Antigoitrogenic Properties of Some 3′-Alkyl-iodothyronines

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Abstract
The thyromimetic activities of several 3[image]-alkyl-3,5-diiodothyronines were studied by the rat antigoitrogenic assay and compared with L-T3 and L-T4. L-3[image]-Isopropyl-3,5-diiodothyronine was the most potent member of this series. On an equimolar basis, this remarkable compound had twice the activity of L-T3 with a 50% effective dose (ED50) of 0.07 compared to 0.13 [mu]g/day for L-T3. Its 5[image]-iodinated derivative was somewhat less potent than L-T3, with an ED50 of 0.25 [mu]g/day, but was more active than L-T4 (ED50 1.2 [mu]g/day). DL-3[image]-Ethyl-diiodothyronine (ED50 0.25 [mu]g/day) had a potency between that of L-T3 and L-T4. L-3[image]-Isobutyl-diiodothyronine (ED50 1.5 [mu]g/day) was less active than L-T4. These synthetic thyroxine analogs exhibit unusually high activity and are of particular interest in that they represent the first group of 3[image] non-halogen-substituted dilodothyronines to have significant thyromimetic properties.