O-(tert-Butyl)-L-threonic acid allyl ester hydrochloride is a chiral chemical intermediate. It is a derivative of L-threonic acid, featuring an allyl ester group and a tert-butyl ether protecting group, and is supplied as its hydrochloride salt. This specific stereochemistry and functional group arrangement make it a valuable building block. This compound is primarily utilized in the synthesis of complex pharmaceutical molecules. Its key application is as a crucial chiral precursor in the production of certain antiviral drugs, most notably for the synthesis of the active pharmaceutical ingredient (API) Tenofovir Alafenamide (TAF), a prodrug of Tenofovir used in the treatment of HIV and hepatitis B. The L-threonate backbone and the protected hydroxyl groups are essential for constructing the specific stereocenter and molecular framework required for biological activity. As a specialized chiral synthon, it is not a commodity chemical but a high-value intermediate in targeted medicinal chemistry routes. Its use is almost exclusively tied to advanced pharmaceutical manufacturing processes.