4-Aminoisoxazole Hydrochloride is the salt form of 4-Aminoisoxazole (A612910), which is a reactant used in the design and synthesis of hydroxyethylene-based HIV-1 protease inhibitor containing a heterocyclic P1'-P2' amide bond isostere. 4-Aminoisoxazole is also used in the development of pyrimidine derivatives as JAK3 inhibitors.