The essential oil ofAchillea ageratifolia(Sm.) Boiss. subsp.serbica(Nyman) Heimerl (Asteraceae) revisited: the stereochemical nomenclature issues, structural elucidation and synthesis of (new) sabinyl esters

Serbian Yarrow (Achillea ageratifolia (Sm.) Boiss. subsp. serbica (Nyman) Heimerl, Asteraceae) is a poorly investigated taxon, endemic to the Central Balkan Peninsula area. A combination of chromatographic and spectroscopic techniques enabled the identification of, in total, 300 constituents (comprising 95.5–97.2% of the total essential oil compositions) from the essential oils of the A. ageratifolia ssp. serbica dry aerial parts. A comparison of the essential-oil compositions from plant material collected from two populations (Jelasnicka klisura gorge and Suva Planina mountain, SE Serbia) in two consecutive years (2013 and 2014) confirmed that the biosynthesis/accumulation of the volatile metabolites for this species is not dependent on the environmental conditions and suggested the existence of a single chemotype of this species. The essential oil compositions were dominated by (1R*,3S*,5R*)-sabinyl derivatives, including two completely new natural products: (1R*,3S*,5R*)-sabinyl nonanoate and (1R*,3S*,5R*)-sabinyl decanoate. The identity of these new esters was unambiguously confirmed by co-injection of the essential oil samples with synthesized standards and their structure was elucidated by NMR (1D and 2D), IR and MS, whereas the stereochemistry of the esters was studied by an NMR methodology that employed lanthanide-induced shift reagents. Additionally, a nomenclature confusion regarding the relative stereochemistry of sabinyl esters, that came from the opposing use of cis and trans for the parent alcohols and the derived esters, was addressed. We propose the use of CIP notation in connection with the trivial names to avoid further ambiguities. Copyright © 2016 John Wiley & Sons, Ltd.