Identification of Chemical Constituents from Leaves and Stems of Alpinia oxyphylla: Potential Antioxidant and Tyrosinase Inhibitory Properties

<i>Alpinia oxyphylla</i> Miq. is an important undergrowth species in southern China. The fruits of <i>A. oxyphylla</i> are recognized as one of "the four famous south medicines" and are also used in the production of preserved fruit. However, as non-medicinal parts, their stems and leaves are unutilized. In order to promote resource recycling, the chemical components of such stems and leaves were investigated, and we evaluated their melanin inhibitory potential through DPPH and ABTS radical scavenging, tyrosinase inhibition, and melanin production inhibition in B16 cells. Five new compounds, aloxy A (<b>1</b>), kaempferol 3-<i>O</i>-<i>α</i>-L-rhamnosyl-(1 → 2)-(3″,4″-diacetyl-<i>β</i>-D-glucuronate methyl ester) (<b>2</b>), quercetin 3-<i>O</i>-<i>α</i>-L-rhamnosyl-(1 → 2)-(3″,4″-diacetyl-<i>β</i>-D-glucuronate methyl ester) (<b>3</b>), kaempferol 3-<i>O</i>-<i>α</i>-L-rhamnosyl-(1 → 3)-(4″-acetyl-<i>β</i>-D-glucuronate methyl ester) (<b>4</b>), and kaempferol 3-<i>O</i>-<i>α</i>-L-rhamnosyl-(1 → 2)-(3″-acetyl-<i>β</i>-D-glucuronate methyl ester) (<b>5</b>), and seventeen known ones (<b>6</b>-<b>22</b>) were isolated and identified from the stems and leaves of <i>A. oxyphylla</i>. Among these compounds, 19 compounds presented tyrosinase inhibitory activities, among which aloxy A (<b>1</b>), hexahydrocurcumin (<b>7</b>), gingerenone A (<b>8</b>) and 4,4'-dimethoxy-3'-hydroxy-7,9':7',9-diepoxylignan-3-<i>O</i>-<i>β</i>-D-glucopyranoside (<b>22</b>) showed strong inhibitory activity, with IC₅₀ values between 6.26 ± 0.42 and 22.04 ± 1.09 μM, lower than the positive control (Kojic acid, IC₅₀ = 37.22 ± 1.64 μM). A total of 15 compounds exhibited varying degrees of DPPH and ABTS radical scavenging activities. In addition, <b>1</b>, <b>2</b>, and <b>7</b> showed melanin production inhibition activity in B16 cells, and the effects presented as concentration-dependent. The above results indicate that the stems and leaves of <i>A. oxyphylla</i> are rich with phenolic compounds, and display tyrosinase inhibition and antioxidant activities, which could lead to potential applications related to melanin production inhibition such as in the development of cosmetics.