.alpha.-Amino-3-chloro-4,5-dihydro-[S-(R*,R*)]-5-isoxazoleacetatic acid and (-)-(2'R,5'S)-1-[2'-Hydroxymethyl-5'-(1,3-oxathiolanyl)]cytosine AIDS-188999 AIDS188999 Acivicin and 3TC Acivicin and Lamivudine