Fluorescence and Structure of Proteins as measured by Incorporation of Fluorophore. II. Synthesis of Maleimide Derivatives as Fluorescence-Labeled Protein-Sulfhydryl Reagents.

A novel approach to studies of structure and function of proteins utilizing fluorescencelabeled specific reagent is proposed. N-[p-(2-Benzoxazolyl) phenyl] maleimide (IIIa) and N-[p-(2-benzthiazolyl) phenyl] maleimide (IIIb) were synthesized as sulfhydryl reagents of this type and the addition reaction with cysteine ester was investigated. Cyclization of maleamic acids with PPA is demonstrated to be a good method for synthesis of N-substituted maleimides.