Formation of Cyclobutane Thymine Dimers from UVA Photosensitization of Pyridopsoralen Monoadducted DNA

The present report provides evidence that thymine dimerization can be UVA photosensitized at a tetranucleotide, 5′-TATT-3′, by a 7-methyl-pyrido(3, 4-c)psoralen monoadduct in DNA. The efficiency of the photoprocess depends on the tetranucleotide flanking sequences. These results demonstrate that one DNA lesion can originate the contiguous formation of a second type of lesion and emphasize the sequence-specific response to interaction of drugs with DNA. Results are related to the sensitivity of DNA to 1, 10-phenanthroline-cuprous ion complex nucleolytic activity and discussed in terms of the major role of local deformability of DNA in interaction with ligands.     

Substituent Effects on Photosensitized Splitting of Thymine Cyclobutane Dimer by an Attached Indole

In chromophore‐containing cyclobutane pyrimidine dimer (CPD) model systems, solvent effects on the splitting efficiency may depend on the length of the linker, the molecular conformation, and the oxidation potential of the donor. To further explore the relationship between chromophore structure and splitting efficiency, we prepared a series of substituted indole–T<>T model compounds 2 a – 2 g and measured their splitting quantum yields in various solvents. Two reverse solvent effects were observed: an increase in splitting efficiency in solvents of lower polarity for models 2 a – 2 d with an electron‐donating group (EDG), and vice versa for models 2 e – 2 g with an electron‐withdrawing group (EWG). According to the Hammett equation, the negative value of the slope of the Hammett plot indicates that the indole moiety during the T<>T‐splitting reaction loses negative charge, and the larger negative value implies that the repair reaction is more sensitive to substituent effects in low‐polarity solvents. The EDGs of the models 2 a – 2 d can delocalize the charge‐separated state, and low‐polarity solvents make it more stable, which leads to higher splitting efficiency in low‐polarity solvents. Conversely, the EWGs of models 2 e – 2 g favor destabilization of the charge‐separated state, and high‐polarity solvents decrease the destabilization and hence lead to more efficient splitting in high‐polarity solvents.     

Quantitative Determination of Cyclobutane Thymine Dimers in DNA by Stable Isotope-Dilution Mass Spectrometry

In order to understand the role of UV-induced DNA lesions in biological processes such as mutagenesis and carcinogenesis, it is essential to detect and quantify DNA damage in cells. In this paper we present a novel and both highly selective and sensitive assay using capillary gas chromatography (GC) combined with mass spectrometry (MS) for the detection and accurate quantitation of a major product of UV-induced DNA damage (cissyn cyclobutadithymine). Quantitation of the cyclobutane thymine dimer was achieved by the use of an internal standard in the form of a stable ²H-labeled analogue. Both isotopically labeled and nonlabeled dimers were prepared directly from their corresponding monomers. Each was identified as their trimethylsilyl ether derivative by GC-MS. Calibration plots were obtained for known quantities of both nonlabeled analyte and internal standard. Quantitation of cis-syn cyclobutadithymine was demonstrated in DNA exposed to UVC radiation over a dose range of 0 to 3500 J m^?2. Under the conditions used, the limit of detection was found to be 20–50 fmol on column (equivalent to 0.02–0.05 nmol dimer per mg DNA). The results of the present study indicate that capillary GC-MS is an ideally suited technique for selective and sensitive quantification of cis-syn cyclobutadithymine in DNA and hence UV-induced DNA damage.     

Retrospective View on Recent Developments in Cyclobutane Synthesis via [2+2] Photocycloaddition of Unsaturated Ketones to Acyclic Dienes

This synopsis addresses cyclobutane formation via light‐induced [2+2] cycloaddition from both cyclic and acyclic unsaturated carbonyl compounds, and 2,3‐dimethylbuta‐1,3‐diene     

萜品油烯的DeMayo光环加成产物的反应研究

通过萜品油烯和2，6-二氧代戊酸甲酯的de Mayo反应，使[2 + 2]环加成产物 3-6经retro-aldol重排，开环生成取代环己烯7和12。在不同反应介质中对开环产 物进行再环合，并对其反应机理进行研究。在碱性条件下，经分子内Claisen缩合 反应形成螺环化合物；以对甲本碘酸为催化剂的环合，除生成正常的Claisen缩合 产物以外，7和12均发生烯键亲核加成反应，生成具有二环[3.3.1]结构的桥环化合 物9-11和二环[3.2.1]结构的桥环化合物16-18。所得新化合物的化学结构均经IR, ~1H NMR，~(13)C NMR及元素分析予以确定。     

Radiation-Induced Crosslinking of Thymine with Cysteamine: Cysteamine Attachment to the Methyl Group of Thymine

5-S-Cysteaminemethyluracil (the product of cysteamine attachment to the methyl group of thymine) was isolated from irradiated solutions containing thymine and cysteamine and identified. This compound was formed in the reaction of thiyl radicals with 5-methyleneuracil-5-yl radicals formed by H-atom abstraction from the methyl group of thymine. This product was not formed in the presence of oxygen.     

重离子辐照胸腺嘧啶产物的毛细管气相色谱分析

对经中能的１８Ｏ８＋离子辐照过的胸腺嘧啶Ｎ２Ｏ饱和水溶液进行了研究,利用气相色谱（ＧＣ）、气相色谱 质谱联用（ＧＣ ＭＳ）、气相色谱 红外光谱联用（ＧＣ ＦＴＩＲ）等仪器对辐照后的产物进行了分析、鉴别,观察到了５,６ 二氢胸腺嘧啶、５ 羟基 ５ 甲基 乙内酰脲、５ 羟基（氢） ６ （氢）羟基胸腺嘧啶、５ 羟甲基尿嘧啶、顺（反）胸腺嘧啶二醇和二聚体等产物。虽然重离子主要是通过辐照水溶液中产生的羟基、氢原子等对胸腺嘧啶分子产生了作用,但与γ射线作用机制和结果是不同的。     

Photocycloaddition of Isocoumarins and Isothiocoumarins to Alkenes

On irradiation in the presence of tetrachloroethene (TCE), both isocoumarins 3 and isothiocoumarins 4 afford in high yields the cis‐fused cycloadducts 8 and 9 , while only the oxacycles 3 undergo photocycloaddition to 2,3‐dimethylbut‐2‐ene (TME) to give mixtures of cis‐ and trans‐fused products 10 and 11 , respectively, in moderate yields. This higher efficiency in reacting with TCE as compared to TME for compounds 3 and 4 contrasts the behavior of simple cyclic enones, e.g., 5,5‐dimethylcyclohex‐2‐enone ( 12 ), which is converted to bicyclooctanones about fifty times faster with TME than with TCE.     

Photocycloaddition of dichloromaleic anhydride to benzene

Conclusions In the photocycloaddition of dichloromaleic anhydride to benzene the processes of addition and substitution in the benzene ring proceed in parallel, and also the subsequent photoreaction of the obtained products to give compounds of the tricyclo[6.2.0^5,6.0^4,7]decene series.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1618–1620, July, 1976.     

Photocycloaddition of ethylvinylether and cyclopentene to 3.5-dimethylanisole

Photocycloadition of ethylvinylether and cyclopentene to 3,5-dimethylanisole yields derivatives of 1-methoxy-2, 4-dimethyltricyclo [3.3.0.0^2,8]oct-3-ene in which the substituents at positions 6 and/or 7 are endo. Structural proofs are based on 250 MHz ¹H and 62.9 MHz ¹³C NMR spectra.     

Structures of Ring-Enlargement Products

Crystal structures have been determined of methyl trans-1-hydroxy-6-nitro-3-oxobicyclo[4.4.0]decane-2-carboxylate ( 19 ), cis-3-methyl-6-nitro-2-oxabicyclo[4.4.0]decan-1-ol ( 2 ), cis-7-hydroxy-1-nitrobicyclo[5.4.0]undecan-9-one ( 13 ), and the medium-ring compounds 2-acetyl-4-nitrocyclooctanone ( 9 ), methyl 5-nitro-2-oxocyclooctane-carboxylate ( 4 ), 2-acetyl-4-nitrocyclononanone ( 11 ), 2-acetyl-4-nitrocyclodecanone ( 15 ), benzyl 5-nitro-2,11-dioxocycloundecanecarboxylate ( 24 ), methyl 5-nitro-2,12-dioxocyclododecanecarboxylate ( 21 ), and 8-nitro-11-oxo-13-tridecanolide ( 7 ), which are intermediates, side products, or end products of the ‘Zip’ ring-enlargement reaction. The conformations of most of the medium-ring compounds are very similar to equal-sized ring compounds previously determine by other authors.     

Photocycloaddition of 2,3-dimethylmaleimide to selenophene and 3,4-dimethylselenophene

Summary The benzophenone sensitized photocycloaddition of 2,3-dimethylmaleimide to selenophene and 3,4-dimethylselenophene was carried out first to generalize the photoaddition reaction of methylmaleic anhydride derivatives to selenophene, using this time the nitrogen analogue, and second to reexamine the composition of the product mixture formed in the reaction. It was found that in adition to the 1:1 adduct isolated in previous investigations, three geometrical isomers may be proposed for the 2:1 adduct (two molecules of maleimide of one of selenophene or its methyl derivative).

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Photocycloaddition von 2,3-Dimethylmaleimid an Selenophen und 3,4,-Dimethylselenophen

Zusammenfassung Die benzophenonsensitivierte Photocycloaddition von 2,3-Dimethylmaleimid an Selenophen und 3,4-Dimethylselenophen wurde durchgeführt, um erstens die Photoadditionsreaktionen von Methylmaleinsäureanhydridderivaten an Selenophen allgemein zu studieren und um zweitens die Zusammensetzung der bei der Reaktion gebildeten Produktgemische erneut zu untersuchen. Zusätzich zu dem bei früheren Arbeiten gefundenen 1:1-Addukt werden drei geometrische Isomere für das 2:1 — Addukt (2 Moleküle Maleimid und 1 Molekül Selenophen oder 3,4-Dimethylselenophen) vorgeschlagen.

     

The Photochemistry of Thymine in Frozen Aqueous Solution: Trimeric and Minor Dimeric Products

Early work identified three compounds, namely the c,s cyclobutane dimer, the so‐called (6‐4) photoproduct (5‐hydroxy‐6‐4′‐(5‐methylpyrimidin‐2′‐one)‐5,6‐dihydrothymine) and a trimer hydrate, as products formed upon UV irradiation of thymine in frozen aqueous solution. More recent work has shown that an (α‐4) product, namely α‐4′‐(5′‐methylpyrimidine‐2′‐one)‐thymine, is a likely product formed under these reaction conditions. During a thorough reinvestigation of the photochemistry of Thy in ice at ?78.5°C, we found that a variety of other products could be detected. In addition to the c,s dimer, the other three known cyclobutane dimers, namely the c,a, t,s and t,a forms, are produced, although in considerably smaller amounts. The so‐called “spore product” of thymine (5,6‐dihydro‐5‐(α‐thyminyl)thymine) is likewise formed. Two other dimers have been identified as minor products; one of these has been determined to be 5‐(thymin‐3‐yl)‐5,6‐dihydrothymine and the other has been tentatively assigned to be a (5‐4) adduct (6‐hydroxy‐5‐4′‐(5‐methylpyrimidin‐2′‐one)‐5,6‐dihydrothymine). Compounds with the behavior expected of true trimeric compounds have been isolated via HPLC and characterized by mass spectrometry and photochemical behavior. One of these materials, putatively containing an oxetane ring, decomposes thermally to a secondary trimeric product that is then converted into the known trimer hydrate.     

Photocycloaddition of 2-benzoylthiophene to methylmaleic anhydrides

Summary Upon direct irradiation with light of wavelengths greater than 300 nm, 2-benzoylthiophene undergoes [2 + 2] cycloadditions withmono- anddi-methylmaleic anhydrides involving the C=C bond of the latter and the benzoyl-substituted thiophene C=C bond.

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Photocycloaddition von 2-Benzoylthiophen an Methylmaleinsäureanhydride

Zusammenfassung Aus 2-Benzoylthiophen entstehen unter direkter Bestrahlung mit Licht von Wellenlängen > 300 nm in Anwesenheit von Methylmaleinsäureanhydriden [2 + 2]-Cycloaddukte. Die Photoreaktion erfolgt an den C=C-Bindungen des Thiophenrings und des Anhydrids.

     

Polarity of Thymine and 6-Methyluracil-Modified Porous Polymers,According to Data from Inverse Gas Chromatography

Russian Journal of Physical Chemistry A - The affinity of surfaces of porous polymer Polysorb-1 samples modified with thymine (5-methyluracil) and 6-methyluracil toward sorbates capable of various...     

Photochemistry of Flavins in Micelles: Specific Effects of Anionic Surfactants on the Monomerization of Thymine Cyclobutane Dimers Photosensitized by Tetra-O-acyl Riboflavins*

It was found that tetra-o-acyl riboflavins efficiently photosensitize the monomerization of the cis, syn-cyclobutane dimers of 1,3-dimethylthymine and 1,3-dimethyluracil in aqueous solution in the presence of such anionic surfactants as sodium dodecyl sulfate and sodium hexadecyl sulfate at concentrations higher than their critical micelle concentration, while little monomerization of the dimers was photosensitized by the flavins in the absence of the surfactants and even in the presence of cationic and nonionic surfactants.     

Theoretical Studies on the Mechanism of Photocycloaddition Reaction Between 6 Azauracil and Acetone

The mechanism of photocycloaddition reaction between 6-azauracll and acetone was studied by using semiemptrical SCFMO AMI method. It was found that this reaction is not a concerted one. The calculated results are as follows:(1) A T1 state exciplex is on the T1 state energy surface; (2) T exciplex as a reactant will proceed along the energy surface of T1 state to form a diradical intermediate. The energy barrier of this reaction step is 63. 6 kJ/mol; (3) The T1 state diradical intermediate happens to be close in energy to the ground state intermediate with a similar geometry. Such a situation turns out to be very favorable for an intersystem crossing (jump from the T, state to the ground state) ; (4) The final product will be formed from the ground S0 state intermediate via an energy barrier 88. 2 kJ/mol.