This study focused on bio-guided isolation based on antioxidant activities from Dicranopteris linearis spores and Averrhoa bilimbi branches. The total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activities of the extracts were determined. For D. linearis spores, the ethyl acetate (EA) extract exhibited the highest TPC (120.13 ± 0.04 mg GAE/g) and TFC (21.94 ± 0.30 mg QE/g), along with strong DPPH antioxidant activity (96.3 ± 0.3% inhibition, IC₅₀ of 39.4 ± 0.3 µg/mL). For A. bilimbi branches, the n-hexane–ethyl acetate (HEA) extract showed the highest TPC (165.21 ± 0.24 mg GAE/g) and TFC (26.20 ± 0.01 mg QE/g), with significant DPPH antioxidant activity (89.6 ± 0.7% inhibition, IC₅₀ of 39.7 ± 1.9 µg/mL). Phytochemical investigation led to the identification of ten compounds (D1–D10) from D. linearis spores and twelve compounds (A1–A12) from A. bilimbi branches. Notably, compound A1 was identified as a new natural compound. The chemical structures were elucidated through NMR spectroscopy and comparison with existing literature. The antioxidant activities of selected compounds (D3–D5, D8–D10, and A1–A11) were evaluated using DPPH and ABTS free radical scavenging assays. Among them, compound A3 exhibited the strongest antioxidant activities (IC₅₀ of 7.1 ± 0.1 µg/mL for DPPH and 14.8 ± 0.1 for ABTS, respectively). The results of this study highlight the potential of D. linearis and A. bilimbi for use in natural product-based antioxidant applications.

Nitric oxide (NO) overproduction by activated macrophages drives inflammatory responses via iNOS activation, prompting the search for natural NO inhibitors. A bioassay-guided investigation targeting NO inhibition was conducted on Averrhoa bilimbi and Schinus terebinthifolia, two Thai medicinal plants. The most active fractions, derived from the branches of A. bilimbi and the stems of S. terebinthifolia, were subjected to chemical analysis. Seventeen compounds were isolated, five (ABS1–ABS5) from A. bilimbi and twelve (ST1–ST12) from S. terebinthifolia, with bilimoside A (ABS1) identified as a new compound. Structural elucidation of all isolated compounds was accomplished through detailed spectroscopic analysis, including NMR and HRESIMS. Their in vitro NO inhibitory activity was evaluated, revealing 3-oxoursolic acid (ST2) as the most potent compound (IC50 28.00 µg/mL), surpassing the positive control L-NMMA (IC50 41.30 µg/mL), while exhibiting minimal cytotoxicity. These findings suggest that ST2 could serve as a promising candidate for further development as an anti-inflammatory agent.