Synthesis and cytotoxic activity of 17-carboxylic acid modified 23-hydroxy betulinic acid ester derivatives

New 17-carboxylic acid modified 23-hydroxy betulinic acid ester derivatives were prepared and tested for cytotoxic activity on five cancer cell lines in vitro: all tested compounds showed stronger cytotoxic activity than 23-hydroxy betulinic acid and betulinic acid. In addition, compound 5a was tested for anti-tumor activity in vivo: it had much better anti-tumor activity than 23-OH betulinic acid and had similar anti-tumor activity with cyclophosphamide and 5-fluorouracil.