Isolation, characterization and antioxidant and cytotoxic activities of constituents from the orchid Oncidium spp.

Isolation from the pseudobulbs of Oncidium spp. 'Honey Angel' yield a previously undescribed phenanthrene, 5-hydroxy-1,2,3,4-tetramethoxyphenanthrene (1), as well as twenty-eight known compounds, most of which are reported for the first time in this genus. Selected phenanthrenes (2-5), dihydrophenanthrenes (6-9), bibenzyls (11-13) and flavonoids (16-18) were evaluated for cytotoxic and antioxidant activities. Compound 3 showed the strongest effect against DLD-1 cells (IC₅₀ = 25.8 µM), while compound 6 was most active against HCT116 cells (IC₅₀ = 14.4 µM). Phenanthrenes 2-5 and dihydrophenanthrene 6 consistently exhibited cytotoxicity in both cancer cell lines. Importantly, neither 2 nor 6 significantly affected the viability of normal IEC-6 cells, even at higher concentrations. In antioxidant assays, phenanthrenes 2-5 and dihydrophenanthrene 7 displayed potent radical scavenging activity. These results indicate that Oncidium spp. is a valuable source of bioactive phenanthrenes and dihydrophenanthrenes with dual anticancer and antioxidant properties, supporting their potential as leads for further pharmacological development.