Syntheses of ¹⁴C-Labeled Pyrethrin I, Allethrin, Phthalthrin, and Dimethrin on a Submillimole Scale

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Studies on the metabolic fate and degradation chemistry of pyrethroid insecticide chemicals are greatly facilitated by the use of compounds radiolabeled, in separate preparations, in the acid and alcohol moieties. Acid-labeled preparations were made by converting d-trans-chrysanthemic acid-1-¹⁴C (88mg, 1.3mCi/mM) into d-trans-d-pyrethrin-1-¹⁴C (68mg, 1.3mCi/mM), d-trans-d-allethrin-¹⁴C (43mg, 1.3 mCi/mM), d-trans-dimethrin-¹⁴C (54mg, 0.294mCi/mM), and d-trans-phthalthrin-¹⁴C (47mg, 0.294mCi/mM), incorporating approximately 81% of the starting radiocarbon into the four pyrethroid preparations. Alcohol-labeled preparations were made by converting acetone-1, 3-¹⁴C into d-trans-dl-allethrin-¹⁴C (146mg, 0.162mCi/mM) and formaldehyde-¹⁴C into d-trans-phthalthrin-¹⁴C (299mg, 0.276mCi/mM). Each labeled compound had a high stereochemical purity and a radiochemical purity of greater than 99%. Detailed procedures were worked out for all conversions which took place in high yields except in one case: the synthesis of allethrin labeled in the alcohol moiety.