## 5 Trepenes
### Pentacyclic Triterpene Acids
#### 5.2.1 Ursolic Acid Derivatives  
Derivatives of **65** were also found in _U. tomentosa_, specifically compounds **67-77** in Table 3. These compounds contain various substitutions to the core structure of unsolic acid **(65)**. The following section will discuss these substitutions. \begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline
**Compound** & **R\({}_{1}\)** & **R\({}_{2}\)** & **R\({}_{3}\)** & **R\({}_{4}\)** & **R\({}_{5}\)** & **R\({}_{6}\)** & **R\({}_{7}\)** & **R\({}_{8}\)** & **R\({}_{9}\)** & **R\({}_{10}\)** \\ \hline (\(\beta\))-3-Hydroxy-7-oxo-urs-12-ene-27,28-dioic acid, **67** & OH & Me & Me & H & =O & CO\({}_{2}\)H & H & Me & H & H \\ (\(\beta\),6,16\(\upmu\)g)-16-Hydroxy-3-methoxy-ursa-12,19(29)-diene-27,28-dioic acid, **68** & MeO & Me & Me & H & H & CO\({}_{2}\)H & OH & = & H \\ (\(\beta\),6,4\(\upmu\)g)-3,19-Dihydroxy-6,23-dioxo-urs-12-en-28-oic acid, **69** & OH & Me & CHO & =O & H & Me & H & Me & OH & H \\ (\(\beta\),6,4\(\upmu\)g)-3,19,23-trihydroxy-6-oxo-urs-12-en-28-oic acid, **70** & OH & Me & CH\({}_{2}\)OH & =O & H & Me & H & Me & OH & H \\ (\(\beta\),6,6)-19-dihydroxy-3-oxo-urs-12-en-28-oic acid, **71** & =O & Me & Me & OH & H & Me & H & Me & OH & H \\ (\(\beta\),6,6)-3,6,19-Hydrooxy-12-en-28-oic acid (uncaric acid), **72** & OH & Me & Me & OH & H & Me & H & Me & OH & H \\ (\(\beta\),6,4\(\upmu\)g)-3,6,19-trihydroxy-23-oxo-urs-12-en-28-oic acid, **73** & OH & =O & OH & H & Me & H & Me & OH & H \\ (\(\beta\),6,4\(\upmu\)g)-3,6,19-trihydroxy-23-oxo-urs-12-en-28-oic acid, **74** & OH & Me & CHO & OH & H & Me & H & Me & OH & H \\ (\(\beta\),6,6)-3,6,19-Tribhydroxy-24-norurus-4(23),12-dien-28-oic acid (floridic acid, **75** & OH & = & OH & H & Me & H & Me & OH & H \\ (\(\beta\),6,8,4\(\upmu\)g)-dimethyl ester-3,6,19-trihydroxy-urs-12-ene-23,28-dioic acid, **76** & OH & Me & CO\({}_{2}\)Me & OH & H & Me & H & Me & OH & Me \\ (\(\beta\),6,9,12,3-tetrahydroxy-urs-12-en-28-oic acid, **77** & OH & Me & CH\({}_{2}\)OH & OH & H & Me & H & Me & OH & H \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Ursolic Acid Derivatives (67–77). Compound 67 contains a ketone at R\({}_{5}\) and a carboxylic acid at R\({}_{6}\). Compound 68 contains a methoxy substitution at R\({}_{1}\), a carboxylic acid at R\({}_{6}\), hydroxy group at R\({}_{7}\), and an ethene at R\({}_{8}\). These compounds were identified in a methanol extract of dried root bark, separated using reverse phase HPLC (RP-HPLC), and characterized with \({}^{1}\)H and \({}^{13}\)C NMR spectroscopy [135]. Compounds 69 and 70 are similar in structure, both contain a ketone at R\({}_{4}\) and a hydroxy at R\({}_{9}\). However, at R\({}_{3}\), compound 69 possesses an aldehyde substituent while 70 possess a hydroxymethyl group. Compound 71 includes a ketone at R\({}_{1}\) and a hydroxy at R\({}_{4}\) and R\({}_{9}\). The characterization of compound 69, 70, and 71 was completed utilizing MS, \({}^{1}\)H, and \({}^{13}\)C NMR spectroscopy, on a methanol extraction of dried plant material, with 69 and 71 first characterized in the paper cited and 70 confirmed by comparison to previously reported data from another plant source [8]. Compound 72 possesses a hydroxy at R\({}_{4}\) and R\({}_{9}\). Antiviral activity for this compound against SARS-CoV-2 was investigated in silico [136]. The findings indicate the compound was a possible candidate of interest due to its binding affinity for an interface between the virus and human receptor cells and its druggability according to the Lipinski rules [136]. Compound 73 contains hydroxy groups at R\({}_{4}\) and R\({}_{9}\), as well as a ketone at R\({}_{2}\). Compound 74 possesses an aldehyde at R\({}_{3}\) and hydroxy substituents at R\({}_{4}\) and R\({}_{9}\). Compound 75 possesses an ethene group at R\({}_{2}\) and hydroxy groups at R\({}_{4}\) and R\({}_{9}\). Compound 75 was also investigated in silico for potential antiviral activity against SARS-CoV-2 [136].