Over the past four decades researchers have successfully utilized photoremovable protecting groups (PPGs) or �cage� compounds for the spatial and temporal control of release of biological substrates (Dynamic Studies in Biology: Phototriggers, photoswitches and caged Biomolecules: Givens, R. S. Goeldner, M., Eds., 2005).  p-Hydroxyphenacyl (pHP) has served as a PPG for an increasing number of substrates employed in various studies (Review: Givens, Rubina and Wirz, Photochem. Photobiol. Sci. 2012,  11, 472). Substituents on the pHP chromophore alter the properties and reactivity, especially the photolysis efficiency without disturbing its robust photochemistry (Givens et al. Can. J. Chem. 2011,  89, 364). Previous studies in our laboratory on pHP-caged carboxylates have indicated that m-methoxy substitution benefits the pHP absorption properties, moving the absorption toward 350 nm (Conrad et al. Org. Lett. 2000,  2, 1545), a more favorable region for biological studies by avoiding deleterious UV radiation effects on biological substrates. Accordingly, shifting the substitution to an o-methoxy attachment to pHP diethyl phosphates allowed us to explore both neighboring group effects and changes in the absorptivity and their further effects on the photochemistry. Whereas m-methoxy efficacies were essentially unchanged even with extended p-p* absorption [quantum yield (F); 0.39 � 0.02 (m-OMe), 0.44 � 0.02 (m-2OMe) versus 0.40 � 0.09 (unsubtituted)], o-methoxy substitution affected both. Interestingly, o-methoxy pHP derivatives shifted the pHP absorption towards the visible region and significantly increased the efficacy [F; 0.59 � 0.03 (o-OMe), 0.69 � 0.03 (o-2OMe) vs. 0.40 � 0.09 (unsubtituted)]. The effects of o- and m-methoxy substitution on pHP release of phosphates and of N2 release will be evaluated. Research supported by NIH grant GM 72910.

Crowded p-hydroxyphenacyl (pHP) cages: <i>Ortho</i> effects on pHP photorelease

246th National Meeting (2013)

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Crowded p-hydroxyphenacyl (pHP) cages: Ortho effects on pHP photorelease