Thyroid Gland (dimethylsulfoxide/visible spectra/sulfur-, nitrogen-, and oxygen-containing goitrogens)

The reactivities of N-iodosuccinimide and iodine with various goitrogenic compounds were studied with dimethylsulfoxide through which nitrogen had been bubbled as a solvent. Although iodine does not react with all of the compounds, N-iodosuccinimide does react with all of them. N-Iodosuccinimide may, therefore, serve as an interesting model for the "active iodine" of the thyroid. The thyroid gland synthesizes the thyroid hormones, thyroxine and triiodothyronine. Inorganic iodide is oxidized by iodide peroxidase to an unknown "active iodine" species that iodinates certain tyrosines of the thyroglobulin molecule to monoand diiodotyrosine residues. Some of these proteinbound iodinated tyrosines are coupled by the same peroxidase to yield thyroglobulin-bound thyroxine and triiodothyronine. The goitrogens are compounds that prevent the biosynthesis of the thyroid hormones by inhibiting the iodination and/ or the coupling reactions (1). Several chemical classes of compounds are now known to have goitrogenic activity. They include: thionamides (2, 3), sulfonamides (2, 3), metahydroxyphenols (4), hydrazines (5), and the compounds 3-amino-1, 2,4-triazole (6) and 1,1,3-tricyano-2-amino-1-propene (7). Little systematic chemical work has been done on the reactivities of the goitrogens with different types of iodinating agents. N-Iodosuccinimide, a "positive iodine" reagent, is similar to 12 in its ability to iodinate the phenol ring, but it has a higher oxidation potential (8). It was therefore of interest to compare the reactivities of I2 and N-iodosuccinimide with the goitrogens. Under the conditions described herein, Niodosuccinimide was found to react with all the classes of goitrogens tested, while 12 reacts only with some classes. These results suggest that N-iodosuccinimide is a better model for the "active iodine" than is I2. Preliminary spectrophotometric studies showed that the yellow color of solutions resulting from the reaction of a compound with N-iodosuccinimide in (CH3)2SO through which N2 had been bubbled was due to the presence of 12 only (420-nm peak) and/or the presence of I3(366-nm peak). 12 is presumed to result from the reduction of N-iodosuccinimide to I by the drug in a multistep reaction (the goitrogen is oxidized simultaneously), and the reaction of this Iwith excess N-iodosuccinimide to give 12 and/or 3-. The iodination of a compound to yield a stable covalent iodine bond (as in iodophenol, etc.) would not result in Iformation. The reaction of a drug with 12 (i.e., 12 reduction) was followed by measurement of the decrease of absorption of the I3peak. 1401 MATERIALS AND METHODS Dimethylsulfoxide [(CH3)2SO] was chosen as the solvent because of its ability to dissolve readily most of the compounds under study. For good reproducibility it was found necessary to bubble the solvent with nitrogen. Since (CH3)2SO is very hygroscopic, and maintenance of anhydrous conditions for routine determinations is difficult, the "Certified Grade" containing 0.2% water supplied by Fischer Scientific Co. was used. (CH3)2SO was bubbled for about 5-10 min with a stream of N2 before each experiment. Most of the compounds used were obtained commercially and were not purified further. A series of rare derivatives was obtained from the collection of Dr. E. B. Astwood. Solutions of the substances were prepared in (CH3)2SO through which N2 had been bubbled and used fresh. N-iodosuccinimide was obtained from K & K Laboratories, Inc., Plainview, N.Y. Solutions in (CH3)2SO through which N2 had been bubbled were prepared in dim light and were kept in darkness as much as possible for up to 3 hr. Spectrophotometric Measurements were performed on a recording Beckman DM spectrophotometer in a range between 600 and 340 nm. Water from a water bath maintained at 250 was circulated through the cuvette chamber. Reactivity of N-lodosuccinimide. Since a slow spontaneous yellowing of N-iodosuccinimide solutions occurs, it was necessary to use a blank containing the identical N-iodosuccinimide solution that is used in the reaction for most measurements. Fresh, almost colorless N-iodosuccinimide solutions were used. Usually the concentration of N-iodosuccinimide in the cuvette was 10 jsrol in 2 ml (5 mM). However, a series of experiments was run with 0.1-100 Amol of N-iodosuccinimide in 2 ml. Every compound was checked at least at four different concentrations (from 0.01 to 2 ,umol/2 ml) with 10 ,umol of Niodosuccinimide. In a routine determination, an aliquot of 0.01-0.1 ml of a (CH3)2SO solution of the compound (usually 10 mM) was added to 2 ml of a (CH3)2SO solution of N-iodosuccirimide in the cuvette, mixed by bubbling with N2, and scanned immediately from 600 to 340 nm. The scan speed was 40 nm/ min. Therefore, the yield of 12, obtained from A420 nm was the result of 5 min of reaction time that included the 30-sec time period for mixing and the N2 bubbling of the cuvette. The reaction for most, but not all, of the compounds was almost finished by this time. 1402 Medical Sciences: Jirousek and Soodak