Further studies on the ceric sulphate-arsenious acid reaction for the detection of various analogues of thyroxine

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Abstract
A method has been presented for roughly determining the deiodination of thyroxine analogues applied under standard conditions to chromatography paper, by using decolorization of the ceric sulphate-arsenious acid reagent. Deiodination of thyronines iodinated at 3,3[image],5,5[image]-positions in any combination appears to be equal to that of mono- and di-iodotyrosine. Altrations in the alanine side chain and the presence of alkyl sub-stituents on the phenolic ring do not alter do not alter deiodination. Removal of the 4[image]-oxygen atom lowers deiodination of 3,5-di-iodothy-ronine analogues to less than 1%. Replacement by a 4[image]-amino group causes a return of activity, but replacement by a 4[image]-methyl group does not Substitution of a thio ether sulphur atom for the usual either oxygen atom or the formation of the diphenyl analogues of 3,5-di-iodothyronine eliminate deiodination. Ceric deiodination of 3,5-iodothyronines is probably initiated by oxidative removal of the outer phenolic ring.