## 3 Results and Discussion  
### Chemistry  
Compounds **1-5, 10, 12-17, 20, 22,** and **25** (Figure 2) were isolated, purified, and characterized in our laboratory from two _Maytenus_ species, _M. blepharodes_ and _M. canariensis_, as previously described [20; 21; 27]. Derivatives **11, 18, 19, 21, 23, 24,** and **26**, achieved by acetylation or methylation from natural compounds, are described by [PERSON] et al. [20] and [PERSON] et al. [21]. Moreover, derivatives **6-9** were prepared from pristimerin (Scheme 1). The semisynthesis of **6** was achieved by acetylation of pristimerin, and derivatives **7-9** were obtained by catalytic reduction and further acetylation of pristimerin, as described in the experimental section. Their structures were greatly aided by comparison of their spectroscopic data with those previously reported for related compounds **24-26**[21]. Even so, a complete set of two-dimensional (2D) NMR spectra (COSY, ROESY, HSQC and HMBC) was acquired for the new derivatives to gain the complete assignment of the \({}^{1}\)H and \({}^{13}\)C NMR resonances (see Experimental Section, Figures S1-S4). Derivative **7** was identified as the previously described 2,3-diacetylpristimerol [31], however, its \({}^{1}\)H and \({}^{13}\)C NMR assignments have not been previously reported. Moreover, derivatives **6**  
Derivative **6** was obtained as a pale yellow amorphous solid with \([\alpha]_{\rm D}^{20}-39.7\) (c 0.15, MeOH). The molecular formula, C\({}_{34}\)H\({}_{46}\)O\({}_{7}\), was established by EI-HRMS (_m/z_ 556.3048 [M\({}^{+}\)], calcd. 556.3032). The IR absorptions revealed the presence of hydroxyl (3517 cm\({}^{-1}\)) and ester carbonyl (1770 and 1730 cm\({}^{-1}\)) groups and an aromatic ring (1459 and 758 cm\({}^{-1}\)). Two acetoxy and a carboxylic methyl ester group in **6** were evident from the \({}^{1}\)H NMR signals at \(\delta\) 2.29 (3H, s), 2.33 (3H, s), and 3.54 (3H, s), in combination with those in the \({}^{13}\)C NMR (\(\delta\) 20.6, 21.0, 51.9, 168.4, and 168.7). Besides the carbons of acetoxy and methoxy groups, the \({}^{13}\)C NMR and DEPT data revealed 29 carbon resonances, including one carboxylic carbon, one aromatic ring, one trisubstituted double bond, one oxymethine carbon, five sp\({}^{3}\) quaternary carbons, one methine, seven methylenes, and six methyls. Analysis of 2D NMR data, including HSQC, \({}^{1}\)H-\({}^{1}\)H COSY, ROESY, and HMDEC experiments, and comparison with data reported for pristimerol (**24**) [30] indicated that **6** is a phenolic triterpene with a pristimerin framework. In particular, HMDEC correlations of Me-23 with C-3, C-4, and C-5; H-1 with C-2, C-3, C-5, C-9, and C-10; H-6 with C-4, C-5, C-8, and C-10, and correlations of Me-25 with C-8, C-9, and C-10 established the structure of A and B rings. The regiosubstitution of the acetate groups and the relative configuration of H-6 were deduced by a ROESY experiment, showing ROEs (Rotating-frame Overhauser Effects) between H-6/OMe-25, H-1/OAc-2, and Me-23/OAc-3 (Figure 3). Thus, the structure of **6** was established as 6\(\alpha\)-hydroxy-2,3-diacetoxy-pristimerol. Derivative **7** was assigned the molecular formula C\({}_{34}\)H\({}_{46}\)O\({}_{6}\), determined by EI-HRMS. The mass spectrum exhibited peaks characteristic to acetate groups (M\({}^{+}\)-15-60, _m/z_ 475, CH\({}_{3}\), CH\({}_{3}\)COOH). This was confirmed by the \({}^{1}\)H and \({}^{13}\)C NMR spectra, which included signals for two acetyl groups (\(\delta_{\rm H}\) 2.28 (s), 2.31 (s), \(\delta_{\rm C}\) 20.4 (q), 20.7 (q), 168.4 (q), 168.7 (s)). Its \({}^{1}\)H NMR spectrum showed signals for six methyl groups (\(\delta_{\rm H}\) 0.58, 1.08, 1.17, 1.22, 1.35, and 2.06), a methoxy group at \(\delta_{\rm H}\) 3.55, a vinylic proton at \(\delta_{\rm H}\) 5.73 (d, \(J\) = 5.1 Hz), and an aromatic proton at \(\delta_{\rm H}\) 7.00 (s).