Deuteration of Indole Compounds: Synthesis of Deuterated Auxins, Indole-3-acetic Acid-d5 and Indole-3-butyric Acid-d5.

In this study, we describe a practical and facile synthesis of deuterium-labeled indoles via acid-catalyzed hydrogen-deuterium exchange. 3-Substituted indoles were efficiently deuterated through treatment with 20 wt % D2SO4 in CD3OD at 60-90 °C. A deuterium incorporation reaction of 3-unsubstituted indoles was accomplished through treatment with CD3CO2D at 150 °C. The in situ preparation of a 20 wt % D2SO4/CH3OD/D2O solution enabled a large-scale and low-cost synthesis of auxins, indole-3-acetic acid-d5 and indole-3-butyric acid-d5.