This compound, with the systematic name [(2R)-1-[(2S)-2-amino-3-methylbutanoyl]pyrrolidin-2-yl]boronic acid methanesulfonate, is a chiral boronic acid derivative featuring a specific stereochemistry at both the amino acid and pyrrolidine moieties. It is a salt form, with methanesulfonic acid as the counterion, which typically enhances its stability and solubility for handling and use in synthetic processes. Its primary and most significant application is in the field of targeted protein degradation, specifically as a key intermediate or building block for the synthesis of Proteolysis-Targeting Chimeras (PROTACs). The structure contains a boronic acid group, which can serve as a warhead or ligand for targeting specific proteins (e.g., certain kinases or other disease-relevant proteins), and a chiral amino acid-derived segment that can be linked to an E3 ligase-recruiting ligand via a linker. This makes it a crucial component for constructing heterobifunctional degraders. As a sophisticated chiral synthon, it is not a general-purpose synthetic reagent but a specialized intermediate designed for advanced medicinal chemistry and chemical biology research aimed at developing novel therapeutic modalities. Its synthesis and use require expertise in handling air- and moisture-sensitive boronic acids and in the assembly of complex bioactive molecules.