Antioxidant and Prolyl Endopeptidase Inhibitory Capacities of Chromone C-glucosides from the Clove Buds (Syzygium aromaticum)

Four chromone derivatives (1-4) were isolated from the clove buds (Syzygium aromaticum). Of these, two chromone C-glucosides (1 and 2) showed significant PEP inhibition with $IC_{50}$ values of $1.48{\pm}0.02$ and $1.74{\pm}0.03{\mu}M$ and $K_i$ values of $0.27{\pm}0.02$ and $0.50{\pm}0.05{\mu}M$, respectively. They also exhibited strong antioxidant capacities against the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid diammonium salt radical system with $EC_{50}$ values of $4.13{\pm}0.04$ and $4.79{\pm}0.03{\mu}M$, respectively.