## 3 Results and Discussion
### Isolation and Characterization of Compounds by NMR  
Fifteen compounds were identified through the purification strategy (Figure 4). The compounds **2-15** were known and characterized by comparison of their \({}^{13}\)C and \({}^{1}\)H NMR chemical shifts with literature references. A comparison table (Table S2) is available in the supplementary information, as well as all NMR analysis. Appendix A provides further details on yields and physical properties. Compounds 2 and 3 (namely terminolic acid and macdessic acid) and compounds 5 and 6 (namely asiatic acid and arjulonic acid) are in 1:1 mixtures, which could be characterized. All other compounds were retrieved pure. Compounds **13** (astragalin) and **14** (5-O-methyldemethoxymatteucinol) belong to the flavonoid family. Compound **15** (2\({}^{\prime}\)/\({}^{\prime}\)A\({}^{\prime}\)-dihydroxy-3\({}^{\prime}\),5\({}^{\prime}\)-dimethyl-6\({}^{\prime}\)-methoxyalcone) is a chalcone. Compounds **2-12** are triterpenes from lupane, oleanane, and ursane subfamilies. Compounds **5** and **10** were previously isolated and characterized in the plant species [5]. Compound **13** has been previously reported with HRMS data but never isolated in the plant [4]. All other 12 compounds (**1-4**, 6-9**, and **11-15**) have never been reported in _P. mauritianum_. Chemical shifts of compound **1** have never been described in the literature. The HRESIMS analysis gave a molecular formula of C\({}_{30}\)H\({}_{48}\)O\({}_{4}\) (\(m/z\) = 495.3447 [M+Na]\({}^{+}\), calculated 495.3445), suggesting a triterpene structure. The \({}^{1}\)H NMR spectrum enabled to show six methyl groups. The signal of diastereotopic methylene protons at \(\delta_{1\rm{H}}\) 4.60 ppm and \(\delta_{1\rm{H}}\) 4.72 ppm (diastereotopicity verified by edited HSQC) and the methyl group at \(\delta_{1\rm{H}}\) 1.70 ppm are typical of isopropenyl moiety of a lupane triterpene. Moreover, compound **1** has many signals in common with compound **12** (betulinic acid, molecular formula C\({}_{30}\)H\({}_{46}\)O\({}_{3}\)). However, the C-3 signal at \(\delta_{1\rm{3C}}\) 221.0 ppm (corresponding to a ketone) present in compound **12** is not found in compound **1**. Instead, a shielded signal at \(\delta_{1\rm{3C}}\) 179.2 ppm suggesting a carboxylic acid function is observed in compound **1** and not in compound **12**. Presumably, compound **1** is an oxidized analog of compound **12**, where the ketone in C-3 has been replaced by a carboxylic group with a ring opening. Furthermore, the signal of the protons of two methyl groups C-23, C-24 in compound **1** appeared as two duplets, whereas all methyl group signals in compound **12** show singlet signals. These two methyls at \(\delta_{1\rm{H}}\) 0.92 and 0.81 ppm, respectively, correlate in HMBC spectrum with a carbone at \(\delta_{1\rm{3C}}\) 26.5 ppm and couple with the same unique proton at \(\delta_{1\rm{H}}\) 1.92 ppm in COSY spectrum. Thus, it can be supposed that these two methyl groups are in positions 23 and 24, connected to the tertiary carbone C4. This validates the hypothesis the C3-C4 bond has been severed. Finally, the structure of compound **1** (Figure 5) has been unambiguously identified by extensive 1D and 2D NMR (COSY, HSQC, HMBC, and NOESY) analyses as (35,45,58,87,98,106,135,14,15R)-4-(2-carboxyethyl)-3-isopropyl-4,9,10-trimethyl-15-(prop-1-en-2 yl)hexadecahydro-13\(H\)-cyclopenta[a]phenanthrene-13-carboxylic acid, named psiloxylic acid. The nine stereocenters have also been determined through NOE correlation. NMR data are reported in Table 1. Finally, the optical rotation was measured: \([\alpha]^{25}_{\rm{D}}\) = + 15.5 (c = 0.3257 g/100 mL, MeOH). Figure 4: Compounds isolated from _P. maurtiianum_ and characterized by NMR spectroscopy.