Synthesis and Nrf2-inducing activity of the isothiocyanates iberverin, iberin and cheirolin.

Numerous studies have reported a potent induction of Nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-dependent gene expression by the isothiocyanate sulforaphane. However, little is known regarding the Nrf2-inducing activities of the lower structure-related sulforaphane homologues, such as iberverin, iberin and cheirolin, which exhibit different sulfur oxidation states. Therefore, in this study we synthesized the isothiocyanates iberverin, iberin and cheirolin with a high yield and purity and determined their Nrf2-inducing activity in NIH3T3 fibroblasts. Iberverin, iberin and cheirolin significantly induced Nrf2 nuclear translocation. The increase in nuclear Nrf2 levels was accompanied by a significant increase in heme oxygenase 1 (HO-1) and γ-glutamylcysteine synthetase (γGCS) mRNA and protein levels. Overall, iberverin, iberin and cheirolin exhibited a similar potency to sulforaphane in inducing Nrf2-dependent gene-expression. Furthermore, our data suggest that the induction of Nrf2 by iberverin, iberin and cheirolin may have occurred via an extracellular signal-related kinase (ERK)-dependent signal-transduction pathway.