AIDS-072947 AIDS072947 Spironucleoside TSAO derivative [1-[2',5'-Bis-O-(tert-butyldimethylsilyl)-.beta.-D-xylofuranosyl]-3-N-methylthymine]-3'-spiro-5''-(4''-N-methylimino-3''-N-methyl-2''-oxazolidinone)