Chemical composition and antioxidant activity of three endemic Nepeta species methanol extracts

Abstract

Methanol extracts of in vitro grown shoots of three Nepeta species (Nepeta rtanjensis Diklić & Milojević, N. sibirica L. and N. nervosa Royle ex Bentham) were studied for their main secondary metabolites using UHPLC/DAD/±HESI-MS/MS analysis. Results showed that the major terpene present in the samples was iridoid monoterpene nepetalactone, wherein trans,cis- isomer was mostly present in methanol extracts of N. rtanjensis, while cis,trans-nepetalactone prevailed in N. sibirica. N. nervosa contained nepetalactone only in traces. Among phenolic acids, rosmarinic acid was predominant in all investigated species, while chlorogenic, neochlorogenic and caffeic acids were present in significantly lower concentrations. The results of ABTS and DPPH assays showed that methanol extracts of N. rtanjensis, N. sibirica and especially N. nervosa possess considerable antioxidant activities, and the FRAP assay revealed high ferric reducing capacity for all the tested samples. Significant antioxidant activity was attributed to phenolic acids, particulary to rosmarinic acid. However, nepetalactone did not contribute notably to the antioxidant potential of the methanol extracts.