L-(-)-Ribose is the unnatural enantiomer of D-ribose and serves as a key chiral building block in organic synthesis, particularly for the preparation of L-nucleosides and L-nucleotides. These analogs are valuable in pharmaceutical research and development, especially for antiviral agents (e.g., against HIV and hepatitis) and anticancer drugs, due to their enhanced stability against nucleases and altered metabolic profiles compared to natural D-nucleosides. It is also employed in the synthesis of modified oligonucleotides for therapeutic applications, such as antisense oligonucleotides and aptamers. In biochemical studies, L-(-)-Ribose facilitates investigations into enzyme specificity, stereochemistry, and the biological activity of non-natural nucleic acids. Unlike D-ribose, it has no direct role in cellular energy metabolism or natural nucleic acid biosynthesis and is not used in food supplements.