Z-D-Phe-ONp is the p-nitrophenyl ester of N-benzyloxycarbonyl-D-phenylalanine, serving as an active ester in peptide synthesis. It enables efficient coupling of the D-phenylalanine carboxyl group to the amino group of another amino acid or peptide, with the p-nitrophenolate acting as a good leaving group to promote amide bond formation under mild conditions. The Z (benzyloxycarbonyl) group protects the α-amino function of phenylalanine, preventing side reactions. This compound is widely used in solution-phase peptide synthesis for selective and high-yield assembly of peptides. Its reactivity also makes it suitable for enzymatic studies and the preparation of complex bioactive molecules, such as in pharmaceutical research.