arbutin and kaempferol

The tyrosinase inhibitory activity of ethanolic extract of kenaf (Hibiscus cannabinus L.) leaf was evaluated before and after subjecting it to far-infrared (FIR) irradiation. The main component of the extract was analyzed as kaempferitrin (kaempferol-3,7-O-α-dirhamnoside). Prior to FIR irradiation, no inhibitory activity of the extract was detected in a tyrosinase assay. However, after FIR irradiation for 1h at 60°C, significant tyrosinase inhibitory activity (IC(50)=3500 ppm) was observed in it. In HPLC analysis, derhamnosylation products (kaempferol, afzelin, and α-rhamnoisorobin) were detected. The inhibitory activity may be due to the existence of derhamnosylation products. This study demonstrated that FIR irradiation can be used as a convenient tool for deglycosylation of flavonoid glycoside.

Topics: Flavonoids; Hibiscus; Infrared Rays; Kaempferols; Mannosides; Monophenol Monooxygenase; Plant Extracts; Plant Leaves; Proanthocyanidins

Three new monoterpenoids, crocusatin-J (1), -K (2), and -L (3), and a new naturally occurring acid, (3S),4-dihydroxybutyric acid (4), together with 31 known compounds were isolated and identified from the methanol extract of the petals of saffron (Crocus sativus). Their structures were established by spectroscopic methods. Among them, crocusatin-K (2), crocusatin-L (3), and 4-hydroxy-3,5,5-trimethylcyclohex-2-enone (8) showed significant antityrosinase activity, and protocatechuic acid (18), kaempferol (24), and kaempferol 7-O-beta-d-glucopyranoside (27) were more effective in scavenging alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) radicals than alpha-tocopherol. In addition, the mechanism of tyrosinase inhibition by crocusatin-K (2) is also discussed.

Topics: China; Crocus; Enzyme Inhibitors; Flowers; Free Radical Scavengers; Hydroxybutyrates; Kaempferols; Molecular Structure; Monophenol Monooxygenase; Monoterpenes; Nuclear Magnetic Resonance, Biomolecular; Plants, Medicinal