Review Question - QID 210595

A 57-year-old man comes to the emergency department because he has been having problems seeing over the last week. He says that he has been seeing specks in his vision and his vision also becomes blurry when he tries to focus on objects. He says that he cannot recall anything that may have precipitated this; however, he has been homeless for several months. His CD4+ cell count is 27 cells/mL so he is started on a new medication. Notably, this drug has the following properties when mixed with various proteins:

Drug alone - drug remains unphosphorylated
Drug and HSV proteins - drug remains unphosphorylated
Drug and CMV proteins - drug remains unphosphorylated
Drug and human proteins - drug is phosphorylated

Which of the following drugs is most consistent with this set of findings?