1 H NMR ( 300 MHz , CDCl 3 ) δ 1 . 70 - 1 . 85 ( m , 4 H ) , 1 . 96 - 2 . 04 ( m , 4 H ) , 2 . 17 ( s , 3 H ) , 2 . 33 ( t , 2 H ) , 2 . 35 ( s , 3 H ) , 2 . 37 ( s , 3 H ) , 2 . 48 ( m , 1 H ) , 2 . 60 ( s , 3 H ) , 2 . 94 ( brd , 2 H ) , 4 . 16 ( t , 2 H ) , 6 . 91 ( d , 1 H , J = 7 . 5 Hz ) , 7 . 12 ( s , 1 H ) , 7 . 21 - 7 . 37 ( m , 2 H ) , 7 . 43 ( m , 2 H ) , 7 . 62 ( brs , 1 H , NH ) ; MS ( m / e , M +): 418 , 403 , 376 , 257 , 245 , 231 , 187 , 174