1 H NMR ( 300 MHz , CDCl 3 ) δ 4 . 51 ( brs , 1 H ) , 4 . 16 ( d , J = 7 . 5 Hz , 2 H ) , 3 . 81 ( dd , J = 11 . 4 , 24 . 9 Hz , 1 H ) , 3 . 57 - 3 . 68 ( m , 1 H ) , 3 . 05 - 3 . 22 ( m , 5 H ) , 1 . 96 - 2 . 04 ( m , 1 H ) , 1 . 64 - 1 . 72 ( m , 1 H ) , 1 . 49 ( s , 9 H ) , 1 . 44 ( s , 9 H ) , 1 . 29 ( s , 3 H ) , 1 . 25 ( t , J = 7 . 5 Hz , 3 H ) ;