# Unlocking the Secrets of Roman Chamomile (Anthemis nobilis L.) Essential Oil: Structural Elucidation and Acute Toxicity of New Esters

## TL;DR

This study identifies new esters in Roman chamomile essential oil and evaluates their toxicity, expanding our understanding of its chemical composition.

## Contribution

The paper reports four new natural ester compounds in Roman chamomile essential oil and confirms their chemical structures.

## Key findings

- Four new esters (methallyl 3-methylbutanoate, methallyl senecioate, 3-methylpentyl 2-methylbutanoate, and 5-methylhexyl angelate) were identified as previously unreported natural products.
- Methacrylates and related esters showed low toxicity in Artemia salina assays at high concentrations.
- The study confirmed the thiol-acceptor reactivity of methacrylates through model Michael additions.

## Abstract

To address gaps in the characterization of Roman chamomile (Anthemis nobilis L., Asteraceae)—an ethnobotanically and commercially important species—we profiled its essential oil (EO), focusing on esters that are incompletely characterized or unreported. Comprehensive GC-MS of two commercial EOs and their chromatographic fractions, combined with synthesis and co-injection of reference compounds, enabled the identification of 190 constituents. We uncovered a homologous series of angelates, tiglates, and senecioates by partial-ion-current (PIC) screening (m/z 55, 83, 100, 101), augmented by co-injection and NMR confirmation. Among these EO constituents, four esters, methallyl 3-methylbutanoate (6h), methallyl senecioate (3h), 3-methylpentyl 2-methylbutanoate (5c), and 5-methylhexyl angelate (2g) are reported here as new natural products and previously unreported compounds in the literature. Selected methacrylates and related α,β-unsaturated esters underwent model Michael additions to methanethiol (generated in situ from dimethyl disulfide and NaBH4), confirming their thiol-acceptor reactivity. In an Artemia salina assay, the EO and most esters were non-toxic; methacrylates showed only low toxicity at the highest concentrations. These results refine the chemical map of A. nobilis EO and highlight specific ester families for future mechanistic and biological evaluation.