Photodecarboxylation: mechanism and synthetic utility

Budac, David; Wan, Peter

doi:10.1016/1010-6030(92)85224-i

Cited by 178 publications

(151 citation statements)

References 114 publications

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“…In aqueous solution, PA undergoes efficient photodecarboxylation from an excited triplet state (19,20). The radicals produced by the low-temperature UV irradiation of the pure acid herein proposed (Methods) are most likely related to intermediary products postulated for this photodecarboxylation mechanism.…”

Section: Resultsmentioning

confidence: 99%

Hyperpolarization without persistent radicals for in vivo real-time metabolic imaging

Eichhorn

Takado

Salameh

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

107

171

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Hyperpolarized substrates prepared via dissolution dynamic nuclear polarization have been proposed as magnetic resonance imaging (MRI) agents for cancer or cardiac failure diagnosis and therapy monitoring through the detection of metabolic impairments in vivo. The use of potentially toxic persistent radicals to hyperpolarize substrates was hitherto required. We demonstrate that by shining UV light for an hour on a frozen pure endogenous substance, namely the glucose metabolic product pyruvic acid, it is possible to generate a concentration of photo-induced radicals that is large enough to highly enhance the 13 C polarization of the substance via dynamic nuclear polarization. These radicals recombine upon dissolution and a solution composed of purely endogenous products is obtained for performing in vivo metabolic hyperpolarized 13 C MRI with high spatial resolution. Our method opens the way to safe and straightforward preclinical and clinical applications of hyperpolarized MRI because the filtering procedure mandatory for clinical applications and the associated pharmacological tests necessary to prevent contamination are eliminated, concurrently allowing a decrease in the delay between preparation and injection of the imaging agents for improved in vivo sensitivity.is a very powerful imaging modality in terms of temporal and spatial resolution of anatomical structures. The modality is widespread, well established in clinical environments, and paramagnetic agents are used extensively for enhanced contrast or perfusion examination. MR is also a unique technique to obtain in vivo metabolic maps using the spectroscopic information that can be extracted from the time-domain acquisitions. In particular, it is possible to monitor the biochemical transformations of specific substrates that are delivered to subjects. Because it gives access to the kinetics of the conversion of substrates into metabolites, MR spectroscopy (MRS) of the carbon nuclei ( 13 C) is one of the most powerful techniques to investigate intermediary metabolism (1).The well-known weakness of MR as a spectroscopic technique is its relatively low sensitivity. It can be offset by so-called hyperpolarization methods, in particular the one based on dynamic nuclear polarization (DNP) (2), which is now commonly referred to as dissolution DNP and was first proposed about a decade ago (3). The hyperpolarized substrates obtained following dissolution DNP are biomolecules in aqueous solution with a largely out-ofequilibrium nuclear spin polarization corresponding to an enhancement of several orders of magnitude compared with the thermal equilibrium polarization attainable in MRI scanners. A basic requirement for DNP is the presence of unpaired electron spins in the sample to be hyperpolarized. These polarizing agents are usually incorporated in the form of persistent radicals. An inherent limit of any hyperpolarization method is that the intrinsic longitudinal nuclear spin relaxation will annihilate the polarization enhancement in the course of time to reach t...

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Section: Resultsmentioning

confidence: 99%

Hyperpolarization without persistent radicals for in vivo real-time metabolic imaging

Eichhorn

Takado

Salameh

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

107

171

View full text Add to dashboard Cite

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“…In the present study, the resulting labile ''photoproduct'' (BLP) is not a single molecule, but rather a whole host of compounds that may or may not undergo subsequent photochemical reactions. When the components of the biologically labile carbon pool are themselves also photolabile, irradiation can lead to the destruction of these compounds through a variety of processes, most importantly photochemical production of CO 2 (Budac and Wan 1992). Because this and similar published studies treat a single microbial response as a proxy for the suite of photochemical carbon products available for uptake at the end of a specified photon dose, results should be viewed as a balance between photochemical production and destruction processes.…”

Section: Discussionmentioning

confidence: 99%

The efficiency and spectral photon dose dependence of photochemically induced changes to the bioavailability of dissolved organic carbon

Reader

Miller

2014

Limnology & Oceanography

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To quantify the effects of photochemistry on the biological lability of dissolved organic carbon in a terrestrially influenced system, a quarterly sampling effort was undertaken at three estuarine locations along the coast of Georgia, producing a total of 15 apparent quantum yield (AQY) spectra for biologically labile products (BLPs). Prefiltered samples were irradiated and then inoculated with natural microbial communities isolated from the same sample. Oxygen consumption was used as a proxy for community carbon utilization over 10-12 d dark incubations. Seasonal microbial response to irradiated samples ranged from 221% to +155% relative to dark controls. AQY spectral shapes were not consistent over the data set, nor were there any apparent patterns in season or location. Progressive photon dose experiments showed that increasing irradiation length strongly decreased the total biolabile product as assayed with microbial community oxygen consumption, as well as altering the spectral shape of the AQY spectra. A conceptual model is presented to explain this dependence on photon dose, by illustrating the competition between the photochemical production and photochemical destruction of BLPs. The varying dependence on photon dose is fundamentally different from published results for other photochemical products and further complicates attempts to quantify the total effect of photochemistry on organic carbon cycles in natural environments.

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“…[16] Budac and Wan also proposed that intramolecular electron transfer in the triplet state could lead to the formation of a carbanion that is the precursor for a biradical-like species. [17] However, ESIPT has seldom been directly observed as an initial step of the decarboxylation reaction for ketoprofen (KP). KP has been widely studied to characterize its photophysical and photochemical behavior, [18][19][20] and the lowest triplet state KP À ( 3 A C H T U N G T R E N N U N G [KP À ]) was observed in picosecond laser flash photolysis studies.…”

Section: Introductionmentioning

confidence: 99%

Water‐ and Acid‐Mediated Excited‐State Intramolecular Proton Transfer and Decarboxylation Reactions of Ketoprofen in Water‐Rich and Acidic Aqueous Solutions

Yeung

Guan

et al. 2011

Chemistry A European J

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We present an investigation of the decarboxylation reaction of ketoprofen (KP) induced by triplet excited-state intramolecular proton transfer in water-rich and acidic solutions. Nanosecond time-resolved resonance Raman spectroscopy results show that the decarboxylation reaction is facile in aqueous solutions with high water ratios (water/acetonitrile ≥50%) or acidic solutions with moderate and strong acid concentration. These experimental results are consistent with results from density functional theory calculations in which 1) the activation energy barriers for the triplet-state intramolecular proton transfer and associated decarboxylation process become lower when more water molecules (from one up to four molecules) are involved in the reaction system and 2) perchloric acid, sulfuric acid, and hydrochloric acid can shuttle a proton from the carboxyl to carbonyl group through an initial intramolecular proton transfer of the triplet excited state, which facilitates the cleavage of the C-C bond, thus leading to the decarboxylation reaction of triplet state KP. During the decarboxylation process, the water molecules and acid molecules may act as bridges to mediate intramolecular proton transfer for the triplet state KP when KP is irradiated by ultraviolet light in water-rich or acidic aqueous solutions and subsequently it generates a triplet-protonated carbanion biradical species. The faster generation of triplet-protonated carbanion biradical in acidic solutions than in water-rich solutions with a high water ratio is also supported by the lower activation energy barrier calculated for the acid-mediated reactions versus those of water-molecule-assisted reactions.

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Photodecarboxylation: mechanism and synthetic utility

Cited by 178 publications

References 114 publications

Hyperpolarization without persistent radicals for in vivo real-time metabolic imaging

Hyperpolarization without persistent radicals for in vivo real-time metabolic imaging

The efficiency and spectral photon dose dependence of photochemically induced changes to the bioavailability of dissolved organic carbon

Water‐ and Acid‐Mediated Excited‐State Intramolecular Proton Transfer and Decarboxylation Reactions of Ketoprofen in Water‐Rich and Acidic Aqueous Solutions

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