Synthesis and biological activity of 23-hydroxybetulinic acid C-28 ester derivatives as antitumor agent candidates.

23-Hydroxybetulinic acid (1) served as the precursor for the synthesis of C-28 ester derivatives. The target compounds were evaluated in vitro for their antitumor activities against five cell lines (A549, BEL-7402, SF-763, B16 and HL-60). Among the obtained compounds, 6i had the most potent antitumor activity, with the IC(50 values of 8.35 µM in HL-60 cells and showed similar antitumor activity as cyclophosphamide in H22 liver tumor and as 5-fluorouracil in B16 melanoma in vivo.