*2.2. Biological Activities of the Isolated Compounds*

All of the isolated compounds were assayed for their activities against Huh7.5 liver tumor cells. Among them, only compounds **4** and **10** displayed significant cytotoxic effects against Huh7.5 with cell viability less than 30% at the concentration of 20 μM. As shown in Figure 6, the growth-inhibiting effects of **4** and **10** were concentration-dependent, with IC50 values of 9.52 and 4.88 μM, respectively, which were comparable to that of the positive control, sorafenib (IC50 8.2 μM). Compounds **4** and **10** were also measured for their cytotoxicity against human normal liver LO2 cell line. The results showed that compound **4** exhibited the inhibitory effects against normal liver cells, similar to that of cancer cells (Figure 6). However, compound **10** was less sensitive to normal liver cells than liver cancer cells, only at a narrow concentration range of 4~10 μM. The results suggested that the disulfide bridge at C-2/C-2' is likely essential for the activity.

**Figure 6.** Cell viability of Huh7.5 liver cancer cells and LO2 normal liver cells treated with compounds **4** (**a**) and **10** (**b**).

## **3. Experimental Section**
