Photochemical Transformations in Salicylanilide Photoallergy

The photochemical transformations of 3,3′,4′,5‐tetrachlorosalicylanilide, have been characterized by isolation and spectroscopic determination of the primary and secondary photoproducts. The photoreactivity cleanly involves photochemical dechlorination; three chlorines are ultimately lost in an efficient stepwise fashion. A radical mechanism was implicated by formation of a dimer and hydrogen atom abstraction from cysteine when present during photolysis. In the presence of HSA or BSA, the initial dehalogenation leads to a photoadduct with the protein, but dehalogenation of the primary photoproduct, a trichloro compound, does not lead to an efficient photobinding to protein.