Antioxidant and Quinone Reductase-Inducing Constituents of Black Chokeberry (Aronia melanocarpa) Fruits

Using in vitro hydroxyl radical-scavenging and quinone reductase-inducing assays, bioactivity-guided fractionation of an ethyl acetate-soluble extract of the fruits of the botanical dietary supplement, black chokeberry (Aronia melanocarpa), led to the isolation of 27 compounds, including a new depside, ethyl 2-[(3,4-dihydroxybenzoyloxy)-4,6-dihydroxyphenyl] acetate (<b>1</b>), along with 26 known compounds (<b>2</b>–<b>27</b>). The structures of the isolated compounds were identified by analysis of their physical and spectroscopic data ([α]_D, NMR, IR, UV, and MS). Altogether, 17 compounds (<b>1</b>–<b>4</b>, <b>9</b>, <b>15</b>–<b>17</b>, and <b>19</b>–<b>27</b>) showed significant antioxidant activity in the hydroxyl radical-scavenging assay, with hyperin (<b>24</b>, ED₅₀ = 0.17 μM) being the most potent. The new compound (<b>1</b>, ED₅₀ = 0.44 μM) also exhibited potent antioxidant activity in this assay. Three constituents of black chokeberry fruits doubled quinone reductase activity at concentrations <20 μM, namely, protocatechuic acid [<b>9</b>, concentration required to double quinone reductase activity (CD) = 4.3 μM], neochlorogenic acid methyl ester (<b>22</b>, CD = 6.7 μM), and quercetin (<b>23</b>, CD = 3.1 μM)