Chemical constituents isolated from Pereskia bleo extracts and their antioxidant and antibacterial activities / Mas Athira Johari

Pereskia bleo is a popular medicinal plant used traditionally to treat cancer-related diseases, hypertension, diabetes, and various illnesses. Previous studies reported various interesting biological activities of different Pereskia species, especially cytotoxic activity. Based on ethnobotany uses of Pereskia species and some earlier data on its biological activities, there should be a unique structure of biologically active compounds that is responsible for its popularity and results that have been reported. Several known compounds have been isolated from previous studies. However, only one flavonoid, Vitexin, was reported in 2012. More work must be carried out on the isolation of pure compounds from this genus. This study aimed to isolate chemical compounds and elucidate their chemical structures using modern spectroscopic methods such as Liquid chromatography-mass spectroscopy (LC-MS), Nuclear magnetic resonance (NMR) spectroscopy, and Infrared (IR) spectroscopy. In addition, selected pure compounds and different solvent extracts were used to determine the antibacterial and antioxidant activities based on 1,2-diphynyl-2pricrylhydrazyl (DPPH), and minimal inhibitory concentrations (MIC) and minimum bacterial concentration (MBC) assays, respectively. In this study, four types of microorganisms were tested, namely Escherichia coli ATCC 10535 (EC), Pseudomonas aeruginos ATCC 9027 (PA), Staphylococcus aureus ATCC 29737 (SA), and Streptococcus pyogenes ATCC 19615 (SP). For the phytochemical study on the stem extract, one new chalcone derivative, 4-Hydroxy-2,3,6-trimethoxy chalcone (PB 2) and one known fatty acid, (Z)-16-methoxy-16-oxohexadec-7-enoic (PB 1) were elucidated through the extensive use of 1D and 2D NMR as well as LCMS. Two known phytosterols identified as beta-sitosterol (PB 3) and stigmasterol (PB 5) and one flavone derivative, namely 5,7dihydroxy-6-methoxy flavone (Oroxylin A) (PB 6), were found in the acetone stem extract. Besides, beta-sitosterol (PB 4) was also isolated from the hexane leaves extract. The methanolic leaf crude extract showed the most potent free radical scavenging activity, while all stem crude extracts showed intermediate antioxidant activity. For antibacterial activity, all chloroform and methanol extracts from its leaves and stem and acetone stem extract showed strong antibacterial activity against all tested bacteria. The antibacterial activity could be contributed by PB 2, PB 5, and PB 6, where the MBC value is less than 500 µg/mL. The result of this study is a significant contribution toward further understanding the chemotaxonomy of this genus and the Cactaceae family. The four bacteria used in this study are all related to food spoilage and food-borne diseases. Therefore, this study suggests that certain P. bleo could be used as a natural preservative in food to replace chemical preservatives.