Fine-tuning alkyne cycloadditions: Insights into photochemistry responsible for the double-strand DNA cleavage via structural perturbations in diaryl alkyne conjugates

• Wang-Yong Yang,
• Samantha A. Marrone,
• Nalisha Minors,
• Diego A. R. Zorio and
• Igor V. Alabugin

Beilstein J. Org. Chem. 2011, 7, 813–823, doi:10.3762/bjoc.7.93

• the kinetics of photoinduced electron transfer (PET). The three analogous isomeric lysine conjugates cleaved DNA with different efficiencies (34, 15, and 0% of ds DNA cleavage for p-, m-, and o-substituted lysine conjugates, respectively) consistent with the alkylating ability of the respective

• conjugates displayed G-selective cleavage, especially at GG and GGG sites adjacent to the AT-rich sequence (the AT-tract), the preferred binding location for protonated amines. The G-selectivity is typical for oxidative DNA damage via PET for the most easily oxidized base, guanine. However, a noticeable

• photophysical step and the involvement of PET from 1,4-cyclohexadiene (1,4-CHD) to the enediyne excited singlet state. In contrast, substituents that accelerate the intersystem crossing (ISC) through a “phantom state” effect [53][54][55] direct reactivity along an alternative triplet cycloaddition pathway. Our

Photoinduced electron-transfer chemistry of the bielectrophoric N-phthaloyl derivatives of the amino acids tyrosine, histidine and tryptophan

• Axel G. Griesbeck,
• Jörg Neudörfl and
• Alan de Kiff

Beilstein J. Org. Chem. 2011, 7, 518–524, doi:10.3762/bjoc.7.60

• and tryptophan 8–10 was studied with respect to photoinduced electron-transfer (PET) induced decarboxylation and Norrish II bond cleavage. Whereas exclusive photodecarboxylation of the tyrosine substrate 8 was observed, the histidine compound 9 resulted in a mixture of histamine and preferential

• Norrish cleavage. The tryptophan derivative 10 is photochemically inert and shows preferential decarboxylation only when induced by intermolecular PET. Keywords: amino acids; decarboxylation; electron transfer; photochemistry; phthalimides; Introduction Phthalimides are versatile electron acceptors in

• photoinduced electron-transfer (PET) reactions. N-Alkylated phthalimides typically absorb in the 295 nm region with extinction coefficients around 103. The quantum yields for intersystem crossing ФISC significantly change with the substitution on the imide nitrogen, e.g., ФISC = 0.5 for N-isobutylphthalimide

Fluorometric recognition of both dihydrogen phosphate and iodide by a new flexible anthracene linked benzimidazolium-based receptor

• Kumaresh Ghosh and
• Debasis Kar

Beilstein J. Org. Chem. 2011, 7, 254–264, doi:10.3762/bjoc.7.34

• anions by the change in intensity due to the photo-induced electron transfer (PET) mechanism. As expected, we observed a change in emission of 1 (c = 5.78 × 10−5 M) in CH3CN upon the addition of anions as their tetrabutylammonium salts. Receptor 1 (c = 5.78 × 10−5 M) in CH3CN gave a structured emission

• less compared to the case of 1 (see Supporting Information File 1). The quenching of emission of 1 upon complexation is attributed to the activation of a PET process occurring between the binding site and the excited state of anthracene. The Stern–Volmer plot in Figure 9 illustrates the quenching

• in absorbance of anthracene and predicted 1 as a PET system [38]. In many cases, the change of absorbance during the titration with the anions was irregular. Figure 10 corroborates the irregular change in absorbance of 1 on titration with H2PO4− and importantly, in the ground state, all the anions

An easy assembled fluorescent sensor for dicarboxylates and acidic amino acids

• Xiao-bo Zhou,
• Yuk-Wang Yip,
• Wing-Hong Chan and
• Albert W. M. Lee

Beilstein J. Org. Chem. 2011, 7, 75–81, doi:10.3762/bjoc.7.11

• charge neutral thiourea-based fluorescent PET sensor motif, which is immune from cross pH interference, was adopted in our approach [28]. The congested mesitylene derivative type of structure built in 1 may confer the molecule with sufficient rigidity favoring its selective binding with guest molecules

• acetonitrile and the guest concentration (as tetrabutylammonium salts) was varied from 5.0 × 10−6 M to 1.0 × 10−4 M. The typical change of emission spectra of 1 caused by isophthalate is shown in Figure 1. Operating on the PET mechanism, the fluorescent emission band of the host at 413 nm was quenched

Anthracene appended pyridinium amide–urea conjugate in selective fluorometric sensing of L-N-acetylvaline salt

• Kumaresh Ghosh,
• Tanmay Sarkar and
• Asoke P. Chattopadhyay

Beilstein J. Org. Chem. 2010, 6, 1211–1218, doi:10.3762/bjoc.6.139

• observation [20]. The different modes of emission (enhancing and quenching) of 1 in the presence of the different guests studied is believed to be due to the structural difference and hydrogen bonding abilities of the guests for which the PET process occurring between the amide-urea binding site and the

Anthracene coupled adenine for the selective sensing of copper ions

• Kumaresh Ghosh and
• Tanushree Sen

Beilstein J. Org. Chem. 2010, 6, No. 44, doi:10.3762/bjoc.6.44

• selective; fluorescence; metal ion recognition; PET sensory systems; Introduction Fluorescent chemosensors for the detection of biologically relevant metal ions have been widely exploited in the field of supramolecular chemistry [1][2][3][4]. Among the various transition metal ions, the copper ion draws

• -butyl bromide in the presence of K2CO3 in dry DMF. Further reaction of 3 with 9-chloromethylanthracene led to the compound 1 [29] in 60% yield. All the compounds were characterized by conventional methods [30]. The adenine-based molecules 1 and 2 were designed according to the design principle of a PET

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

• was established as 1:1 in all cases. For ammonium salts of increased steric demand, the binding values generally decrease. The 18-crown-6 based PET sensors output was linked to the changes in the sensors’ conformational dynamics on complexation (Figure 10). The fluorescence enhancements upon guest

• alkyldiammonium ions in ethanol or in a chloroform/methanol mixture (9:1) based on the PET principle [191]. The fluorescence of the anthracene function is quenched by the free electron pairs of the nitrogen atoms. When hydrogen bonds are formed by both nitrogen atoms to the bis-ammonium guests, the photoinduced

• electron transfer (PET) is inhibited and the system shows an enhanced fluorescence. The binding was dependent on the chain length between the two cations, displaying a maximum stability in the case of the protonated 1,3-diaminopropane. for the bis(aza-15-crown-5) chemosensor 48a the following binding

Studies on polynuclear furoquinones. Part 1: Synthesis of tri- and tetra- cyclic furoquinones simulating BCD/ABCD ring system of furoquinone diterpenoids

• Faruk H. Shaik and
• Gandhi K. Kar

Beilstein J. Org. Chem. 2009, 5, No. 47, doi:10.3762/bjoc.5.47

• purified by column chromatography [silica gel/ pet. ether (60–80 °C) and ethyl acetate mixture, 10:1]. Compound 8 was obtained as a white solid (110 mg) in 77% yield, m.p., 109–111 °C. IR(KBr) νmax : 1737.6 cm−1; 1H NMR (400 MHz, CDCl3) δ: 3.72 (3H, s), 4.33 (2H, s), 6.53 (1H, dd, J = 1.7 and 3 Hz), 6.67

• CH2Cl2. The organic layer was washed with aq. NaHCO3 solution and finally with H2O and dried (Na2SO4). Removal of solvent afforded the crude product which was purified by column chromatography [silica gel/pet. ether (60–80 °C) and ethyl acetate mixture, 19:1] to furnish 65 mg (71%) of 12 as a light

• wise. Stirring was continued at 0–5 °C for 2 h and then left overnight in freeze. The dark red solid separated was filtered and purified by column chromatography [silica gel/ pet. ether (60–80 °C) and ethyl acetate, 10:1]. An analytical sample was prepared further by recrystallisation from pet ether

Themed series in organo- fluorine chemistry

• David O'Hagan

Beilstein J. Org. Chem. 2008, 4, No. 11, doi:10.3762/bjoc.4.11

• the area of medical imaging, positron emission tomography (PET) has undergone a step change in growth across all developing countries, with an exponential increase in the installation of PET cameras and cyclotrons to generate isotope for labelling ligands and diagnostic probes. 18F is an important

• isotope in PET because it has a relatively long half life (t1/2 = 110 min) and methods for introducing fluorine, appropriate to PET synthesis are in demand and will continue to grow. So the field is active and exciting and it is in that context that the BJOC feels it appropriate to profile a themed series

Flexible synthesis of poison- frog alkaloids of the 5,8-disubstituted indolizidine- class. II: Synthesis of (-)-209B, (-)-231C, (-)-233D, (-)-235B", (-)-221I, and an epimer of 193E and pharmacological effects at neuronal nicotinic acetylcholine receptors

• Soushi Kobayashi,
• Naoki Toyooka,
• Dejun Zhou,
• Hiroshi Tsuneki,
• Tsutomu Wada,
• Toshiyasu Sasaoka,
• Hideki Sakai,
• Hideo Nemoto,
• H. Martin Garraffo,
• Thomas F. Spande and
• John W. Daly

Beilstein J. Org. Chem. 2007, 3, No. 30, doi:10.1186/1860-5397-3-30

• in vivo mapping of brain receptors, positron emission tomography (PET) and single photon emission computed tomography (SPECT) using specific ligands are powerful, non-invasive techniques. Although 125I-methyllycaconitine has been used for α7-selective binding in rat brain, [18] neither PET nor SPECT