1 H - NMR ( 400 MHz , DMSO - d 6 ) δ : 7 . 94 ( 1 H , t , J = 6 . 4 Hz ) , 7 . 61 ( 1 H , s ) , 7 . 56 ( 1 H , d , J = 6 . 0 Hz ) , 7 . 31 - 7 . 21 ( 5 H , m ) , 6 . 90 ( 1 H , d , J = 8 . 4 Hz ) , 4 . 64 ( 2 H , t , J = 8 . 8 Hz ) , 3 . 93 ( 2 H , d , J = 6 . 4 Hz ) , 3 . 34 ( 1 H , s ) , 3 . 23 ( 2 H , J = 8 . 8 Hz ) .