Phytochemicals thiophenes

Acetylenes, beta-carboline alkaloids, furocoumarins and lignans occur widely among the families listed in Table 1. Acetophenones (benzofurans and benzopyrans) and extended quinones have a much more limited distribution while furochromones, furoquinoline alkaloids and thiophenes are apparently restricted to single families. It should be mentioned that although acetylenic polylnes are phytochemical components of plants from numerous families (4), only those derivatives produced by members of the Asteraceae have been shown to be phototoxic Q). 

Figure 1. Structures of representative phototoxic plant products from various phytochemical classes. (I) 1-phenylhepta-1,2,3-triyne (acetylenic polyine) (II) 6-methoxyeuparin (benzofuran) (III) harmane (beta-carboline alkaloid) (IV) khellin (furo-chromone) (V) 8-methoxypsoralen (furocoumarin) (VI) dictamnine (furoqulnoline alkaloid) (VII) nordihydroguaiaretic acid (lignan) and (VIII) alpha-terthienyl (thiophene).

Photoaddition of thiochromone 1,1-dioxide in the presence of benzene, for example, gave a 2 1 adduct (180) in 32% yield. A correlation was observed between the behaviour of the benzenoid compounds and their ionization potentials.5-Aryl esters of thiophen-2-thiolocarboxylic acids undergo a phytochemical transformation into a mixture of products, including the thienobenzothiopyranones (Scheme 4)/ ... 

Arnason, J.T., B.J.R. Philogene, C. Berg, A. Maceachern, J. Kaminski, L.C. Leitch, P. Morand, and J. Lam Phototoxicity of Naturally Occurring and Synthetic Thiophene and Acetylene Analogues to Mosquito Larvae. Phytochem. 25, 1609 (1986). 

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