| Summary: | Mosses from the genus <i>Polytrichum</i> have been shown to contain rare benzonaphthoxanthenones compounds, and many of these have been reported to have important biological activities. In this study, extracts from <i>Polytrichum formosum</i> were analyzed in vitro for their inhibitory properties on collagenase and tyrosinase activity, two important cosmetic target enzymes involved respectively in skin aging and pigmentation. The 70% ethanol extract showed a dose-dependent inhibitory effect against collagenase (IC<sub>50</sub> = 4.65 mg/mL). The methanol extract showed a mild inhibitory effect of 44% against tyrosinase at 5.33 mg/mL. Both extracts were investigated to find the constituents having a specific affinity to the enzyme targets collagenase and tyrosinase. The known compounds ohioensin A (<b>1</b>), ohioensin C (<b>3</b>), and communin B (<b>4</b>), together with <i>nor</i>-ohioensin D (<b>2</b>), a new benzonaphthoxanthenone, were isolated from <i>P. formosum</i>. Their structures were determined by mass spectrometry and NMR spectroscopy. Compounds <b>1</b> (IC<sub>50</sub> = 71.99 µM) and <b>2</b> (IC<sub>50</sub> = 167.33 µM) showed inhibitory activity against collagenase. Compound <b>1</b> also exhibited inhibition of 30% against tyrosinase activity at 200 µM. The binding mode of the active compounds was theoretically generated by an in-silico approach against the 3D structures of collagenase and tyrosinase. These current results present the potential application from the moss <i>P. formosum</i> as a new natural source of collagenase and tyrosinase inhibitors.
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