Inhibition of mushroom tyrosinase and melanogenesis B16 mouse melanoma cells by components isolated from Curcuma longa

The methanol extract of the rhizomes of Curcuma longa was found to inhibit tyrosinase activity. After partition, various column chromatographic and preparative HPLC procedures were used for bioassay guided isolation from the active ethyl acetate-soluble fraction. Various spectroscopic (1D-, 2D-NMR) and mass spectrometric techniques, and Mosher's esterification were applied to elucidate the structures of the isolated compounds. The isolates were tested using an in vitro mushroom tyrosinase assay. Inhibition of melanin formation by the active compounds was further evaluated using B16 mouse melanoma cells. Eleven compounds (1-11) were isolated from the rhizomes of C. longa by bioassay guided fractionation. The configuration at the C-4 position of 4-hydroxy-1,3(15),10-bisabolatrien-9-one (11) was confirmed by Mosher's method. Of the isolates, curcuminoids 5-7 showed potent inhibitory activity in the tyrosinase assay. Melanin formation of the active compounds in the B16 mouse melanoma cells corresponded with the tyrosinase inhibitory activity. The findings support the view that either curcuminoids or the extract of C. longa rhizomes containing them may be useful for the treatment of hyperpigmentation.