Metabolomic evaluation of five Nepeta species (fam. Lamiaceae) using liquid chromatography with multistage mass spectrometry

Abstract

The aim of this study was to determine qualitative composition of methanol-soluble metabolites in leaves from in vitro-grown plants of phylogenetically distinct Nepeta species producing iridoids (N. sibirica L., N. spicata Benth., N. argolica Bory & Chaub., and N. rtanjensis Diklić & Milojević) and iridoid-lacking N. nervosa Royle ex Benth., adopting UHPLC-LTQ OrbiTrap MS technique. Totally, 52 compounds were identified based on their monoisotopic masses, MSn fragmentation, and previously reported MS data and they were clustered into four major groups: phenolic acid derivatives (23 compounds), flavonoids (10 compounds), iridoids (13 compounds), and 6 compounds belonging to other classes. Both phenolic and iridoid profiles of the tested species were found to be very diverse regarding both qualitative content of compounds and their relative representation in extracts. Rosmarinic, 5-O-cafeoylquinic, and caffeic acids were found to be the dominant phenolics in all analyzed species, especially in N. argolica, N. rtanjensis, and N. nervosa. Iridoids were present in the form of glucosides and the most abundant compounds from this group were epideoxyloganic acid, geniposide, and aucubin. Although iridoids were not detected in N. nervosa extracts, this species was revealed as a rich source of phenolic acids and flavonoids. Conversely, N. spicata was found to produce iridoids but negligible amounts of phenolic compounds. Extracts of two closely related endemic species originating from the Balkan Peninsula, N. argolica and N. rtanjensis, were very similar in both phenolic and iridoid profiles. The UHPLC-LTQ OrbiTrap MS method, in combination with chemometrics data processing, was proved to be simple, rapid, and accurate strategy for unambiguous taxonomic determination and chemical differentiation of Nepeta species.