142102-75-8 5Et-2',5'SilylSpiroU AIDS-004709 AIDS004709 TSAO deriv. [1-[2',5'-Bis-O-(tert-butyldimethylsilyl)-.beta.-D-ribofuranosyl]-5- ethyluracil]-3'-spiro-5-(4-amino-1,2-oxathiole-2,2-dioxide)