Polarity-Guided Fractionation Separates Antioxidant from α-Glucosidase Inhibitory Activities in Solenostemma argel from Central Sahara, Algeria

Abstract

Solenostemma argel (Delile) Hayne (Apocynaceae) is a Saharan shrub used in traditional medicine to treat digestive and metabolic disorders, yet data on Algerian material, particularly at the fraction level, remain scarce. We studied the aerial parts collected in Djanet (Central Sahara, Algeria) and compared four fractions of increasing polarity (petroleum ether, chloroform, ethyl acetate, and n-butanol) obtained from a 70% methanolic crude extract. Proximate composition and total phenolic and flavonoid contents were determined, and biological activities were evaluated by three antioxidant assays (DPPH, ABTS•⁺, and phenanthroline), α-glucosidase inhibition, disc diffusion, and radial mycelial growth. The plant material exhibited a moisture content of 10.39 ± 0.31% and a dry matter content of 89.61 ± 0.31%. The dry matter consisted of 3.99 ± 0.21% total ash and 85.62 ± 0.23% organic matter, while the crude fat content was 1.64 ± 0.06%.The n-BuOH and EtOAc fractions had the highest phenolic (339.33 ± 2.85 and 324.46 ± 1.99 μg GAE/mg, respectively) and flavonoid (233.47 ± 1.87 and 218.06 ± 1.95 μg QE/mg, respectively) contents. The n-BuOH fraction was the most active in the DPPH and ABTS assays (IC₅₀ = 76,70 ±3.41 and 53.45 ± 1.07μg/mL, respectively), followed by EtOAc. In contrast, within the tested range (6.25–400 μg/mL), only the CHCl₃ extract inhibited α-glucosidase (IC50 = 164 ± 0.50 μg/mL), a lower value than that of acarbose (275.43±1.59 μg/mL). Against three strains tested, the EtOAc fraction was the most effective against Escherichia coli and Fusarium oxysporum f. sp. lycopersici, followed by the CHCl₃ fraction. Polarity-guided fractionation thus separated radical-scavenging activity from α-glucosidase inhibition, suggesting that different constituents are involved. These in vitro findings offer only partial support for the traditional metabolic use of the plant, and targeted phytochemical profiling is now needed to isolate and identify the active compounds.