title: Photobiological properties of hydroxy-substituted flavothiones.
abstract: Flavothione (FT) and a series of 18 hydroxy- and methoxy-substituted flavothiones were screened for photobiological activity. The 5-hydroxy-substituted compounds (group 3) and the methoxy-substituted flavothiones were inactive. FT and the remaining hydroxy-substituted compounds, all displayed photobiological activity. Among these, the 3-hydroxy-substituted compounds (group 2) were the most efficient photosensitizers overall in spite of their concurrent fast photodegradation. FT and all other hydroxyflavothiones, not substituted in the 3- or 5-positions (group 1), were inefficient compared with group 2. Detailed photobiological tests were carried out for four flavothiones of groups 1 and 2. The biological tests included fungi, several strains of Escherichia coli, Salmonella typhimurium and mammalian cells. In addition, the ability of these flavothiones to perform lipid peroxidation was evaluated. FT and 6-hydroxyflavothione (group 1) induce DNA damage via H-atom abstraction from the lowest n, pi* triplet state of the thione (oxygen independent). For 3-hydroxy and 3,6-dihydroxyflavothione (group 2), both DNA and the membrane are targets. The mechanism likely involves both energy transfer and electron transfer from the lowest pi, pi* triplet state to oxygen, to form singlet oxygen and the superoxide anion. Some of these compounds could be considered as models for environmentally safe photopesticides.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Oeiras, Portugal. macanita@itqb.unl.pt
authors.forename: Marta
authors.initials: M
authors.lastname: Borges
authors.forename: Ana
authors.initials: A
authors.lastname: Romão
authors.forename: Olívia
authors.initials: O
authors.lastname: Matos
authors.forename: Christine
authors.initials: C
authors.lastname: Marzano
authors.forename: Sergio
authors.initials: S
authors.lastname: Caffieri
authors.forename: Ralph S
authors.initials: RS
authors.lastname: Becker
authors.forename: António L
authors.initials: AL
authors.lastname: Maçanita
mesh_terms: D001419:Bacteria / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D005419:Flavonoids / Q000737:chemistry / Q000528:radiation effects / Q000633:toxicity*; D005658:Fungi / Q000187:drug effects / Q000528:radiation effects; D006367:HeLa Cells / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D006900:Hydroxylation; D015227:Lipid Peroxidation / Q000187:drug effects / Q000528:radiation effects; D009152:Mutagenicity Tests; D017319:Photosensitizing Agents / Q000737:chemistry / Q000528:radiation effects / Q000633:toxicity*; D013329:Structure-Activity Relationship; D013871:Thiones / Q000737:chemistry / Q000528:radiation effects / Q000633:toxicity; D014466:Ultraviolet Rays
chemical_list: D005419:Flavonoids; D017319:Photosensitizing Agents; D013871:Thiones