1 H - NMR ( CDCl 3 ) δ 4 . 75 ( pseudo t , 1 H , J = 7 . 4 Hz ) , 4 . 33 - 4 . 45 ( m , 4 H ) , 4 . 06 - 4 . 20 ( m , 3 H ) , 3 . 12 ( s , 3 H ) , 3 . 07 ( s , 3 H ) , 1 . 51 ( s , 3 H ) , 1 . 43 ( s , 3 H ) , 1 . 37 ( s , 3 H ) , 1 . 33 ( s , 3 H ) ;