Structure and In Vitro Bioactivity of Phenolic Compounds Isolated from Alpinia monopleura Fruit

Phenolic compounds are widely recognized for their diverse pharmacological properties, including antioxidant, anti-inflammatory, and antidiabetic effects. Alpinia species are known to be rich in bioactive constituents; however, the chemical profile and biological activities of Alpinia monopleura fruit remain poorly explored. This study aimed to isolate, identify, and evaluate the antioxidant, anti-inflammatory, and antidiabetic activities of phenolic compounds from the fruit of A. monopleura. Maceration extraction was carried out using methanol as the solvent, followed by fractionation and purification through chromatographic techniques, resulting in four pure compounds. Structural identification was performed based on ¹H-NMR and ¹³C-NMR spectroscopic data, which were consistent with those reported in reference literature for each compound, namely hexadecyl ferulate (A1), 4-hydroxybenzaldehyde (A2), methyl p-coumarate (A3), and methyl 4-hydroxy-3-methoxybenzoate (A4). Antioxidant activity was evaluated using the DPPH radical scavenging method, anti-inflammatory activity was determined through nitric oxide (NO) inhibition, and antidiabetic activity was assessed using the α-glucosidase inhibition assay. The results showed that all four compounds exhibited biological activities with varying degrees of effectiveness. The IC₅₀ values for the DPPH assay of compounds A1–A4 were 27.60±1.19, 13.52±0.94, 10.30±0.95, and 8.20±0.95 µg/mL, respectively. For NO inhibition, the IC₅₀ values were 42.86±1.08, 16.25±1.06, 11.35±0.96, and 9.69±1.12 µg/mL, while for α-glucosidase inhibition, the IC₅₀ values were 47.39±1.45, 40.67±1.05, 28.59±0.98, and 16.54±0.87 µg/mL, respectively. Methyl 4-hydroxy-3-methoxybenzoate (A4) consistently demonstrated the strongest activity across all assays. These findings confirm that the combination of hydroxyl and methoxy groups plays a crucial role in enhancing the biological activity of phenolic compounds from A. monopleura, suggesting their potential for development as natural bioactive agents.