143379-89-9 4-(2,5-Dihydro-2,5-dioxo-1H-pyrrol-1-yl)benzenebutanoic acid hydrazide 4-(4-N-Maleimidophenyl)butyric acid hydrazide Benzenebutanoic acid, 4-(2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl)-, hydrazide MPBH