Isolation, characterization and antioxidant and cytotoxic activities of constituents from the orchid <i>Oncidium</i> spp.

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