[2-[[(4S,6S)-6-Methyl-7,7-dioxo-2sulfamoyl-4,5,6,7-tetrahydro-7ฮป6 -thieno[2,3-b]thiopyran-4yl]amino]ethyl]boronic acid,[2-[[(4S,6S)-6-Methyl-7,7-dioxo-2sulfamoyl-4,5,6,7-tetrahydro-7ฮป6 -thieno[2,3-b]thiopyran-4yl]amino]ethyl]boronic acid,Dorzolamide Impurity