New Alk(en)ylhydroxycyclohexanes with Tyrosinase Inhibition Potential from Harpephyllum caffrum Bernh. Gum Exudate.

This work presents the first report on the phytochemical investigation of Harpephyllum caffrum Bernh. gum exudate. A known cardanol, 3-heptadec-12'- Z -enyl phenol ( 1 ) and three new alk(en)ylhydroxycyclohexanes, namely, (1 R ,3 R )-1,3-dihydroxy-3-[heptadec-12'( Z )-enyl]cyclohexane ( 2 ) (1 S ,2 S ,3 S, 4 S, 5 R )-1,2,3,4,5-pentahydroxy-5-[octadec-13'( Z )-enyl]cyclohexane ( 3 ) and (1 R ,2 S ,4 R )-1,2,4-trihydroxy-4-[heptadec-12'( Z )-enyl]cyclohexane ( 4 ) were isolated from the gum. The structures of the compounds were determined by extensive 1D and 2D NMR spectroscopy and HR-ESI-MS data. The ethanolic extract of the gum was found to be the most potent tyrosinase inhibitor with IC 50 of 11.32 µg/mL while compounds 2 and 3, with IC 50 values of 24.90 and 26.99 µg/mL, respectively, were found to be potential anti-tyrosinase candidates from the gum. Gum exudate may be a potential source for non-destructive harvesting of selective pharmacologically active compounds from plants. The results also provide evidence that H. caffrum gum may find application in cosmetics as a potential anti-tyrosinase agent.