title: Evidence for [2 + 2] photoreaction of alpha-methylene-gamma-butyrolactones with thymine: an explanation for chronic actinic dermatitis to sesquiterpene lactones?
abstract: The photoreactivity of isoalantolactone, a natural sesquiterpene lactone, toward thymine was studied. After 313 nm irradiation of a deoxygenated acetone solution of isoalantolactone (2 x 10(-3) M) and thymine (4 x 10(-3) M), two intermolecular [2 + 2] photoadducts, 3 and 4, were isolated with respective yields of 30% and 18%. The structures of these two photoadducts were determined by a combination of NMR experiments. Compound 3 was identified as a cis-syn-exo intermolecular [2 + 2] photoadduct involving the 5,6 double bond of thymine and the exomethylenic double bond of the lactone, while compound 4 was identified as an intermolecular [2 + 2] photoadduct involving the same bonds but with the cis-syn-endo conformation. This high photoreactivity of sesquiterpene lactones toward thymine could be an explanation of the progressive evolution of allergic contact dermatitis toward chronic actinic dermatitis.
authors.affiliation: Laboratoire de Dermatochimie associé au CNRS, Université Louis Pasteur, Strasbourg, France.
authors.forename: V
authors.initials: V
authors.lastname: Berl
authors.forename: J P
authors.initials: JP
authors.lastname: Lepoittevin
mesh_terms: D017449:Dermatitis, Allergic Contact / Q000209:etiology; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D010777:Photochemistry; D010787:Photosensitivity Disorders / Q000209:etiology*; D012717:Sesquiterpenes / Q000009:adverse effects* / Q000737:chemistry / Q000528:radiation effects*; D013941:Thymine / Q000737:chemistry / Q000528:radiation effects*
chemical_list: D012717:Sesquiterpenes; C032787:isoalantolactone; D013941:Thymine