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YELLOW TO YELLOW-BROWN POWDER

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α-Terthienyl was first recognized as a nematicidal constituent of marigolds, but in the presence of light, it is also highly toxic to larvae of several insect species, including mosquitoes. This electron donor thiophenederivative phototoxin is biosynthesized from polyacetylene precursors and appears to function as a photosensitizer catalyzing the formation of reactive oxygen species at the target site (25).

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2,2′:5′,2′′-Terthiophene (TTh) may be prepared by nickel catalysed coupling reaction of grignard′s reagent derived from 2-bromothiophene and magnesium. It generates singlet oxygen. In nature, it is found in the floral extract of Tagetes minuta and Echinops grijisii. It is known to be toxic to mosquitoes. It also exihibits antifungal activity.

Synthesis

A common method for synthesizing 2,2':5',2''-terthiophene is a metal-catalyzed coupling reaction. This reaction can be obtained by coupling a Grignard reagent prepared with 2,5-dibromothiophene and 2-bromothiophene under nickel or palladium catalysis.

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When 14C-a-terthienyl is administered orally to rats in a single dose, two metabolites [1,4-di(2'-thienyl)]-1,4- butadione and 2-2' -bithiophene-5-carboxylic acid are identified in the urine.

Purification Methods

Possible impurities are bithienyl and polythienyls. Suspend it in H2O and steam distil it to remove bithienyl. The residue is cooled and extracted with CHCl3, dried (MgSO4), filtered, evaporated and the residue chromatographed on Al2O3 using pet ether/3% Me2CO as eluent. The terphenyl zone is then eluted from the Al2O3 with Et2O, the extract is evaporated and the residue is recrystallised from MeOH (40mL per g). The platelets are washed with cold MeOH and dried in air. [UV: Sease & Zechmeister J Am Chem Soc 69 270 1947; Uhlenbroek & Bijloo Recl Trav Chim Pays-Bas 79 1181 1960.] It has also been recrystallised from MeOH, *C6H6, pet ether or AcOH. [UV: Zechmeister & Sease J Am Chem Soc 69 273 1947, Steinkopf et al. Justus Liebigs Ann Chem 546 180 1941.] It is a phototoxic nematocide [Cooper & Nitsche Bioorg Chem 13 36 1985, Chan et al. Phytochem 14 2295 1975]. [Beilstein 19 III/IV 4763, 19/9 V 226.]

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