# _applied sciences_
## 3 Results and Discussion
### Biological Evaluation  
#### 3.2.1 Enzymatic Screening  
Based on our previous results [30], the synthesized compounds were evaluated as \(\alpha\)-glucosidase inhibitors. Screening in 100 uM concentration was performed, followed by IC\({}_{50}\) evaluation for active compounds. As Table 1 shows, the majority of oleanolic acid derivatives proved to be effective \(\alpha\)-glucosidase inhibitors, significantly exceeding the activity of acarbose. The structure-activity relationship of compounds **4-30** was analyzed according to the experimental data in Table 1. One can see that the enzyme inhibition was increased when the 3,28-dihydroxy-groups of erythroido! were esterified with \(m\)-methoxy-cinnamic acid (compound **4**) and isonicotinic acid (compound **5**). Compounds **4** and **5** exhibited much better potent inhibitory activity with IC\({}_{50}\) values of 2.40 \(\pm\) 0.47 uM, 4.56 \(\pm\) 1.1 uM, respectively, which were about 96- to 182-fold higher than that of acarbose (IC\({}_{50}\) 436 uM). Compound **6** with 3,28-bisnicotinic moieties was not active (IC\({}_{50}\) 752.6 uM). The replacement of C28 \begin{table}
\begin{tabular}{c c c c c c} \hline
**Cmpd** & **Glucosidase IC\({}_{50}\)\(\pm\) SD, uM** & **\% NO (10 uM)** & **\% MTT Viability** & **MTT** & **NO** \\  & & & **(10 uM)** & **CC\({}_{50}\) (uM)** & **IC\({}_{50}\) (uM)** \\ \hline
**4** & 2.4 \(\pm\) 0.47 & insoluble & insoluble & & & \\
**5** & 4.56 \(\pm\) 1.1 & insoluble & insoluble & & & \\
**6** & 752.6 \(\pm\) 536.5 & insoluble & insoluble & & & \\
**7** & \textgreater{}600 & 66.83 & 43.79 & & & \\
**8** & 6.5 \(\pm\) 4.4 & \textasci{-}51.7 & 4.74 & & & \\
**9** & 4.5 \(\pm\) 0.9 & 105.42 & 116.07 & & & \\
**10** & \textgreater{}600 & \textasci{-}30.35 & 1.88 & & & \\
**11** & 139.1 \(\pm\) 73.82 & 34.22 & 103.18 & \textgreater{}100 & \textgreater{}100 \\
**12** & 4.71 \(\pm\) 1.17 & 98.19 & 90.61 & & & \\
**13** & 170.2 \(\pm\) 36.04 & 89.13 & 100.77 & & & \\
**14** & 38.3 \(\pm\) 6.9 & 51.97 & 16.56 & & & \\
**15** & 3.01 \(\pm\) 0.53 & 26.11 & 18.24 & 4.66 & 4.83 \\
**16** & 13.91 \(\pm\) 3.08 & insoluble & insoluble & insoluble & & \\
**17** & 223.5 \(\pm\) 44.19 & insoluble & insoluble & & \\
**18** & 12.37 \(\pm\) 3.34 & 33.37 & 72.59 & & \textgreater{}100 \\
**19** & 14.2 \(\pm\) 6.71 & insoluble & insoluble & insoluble & & \\
**20** & 18.88 \(\pm\) 7.35 & 59.67 & 140.65 & & 39.11 \\
**21** & 5.56 \(\pm\) 1.88 & 75.26 & 94.15 & & \\
**22** & inactive & 42.56 & 111.77 & & \textgreater{}100 \\
**23** & 6.6 \(\pm\) 1.12 & \textasci{-}4.33 & 6.17 & & & \\
**24** & inactive & 7.69 & 194.19 & \textgreater{}100 & 7.89 \\
**25** & 79.35 \(\pm\) 14.04 & 54.7 & 98.83 & & 38.17 \\
**26** & 38.84 \(\pm\) 6.63 & insoluble & insoluble & & \\
**27** & \textgreater{}600 & \textasci{-}6.13 & 124.59 & 35.2 & 10.71 \\
**28** & inactive & 77.79 & 82.68 & & & \\
**29** & inactive & \textasci{-}133.47 & 22.47 & & & \\
**30** & 20.5 \(\pm\) 1 & \textasci{-}66.87 & 2.38 & & & \\ Acarbose & 436 & — & — & — & — \\ Dexamethasone & — & 2.01 & 98.77 & \textgreater{}100 & 0.003 \\ \hline \end{tabular}
\end{table} 
Table 1: Biological activity of compounds **4-30**. to a free carboxy group in the case of compound **7** was not successful (IC\({}_{50}\) >600 \(\upmu\)M). OA succinate **8** is more active than **7** with IC\({}_{50}\) value 6.50 \(\pm\) 0.47 \(\upmu\)M being 98-fold more efficient than the acarbose. 3\(\upbeta\)-Acetoxy-OA spermidine amide **9** exhibited significantly better activity (IC\({}_{50}\) 4.50 \(\pm\) 0.9 \(\upmu\)M) than another long-chain polyamine amide **10** (IC\({}_{50}\) >600 \(\upmu\)M). Modification of 2,3-indol-OA propargyl amide **11** (IC\({}_{50}\) 139.1 \(\pm\) 73.82 \(\upmu\)M) to Mannich bases with \(N\)-methylpiperazine- **15** and morpholine- **16** moieties led to an increase in activity with IC\({}_{50}\) values of 3.01 \(\pm\) 0.53 \(\upmu\)M and 13.91 \(\pm\) 3.08 \(\upmu\)M, respectively, that were about 31- to 145-fold higher than that of acarbose.