Kushenol A and 8-prenylkaempferol, tyrosinase inhibitors, derived from <i>Sophora flavescens</i>

<p>Tyrosinase is known for an enzyme that plays a key role in producing the initial precursor of melanin biosynthesis. Inhibition of the catalytic reaction of this enzyme led to some advantage such as skin-whitening and anti-insect agents. To find a natural compound with inhibitory activity towards tyrosinase, the five flavonoids of kushenol A (<b>1</b>), 8-prenylkaempferol (<b>2</b>), kushenol C (<b>3</b>), formononetin (<b>4</b>) and 8-prenylnaringenin (<b>5</b>) were isolated by column chromatography from a 95% methanol extract of <i>Sophora flavescens</i>. The ability of these flavonoids to block the conversion of L-tyrosine to L-DOPA by tyrosinase was tested <i>in vitro</i>. Compounds <b>1</b> and <b>2</b> exhibited potent inhibitory activity, with IC50 values less than 10<b> </b>µM. Furthermore, enzyme kinetics and molecular docking analysis revealed the formation of a binary encounter complex between compounds <b>1–4</b> and the enzyme. Also, all of the isolated compounds (<b>1–5</b>) were confirmed to possess antioxidant activity.</p

Tyrosinase inhibitory components from <i>Aloe vera</i> and their antiviral activity

<p>A new compound, 9-dihydroxyl-2'-<i>O</i>-(<i>Z</i>)-cinnamoyl-7-methoxy-aloesin (<b>1</b>), and eight known compounds (<b>2</b>–<b>9</b>) were isolated from <i>Aloe vera.</i> Their structures were elucidated using 1D/2D nuclear magnetic resonance and mass spectra. Compound <b>9</b> exhibited reversible competitive inhibitory activity against the enzyme tyrosinase, with an IC₅₀ value of 9.8 ± 0.9 µM. A molecular simulation revealed that compound <b>9</b> interacts via hydrogen bonding with residues His244, Thr261, and Val283 of tyrosinase. Additionally, compounds <b>3</b> and <b>7</b> were shown by half-leaf assays to exhibit inhibitory activity towards <i>Pepper mild mottle virus</i>.</p