Steady-State and Time-Resolved Studies on Oxetane Cycloreversion Using (Thia)pyrylium Salts as Electron-Transfer Photosensitizers

Miranda, Miguel A.; Izquierdo, and M. Angeles; Galindo, Francisco

doi:10.1021/ol0158516

Cited by 33 publications

(29 citation statements)

References 15 publications

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“…Quantum chemical calculations (in the gas phase) predict that oxetanes cleave spontaneously after single electron donation or after single electron abstraction 24. Laser flash photolysis experiments by Falvey and co‐workers25 and Miranda et al26 recently provided experimental evidence that oxetanes do indeed split in the presence of various electron donors and acceptors in a light‐dependent reaction 27. So far, experiments which could clarify the function of the flavin coenzyme in (6‐4) photolyases and in particular the direction of the electron transfer within the enzyme active site are not reported.…”

Section: Methodsmentioning

confidence: 99%

A (6-4) Photolyase Model: Repair of DNA (6-4) Lesions Requires a Reduced and Deprotonated Flavin

2002

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Ultraviolet irradiation of cells causes the formation of a variety of DNA lesions with known mutagenic, carcinogenic, and lethal effects. [1,2] The main UV lesions are cyclobutane ± pyrimidine dimers (CPD lesions) formed in a photochemically allowed [2p 2p] cycloaddition and (6-4) photoadducts; the latter are presumably more mutagenic. [3,4] The highly mutagenic (6-4) lesions are believed to be formed in a Paterno ¬ -B¸chi reaction between two adjacent pyrimidines in the DNA duplex to give initially an oxetane intermediate, which rearranges above À 80 8C to the (6-4) photoadduct by a proton shift and a CÀO bond scission (Scheme 1). [5] Both types of DNA lesions are repaired in many organisms by a special class of repair enzymes, namely DNA photolyases, which cleave both lesions back into the monomers in a lightdependent, single electron transfer based repair reaction. [6] In the last decade, crystallographic, [7, 8] enzymatic, [9, 10] and model compound studies [11±14] showed that the photolyases, [15] which are responsible for the repair of CPD lesions, contain a[5] K.[17] Initial synthesis of 1: A solution of 1,3,5-tris(diphenylphosphanyl)benzene (L; 63 mg, 0.1 mmol) in CH 2 Cl 2 (3 mL) was added to a solution of AgOTf (38.5 mg, 0.15 mmol) in CH 3 NO 2 (1 mL). Diffusion of diethyl ether vapor into the resulting solution over one week gave colorless hexagonal crystals of 1 in 10 % yield, together with powdery amorphous material. Higher yield synthesis: 1,3,5-tris(diphenylphosphanyl)benzene (L; 31.5 mg, 0.05 mmol) and AgOTf (17.0 mg, 0.067 mmol) were dissolved in a mixture of ethanol (7 mL) and nitromethane (3 mL), placed in a loosely stoppered polypropylene flask and partially evaporated at 88 8C overnight. Block and hexagonal colorless crystals were manually separated from the powdery amorphous byproduct. Yield: 50 ± 80 %; elemental analysis calcd (%) for [Ag 4 L 3 (OTf) 4 ] ¥ CH 3 NO 2 : C 52.79, H 3.42; found: C 52.55, H 3.32. [18] X-ray data were collected on a BrukerAXS SMART diffractometer using the SAINT-NT [26] software with omega/phi scans. A crystal was mounted on to the diffractometer under dinitrogen at approximately 120 K. The structure was solved using direct methods with the SHELXTL program package. [27] Crystal Data for the hexagonal plate crystals {C 130 H 99 F 12 Ag 4 P 9 S 4 O 12 } n (1): M 2919.54, hexagonal, space group P3 ≈ c, a 29.949(8), c 25.929(10) ä, V 20 141(11) ä À3 , Z 4, m 0.545 mm À1 . A total of 39 337 reflections were measured for the angle range 4 < 2q < 45 and 8797 independent reflections were used in the refinement. The final parameters were wR2 0.3009 and R1 0.0906 [I > 2sI]. Cell parameters for the block crystals [{C 130 H 99 F 12 Ag 4 -P 9 S 4 O 12 } n ] (1') [23] : M 2919.54, hexagonal, space group P3 ≈ c, a 30.076(1), c 25.791(1) ä, V 20 204(1) ä À3 . The residual densities (< 1 electron ä À3 ) associated with the voids indicate small amounts of very diffuse solvent molecules. Consequently, the nature of the solvent could not be determined using X-ray diffraction m...

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Section: Methodsmentioning

confidence: 99%

A (6-4) Photolyase Model: Repair of DNA (6-4) Lesions Requires a Reduced and Deprotonated Flavin

2002

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“…[23][24][25][26][27][28] Besides, it has been shown that, for diaryl-substituted oxetanes, splitting can also occur both from radical anions and cations. [29,30] The results obtained so far concern either the pyrimidine base alone or DNA hairpin model compounds; [31] no study has been realized on nucleoside-derived oxetanes.…”

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confidence: 99%

Model Studies on a Carprofen Derivative as Dual Photosensitizer for Thymine Dimerization and (6–4) Photoproduct Repair

et al. 2007

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Cyclobutane pyrimidine dimers (CPD) and (6-4) photoproducts are among the main UV-induced DNA lesions. Both types of damage are mostly repaired in prokaryotes by photolyase enzymes. The repair mechanism of (6-4) photolyases has still not been fully elucidated, but it is assumed that back rearrangement to the oxetane occurs prior to repair. In this work, a non-steroidal anti-inflammatory drug derivative corresponding to the dechlorinated methyl ester of carprofen (namely methyl 2-(carbazol-2-yl)propanoate, PPMe) has been used to achieve the photosensitized cycloreversion of model oxetanes (formally resulting from photocycloaddition between benzophenone and 1,3-dimethylthymine or 2'-deoxyuridine), by employing fluorescence spectroscopy, laser flash photolysis, HPLC and NMR. Although PPMe is able to photoinduce the cycloreversion of both oxetanes, the fluorescence quenching of PPMe is faster for the 2'-deoxyribose-containing oxetane; this underlines the importance of the structure in such studies. Moreover, PPMe was shown to photoinduce the formation of thymidine cyclobutane dimers through a triplet-triplet energy transfer from a vibrationally excited state, as suggested by the enhanced PPMe triplet quenching by thymidine with increasing temperature. These results reveal a dual role of PPMe in DNA photosensitization, in that it photoinduces either damage or repair.

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“…43 The radical cation of (E )-stilbene but not 1-phenylpropene was observed in laser flash photolysis experiments. The reaction is thought to occur from the triplet state of the photosensitizer.…”

Section: [2؉2] Cycloadditionsmentioning

confidence: 99%

6 Reaction mechanisms : Part (ii) Pericyclic reactions

Morgan

2002

Annu. Rep. Prog. Chem., Sect. B: Org. Chem.

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Steady-State and Time-Resolved Studies on Oxetane Cycloreversion Using (Thia)pyrylium Salts as Electron-Transfer Photosensitizers

Cited by 33 publications

References 15 publications

A (6-4) Photolyase Model: Repair of DNA (6-4) Lesions Requires a Reduced and Deprotonated Flavin

A (6-4) Photolyase Model: Repair of DNA (6-4) Lesions Requires a Reduced and Deprotonated Flavin

Model Studies on a Carprofen Derivative as Dual Photosensitizer for Thymine Dimerization and (6–4) Photoproduct Repair

6 Reaction mechanisms : Part (ii) Pericyclic reactions

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