.beta.-Methylene TAD 102977-57-1 AIDS-014333 AIDS014333 NSC617998 {[(2R,3S,4R,5R)-5-(6-Amino-purin-9-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethoxy]-hydroxy-phosphorylmethyl}-phosphonic acid mono-[(2R,3S,4R,5R)-5-(4-carbamoyl-thiazol-2-yl)-3,4-dihydroxy-tetrahydro-furan-2-ylmethyl] ester