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Photosensitizing thiophenes from the Tageteae Downum, Kelsey


Two separate aspects involving the thiophenes of the Tageteae (Asteraceae) were investigated. The first concerned the distribution of four thiophenes in Tagetes patula L. which were examined by high pressure liquid chromatography (HPLC). The derivatives were found to be differentially distributed throughout hydroponically grown plants. The predominant thiophenes in roots were 5-(4-acetoxy-1-butenyl)-2,2'-bithienyl (BBT-OAc) and 5-(buten-3-ynyl)-2,2'-bithienyl (BBT). BBT-OAc was the main derivative in shoots, whereas 2,2':5',2''-terthienyl (alpha-T) was the major compound in flower petals. BBT and one unidentified compound were found to occur in leaf glands. The levels of BBT-OAc in shoots and BBT-OAc and BBT in roots increased over the life of the plant and reached a plateau following flowering. Alpha-T in roots and both alpha-T and BBT in shoots remained at low levels over the life of the plant while 5-(4-hydroxy-1-butenyl)-2,2'-bithienyl (BBT-OH) was found to be an minor component of roots or shoots. Fourteen species from four genera of the tribe Tageteae were also screened for the presence of thiophenes by HPLC. Representatives of Dyssodia, Porophyllum, and Tagetes all contained thiophenes, but none were detected in species of Pectis. The second part of this study concerned the photobiocidal effects of isolated thiophenes on Escherichia coli B which was used as a model biological system. Alpha-terthienyl (alpha-T), in the presence of UV-A irradiation (320nm-400nm), was found to be a Type II photosensitizer which required oxygen for the expression of biological activity. Scavenger studies with sodium azide and BHT suggested that both singlet oxygen and superoxide were generated by the photosensitized reaction. Cellular inactivation by alpha-T was sensitive to temperature and studies with recombination deficient mutants of E. coli K-12 did not indicate that damage to cellular DNA occurred. Proteins were found to be substantially affected by the photoactivated reaction. SDS-gel electrophoresis revealed that both cytoplasmic and membrane-associated proteins might be. crosslinked following treatment with alpha-T and UV-A.

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