Tyrosinase inhibition activity of monoterpene glucosides from brugmansia arborea flowers

Three monoterpene glucosides were isolated from the flowers of Brugmansia arborea L. using repeated silica gel and octadecyl SiO₂ column chromatography. Based on spectroscopic data including 1d-NMR (¹H, ¹³C, and distortionless enhancement by polarization transfer (DEPT)), 2D-NMR (gradient correlation spectroscopy (gCOSY), gradient heteronuclear single quantum coherence (gHSQC), and gradient heteronuclear multiple bond coherence (gHMBC)), Infrared Spectroscophy, and Mass Spectroscophy, the glucosides were identified as citronellol O-β-D-glucopyranoside (1), jasminoside N (2), and jasminoside P (3). The EtOAc (Brugmansia arborea Flowers ethyl acetate fraction [BAFE]) and n-BuOH (Brugmansia arborea Flowers n-butanol fraction [BAFB]) fractions showed high inhibition of tyrosinase activity (BAFE: IC₅₀ = 68.0 and BAFB: IC₅₀ = 59.3 μg/mL), and all isolated monoterpenes inhibited tyrosinase activity (1: IC₅₀ = 156.5, 2: IC₅₀ = 198.2, and 3: IC₅₀ = 191.0 μM).