1-O-benzyl 2-O-(2,5-dioxopyrrolidin-1-yl) pyrrolidine-1,2-dicarboxylate, commonly known as Z-Pro-OSu, is a white to off-white crystalline powder. It is a derivative of L-proline, where the amino group is protected by a benzyloxycarbonyl (Cbz or Z) group, and the carboxylic acid is activated as an N-hydroxysuccinimide (NHS) ester. This specific structure makes it a highly reactive and valuable reagent in synthetic chemistry. Its primary and most significant application is in peptide synthesis, particularly in solid-phase peptide synthesis (SPPS) and solution-phase methods. The NHS ester moiety is a well-established active ester that reacts efficiently with the amino groups of other amino acids or peptide fragments under mild conditions to form amide (peptide) bonds. The Z-protecting group on the proline nitrogen is stable under the coupling conditions but can be selectively removed later using catalytic hydrogenation or other methods. Therefore, this compound serves as a crucial protected and activated building block for introducing proline residues into peptide chains. Due to the conformational influence of the proline ring, its incorporation is essential for designing peptides with specific turns, folds, or biological activities. Z-Pro-OSu is thus a standard reagent in research laboratories and pharmaceutical development for the synthesis of bioactive peptides, peptide hormones, and peptidomimetics.