1 H NMR ( 499 . 8 MHz , DMSO - d 6 ) δ 2 . 57 ( 4 H , t ) , 3 . 62 ( 4 H , t ) , 3 . 71 ( 2 H , s ) , 7 . 57 ( 1 H , d ) , 7 . 64 ( 1 H , t ) , 7 . 80 ( 1 H , d ) , 8 . 12 - 8 . 15 ( 1 H , m ) , 8 . 21 ( 1 H , s ) , 8 . 24 ( 1 H , d ) ; m / z = 408 [ M + H ] +.