The best described pharmacological property of flavonoids is their capacity to act as potent antioxidant that has been reported to play an important role in the alleviation of diabetes mellitus. Flavonoids biochemical properties are structure dependent; however, they are yet to be thoroughly understood. Hence, the main aim of this work was to investigate the antioxidant and antidiabetic properties of some structurally related flavonoids to identify key positions responsible, their correlation, and the effect of methylation and acetylation on the same properties. Antioxidant potential was evaluated through dot blot, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, ABTS+ radical scavenging, ferric reducing antioxidant power (FRAP), and xanthine oxidase inhibitory (XOI) assays. Antidiabetic effect was investigated through α-glucosidase and dipeptidyl peptidase-4 (DPP-4) assays. Results showed that the total number and the configuration of hydroxyl groups played an important role in regulating antioxidant and antidiabetic properties in scavenging DPPH radical, ABTS+ radical, and FRAP assays and improved both α-glucosidase and DPP-4 activities. Presence of C-2-C-3 double bond and C-4 ketonic group are two essential structural features in the bioactivity of flavonoids especially for antidiabetic property. Methylation and acetylation of hydroxyl groups were found to diminish the in vitro antioxidant and antidiabetic properties of the flavonoids.

Introduction: Entada Spiralis Ridl., or locally identified as Sintok, contains flavonoid, saponin, tannin, and glycoside, compounds that have antifungal and antibacterial activities. This research aims to identify bioactive compounds and determine the antimicrobial activity from crude and fraction of E. spiralis extract. Methods: The crude extract was prepared by macerating the leaves with chloroform, and then proceeded to fraction it by vacuum liquid chromatography with Dichloromethane (DCM)/Hexane (Hex) (1/9) and Dichloromethane (DCM)/Methanol (MeOH) (9/1) solvent system. Disk Diffusion Test and Microdilution Assay evaluated the extracts' antimicrobial activity against S. aureus, E. coli and C. albicans. The determination of bioactive compounds was done by Thin Layer Chromatography (TLC). Determination of Total Phenolic (TPC) and Flavonoid Content (TFC) were performed by Folin-Ciocalteu and AlCl3 Colourimetric Assay Results: The greatest inhibition zone against C. albicans was obtained from fraction Chloroform (CHCl3) extract with an inhibition zone of 10.33 mm. DCM/MeOH (9/1) effectively killed S. aureus and E.coli with an inhibition zone of 11.67 and 12 mm, respectively. The minimum inhibitory concentration (MIC) of CHCl3 crude extract were 1.563 mg/mL for both E. coli and S. aureus, and 0.781 mg/mL for C. albicans. The TLC revealed the presence of tannins, saponin, glycosides, phenol, flavonoid, triterpenoid, and aromatic compound in CHCl3 crude extract. TPC of DCM/MeOH (9/1), CHCl3, and DCM/Hex (1/9) were 50.56 ± 0.188, 51.913± 0.089, 24.16 ± 0.175 mg GAE/g extract. Conclusion: In conclusion, E. spiralis leaves could be a source of active antifungal and antimicrobial agents used for food preservation by using a semipolar solvent for extraction.

Cosmos caudatus (Asteraceae), is known as Ulam raja in Malaysia or kenikir in Indonesia also sometimes referred to as "King's salad." It is usually consumed as a salad and the leaves have been widely used as a traditional medicine due to their pharmacological activities and beneficial effects on human health. The leaves have been reported to contain several phytoconstituents such as flavonoids and their derivatives, other phenolics, and essential oil, while the roots only contain non-flavonoids. Furthermore, the leaves have been reported to contain a high total phenolic content (TPC) which is attributable for various activities including antidiabetes, antioxidant, anti-inflammation, antibacterial, antifungal, antiosteoporosis, anti-hyperlipidemic, anticancer, antihypertensive, anti-hepatoprotective, and to manage fertility problems. However, further research needs to be done in order to determine whether C. caudatus is effective in treating thrombolytic and leishmanial disorder. Clinical study regarding the use of C. caudatus as an antidiabetic agent has been reported as a supplement to improve insulin resistance and sensitivity in type 2 diabetes patients [NCT02322268]. The findings of the toxicity tests revealed that the leaves are nontoxic and that they can be taken without risk. It is still need to conduct an additional in vitro and in vivo investigations to confirm various traditional claims about the therapeutic potential of this plant in the treatment of various ailments. This traditional medicinal plant's genuine medicinal benefit will be further confirmed by additional clinical trials and toxicity assessments.

The potency of O. stamineus as a herbal candidate has been evaluated by previous studies. The goal of this study is to compare water and a 100% ethanolic extract of O. stamineus to see which one is more effective as an α-glucosidase inhibitor and antioxidant. However, these parameters are critical in the development of herbal medicines. Furthermore, the toxicity of this herb is assessed. According to this study, water extract of O. stamineus leaves has a better inhibition activity of α-glucosidase, ABTS, and DPPH, with IC50 values of approximately 43.623±0.039 µg/mL, 27.556±0.125 µg/mL, and 95.047±1.587 µg/mL, respectively. The major active compounds are fatty acid groups such as Ethyl myristate (Tr: 20.8 min); 6-(Stearoyloxy)octadecanoic acid (Tr: 20.75 min); Linoleic acid (Tr: 23.09 min); Oleic acid (Tr: 23.22 min); and phenolic groups including D-(-)-Quinic acid (Tr:1.3 min) and Caffeic acid (Tr: 5.2 min); and carboxylic acid groups and its derivate including 2-(Benzoyloxy)-3-hydroxysuccinic acid (Tr: 7.85 min) and Tuberonic acid (Tr: 9.67 min). Therefore, this study also found that the water extract of this herb is non-toxic to zebrafish embryos and has no effect on zebrafish larvae development at concentrations less than 500 g/mL.