Bioassay-Guided Isolation of Chemical Constituents from Lycopodiastrum casuarinoides and Targeted Evaluation of Their Potential Efficacy in Cosmetics

Natural tyrosinase inhibitors are currently a hot research topic due to their potential application in cosmetic and medicinal products. For the plant Lycopodiastrum casuarinoides, the chemical constituents with a tyrosinase inhibitory effect have not been investigated yet. Bioassay-guided isolation was conducted on the aboveground parts, resulting in the isolation of 10 compounds (1–10). Their chemical structures were confirmed by their spectral data and comparison with literature data. It might be worth pointing out that compounds 3–9 were isolated from the genus Lycopodiastrum for the first time. The bioassay revealed that compounds 6 and 7 displayed moderate mushroom tyrosinase inhibitory activity (IC50 = 1.90 and 2.43 mM, respectively), which was close to the positive control kojic acid (IC50 = 0.17 mM). Moreover, the in silico experiments disclosed that Lys180, His178 and other amino residues played key roles in the binding modes between compounds 6 and 7 and mushroom tyrosinase (PDB: 2Y9X). These findings suggested potential for further investigation on this species as a source of cosmetic ingredients.