2-[(2S)-2-amino-4-({[5-(5-methyl-2,4-dioxo(1,3-dihydropyrimidinyl))(2-2,5-dihydrofuryl)]methyl}oxycarbonyl)butanoylamino](2S)-3-indol-3-ylpropanoic acid AIDS-095356 AIDS095356 Thymogen-2',3'-didehydro-3'-deoxythymidine conjugate