*3.7. Copper Reducing Assay*

Oxyresveratrol was colorimetrically determined using the Cu(I)-stabilizing reagent bathocuproine disulfonic acid. The reaction mixture (total volume for each tested concentration 200 μL) contained 50 μL of 2,000 mM (2M) bathocuproine disulfonic acid and 100 μL of oxyresveratrol in 10 mM HEPES buffer. The reaction was initiated by adding 50 μL of 200 mM Cu(OAc)2 in the sample tubes and the absorbance of the mixture at 484 nm was read at the end of 5 min.

#### **4. Conclusions**

Oxyresveratrol was the major stilbenoid found in all three extracts tested (water, ethanol and ethyl acetate). The compound exhibited both dose-dependent DNA damage in the presence of copper ions and ROS generation. In consideration of these findings, it can be concluded that oxyresveratrol has the potential to be developed as a promising anticancer drug candidate.

**Supplementary Materials:** The following are available online, Figure S1: 1H-NMR Oxyresveratrol, Figure S2: 13C-NMR Oxyresveratrol, Figure S3: ESI-MS spectrum of standard oxyresveratrol, Figure S4: ESI-MS spectrum of the peak RT 14.0 in the water extract, Figure S5: ESI-MS spectrum of the peak RT 14.0 in the ethanol extract, Figure S6: ESI-MS spectrum of the peak RT 14.0 in the ethyl acetate extract.

**Author Contributions:** Conceptualization, S.R., S.D.S. and K.J.R.; methodology, S.R. and K.J.R.; software, K.J.R.; validation, S.R., S.D.S. and K.J.R.; formal analysis, S.R.; investigation, S.R. and K.J.R.; resources, S.R., S.D.S. and K.J.R.; data curation, S.R.; writing—original draft preparation, S.R.; writing—review and editing, S.D.S. and K.J.R.; visualization, S.R.; supervision, S.D.S. and K.J.R.; project administration, K.J.R.; funding acquisition, S.D.S. and K.J.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by The Royal Thai government, Thailand; in the PhD project no. R253184.

**Acknowledgments:** The author would like to express profound gratitude to The Medicinal Plant Research Institute, Department of Medical Sciences, Thailand for providing the plant materials and identifying the plant species and the excellent support from Liverpool John Moores University for the laboratory facilities.

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