New neryl esters from Helichrysum italicum essential oil

Abstract

Helichrysum italicum (Roth) G. Don (Asteraceae), commonly known as the everlasting or curry plant, is endemic to the Mediterranean region where at least 3 subspecies can be found. The typical subspecies (italicum) produces an essential oil rich in the acetate (≥ 30%) and propionate (≥ 5%) of nerol, and the characteristic β-diketones (≥ 10%). It is appreciated by perfumers because of the spicy saffron character well complemented with curry, nutty and celery facets [1]. As esters are an important group of aroma-active volatiles, in this work we aimed to study the composition of the ester fraction of the mentioned everlasting essential-oil chemotype. After chromatographic separations, our attention was focused on the ester fraction that contained numerous minor neryl and angeloyl esters undetectable in the direct GC-MS analyses of the unfractioned oil (series A and B, respectively; Fig. 1). Three esters of nerol and medium-chain anteiso-fatty acids (C₆, C₈ and C₁₀) represented new natural products, while several other esters (e.g. neryl decanoate and dodecanote, and phenethyl, heptyl and octyl angelates) have a rather restricted occurrence in the Plant Kingdom. Our study disclosed an extensive diversity of volatile esters present in the studied chemotype, some of which may contribute to the overall aroma-profile of the essential oil.