## 2 Results
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Position**} & \multicolumn{2}{c}{**1**} & \multicolumn{2}{c}{**2**} & \multicolumn{2}{c}{**3**} \\ \cline{2-7}  & **HMPC** & **ROESY** & **HMDC** & **ROESY** & **HMDC** & **ROESY** \\ \hline
1 & & & & & & \\
2 & 4,6,7 & 3 & 4,6,7 & 3 & 4,6,7 & 3 \\
3 & 1,5 & 2 & 1,5 & 2,15,16,17 & 1,5 & 2 \\
4 & & & & & & \\
6 & 2,4,7,8 & 8 & 2,4,7,8 & 8 & 2,4,7,8 & 8 \\
7 & & 9,16,18 & 4,5,6,9,10 & 9,18 & 4,5,6,9,10 & 9,11,18 \\
9 & 8,10,14,15,16,18 & 8,11 ax,15 & 8,10,18 & 8,11,12 & 5, 8,10,18 & 8,10,11,12,18 \\
10 & & & & & \\
11 & 9,10,12,13,18 & 18,12 ax,12 eq & 10,12,13,18 & 12,18 & 10,12,13,18 & 12 \\
12 & 10,11,13,14,17 & 16,17,18 & 11,13,14,17 & 11,15,17 & 11,13,14,17 & 11,15,16,17 \\
13 & & & & & \\
14 & & & & & \\
15 & 9,13,14,16 & 8,9,16,17 & 13,14,16 & 12, 16,17 & 13,14,16 & 12, 16, 17 \\
16 & 9,13,14,15 & 12 ax,15,17,18 & 13,14,15 & 12, 15,17 & 13,14,15 & 12, 15, 17 \\
17 & 12,13,14 & 12 ax,12 eq,15,16 & 12,13,14 & 12, 15,16 & 11,12,13,14 & 12, 15, 16 \\
18 & 10,11,19 & 8 ax,11,12 ax,16 & 9,10,11,19 & 8,11 & 9,10,11,19 & 8, 9, 11 \\
19 & 18 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The HMBC and ROESY correlations of compounds **1–3** (CD\({}_{3}\)OD). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Position**} & \multicolumn{2}{c}{**1**} & \multicolumn{2}{c}{**2**} & \multicolumn{2}{c}{**3**} \\ \cline{2-5}  & **H-NMR** & **13C-NMR** & **1H-NMR** & **13C-NMR** & **1H-NMR** & **13C-NMR** \\ \hline
1 & & 119.6 & & 117.8 & & 117.4 \\
2 & 7.57, (d, 8.4) & 128.8 & 7.61, (d, 8.4) & 127.8 & 7.64, (d, 8.4) & 129.3 \\
3 & 6.50, (d, 8.4) & 112.8 & 7.83, (d, 8.4) & 117.6 & 6.62, (d, 8.4) & 112.8 \\
4 & & 148.4 & & 147.0 & & 147.4 \\
5 & & 117.2 & & 121.5 & & 115.4 \\
6 & 7.62, s & 131.4 & 7.63, s & 131.2 & 7.63, s & 131.6 \\
7 & & 169.9 & & 169.5 & & 169.3 \\
8 & 2.72, (dd, 16.2, 14.4) & 23.9 & 2.88, m & 33.3 & 3.37, (dd, 16.8, 4.8) & 33.1 \\
9 & 2.64, (dd, 16.2, 4.8) & 42.7 & 3.60, (t, 8.4) & 63.4 & 4.45, (t, 4.8) & 56.9 \\
10 & & 54.5 & & 71.0 & & 57.4 \\
11 & 1.97, m & 28.2 & 2.29, m & 29.3 & 1.69, m & 32.7 \\
12 & 1.85, m & & 2.04, m & & 1.60, m & 32.7 \\
13 & 1.48, m & 31.9 & 2.30, m & & 2.22, m & \\
14 & & 1.72, m & 35.9 & 2.09, m & 27.8 \\
15 & & 73.6 & & 75.4 & & 131.7 \\
14 & & 39.3 & & 76.5 & & 127.9 \\
15 &All isolated compounds were tested for anti-PRV activity and cytotoxicity, and the results are shown in Table 3. Compounds **3** and **7** are active against PRV with the IC\({}_{50}\) equals to 1.74 and 6.46 \(\upmu\)g/mL, respectively. The CC\({}_{50}\) of **7** is 1.68 \(\upmu\)g/mL and the SI index of **7** is less than one, indicating the antiviral activity of **7** depends on its toxicity. Compound **3** also has slightly cytotoxic effect at a concentration of 20 \(\upmu\)g/mL (only 80% viable cells compared to blank group). Compound **4** does not show any toxic effect on the tested cells at 20 \(\upmu\)g/mL and presents significant anti-PRV activity that is superior to the positive controls ribavirin and acyclovir. Compound **4** could protect the Vero cells against PRV, with more than 50% of cells being alive even when the concentration is diluted to 0.01 \(\upmu\)g/mL. These results are similar to those reported in the literature [21]. In order to examine the post-treatment effect, Vero cells were infected with PRV for 1.5 h, and then the cells were treated with compound **4**. After 24 h infection, the results of an indirect immunofluorescence assay indicated that the virus infection in the PRV-infected cells was significantly reduced by compound **4** (Figure 6). After 48 h, the total DNA isolated from the supernatant was subjected to qPCR analysis by using PRV gE-specific primers. As shown in Figure 7, **4** inhibits PRV proliferation in a dose-dependent manner. These results demonstrate that **4** exhibits significant antiviral activity against PRV. Figure 6: Indirect immunofluorescence assay of compound 2.