3,4 and 4′,5′‐photocycloadducts Between 4′‐methylangelicin and Thymine From Dna

Two C 4 ‐cycloadducts between 4′‐methylangelicin and thymine were isolated from the photo‐reaction (365 nm) between this furocoumarin and DNA. Their capacity to undergo photoreversion at 254 nm and their spectroscopic and NMR data allowed us to assign furan‐ and pyrone‐side structures, respectively, to these photocompounds. The former adduct has a cis‐syn configuration; the latter. which was also isolated from a photoreaction between the furocoumarin and thymine in water‐methanol solution, was assigned a cis‐anti structure.