Four 4-methyl-3',4'-di-O-(-)-camphanoyl-(+)-cis-khellactone (4-methyl DCK) analogs (7a-d) with different alkyl substituents at the 2'-position were synthesized and evaluated for inhibition of HIV-1 replication in H9 lymphocytes. 2'-Methyl-2'ethyl-4-methyl DCK (7b) was more potent (EC50 = 0.22muM TI > 175) than the other three compounds (7a, 7c, and 7d), but significantly less potent than 4-methyl DCK (2, EC50 = 0.0059muM, TI > 6600). The bioassay results indicated that the 2'-substituents had a strong effect on the anti-HIV activity, and gem-dimethyl substitution at the 2'-position was greatly preferable to larger alkyl substituents or hydrogen atoms. (C) 2004 Elsevier Ltd. All rights reserved.