8-(Methoxycarbonyl)octyl 5-O-{5-O-[5-deoxy-5-(1,4-dideoxy-1,4-imino-D-arabinitol-N-yl)-.alpha.-D-arabinofuranosyl]-.alpha.-D-arabino-furanosyl}-.alpha.-D-arabinofuranoside AIDS-180837 AIDS180837