Time-resolved pH jump study of photochemical cleavage and release of carboxylic acids from α-keto amides

Ma, Chicheng; Steinmetz, Mark G.; Kopatz, Erica J.; Rathore, Rajendra

doi:10.1016/j.tetlet.2004.11.167

Cited by 11 publications

(5 citation statements)

References 28 publications

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“…Photohydroxide emitters are a class of compounds that release hydroxide anions ( − OH) to induce a pOH jump upon UV–vis irradiation. This process is similar to the pH jump methods achieved using various photoacids. − The pOH jump is generally achieved through heterolytic cleavage of the C–O bond, as is exhibited by compounds such as 9-fluorenol, , 9-phenylxanthen-9-ol, and triphenylmethane hydroxide, , whose resonance structures stabilize the resulting carbocations. The application of these compounds in driving a photochemical pOH jump is mostly limited by the fast recombination of hydroxide and the carbocation. − Additionally, homolytic C–O bond cleavage can complicate the chemistry with the formation of hydroxyl radical ( • OH). ,, …”

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confidence: 80%

Mechanistic Study of the Photochemical Hydroxide Ion Release from 9-Hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine

et al. 2012

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The excited-state behavior of 9-hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine and its derivative, 9-methoxy-10-methyl-9-phenyl-9,10-dihydroacridine (AcrOR, R = H, Me), was studied via femtosecond and nanosecond UV-vis transient absorption spectroscopy. The solvent effects on C-O bond cleavage were clearly identified: a fast heterolytic cleavage (τ = 108 ps) was observed in protic solvents, while intersystem crossing was observed in aprotic solvents. Fast heterolysis generates 10-methyl-9-phenylacridinium (Acr(+)) and (-)OH, which have a long recombination lifetime (no signal decay was observed within 100 μs). AcrOH exhibits the characteristic behavior needed for its utilization as a chromophore in the pOH jump experiment.

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confidence: 80%

Mechanistic Study of the Photochemical Hydroxide Ion Release from 9-Hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine

et al. 2012

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“…We recently determined the rate constants for release of carboxylate groups from 1a by a pH jump method that used laser flash photolysis . In this paper, we report complete results of this study and additional results for 1b .…”

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confidence: 88%

Photochemical Cleavage and Release of Carboxylic Acids from α-Keto Amides

Steinmetz

Kopatz

et al. 2005

J. Org. Chem.

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In aqueous media, alpha-keto amides LGCH(2)COCON(R)CH(R')CH(3) (1a, R = Et, R' = H; 1b, R = (i)()Pr, R' = Me; 1c, R = Ph, R' = H) with various carboxylate leaving groups (LG) at the C-3 position undergo photocleavage and release of carboxylic acids with formation of diastereomeric 5-hydroxyoxazolidin-4-ones 2a,c in the cases of 1a,c or 5-methyleneoxazolidin-4-ones 3b in the case of 1b. For 1a,b, Phi(photocleavage) = 0.24-0.38, whereas Phi(photocleavage) = ca. 0.05 for 1c. The proposed mechanism involves transfer of hydrogen from an N-alkyl group to the keto oxygen to produce zwitterionic intermediates 4a-c that eliminate carboxylate anions. The resultant imminium ions, H(2)C=C(OH)CON(+)(R)=C(R')CH(3) 5a-c, cyclize intramolecularly to 3b or undergo intermolecular addition of water followed by tautomerization and cyclization to give 2a,c. These inter- or intramolecular trapping reactions of 5 release protons that decrease the pH and cause bleaching of the 620 nm band of the pH indicator, bromocresol green. Determination of the bleaching kinetics by laser flash photolysis methods in the case of 1a gives time constants of 18-137 mus, depending on the leaving group ability of the carboxylate anion, whereas amides 1b show only a small leaving group effect. For 1a, the large leaving group effect is consistent with rate-limiting carboxylate elimination from 4a, whereas the proton release step would be largely rate determining for 1b. Photolyses of 1a (LG = CH(3)CO(2)(-), PhCH(2)CO(2)(-)) in neat CH(3)CN results in carboxylate elimination to form imminium ion 5a, followed by internal return to give aminals.

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“…396 The yield of 219 was found to depend strongly on the type of alkyl substituent on the carbon adjacent to the amide nitrogen. 397 Time-resolved pH-jump experiments showed that the reaction rate is on the microsecond time scale and that carboxylate release occurs in the rate-determining step. 398 Phenolates can also be liberated from 216 .…”

Section: Miscellaneous Groupsmentioning

confidence: 99%

“…Steinmetz and co-workers reported that the carboxylates (including GABA, BocAla, and Glu) attached to the α-carbon of α-ketoamides ( 216 ) could be photochemically released, possibly through a zwitterionic intermediate 217 , in very good chemical (<93%) and quantum (0.28–0.37) yields, along with the formation of a mixture of two diastereomeric hemiacetals 218 and a small amount of oxazolidinone 219 as byproducts (Scheme ) . The yield of 219 was found to depend strongly on the type of alkyl substituent on the carbon adjacent to the amide nitrogen . Time-resolved pH-jump experiments showed that the reaction rate is on the microsecond time scale and that carboxylate release occurs in the rate-determining step .…”

Section: Miscellaneous Groupsmentioning

confidence: 99%

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

et al. 2012

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Time-resolved pH jump study of photochemical cleavage and release of carboxylic acids from α-keto amides

Cited by 11 publications

References 28 publications

Mechanistic Study of the Photochemical Hydroxide Ion Release from 9-Hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine

Mechanistic Study of the Photochemical Hydroxide Ion Release from 9-Hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine

Photochemical Cleavage and Release of Carboxylic Acids from α-Keto Amides

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

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