Photocatalysis of a [2+ 2] Cycloaddition in Aqueous Solution Using DNA Three-Way Junctions as Chiral PhotoDNAzymes

Two DNA three-way junctions bearing 4-methylbenzophenone and 4-methoxybenzophenone as C-nucleosides at the hydrophobic binding pocket were synthesized. They were applied as aptamers and photoDNAzymes to gain enantioselectivity for the photosensitized intramolecular [2+ 2] cycloaddition of a quinolinone substrate in aqueous solution. Irradiation by two lambda-369 nm LEDs for 10 h yielded 58% of the regioisomeric product mixture with an enantiomeric excess of 28%. The enantiomeric excess in the presence of the three-way junction with 4methylbenzophenone yields higher enantiomeric excess than that with 4-methoxybenzophenone which can be explained by differences in binding of the substrate according to melting 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.