Semi-Synthesis and Biological Evaluation of 25(R)-26-Acetoxy-3 beta,5 alpha-Dihydroxycholest-6-One

Previously, we identified a series of steroids (1-6) that showed potent anti-virus activities against respiratory syncytial virus (RSV), with IC50 values ranging from 3.23 to 0.19 mu M. In this work, we first semi-synthesized and characterized the single isomer of 5, 25(R)-26-acetoxy-3 beta,5 alpha-dihydroxycholest-6-one, named as (25R)-5, in seven steps from a commercially available compound diosgenin (7), with a total yield of 2.8%. Unfortunately, compound (25R)-5 and the intermediates only showed slight inhibitions against RSV replication at the concentration of 10 mu M, but they possessed potent cytotoxicity activities against human bladder cancer 5637 (HTB-9) and hepatic cancer HepG2, with IC50 values ranging from 3.0 to 15.5 mu M without any impression of normal liver cell proliferation at 20 mu M. Among them, the target compound (25R)-5 possessed cytotoxicity activities against 5637 (HTB-9) and HepG2 with IC50 values of 4.8 mu M and 15.5 mu M, respectively. Further studies indicated that compound (25R)-5 inhibited cancer cell proliferation through inducing early and late-stage apoptosis. Collectively, we have semi-synthesized, characterized and biologically evaluated the 25R-isomer of compound 5; the biological results suggested that compound (25R)-5 could be a good lead for further anti-cancer studies, especially for anti-human liver cancer.