## 2 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multicolumn{2}{c}{**1**} & \multicolumn{2}{c}{**2**} \\ \cline{2-5}  & \(\delta_{\rm C}\) & \(\delta_{\rm H}\) & \(\delta_{\rm C}\) & \(\delta_{\rm H}\) \\ \hline
1 & 170.4, C & & 211.6, C & \\
2 & 117.0, CH & 5.77, s & 130.1, CH & 5.89, brs \\
3 & 162.0, C & & 184.4, C & \\
4 & 43.8, CH & 3.36, m & 44.8, CH & 2.76, m \\
5 & 144.5, CH & 6.66, d (9.0) & 58.4, CH & 2.21, dd (4.9, 2.5) \\
6 & 130.2, C & & 41.2, CH & 2.94, m \\
7 & 171.5, C & & 178.5, C & \\
8 & 12.8, CH\({}_{3}\) & 1.88, d (0.6) & 15.3, CH\({}_{3}\) & 1.29, d (7.2) \\
9 & 19.0, CH\({}_{3}\) & 1.24, d (6.8) & 18.9, CH\({}_{3}\) & 1.28, d (7.1) \\
10 & 17.0, CH\({}_{3}\) & 2.14, s & 17.1, CH\({}_{3}\) & 2.13, s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: \({}^{1}\)H (400 MHz) and \({}^{13}\)C (100 MHz) NMR spectroscopic data of **1** and **2** in CD\({}_{3}\)OD. Figure 2: Key COSY, HMPC, and NOESY correlations of **1** and **2**. 2.76)/H-5 (\(\delta_{\rm H}\) 2.21)/H-6 (\(\delta_{\rm H}\) 2.94) and the HMBC correlations from H\({}_{3}\)-8 (\(\delta_{\rm H}\) 1.29) to C-5 (\(\delta_{\rm C}\) 58.4)/C-6 (\(\delta_{\rm C}\) 41.2)/C-7 (\(\delta_{\rm C}\) 178.5), H\({}_{3}\)-9 (\(\delta_{\rm H}\) 1.28) to C-3 (\(\delta_{\rm C}\) 184.4)/C-4 (\(\delta_{\rm C}\) 44.8)/C-5, H\({}_{3}\)-10 (\(\delta_{\rm H}\) 2.13) to C-2 (\(\delta_{\rm C}\) 130.1)/C-3/C-4, and from H-2 (\(\delta_{\rm H}\) 5.89) to C-1 (\(\delta_{\rm C}\) 211.6)/C-4/C-5 deduced the structure of 2 to be 3.4-dimethyl-5-isopropamic acidated cyclopentene (Figure 2). The relative configuration of C-4 and C-5 in cyclopentenone ring moiety was determined as 4S* and 5R* on the basis of the NOESY correlation from H\({}_{3}\)-9 to H-5, in addition to the very weak interaction between H-4 and H-5 (Figure 2). Additionally, the relative configuration of C-6 was unreliable to be deduced by the NOESY data because of its location at the soft side chain. In order to assign the relative configuration, the two possible epimers (4S*,5R*,6S*)-**2 (2a)** and (4S*,5R*,6R*)-**2 (2b)** were subjected to the \({}^{13}\)C NMR chemical shift theoretical calculation at the mPW1 PW91/6-311+G(2d,p) level in methanol using Gaussian 09. As shown in Figure 3, the calculated \({}^{13}\)C NMR data of 2**a** were nearly identical to those of the experimental NMR data, as corroborated by the correlation coefficient (\(R^{2}\)) and root mean square error (RMSE) of **2a** (\(R^{2}\) = 0.9992, RMSE = 2.4436) and **2b** (\(R^{2}\) = 0.9988, RMSE = 2.7912), suggesting the 4S*, 5R*, and 6S* configurations. The absolute configuration of **2** was resolved on the basis of the ECD calculation, which was carried out at the B3 LYP/6-311+G(2d,p) level in MeOH using the optimized geometries at the B3 LYP/6-31+G(d,p) level in gas phase after conformational searches via the OPLS3 force field using Maestro 10.2. The ECD spectrum of 2**a** was calculated by the TDDFT method, which was in good agreement with the experimental ECD curve, indicating the 4S, 5R, and 6S configurations (Figure 4). Interestingly, **2** was the first representative of the osmane-type monoterpenoids discovered from the fungi. (\(\delta_{\rm C}\) 124.6), and from the methoxy protons (\(\delta_{\rm H}\) 3.85) to C-3\" deduced the \(p\)-methoxyphenyl moiety (ring C) to be tethered at C-3 (Figure 5). Additional COSY correlation between H-1' (\(\delta_{\rm H}\) 7.29)/H-2' (\(\delta_{\rm H}\) 6.85) and the HMBC correlations from H-1'/H-5' to C-3' (\(\delta_{\rm C}\) 158.9) and C-5 (\(\delta_{\rm C}\) 120.4) and from H-2'/H-4' to C-3' and C-6' (\(\delta_{\rm C}\) 123.5) in association with the chemical shift of C-3' established the \(p\)-hydroxyphenyl unit (ring A) to be resided at C-5.