8-(Methoxycarbonyl)octyl 5-O-{5-deoxy-5-(1,2,4-trideoxy-2-fluro-1,4-imino-d-arabinitol-N-yl)-.alpha.-D-arabino-furanosyl]-.alpha.-D-arabinofuranosyl}-.alpha.-D-arabinofuranoside AIDS-180838 AIDS180838