(5S)-5-[(4-Amino-2-oxohydropyrimidinyl)methyl]-2-(3-hexadecyloxypropoxy)-1,4,2-dioxaphosphan-2-one 1-O-Hexadecylpropanediol-cyclic CDV AIDS-104903 AIDS104903 HDP-cCDV Hexadecyloxypropyl-cyclic cidofovir