(3S,4S)-Pyrrolidine-3,4-diol hydrochloride is a chiral, cyclic amino alcohol derivative. It features a pyrrolidine ring substituted with two hydroxyl groups at the 3 and 4 positions, both in the (S) configuration, and is supplied as its hydrochloride salt. This compound is a valuable building block in organic synthesis, particularly for the construction of complex molecules with defined stereochemistry. Its primary and most significant application is in pharmaceutical research and development as a key intermediate. The (3S,4S)-dihydroxypyrrolidine scaffold is a privileged structure found in numerous biologically active compounds, including glycosidase inhibitors and antiviral agents. For instance, it serves as a crucial precursor in the synthesis of potent and selective inhibitors of enzymes like α-glucosidase, which are investigated for the treatment of diabetes and viral infections. The defined stereochemistry is essential for its biological activity. As a bifunctional chiral synthon containing both amine and diol functionalities, it is also employed in asymmetric synthesis and catalysis. It can act as a ligand precursor or be incorporated into more complex molecular architectures requiring rigid, polar scaffolds.