*3.4. Spectral Data*

*Huberine: 1,2-Dimethoxy-canthin-6-one* (**1**). Yellow amorphous powder; UV (MeOH, max, nm): 207, 266, 294, 354, 369. IR (KBr, n, cm<sup>−</sup>1): 1664, 1550, 1439, 1214, 1086, 753; 1H- and 13C-NMR data, see Table 1; MS: Waters LCT Premier (ESI-TOF) spectrometer at *m*/*z* 281.0926 [M + H]+; calcd. for C16H12N2O3, 281.0926.

*1-Hydroxy-canthin-6-one* (**2**). Yellow amorphous powder. UV (MeOH, nm): 210, 249, 256,288, 341, 415. IR (KBr, cm−1): 3276, 1567, 1600, 1629. 1H-NMR (600 MHz, MeOD-*d*4, δ in ppm, *J*), 8.60 (d, 1H, 8.4Hz), 8.35 (s, 1H), 8.27 (d, 1H, 7.7Hz), 8.02 (d, 1H, 9.7Hz), 7.69 (t, 1H, 8.4Hz), 7.58 (t, 1H, 8.0Hz), 6.80 (d, 1H, 9.7Hz). 13C-NMR (150 MHz, DMSO-*d*6, δ in ppm): 151.39 (C-1), 135.55 (C-2), 139.48 (C-4), 123.38 (C-5), 159.66 (C-6), 123.60 (C-8), 125.79 (C-9), 129.16 (C-10), 116.22 (C-11), 137.61 (C-12), 137.5 (C-13), 114.31(C-14), 133.32 (C-15), 128.11 (C-16). MS TOF ES+ spectrometer at *m*/*z* 237.0708 [M + H]+.

*Canthin-6-one* (**3**). Yellow amorphous powder. UV (MeOH, nm): 210, 249, 256,288, 341, 415. IR (KBr, cm<sup>−</sup>1): 3276, 1567, 1600, 1629. 1H-NMR (600 MHz, DMSO-*d*6, δ, ppm, *J*/Hz): 8.35 (1H, d, *J* = 4.8 Hz, H-1, 8.86 (1H, d, *J* = 4.8 Hz, H-2), 8.7 (1H, d, *J* = 9.7 Hz, H-4), 7.02 (1H, d, *J* = 9.7 Hz, H-5), 8.55 (1H, d, *J* = 8.1 Hz, H-8), 7.79 (1H, t, *J* = 7.6 Hz, H-9), 7.62 (1H, t, *J* = 7.6 Hz, H-10), 8.42 (1H, d, *J* = 7.8 Hz, H-11). MS TOF ES+ spectrometer at *m*/*z* 221.0715 [M + H]+. Supplementary material is available online.

#### **4. Conclusions**

Huberine, a new canthin-6-one alkaloid (**1**) and **3** known compounds (**2**, **3** and **4**) were isolated from the stem bark of *P. huberi*. The structure of the new compound (**1**) was elucidated by spectroscopic data Huberine (**1**); it was isolated from this plant for the first time. The isolates were screened for inhibitory activity against *Plasmodium falciparum* strains. Compounds **1**, and **2** showed no effective antiplasmodial activity.

**Supplementary Materials:** The following are available online. Figure S1: Huberine: 1,2-Dimethoxy-canthin-6-one (**1**). 1H-NMR (CDCl3, 600 MHz); Huberine: 1,2-Dimethoxy-canthin-6-one (**1**). 13C-NMR (CDCl3, 150 MHz); Huberine: 1,2-Dimethoxy-canthin-6-one (**1**). COSY H-H (CDCl3); Huberine: 1,2-Dimethoxy-canthin-6-one (**1**). HSQC (CDCl3); Huberine: 1,2-Dimethoxy-canthin-6-one (**1**). HMBC (CDCl3); Huberine: 1,2-Dimethoxy-canthin-6-one (**1**). HRMS; Huberine: 1,2-Dimethoxy-canthin-6-one (**1**). FT-IR, 1-Hydroxy-canthin-6-one (**2**). 1H-NMR (MeOD-d4, 600 MHz); 1-Hydroxy-canthin-6-one (**2**). 13C-NMR (DMSO-*d*6, 150 MHz); 1-Hydroxy-canthin-6-one (2). COSY H-H (MeOD-*d*4); 1-Hydroxy-canthin-6-one (**2**). HSQC (MeOD-*d*4); 1-Hydroxy-canthin-6-one (**2**). HRMS; Canthin-6-one (**3**). 1H-NMR (DMOS-*d*6, 600 MHz); Canthin-6-one (**3**). HRMS.

**Acknowledgments:** This work was funded by General system of Royalties of Colombia (SGR), contract RC:20702305-8399DZZZZ.The authors would like to give special thanks to Silvia Blair for being the manager of this project and obtaining their funding. Also, to Jairo Saez for the advice on identification of the compounds from *P. huberi* and to Juan Pablo Tobón Agudelo who very kindly accompanied us to the collection of plant material. The authors are also very grateful to Bruno Figadere of l'UMR 8076 Bio CIS-Laboratoire Pharmacognosie, Faculté de Pharmacie—Université Paris-Sud for the high-resolution mass spectra.

**Author Contributions:** C.L.: Identification of the compounds from *P. huberi* and writing of the manuscript; M.P.: Preparation of extracts, isolation and purification of the compounds; A.R.: Conducting biological tests; A.C.: Identification, classification, collection and knowledge of the plant; A.P.: Conception, design, analysis and interpretation of results, and writing of the manuscript

**Conflicts of Interest:** The authors declare no conflict of interest.
