Anti-AIDS agents--XXVII. Synthesis and anti-HIV activity of betulinic acid and dihydrobetulinic acid derivatives.

Two series of lupane-type triterpenoic acid derivatives were synthesized and evaluated for their inhibitory activity against HIV-1 replication in acutely infected H9 cells, based on the fact that betulinic acid (1) and dihydrobetulinic acid (9) were identified as anti-HIV agents. Among the derivatives, 3-O-(3',3'-dimethylsuccinyl)-betulinic acid (3) and 3-O-(3',3'-dimethylsuccinyl)-dihydrobetulinic acid (11) both demonstrated extremely potent inhibitory activity with EC50 values of < 3.5 x 10(-4) microM, and remarkable in vitro therapeutic index (TI) values of 20,000 and 14,000, respectively. 3-O-(3',3'-dimethylglutaryl)-betulinic acid (4) and-dihydrobetulinic acid (12), 3-O-diglycolyl-betulinic acid (5) and -dihydrobetulinic acid (13) and 3-O-glutaryl-betulinic acid (6) were also potent inhibitors of HIV replication with EC50 values ranging from 0.04 to 2.3 x 10(-3) microM and TI values from 292 to 2344. In addition, compounds 11 and 12 were also active against HIV replication in a monocyte cell line and in peripheral blood mononuclear cells. Our in vitro assay indicated that these compounds are not inhibitors of HIV-1 reverse transcriptase, whereas they inhibited syncytia formation completely in a concentration range of 20-40 micrograms/mL. However, 3-O-(2',2'-dimethylsuccinyl)-betulinic acid (2) was also found to be an inhibitor of HIV-induced membrane fusion with an IC100 value of 20 micrograms/mL, though it displayed significantly lower anti-HIV activity than foregoing compounds with an EC50 value of 2.7 microM and TI of 6.7. Further study is underway to determine the mechanisms of action of these compounds.