, Φ r = 0.35 and 0.033 for 5′- O -nucleoside carbonate photorelease from 18 and 5a , respectively), leading to their use in automated light-mediated oligonucleotide synthesis (DNA-chips), , the preparation of peptide − and RNA , microarrays, the synthesis of aptamers and carbohydrates, and gene assembly …”

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

“…74 A recent methodical investigation by Pirrung and his co-workers was carried out to elucidate the scope and limitations of the deprotection reaction. 75 Alternatively, Wirz 7a and later Banerjee and their co-workers 76 proposed a similar photoremovable protecting group based on the 1-[2-(2-hydroxyalkyl)phenyl]ethanone 19 (R = alkyl, Scheme 11). The leaving group was reported to be released with a low photochemical efficiency.…”

“…The leaving group was reported to be released with a low photochemical efficiency. 76 Interestingly, irradiation of 2-acetylphenyl- or 2-benzoylphenylacetic acid results in efficient release of CO 2 . 77 …”

13 Organic photochemistry

“…32 A new photoremovable protecting group for carboxylic acids, 1-[2-(2-hydroxyalkyl)phenyl]ethanone, HAPE, released the acids in very good yields upon irradiation. 33…”