141781-17-1 2',5'diSilySpiroT AIDS-003915 AIDS003915 TSAO-T [1-[2',5'-Bis-O-(tert-butyldimethylsilyl)-.beta.-D-ribofuranosyl]thymine]-(R)(ribo)-3'-spiro-5-(4-amino-1,2-oxathiole-2,2-dioxide)