Fluorescent DNA probes were prepared in a modular approach using the “click” post-synthetic modification strategy. The new glycol-based module and DNA building block place just two carbons between the phosphodiester bridges and anchor the dye by an additional alkyne group. This creates a stereocenter in the middle of this artificial nucleoside substitute. Both enantiomers and a variety of photostable cyanine–styryl dyes as well as thiazole orange derivatives were screened as “clicked” conjugates in different surrounding DNA sequences. The combination of the (S)-configured DNA anchor and the cyanylated cyanine–styryl dye shows the highest fluorescence light-up effect of 9.2 and a brightness of approximately 11,000 M–1 cm–1. This hybridization sensitivity and fluorescence readout were further developed utilizing electron transfer and energy transfer processes. The combination of the hybridization-sensitive DNA building block with the nucleotide of 5-nitroindole as an electron acceptor and a quencher increases the light-up effect to 20 with the DNA target and to 15 with the RNA target. The fluorescence readout could significantly be enhanced to values between 50 and 360 by the use of energy transfer to a second DNA probe with commercially available dyes, like Cy3.5, Cy5, and Atto590, as energy acceptors at the 5′-end. The latter binary probes shift the fluorescent readout from the range of 500–550 nm to the range of 610–670 nm. The optical properties make these fluorescent DNA probes potentially useful for RNA imaging. Due to the strong light-up effect, they will not require washing procedures and will thus be suitable for live-cell imaging.

TwoD NA three-way junctions bearing 4-methylbenzophenone and 4-methoxybenzophenone as C-nucleosides at the hydrophobic binding pocket were synthesized.T hey were applieda s aptamersa nd photoDNAzymes to gain enantioselectivity for the photosensitized intramolecular [2+ +2] cycloaddition of aquinolinones ubstrate in aqueous solution. Irradiation by two l = 369 nm LEDs for 10 hy ielded5 8% of the regioisomeric product mixture with an enantiomeric excesso f2 8%.T he enantiomeric excess in the presenceo ft he three-wayj unction with 4methylbenzophenone yields higher enantiomeric excesst han that with 4-methoxybenzophenone which can be explained by differences in binding of the substrate accordingt om elting temperature analysis. This is the first time that the chirality of double-stranded DNA can be transferred to an asymmetric photosensitized reaction and opens the way for in vivo applications of chiral photosensitizing in biology.Benzophenone is am ajor tool in photochemistry [1] since 1) it is chemically and photochemicallys table, 2) the intersystem crossingt ot he triplet T 1 state occurs with quantitative yield, 3) the T 1 state has al ifetime in the ms time range, and 4) the distinct np*t ransition allows the use of UV-A light-emitting diodes (LEDs)f or photochemical and photocatalytical experiments.H ighly enantioselective photocatalysis with benzophenones [1b, d-g] was achieved by template-assisted triplet-triplet energy transfer,b ut only in organic media. [2] To bring this type of photocatalysis to aqueous media and to achievee nantioselectivity by the chirality of DNA, thereby enhancing the sustainability (as demonstrated previously for av ariety of thermal reactions), [3] we recently synthesized the C-nucleoside with benzophenone as an artificial DNA base. [4] However,p hotocatalysis of the intramolecular [2+ +2] cycloaddition of quinolinone substrate 1 to the regioisomeric products 2 and 3 by this artificial C-nucleoside in double-stranded DNA failed completely (see Scheme 1f or compound structures). The careful study of benzophenone dinucleotides by time-resolved transienta bsorptions pectroscopy and theoretical methodsi ncluding mo-lecular dynamics showed that photoinduced charget ransfero f base-stacked benzophenone (especially with guanosine) competes with the triplet-triplet energy transfer that is required for this [2+ +2] cycloaddition. [5] For alternative benzophenone nucleosides,the electron density had to be increased in order to inhibitc harge transfer in DNA while keeping the triplet energy as high as possible. With respect to quinolone 1 at riplet energy (E T )o fa tl east E T = 2.86 eV [6] is required and the extinctionc oefficienti nt he UV-A range (separate from the substrate absorption) must be sufficiently high to allow selective excitation.C onventional benzophenone has at riplet energy of E T = 2.98 eV that clearly fulfills this requirement, [7] butt he T 1 energies of 4-methylbenzophenone (E T = 3.00 eV) [8] and4 -methoxybenzophenone (BpOMe; E T = 3.01 eV) [8] are also about 15 ...

The Front Cover picture shows a three‐dimensional model of a DNA three‐way junction with an internal benzophenone nucleotide in the photoreactive center that induces asymmetry during substrate conversion. More information can be found in the Communication by H.‐A. Wagenknecht and co‐workers on page 48 in Issue 2, 2017 (DOI: 10.1002/cptc.201600034).

The front cover artwork is provided by the Wagenknecht group at KIT. The image shows a three‐dimensional model of the DNA three‐way junction with an internal benzophenone nucleotide in the photoreactive center that induces asymmetry during substrate conversion. Read the full text of the article at 10.1002/cptc.201600034.