Intramolecular transesterification of depsides yields fluorescent 1H-isochromen-1-ones: Application as a chemical probe for lichen determination

• Published in: Phytochemistry (Oxford) Vol. 198; p. 113139
• Main Authors: Ferron, S., Jéhan, P., Guillory, X., Uriac, P.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.06.2022
• Subjects: Ascomycota; Chemical lichen determination; Chemical Sciences; Depsides; Depsides - chemistry; Enolate; Fluorescent 1H-isochromen-1-ones; KUV probe; Lichens - chemistry; Transesterification; δ-keto esters; Reagent K or K; Depsides; If a blue fluorescence appears; Transesterification; δ-keto esters; Enolate; Fluorescent 1H-isochromen-1-ones; Chemical lichen determination; KUV probe
• ISSN: 0031-9422; 1873-3700; 0031-9422
• DOI: 10.1016/j.phytochem.2022.113139

The reactivity of eight purified depsides obtained from six european lichens and that display as 2-oxoalkyl chain in ortho-position of the ester bond was explored. These depsides were found to lead to 1H-Isochromen-1-ones, which exhibit a distinctive blue fluorescence at 365 nm, in the presence of a 10% aqueous solution of KOH. A mechanistic explanation, involving the formation of an enolate intermediate and intramolecular transesterification, was proposed and validated by DFT. By exploiting this fluorescent phenomenon, we conceived a chemical probe (the KUV probe) that is useful for lichen determination, as exemplified on a selection of European Porpidia species. [Display omitted] •Extraction from lichens and purification of eight depsides bearing a δ-keto ester moiety.•Intramolecular transesterification under basic conditions yield blue fluorescent 1H-isochromen-1-ones.•Mechanistic proposition and DFT validation of this rearrangement involving an enolate intermediate.•Conception of a new chemical probe named KUV probe for lichen determination: application to European Porpidia lichens.