Photoprotective and antioxidative constituents of an alpine Scabiosa species

Abstract

UV-related damage is one of the main factors leading to skin cancer. The cosmetic industry puts intensive research efforts into the discovery of new ingredients with photoprotective and antioxidative properties, as it has been recognized that high sun protection factors alone are not sufficient to block UV-induced effects. Switzerland possesses a rich and diverse alpine flora which represents an attractive source of new ingredients with skin-protective effects, as alpine plants typically produce UV-protective secondary metabolites in response to high UV exposure. More than 30 ethanolic extracts from alpine plants were tested for protecting activity against cyclobutane pyrimidine dimer (CPD) formation in keratinocytes, and for DPPH radical scavenging properties. A Scabiosa species was identified as a promising candidate in both assays, and was selected for comprehensive investigation of its metabolite profile, and characterization of the bioactive constituents. The leaves were extracted successively by dichloromethane and methanol. Fractionation of the methanolic extract by a combination of different chromatographic methods, such as column chromatography on Sephadex LH-20, and preparative and semipreparative HPLC afforded 14 compounds including flavonoids (luteolin and isoorientin O- and C-glucosides), caffeic acid derivatives, and iridoid and secoiridoid glucosides. These metabolites account for most peaks detected in the HPLC-UV/ESIMS profile of the crude extract. Flavone glucosides with catechol groups and caffeoylquinic acid derivatives are responsible for the DPPH scavenging activity. Protection against CPD formation could be assigned to fractions containing caffeoylquinic acid derivatives. Compound 1, consisting of an ester of menthiafolic acid with secologanol, is a new secondary metabolite.