Antityrosinase principles and constituents of the petals of Crocus sativus

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.