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.