Four different isomers of 2',3'-dideoxy-3'-thiacytidine [beta-DL-(+-)-BCH-189] were evaluated in primary human lymphocytes infected with human immunodeficiency virus type 1. The beta-L-(-) isomer was the most potent enantiomer, with a median effective concentration of 1.8 nM and no discernible cytotoxicity up to 100 microM. The relative order of potencies for the isomers was beta-L-(-) greater than beta-DL-(+-) racemic greater than beta-D-(+) greater than alpha-L-(+) greater than alpha-D-(-). The beta-L-(-) enantiomer was as potent as 3'-azido-3'-deoxythymidine.
