Plant secondary metabolites are useful for medicinal and pharmaceutical applications because of their variety of bioactivities. This study analyzes ethanol (GJ-E), petroleum ether (GJ-Pe), chloroform (GJ-C), and aqueous (GJ-A) extracts of Gardenia jasminoides leaves, which subjected to qualitative and quantitative phytochemical analysis, FT-IR and GC–MS characterization, and further evaluated for antioxidant, antidiabetic, and antibacterial activities, supported by molecular docking studies. GJ-E extract exhibited the highest phenol (45.56 ± 0.21 mg GAE/g), flavonoid (68.56 ± 0.91 mg/g rutin equivalent), and steroid (36.55 ± 0.25 mgE/g diosgenin) contents. FT-IR confirmed diverse functional groups, while GC–MS identified 39 compounds, with 3-oxo-9β-lanosta-7,24-dien-26,23-ol (39.27%) being predominant. It showed the strongest antioxidant activity (DPPH: 74.13 ± 0.79%, IC50 = 202.56 µg/mL). The highest antidiabetic inhibition was recorded in GJ-E where \(\alpha\) -amylase assay exhibits 86.21% inhibition rate and α-glucosidase assay exhibits 87.95% inhibition rate. Antibacterial assays revealed strong activity, with MIC and MBC values at 18.75 and > 18.75 µg/mL. Molecular docking revealed that 3-oxo-9β-lanosta-7,24-dien-26,23-o (Com1) exhibited stronger binding affinities than tris(2,4-di-tert-butylphenyl) phosphate (Com2) against Klebsiella pneumoniae and Pseudomonas aeruginosa, forming diverse interactions despite some unfavorable contacts. In contrast, Com2 exhibited weaker binding and fewer interaction profiles. GJ-E emerged as most promising, rich in bioactive compounds with strong antioxidant, antidiabetic, and antibacterial potential.
