Coumarin-Induced DNA Ligation, Rearrangement to DNA Interstrand Crosslinks, and Photorelease of Coumarin Moiety

Coumarin moieties react with thymine and cytosine in DNA by photoinduced [2+2] cycloaddition, which allows quantitative DNA interstrand crosslink (ICL) formation. Here, we report the application of coumarin analogues for DNA photoligation and the rearrangement of coumarin‐induced ligation to ICL products. Both DNA sequences and the linker units at position 4 of the coumarin moieties affected coumarin‐induced DNA photoligation. A flexible linker unit favored DNA ICL formation but led to inefficient photoligation, whereas coumarins without linker units greatly increased DNA photoligation efficiency. DNA photoligation induced by the coumarin moiety was photoswitchable. Ligation products were formed between coumarin and dT or dC upon 350 nm irradiation but reverted to the original single‐stranded oligodeoxyribonucleotides (ODNs) upon 254 nm irradiation. Rearrangement of ligated ODNs into ICL products occurred during the switchable (350 nm/254 nm) processes. Additionally, photoinduced cleavage of coumarin 3 occurred with dC‐3 cycloadducts upon 254 nm irradiation, which was confirmed by mass spectrometry analysis. UV control: Coumarin analogues were shown to photo‐crosslink dT‐ or dC‐forming ligation products in addition to interstrand crosslink (ICL) adducts. The photoligation was photoswitchable: ligation products formed at 350 nm irradiation reverted to the original single‐stranded ODNs upon 254 nm irradiation. Rearrangement of ligated ODNs into ICL products also occurred during the switchable processes.