H-Ile-pNA, also known as (2S,3S)-2-amino-3-methyl-N-(4-nitrophenyl)pentanamide, is a chromogenic peptide substrate. It consists of the amino acid L-isoleucine (Ile) coupled to a para-nitroaniline (pNA) leaving group via an amide bond. The compound is characterized by its specific stereochemistry at the chiral centers. This substrate is primarily used in biochemical and enzymatic research. It serves as a specific and sensitive substrate for various proteolytic enzymes, particularly serine proteases such as trypsin and thrombin. Upon enzymatic cleavage of the amide bond between the isoleucine residue and the pNA group, the yellow-colored para-nitroaniline is released, allowing for convenient spectrophotometric monitoring of enzyme activity at around 405 nm. This makes it a valuable tool for kinetic studies, enzyme characterization, and inhibitor screening assays. While its primary role is as a research reagent in life sciences, its well-defined structure containing a chiral amine and an amide linkage also makes it a potential building block in specialized organic synthesis, particularly for constructing peptide mimetics or other bioactive molecules.