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Effect of thione—thiol tautomerism on the inhibition of lactoperoxidase by anti-thyroid drugs and their analogues

Jayaram, PN and Roy, Gouriprasanna and Mugesh, Govindasamy (2008) Effect of thione—thiol tautomerism on the inhibition of lactoperoxidase by anti-thyroid drugs and their analogues. In: Proceedings of the Indian Academy of Sciences - Chemical Sciences, 120 (1). 143 -154.

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The keto-enol type tautomerism in anti-thyroid drugs and their selenium analogues are described. The commonly used anti-thyroid drug methimazole exists predominantly in its thione form, whereas its selenium analogue exists in a zwitterionic form. To understand the effect of thione/thiol and selone/selenol tautomerism on the inhibition of peroxidase-catalysed reactions, we have synthesized some thiones and selones in which the formation of thiol/selenol forms are blocked by different substituents. These compounds were synthesized by a carbene route utilizing an imidazolium salt. The crystal structures of these compounds reveal that the C=Se bonds in the selones are more polarized than the C=S bonds in the corresponding thiones. The structures of selones were studied in solution by NMR spectroscopy and the 77Se NMR chemical shifts for the selones show large upfield shifts in the signals, confirming their zwitterionic structures in solution. The inhibition of lactoperoxidase by the synthetic thiones indicates that the presence of a free N-H moiety is essential for an efficient inhibition. In contrast, such moiety is not required for an inhibition by the selenium compounds.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Indian Academy of Sciences.
Keywords: Anti;thyroid drugs;bioinorganic chemistry;enzyme inhibition; lactoperoxidase;methimazole.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Depositing User: K.S. Satyashree
Date Deposited: 04 Jun 2010 06:52
Last Modified: 19 Sep 2010 05:56
URI: http://eprints.iisc.ac.in/id/eprint/26177

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