The compounds encompassed by Formula I include compounds which are HIV protease inhibitors and other compounds which can be metabolized in vivo to HIV protease inhibitors. The compounds and their pharmaceutically acceptable salts are useful for the prophylaxis or treatment of infection by HIV and the prophylaxis, treatment, or delay in the onset of AIDS. The compounds and their salts can be employed as ingredients in pharmaceutical compositions, optionally in combination with other antivirals, immunomodulators, antibiotics or vaccines.