4-(Methylmercapto)phenyl succinimidyl succinate 4-(Methylthio)phenyl 4-((2,5-dioxo-1-pyrrolidinyl)oxy)-4-oxobutanoate 86451-38-9 Butanoic acid, 4-((2,5-dioxo-1-pyrrolidinyl)oxy)-4-oxo-, 4-(methylthio)phenyl ester MMPSS