主权项 |
1. A compound of formula (I): wherein R1 is lower alkyl, cycloalkyl or —CH2C(O)OCH3; R2 and R2′, independently of each other, are hydrogen, halogen, lower alkyl or lower haloalkyl; and R3 and R3′, independently of each other, are hydrogen, halogen, cyano or ethynyl; or a pharmaceutically acceptable salt thereof. |