Nitrenium Ions and Related Species in Photoaffinity Labeling

Wilson, R. Marshall; Voskresenska, Valentyna D.

doi:10.1002/9781118560907.ch3

Cited by 2 publications

(2 citation statements)

References 149 publications

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“…This compound or similar azidoaurones are expected to be suitable substrates for photoaffinity labeling via nitrene generation and thus find application in studies to better understand the interaction of these compound with biological systems. 4 With these twin goals in mind, iodoaurone 1 was selected as a substrate for an in situ azidation/click reaction. Initial attempts did result in consumption of the iodoaurone, but failed to afford any of the anticipated triazole 2 (Scheme 2).…”

Section: Scheme 1 Condensation Route To Auronesmentioning

confidence: 99%

An Unusual Triazole Synthesis from Aurones

2020

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Attempts to prepare azido-substituted aurones via a copper-catalyzed azidation failed to afford the desired product, but instead resulted in an unusual triazole formation reaction. Further efforts noted that copper was not required for this reaction, but simply thermal treatment with sodium azide in a polar aprotic solvent. A wide range of substitution patterns were tolerated in this reaction to afford the interesting salicyl-substituted triazoles in modest to excellent yield. While the mechanism is not yet clear, a simple elimination/cyclization pathway seems unlikely given the failure of the reaction on the corresponding thioaurones, which feature an even better thiol leaving group. Regardless, the potential utility of these easily accessible, multifunctional compounds should engender further interest and applications.

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Section: Scheme 1 Condensation Route To Auronesmentioning

confidence: 99%

An Unusual Triazole Synthesis from Aurones

2020

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“…The PAL agent, 4-fluoro-3-nitrophenyl azide, is a system that has been widely applied in photoaffinity studies with different classes of biological molecules in recent years. − Recently, we have studied the photochemical mechanism of its amine analogue, 4-amino-3-nitrophenyl azide ( 1 ), in the presence of nucleophiles using ultrafast transient absoprtion and quantum chemical computational techniques . This molecule is promoted to its first excited singlet S 1 -state (π, π*) by absorption of a 420-nm photon and undergoes unproductive fast internal conversion to the vibrational manifold of the ground electronic state on a ∼350-fs time scale.…”

Section: Introductionmentioning

confidence: 99%

5-Azido-2-aminopyridine, a New Nitrene/Nitrenium Ion Photoaffinity Labeling Agent That Exhibits Reversible Intersystem Crossing between Singlet and Triplet Nitrenes

et al. 2013

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The photochemistry of a new photoaffinity labeling (PAL) agent, 5-azido-2-(N,N-diethylamino)pyridine, was studied in aprotic and protic solvents using femtosecond-to-microsecond transient absorption and product analysis, in conjunction with ab initio multiconfigurational and multireference quantum chemical calculations. The excited singlet S1 state is spectroscopically dark, whereas photoexcitation to higher-lying singlet excited S2 and S3 states drives the photochemical reaction toward a barrierless ultrafast relaxation path via two conical intersections to S1, where N2 elimination leads to the formation of the closed-shell singlet nitrene. The singlet nitrene undergoes intersystem crossing (ISC) to the triplet nitrene in aprotic and protic solvents as well as protonation to form the nitrenium ion. The ISC rate constants in aprotic solvents increase with solvent polarity, displaying a "direct" gap effect, whereas an "inverse" gap effect is observed in protic solvents. Transient absorption actinometry experiments suggest that a solvent-dependent fraction from 20% to 50% of nitrenium ions is generated on a time scale of a few tens of picoseconds. The closed-shell singlet and triplet nitrene are separated by a small energy gap in protic solvents. As a result, the unreactive triplet state nitrene undergoes delayed, thermally activated reverse ISC to reform the reactive closed-shell singlet nitrene, which subsequently protonates, forming the remaining fraction of nitrenium ions. The product studies demonstrate that the resulting nitrenium ion stabilized by the electron-donating 4-amino group yields the final cross-linked product with high, almost quantitative efficiency. The enhanced PAL function of this new azide with respect to the widely applied 4-amino-3-nitrophenyl azide is discussed.

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Nitrenium Ions and Related Species in Photoaffinity Labeling

Cited by 2 publications

References 149 publications

An Unusual Triazole Synthesis from Aurones

An Unusual Triazole Synthesis from Aurones

5-Azido-2-aminopyridine, a New Nitrene/Nitrenium Ion Photoaffinity Labeling Agent That Exhibits Reversible Intersystem Crossing between Singlet and Triplet Nitrenes

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