p-Hydroxyphenacyl bromide as photoremoveable thiol label: a potential phototrigger for thiol-containing biomolecules (original) (raw)
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Evaluation of Aromatic Thiols as Photoinitiators
The unique photodynamics of aromatic thiols (relative to alkyl thiols) allowed their employment as effective ultraviolet and visible light photoinitiators (PIs) for acrylate photopolymerizations, radicalmediated thiol−ene coupling (TEC) network polymerizations, solventless and initiatorless small-molecule TEC reactions, and hydrogel network polymerizations. Twenty-six thiol structures were evaluated as radical generating PIs in the polymerization of n-hexyl acrylate. Initiator effectiveness follows the trend nonheterocyclic aromatic thiols > heterocyclic aromatic thiols ≈ thioacids > alkyl thiols. Substituted versions of thiophenol exhibited the highest photoinitiation efficiency with electron-withdrawing substituents increasing effectiveness. Ortho-and para-substituted mercaptobenzoic acids and (trifluoromethyl)thiophenols were generally the most effective, leading to 100% acrylate conversion at a loading of 3 mM (0.1 mol % with respect to acrylate) when irradiated with 320−390 nm light and at loadings of 30 mM when irradiated with 405 nm light. Results demonstrate the potential of aromatic thiols as oxygen insensitive photoinitiators for bulk polymerizations and for specialty polymer synthesis via aromatic thiol-functionalized macroinitiators.
Canadian Journal of Chemistry, 2011
A broadly based investigation of the effects of a diverse array of substituents on the photochemical rearrangement of p-hydroxyphenacyl esters has demonstrated that common substituents such as F, MeO, CN, CO 2 R, CONH 2 , and CH 3 have little effect on the rate and quantum efficiencies for the photo-Favorskii rearrangement and the release of the acid leaving group or on the lifetimes of the reactive triplet state. A decrease in the quantum yields across all substituents was observed for the release and rearrangement when the photolyses were carried out in buffered aqueous media at pHs that exceeded the ground-state pKa of the chromophore where the conjugate base is the predominant form. Otherwise, substituents have only a very modest effect on the photoreaction of these robust chromophores.
The photochemical release of chemical reagents and bioactive molecules provides a useful tool for spatio-temporal control of biological processes. However, achieving this goal requires the development of highly efficient one-and two-photon sensitive photo-cleavable protecting groups. Thiol-containing compounds play critical roles in biological systems and bioengineering applications. While potentially useful for sulfhydryl protection, the 6-bromo-7-hydroxy coumarin-4-ylmethyl (Bhc) group can undergo an undesired photoisomerization reaction upon irradiation that limits its uncaging efficiency. To address this issue, here we describe the development of 6-bromo-7-hydroxy-3-methylcoumarin-4-ylmethyl (mBhc) as an improved group for thiol-protection. One-and two-photon photolysis reactions demonstrate that a peptide containing a mBhc-caged thiol undergoes clean and efficient photo-cleavage upon irradiation without detectable photoisomer production. To test its utility for biological studies, a K-Ras-derived peptide containing an mBhc-protected thiol was prepared by solid phase peptide synthesis using Fmoc-Cys(mBhc)-OH for the introduction of the caged thiol. Irradiation of that peptide using either UV or near IR light in presence of protein farnesyltransferase (PFTase), resulted in generation of the free peptide which was then recognized by the enzyme and became farnesylated. To show the utility of this caging group in biomaterial applications, we covalently modified hydrogels with mBhc-protected cyste-amine. Using multi-photon confocal microscopy, highly defined volumes of free thiols were generated inside the hydrogels and visualized via reaction with a sulfhydryl-reactive fluorophore. The simple synthesis of mBhc and its efficient removal by one-and two-photon processes make it an attractive protecting group for thiol caging in a variety of applications.
Organic & biomolecular chemistry, 2016
The photochemical release of chemical reagents and bioactive molecules provides a useful tool for spatio-temporal control of biological processes. However, achieving this goal requires the development of highly efficient one- and two-photon sensitive photo-cleavable protecting groups. Thiol-containing compounds play critical roles in biological systems and bioengineering applications. While potentially useful for sulfhydryl protection, the 6-bromo-7-hydroxy coumarin-4-ylmethyl (Bhc) group can undergo an undesired photoisomerization reaction upon irradiation that limits its uncaging efficiency. To address this issue, here we describe the development of 6-bromo-7-hydroxy-3-methylcoumarin-4-ylmethyl (mBhc) as an improved group for thiol-protection. One- and two-photon photolysis reactions demonstrate that a peptide containing a mBhc-caged thiol undergoes clean and efficient photo-cleavage upon irradiation without detectable photoisomer production. To test its utility for biological stu...
The P-Hydroxyphenacyl Photoremovable Protecting Group
ChemInform, 2004
A review of the background and development of the p-hydroxyphenacyl group (pHP) as a photoprotecting group for biological substrates is chronicled. The pHP group has promise as an efficient, rapid phototrigger for the study of very fast biological processes. Applications including the release of neurotransmittors and second messengers, enzyme switches and nucleotides have been included.
Macromolecules, 2006
The heteroaromatic thiols (imidazole, oxazole, and thiazole derivatives) were investigated in regard to their abilities to function as co-initiators in free-radical photopolymerizations induced by camphorquinone and isopropylthioxanthone. As shown by the kinetic data, these heteroaromatic thiols are efficient co-initiators with activities comparable to aromatic amines. They quenched the triplet states of isopropylthioxanthone and camphorquinone with rate constants determined to be on the order of 10 9 and 10 8 M -1 s -1 , respectively. The results suggested that rates of polymerization of a low-viscosity monomer (triethylene glycol dimethacrylate) in an inert atmosphere are dependent on the quantum yields of formation of primary thiyl radicals Φ. However, this effect was also moderated by the reactivities of the thiyl radicals that were generated in the photosensitization stage. The observed activities of the initiator/thiol systems also depended on the possibility of initiator photoreduction by the monomer and, in air, on the ability of the co-initiators to reduce oxygen inhibition.
Photoremovable protecting groups used for the caging of biomolecules
Dynamic Studies in …, 2005
Scheme 1.1.1 Overall photolysis reaction of NPE-caged ATP 1. 1.1.1.2 Historical Perspective The pioneering work of Kaplan et al. [7], although preceded by other examples of 2-nitrobenzyl photolysis in synthetic organic chemistry, was the first to apply this to a biological problem, the erythrocytic Na : K ion pump. As well as laying the foundation for the field, the paper contains some early pointers to difficulties and pitfalls in the design of caged compounds. Specifically, it was shown that 2-nitrobenzyl phosphate 3 and its 1-(2-nitrophenyl)ethyl analog 4 both released inorganic phosphate in near-quantitative yield upon prolonged irradiation. However, when the same two caging groups were used on ATP, namely 1 and its non-methylated analog 5, the maximum yield of released ATP from 5 was only *25%, whereas that from 1 was at least 80%. It was suggested that the 2-nitrosobenzaldehyde by-product released from 5, in contrast to nitrosoketone 2 released from 1, might react with the liberated ATP to render it inactive. This hypothesis has not been further studied, but the observations provide an indication that different substituents on the caging group may have unexpected effects. We return to this in later sections that consider rates and mechanisms of caged-compound photolysis. 1.1 2-Nitrobenzyl and 7-Nitroindoline Derivatives 3 Scheme 1.1.2 Photolysis reaction of 1-acyl-nitroindolines in aprotic organic solvent containing a low proportion of water, an alcohol, or an amine. 1.1 2-Nitrobenzyl and 7-Nitroindoline Derivatives 7 Scheme 1.1.3 Detailed reaction scheme for photolysis of generalized nitrobenzyl-caged compounds. The scheme incorporates results of recent studies by Wirz and colleagues [43, 44]. 1.1 2-Nitrobenzyl and 7-Nitroindoline Derivatives 21 Scheme 1.1.8 Photolysis reaction of 1-acyl-nitroindolines in aqueous solution, showing formation of the nitrosoindole by-product.
Photopolymerization of Thiol-Enes: Some Recent Advances
Rad'Tech Europe …, 2001
2 Summer REU Student, The University of Southern Mississippi, Department of Polymer Science, Hattiesburg, Mississippi 3 The University of Colorado, Department of Chemical Engineering, Boulder, Colorado, ... 4 Fusion UV Curing Systems, Gaithersburg, ...
Biomacromolecules, 2012
Photoinitiated polymerization remains a robust method for fabrication of hydrogels, as these reactions allow facile spatial and temporal control of gelation and high compatibility for encapsulation of cells and biologics. The chain-growth reaction of macromolecular monomers, such as acrylated PEG and hyaluronan, is commonly used to form hydrogels, but there is growing interest in step-growth photopolymerizations, such as the thiol−ene "click" reaction, as an alternative. Thiol−ene reactions are not susceptible to oxygen inhibition and rapidly form hydrogels using low initiator concentrations. In this work, we characterize the differences in recovery of bioactive proteins when exposed to similar photoinitiation conditions during thiol−ene versus acrylate polymerizations. Following exposure to chain polymerization of acrylates, lysozyme bioactivity was approximately 50%; after step-growth thiol−ene reaction, lysozyme retained nearly 100% of its prereaction activity. Bioactive protein recovery was enhanced 1000-fold in the presence of a thiol−ene reaction, relative to recovery from solutions containing identical primary radical concentrations, but without the thiol−ene components. When the cytokine TGFβ was encapsulated in PEG hydrogels formed via the thiol−ene reaction, full protein bioactivity was preserved.