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

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 × 10−4 μM, 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 × 10−3 μM 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 μg/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 μ/mL, though it displayed significantly lower anti-HIV activity than foregoing compounds with an EC50 value of 2.7 μM and TI of 6.7. Further study is underway to determine the mechanisms of action of these compounds.