Sub-nanomolar potent, non-competitive mGlu1 antagonist (Ki = 0.34 nM). Inhibits glutamate-induced Ca2+ response at the human mGlu1 receptor with an IC50 value of 0.55 nM. Selective over mGlu5 (> 400-fold) and displays no activity at mGlu2, mGlu3, mGlu4, mGlu6, AMPA or NMDA receptors (IC50 > 10 μM). Centrally active following systemic administration.