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The human body naturally has an antioxidant system to counteract free radical reactivity in a sustainable manner, but if the number of free radicals in the body is excessive, additional antioxidants are needed from food intake, namely vitamin C, vitamin E, carotenes and flavonoids. One plant that has the potential as an antioxidant is Ziziphus spina-christi (ZSC) because it contains phenolics and flavonoids. This study aims to determine the flavonoid content both qualitatively and quantitatively and to test the antioxidant activity of ZSC leaf extract using in vitro and in silico attenuation methods. Determination of the total flavonoid content of ZSC leaf extract using a comparison of quercetin. In vitro the antioxidant activity assay of ZSC leaf extract was carried out by measuring the reducing activity of ZSC leaf extract against the radical DPPH using ascorbic acid as a comparison, while the in silico method used QSAR and pharmacophore modelling techniques. The results showed that the total flavonoid content obtained from ZSC leaf extract was 0.2515 ± 0.0013 mg QE/g D.W with an IC50 of 58.9296 ppm. Furthermore, from the in silico method using pharmacophore modeling and QSAR techniques, 8 hit compounds were obtained from the content of ZSC with IC50 QSAR ranging from 6.57 μM to 0.0004 μM, which was thought to be the metabolite that had the most role in its antioxidant activity. This value indicates that ZSC leaf extract has potential as a very strong antioxidant. ZSC leaf extract can be used as an antioxidant candidate in drug and cosmetic preparations through the oral or percutaneous route. It also proves that QSAR and pharmacophore modelling techniques can be used as confirmatory tests for in vitro results in determining the antioxidant activity of natural materials.

Coronavirus 19 (COVID-19) is still a global health issue to date, SARS-CoV-2 is a novel coronavirus that is responsible for this sickness. The receptor-binding domain of the SARS-CoV-2 virus associates with angiotensin-converting enzyme 2 (ACE-2) and allows the virus to enter human cells. Natural peptides such alpha-defensin are thought to attach to the SARS-CoV-2 RBD and prohibit it from engaging with ACE-2. Molecular dynamics simulations using a computational approach are utilized to understand the stability of six alpha-defensin macromolecules using the Gromacs 2016 software. The trajectories formed are then analyzed using VMD 1.9.4 and BIOVIA Discovery Studio 2020 software. Finally, the free energy is estimated using the MM/PBSA method. The alpha-defensins 2 macromolecules were found to have the best stability based on numerous study results (trajectory visualization, RMSD, RMSF, and free energy calculations). As a result, these macromolecules could be used to build new antiviral treatments for COVID-19 infectious disease candidates.

Arabian bidara leaves (Ziziphus spina-christi, L.) are known to have strong antimicrobial activity against microorganisms that cause infection in the female genital area, namely Staphylococcus aureus bacteria and Candida albicans fungi. They contain main secondary metabolites such as flavonoids, alkaloids, and saponins. Christinin is a saponin glycoside derivative compound which consists of four types, namely christinin-A, B, C, and D. The role of computational studies in the discovery of new drugs is crucial and interesting nowadays because it is relatively cheap, effective, fast, and precise with a reliable level of accuracy. This computational study result will later be used to confirm in vitro test results which are carried out using experimental microbiological testing methods in the laboratory. This study identified, evaluated, and explored the interactions between christinin-A, B, C, and D compounds with Penicillin Binding Protein (PBP) from Staphylococcus aureus and Dihydrofolate Reductase from the fungus Candida albicans using computational study were carried out using the molecular docking. The christinin-A, B, C, and D compounds were modeled into 3D conformation using GaussView 5.0.8 and Gaussian09 software. The best conformation was selected for molecular interaction studies on Penicillin Binding Protein (PBP) from Staphylococcus aureus bacteria and Dihydrofolate Reductase from Candida albicans using MGLTools 1.5.6 software with AutoDock 4.2. The molecular interactions that occurred were further observed using the BIOVIA Discovery Studio 2020 software. Based on the molecular docking results, the christinin-B compound had the highest affinity for Penicillin Binding Protein (PBP) from Staphylococcus aureus bacteria, with a binding-free energy value of −7.67 kcal/mol. Meanwhile, the christinin-A compound has the highest affinity for Dihydrofolate Reductase from the fungus Candida albicans, with a binding-free energy value of −8.38 kcal/mol. Thus, it is predicted that christinin compounds can be chosen as the main component in feminine hygiene preparations to maintain the female genital area's health.