Compounds of Formula I: and their pharmaceutically acceptable salts are useful for the inhibition of HIV reverse transcriptase. The compounds may also be useful for the prophylaxis or treatment of infection by HIV and in the prophylaxis, delay in the onset or progression, and treatment of AIDS. The compounds and their salts can be employed as ingredients in pharmaceutical compositions, optionally in combination with other antiviral agents, immunomodulators, antibiotics or vaccines.本發明提供式I化合物：及其醫藥學上可接受之鹽，其用於抑制HIV反轉錄酶。該等化合物亦可用於預防或治療HIV感染及用於預防AIDS、延緩AIDS之發病或進展及治療AIDS。該等化合物及其鹽可用作醫藥組合物中之成分，視情況與其他抗病毒劑、免疫調節劑、抗生素或疫苗組合使用。
