Tenofovir Disoproxil Related Compound A – (S)-5-[[2-(6-Amino-9H-purin-9-yl)-1-methylethoxy]methyl]-2,4,6,8-tetraoxa-5-phosphanonanedioic acid, bis(1-methylethyl)ester,5-oxide, (E)-2-butenedioate (1:1)