This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemotherapy, Subject name: Pharmacology
All are protease inhibitor EXCEPT: 
Select and explain. 
A. Ritonavir, B. Amprenavir, C. Tenofovir, D. Nelfinavir
C: Tenofovir
Answer: C: Tenofovir 
Explanation: Retroviral protease Inhibitors (Pis) An aspaic protease enzyme encoded by HIV is involved in the production of structural proteins and enzymes (including reverse transcriptase) of the virus. The large viral polyprotein is broken into various functional components by this enzyme. This protease acts at a late step in HIV replication, i.e. maturation of the new virus paicles when the RNA genome acquires the core proteins and enzymes. Five protease inhibitors-Indinavir (IDV), Nelfinavir (NFV), Saquinavir (SQV), Ritonavir (V) and Lopinavir (in combination with ritonavir LPV /r) have been marketed in India for use against HIV. Tenofovir disoproxil is an antiretroviral medication used to prevent and treat HIV/AIDS and to treat chronic hepatitis B.The active substance is tenofovir, while tenofovir disoproxil is a prodrug that is used because of its better absorption in the gut. ESSENTIALS OF MEDICAL PHARMACOLOGY, en.wikipedia.org K.D.TRIPATHI SIXTH EDITION PAGE NO:772