6′-<i>O</i>-Caffeoylarbutin inhibits melanogenesis in zebrafish

<div><p>6′-<i>O</i>-Caffeoylarbutin, an arbutin derivative, is a naturally occurring glucoside of hydroquinone from <i>Vaccinium dunalianum</i>. On anti-melanogenic effect assay, 6′-<i>O</i>-caffeoylarbutin expressed a stronger anti-melanin activity in a dose-dependent manner with about a two-fold more than that of arbutin, but with less toxicity about a two-fold lower than that of arbutin. In addition, melanin synthesis could be fully recovered after the removal of 6′-<i>O</i>-caffeoylarbutin. The result suggested that 6′-<i>O</i>-caffeoylarbutin could be a candidate natural product to serve as a skin-whitening ingredient with the merits of potent melanin inhibition, less toxicity and reversible melanin synthesis after stopping use.</p></div

Total Syntheses and Biological Activities of Vinylamycin Analogues

Natural depsipeptide vinylamycin was reported to be an antibiotic previously. Herein we report vinylamycin to be active against K562 leukemia cells (IC₅₀ = 4.86 μM) and be unstable in plasma (<i>t</i>_1/2 = 0.54 h). A total of 24 vinylamycin analogues with modification of the OH group and chiral centers were generated via a combinatorial approach. The lead compound <b>1a</b> was subsequently characterized as having the following: no antimicrobial activity, significantly higher plasma stability (<i>t</i>_1/2 = 14.3 h), improved activity against K562 leukemia cells (IC₅₀ = 0.64 μM), and up to 75% cell inhibition without significant toxicities in K562 cells xenograft zebrafish model. Furthermore, compound <b>1a</b> maintained its activity against the breast cancer cell line MCF-7 under hypoxic conditions. In comparison, the activity of gemcitabine in the same hypoxic in vitro model of MCF-7 cells was 15-fold lower. Therefore, the present results demonstrate that <b>1a</b> has great potential as an anticancer agent