Synthesis and receptor binding of 5-amino[3H]2methyl-3-isothiazolol ([3H]thiomuscimol), a specific GABAa agonist photoaffinity label

✍ Scribed by B. Frølund; B. Ebert; L. W. Lawrence; S. D. Hurt; P. Krogsgaard-Larsen

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: French
• Weight: 524 KB
• Volume: 36
• Category: Article
• ISSN: 0022-2135
• DOI: 10.1002/jlcr.2580360909

✦ Synopsis

Abstract

The synthesis of tritium labelled thiomuscimol(5‐amino[^3^H]~2~methyl‐3‐isothiazolol) (7c), a specific and high‐affinity agonist photoaffinity label for GABA~A~ receptors, is described. The synthesis of 7c is based on a procedure for the preparation of 5‐amino[^2^H]~2~methyl‐3‐isothiazolol (7b). Methyl 3‐ethoxyisothiazole‐5‐carboxylate (3), synthesized from 3‐hydroxyisothiazole‐5‐carboxamide (1) via the corresponding methyl ester (2), was reduced with sodium borotritide to give 3‐ethoxy‐5‐hydroxy[^3^H]~2~methyl‐3‐isothiazole (4c). 3‐Ethoxy‐5‐phthalimido[^3^H]~2~‐methylisothiazole (6c), synthesized from the 5‐chloro[^3^H]~2~methyl analogue (5c) of (4c), was deprotected by treatment with concentrated hydrochloric acid to give 7c with a specific radioactivity of 29 Ci/mmol. In pilot binding assays, 7c was shown to bind to membranes from rat forebrain in a saturable manner and with K~D~ and B~max~ values of 28 ± 6 nM and 50 ± 4 fmol/mg original tissue, respectively.