Comparative phytochemical screening, antioxidant, and antidiabetic activities of selected medicinal plant leaves extracts

Abstract Oxidative stress and impaired glucose metabolism are central to the development of chronic diseases such as diabetes mellitus. Medicinal plants provide valuable sources of bioactive compounds with antioxidant and antidiabetic properties, offering safer alternatives or adjuncts to synthetic drugs. This study conducted a comparative phytochemical screening and evaluation of the antioxidant and antidiabetic activities of methanolic leaf extracts of Psidium guajava, Polyalthia longifolia, and Jatropha tanjorensis. Fresh leaves were collected, shade-dried, and extracted with methanol. Qualitative phytochemical screening identified major secondary metabolites, while antioxidant activity was determined using the DPPH radical scavenging assay. In-vitro antidiabetic activity was assessed by α-amylase inhibition, with acarbose as the reference standard. Phytochemical analysis revealed diverse constituents including flavonoids, phenols, terpenoids, and steroids, though their distribution varied among the plants. All extracts exhibited concentration-dependent antioxidant and antidiabetic effects. P. guajava displayed the strongest DPPH scavenging activity (IC50 = 9.67 mg/mL), followed by P. longifolia (12.17 mg/mL) and J. tanjorensis (15.03 mg/mL). In α-amylase inhibition, P. longifolia was most active (IC50 = 455.76 µg/mL), closely followed by P. guajava (465.96 µg/mL), whereas J. tanjorensis was less effective (544.55 µg/mL). Acarbose showed superior potency (IC50 = 231.77 µg/mL). The results confirm that all three plants possess notable antioxidant and α-amylase inhibitory properties, supporting their ethnomedicinal use in managing oxidative stress and hyperglycemia. While less potent than acarbose, their activities suggest potential as complementary therapies with fewer side effects. Further phytochemical characterization, in vivo studies, and clinical validation are required to fully establish their therapeutic relevance.