8-(Metoxycarbonyl)octyl 5-O-{5-O-[5-(1,2,4-trideoxy-2-fluoro-1,4-imino-L-galactitol-N-yl)-.alpha.-D-arabinofuranosyl]-.alpha.-D-arabinofuranosyl}-.alpha.-D-arabinofuranoside AIDS-180839 AIDS180839