**4. Conclusions**

The phytochemical and in vitro bio-activity investigation of the *S. africana-lutea* methanolic extract revealed that this plant is a rich source of abietane diterpenes and triterpenes with significant alpha glucosidase and alpha amylase inhibitory activities, as well as significant antioxidant activity when considering the FRAP, TEAC, ORAC assays. The present work is the first scientific report on *S. africana-lutea*, and the results sugges<sup>t</sup> that the methanolic extract of this plant and/or its individual constituents might become prominent natural therapeutic agents for the inhibition of alpha glucosidase and alpha amylase enzymes and oxidative stress, which both play an important role in the development of diabetic related diseases. Therefore, compounds with high antioxidant and anti-diabetic activities are the most logical choice for reducing diabetes-induced ROS.

**Supplementary Materials:** The supplementary materials are available online at http://www.mdpi.com/2076- 3921/8/10/421/s1, Supplementary Figures 1–10: 1H-NMR (400 MHz, CDCl3) Spectrum, 13C-NMR (400 MHz, CDCl3) Spectrum, DEPT-NMR (400 MHz, CDCl3) Spectrum, COSY (400 MHz, CDCl3) Spectrum, HSQC (400 MHz, CDCl3) Spectrum, HMBC (400 MHz, CDCl3) Spectrum, NOESY (400 MHz, CDCl3) Spectrum, HR-MS Spectrum, UV Spectrum and FTIR Spectrum of Compound **1**; Supplementary Figures 11–20: 1H-NMR (400 MHz, CDCl3) Spectrum, 13C-NMR (400 MHz, CDCl3) Spectrum, DEPT-NMR (400 MHz, CDCl3) Spectrum, COSY (400 MHz, CDCl3) Spectrum, HSQC (400 MHz, CDCl3) Spectrum, HMBC (400 MHz, CDCl3) Spectrum, NOESY (400 MHz, CDCl3) Spectrum, HR-MS Spectrum, UV Spectrum and FTIR Spectrum of Compound **2**; Supplementary Figures 21–28: 1H-NMR (400 MHz, CDCl3) Spectrum, 13C-NMR (400 MHz, CDCl3) Spectrum, DEPT-NMR (400 MHz, CDCl3) Spectrum, HSQC (400 MHz, CDCl3) Spectrum, HMBC (400 MHz, CDCl3) Spectrum, HR-MS Spectrum, UV Spectrum, FTIR Spectrum of Compound **3**; Supplementary Figures 29–37: 1H-NMR (400 MHz, CDCl3) Spectrum, 13C-NMR (400 MHz, CDCl3) Spectrum, DEPT-NMR (400 MHz, CDCl3) Spectrum, COSY (400 MHz, CDCl3) Spectrum, HSQC (400 MHz, CDCl3) Spectrum, HMBC (400 MHz, CDCl3) Spectrum, HR-MS Spectrum, UV Spectrum, FTIR Spectrum of Compound **4**.

**Author Contributions:** Designing and performing of experiments and manuscript drafting, N.G.E.R.E.; biological activity experiments, data curation, and manuscript drafting, J.A.B.; characterization of compounds, T.T.W.; bioactivity experiments, data curation, and manuscript drafting, J.L.M.; bioactivity experiments and plant taxonomy, C.N.C.; conceptualization, project supervision, and manuscript review, A.A.H.; and project supervision and manuscript review, E.I.I.

**Funding:** The National Research Foundation (NRF) of South Africa provided the research grants (NRF SARChI Chair UID 85102 and NRF CPRR160506164193) for the project.

**Acknowledgments:** The authors would like to thank the National Research Foundation (NRF) of South Africa for providing the funding for this project.

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