2,6-Disubstituted pyrazines and related analogs as NR2B site antagonists of the NMDA receptor with anti-depressant activity

Herein we describe the discovery of compounds that are competitive antagonists of the CP101-606 binding site within the NR2B subtype of the NMDA receptor. The compounds identified do not possess phenolic functional groups such as those in ifenprodil and related analogs. Initial identification of hits in this series focused on a basic, secondary amine side chain which led to good potency, but also presented a hERG liability. Further modifications led to examples of non-basic replacements which demonstrated much less liability in this regard. Finally, one compound in the series, 6a, was tested in the mouse forced swim depression assay and found to show activity (sc 60 mg/kg).