The guanidine group of (2) was hung around the cavity of three loops, and the aromatic ring docked within the active site or the other. of bicyclol in HL-7702 cells [12]. The objective of this study was to evaluate the inhibitory activities of compounds from on tyrosinase. The pseudoalkaloids 10-methoxy-leonurine and leonurine, at micromolar concentrations, were revealed to be potential inhibitors of tyrosinase. These compounds disrupt the catalytic reactions of tyrosinase by binding to its active site. Molecular docking simulations showed that these compounds fit into the active site of the enzyme. Thus, pseudoalkaloids may be lead candidates for the development of tyrosinase inhibitors from (5 kg) was extracted with 80% methanol at 27 C. The concentrated methanol extract (0.8 kg) was Epothilone B (EPO906) suspended in distilled water and successively partitioned with n-hexane, ethyl acetate, and aqueous layers. The ethyl acetate portion (73.1 g) was subjected to silica gel column chromatography with a gradient of = 3). All values were analyzed using SigmaPlot (Systat Software Inc., San Jose, CA, USA) to determine treatment variations. 3. Results 3.1. Identification and Determination of the Tyrosinase Inhibitory Activity of Compounds Compounds 1C5 were isolated from by column chromatography. The structures were elucidated by nuclear magnetic resonance spectroscopy and compared with previously reported mass spectra. The compounds were determined to be 10-methoxy-leonurine (1) [17], leonurine (2) [17], syringic acid (3) [17], isoquercitrin (4) [18], and leonurusoide E (5) [18] (Physique 1). Open in a separate window Physique 1 The structure of components 1C5 from toward tyrosinase. Vegfa were shown to stimulate melanogenesis in B16F10 cells [15]. The guanidine pseudoalkaloid leonurine (2) was first recognized in 1930 as an important compound of [21]; leonurine decreases the interleukin-1-induced expression of cyclooxygenase-2 and inducible nitric oxide synthase, Epothilone B (EPO906) as well as activation of nuclear factor-B p65 in chondrocytes [22]. Doxycycline-induced apoptosis of H9c2 cells was analyzed to be guarded and doxycycline-induced dissipation of was recovered by 10 M leonurine Epothilone B (EPO906) [23]. 10-Methoxy-leonurine (1) was first isolated from and reported to inhibit soluble epoxide hydrolases [17]. In this study, compounds 1 and 2 were identified as potential tyrosinase inhibitors that block the catalytic reactions of tyrosinase at approximately 10 M. Upon binding to tyrosinase, both inhibitors blocked the conversation of the substrate with the tyrosinase active site. Molecular simulation is one of the essential methods for drug development by providing a clue to the ligand-receptor conversation by theoretical computational chemistry [24,25]. According to the molecular docking, the guanidine group occupied the cavity by three loops (Asn243 to er254, Gly62 to Leu89, and Arg321 to Gly330). Keton of ester in (1) was tied within 3.5 ? by His244, and the aromatic ring was anchored within the inner active site via hydrophobic interactions only. As a result, inhibitor (1) occupied a stable position extending from your cavity to the active site, whereas the hydroxyl group of the aromatic ring in (2) created hydrogen bonds with His85, Asn81, Cys83, and Ala323, according to the top 10 10 ranks. The guanidine group of (2) was hung around the cavity of three loops, and the aromatic ring docked within the active Epothilone B (EPO906) site or the other. These findings likely explain the greater inhibitory activity of 10-methoxy-leonurine (1) than leonurine (2). Further studies will be necessary to increase the hydrophobicity of the aromatic ring of guanidine pseudoalkaloids for the development of novel tyrosinase inhibitors. 5. Conclusion To identify novel tyrosinase inhibitors from plants,.