Bioconstituents from stems of Synsepalum dulcificum Daniell (Sapotaceae) inhibit human melanoma proliferation, reduce mushroom tyrosinase activity and have antioxidant properties

A new amide, dihydro-feruloyl-5-methoxytyramine (1), along with 13 known compounds, including (+)-syringaresinol (2), (+)-epi-syringaresinol (3), 4-acetonyl-3,5-dimethoxy-p-quinol (4), cis-p-coumaric acid (5), trans-p-coumaric acid (6), p-hydroxybenzoic acid (7), syringic acid (8), vanillic acid (9), veratric acid (10), N-cis-feruloyltyramine (11), N-trans-feruloyltyramine (12) and N-cis-caffeoyltyramine (13), were isolated from the stems of Synsepalum dulcificum Daniell (Sapotaceae). The structures of these compounds were established on the basis of spectroscopic analysis. One of the purposes of this study was to survey the antioxidant properties of 13 pure constituents. The radical scavenging and antioxidant activities were investigated by: scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals; metal chelating power was completed by ferrous ions; and reducing power was demonstrated by iron ions reduction reaction. In addition, all compounds were evaluated for their cell proliferation inhibition activities on human skin melanoma cells and tyrosinase inhibitions. The anti-tyrosinase effects were to calculate the hydroxylation of l-tyrosine to l-dopa according to in vitro mushroom tyrosinase assay. In sum, the inhibition effects of compounds (2–3) on human melanoma cells were significant. Besides, DPPH, ABTS radical scavenging, metal chelating and reducing power were found to be moderate compared with the positive controls.