Disclosed are chemical entities of formula I: [INSERT CHEMICAL FORMULA HERE] wherein X Y Z R1 R3 R4 R5 and R6 are defined herein as NR2B subtype selective receptor antagonists. Also disclosed are pharmaceutical compositions comprising a chemical entity of formula I and methods of treating various diseases and disorders associated with NR2B antagonism e.g. diseases and disorders of the CNS such as depression by administering a chemical entity of formula I.
