**4. Conclusions**

*A. bilimbi* is an important medicinal plant widely used in traditional medicine. The findings of this research study demonstrate that the leaves of *A. bilimbi* possess strong in-vitro antioxidant capacity, which is partly displayed through scavenging of free radicals and inhibition of xanthine oxidase activity. This antioxidant property was found to be significant in the n-butanol fraction, as revealed by the IC50 value. LC-MS-QTOF analysis, as well as molecular docking studies, led to the tentative identification of 5,7,4-trihydroxy-6-(1-ethyl-4-hydroxyphenyl) flavone-8-glucoside (cucumerin A) and afzelechin 3-*O*-alpha-L-rhamnopyranoside as the compounds that are likely to be responsible for the antioxidant effect of this plant. However, other phytoconstituents which were not present in the library of the LC-MS system could not be identified from their accurate mass, and may also play some roles. Further research is needed to obtain such bioactive compounds in pure form for complete pharmacological evaluations.

**Author Contributions:** Q.U.A. conceived and designed the experiments, Q.U.A. and A.M.A. performed the experiments and prepared the article, A.K., S.A.A.S., M.M.H. and M.N.S. discussed and analysed some of the data obtained during the experiments. All authors revised the paper thoroughly and approved the final manuscript prior to submission.

**Funding:** Corresponding author (Q.U.A.) is grateful to the Research Management Centre, IIUM for providing financial assistance through Research Initiative Grant Schemes (RIGS 16-294-0458) to accomplish this work.

**Acknowledgments:** LCMS Laboratory, Jeffrey Cheah School of Medicine and Health Sciences, Monash University Malaysia is acknowledged for LCMS analysis.

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