3 ) 1 H - NMR ( 500 MHz , DMSO - d 6 ) : δ 7 . 80 ( 1 H , d , J = 8 . 7 Hz , H - 1 ) , 7 . 10 ( 1 H , s , H - 11 ) , 6 . 56 ( 1 H , d , J = 8 . 5 Hz , H - 2 ) , 6 . 35 ( 1 H , s , H - 4 ) , 6 . 32 ( 1 H , s , H - 8 ) , 4 . 45 ( 1 H , d , J = 11 . 7 Hz , H - 6 a ) , 4 . 00 ( 1 H , d , J = 11 . 7 Hz , H - 6 b ) , 2 . 85 ( 2 H , d , J = 3 . 7 Hz , H - 7 )