An Efficient Synthesis Of Carbon-14-Labeled 6-[2-(Dimethylamino)Ethyl]-14-(1-Ethylpropyl)-5,6,7,8-Tetrahydroindolo [2,1-Alpha] [2,5]Benzodiazocine-11-Carboxylic Acid Using Curtius Rearrangement Reaction As A Key Step

Here we report an efficient synthesis of (14)C-labeled 6-[2-(dimethylamino)ethyl]-14-(1-ethylpropyl)-5,6,7,8-tetrahydroindolo-[2,1-alpha][2,5]benzodiazocine-11-carboxylic acid (1) using the Curtius rearrangement as a key step. The synthesis was initiated by converting the unlabeled aryl carboxylic acid to an aryl amine via Curtius rearrangement reaction. The resulting aryl amine was then converted to an aryl iodide which was coupled with zinc [(14)C] cyanide to form an aryl [(14)C] nitrile. Subsequent hydrolysis yielded the (14)C-labeled carboxylic acid [(14)C]-1. This overall process represents a mild and potentially general approach for conversion of unlabeled carboxylic acids to isotopically labeled carboxylic acids.