Structure and Chemical Analysis of Major Specialized Metabolites Produced by the Lichen Evernia prunastri

Abstract

We performed comparative profiling of four specialized metabolites in the lichen Evernia prunastri, collected at three different geographic locations, California and Maine, USA, and Yoshkar Ola, Mari El, Russia. Among the compounds produced at high concentrations that were identified in all three specimens, evernic acid, usnic acid, lecanoric acid and chloroatranorin, evernic acid was the most abundant. Two depsidones, salazinic acid and physodic acid, were detected in the Yoshkar-Ola collection only. The crystalline structure of evernic acid (2hydroxy-4-[(2-hydroxy-4-methoxy-6-methylbenzoyl)oxy]-6-methylbenzoate) (hmb) revealed two crystallographically and conformationally distinct hmb anions, along with two monovalent sodium atoms. One hmb moiety contained an exotetradentate binding mode to sodium, whereas the other exhibited an exohexadentate binding mode to sodium. Embedded edge-sharing {Na 2 O 8 } n sodium-oxygen chains connected the hmb anions into the full three-dimensional crystal structure of the title compound. The crystal used for single-crystal X-ray diffraction exhibited non-merohedral twinning. The data suggest the importance of the acetyl-polymalonyl pathway products to processes of maintaining integrity of the lichen holobiont community.[a] Data for one replicate.

Antimicrobial and antioxidant activity of Evernia prunastri extracts and their isolates

“…The chemical characterization of the total extract of E. prunastri earlier (Staples et al 2020 ) showed that usnic acid, lecanoric acid and chloroatranorin were among the compounds produced in addition to evernic acid at high concentrations, with evernic acid being the most abundant compound (Staples et al 2020 ). Besides chloroatranorin also atranorin was present but in smaller amounts.…”

“…Compounds of the E. prunastri extract (Staples et al 2020 ) were structurally compared with main drugs of different antibiotics classes. The comparative study and visualization were performed using the DataWarrior software (5.2.1) (Sander et al 2015 ).…”

“…So far over 70 different metabolites have been identified and characterized in E. prunastri (Joulain and Tabacchi 2009). The most studied compounds are usnic and evernic acids, atranorin (Golubkova et al 1996;Joulain and Tabacchi 2009;Staples et al 2020), chloroatranorin (Avalos and Vicente 1987;Staples et al 2020), atranol and chlorobutanol (Joulain and Tabacchi 2009;Uter et al 2013;Mowitz et al 2013;Andersen et al 2015).…”

Activity throughout the lichen phylogeny indicates a focus on regulation of specialized metabolites

“…Analyses were performed at the MSU Mass Spectrometry Facility. LC/MS/MS was performed as previously described (Staples et al 2019). Briefly, to prepare samples for profiling of small molecules by LC-MS/MS, dried thallus from lichens was cut into small pieces (from 1 mm ×1 mm to 1 mm × 2 mm) and extracted twice with 2 ml ethanol or acetone.…”

“…The HPLC analysis was performed as described by Feige et al (1993) with modifications described by (Staples et al 2019). Briefly, a Spherisorb 5 ODS2 silica-based, reversed-phase C18 column (5 µm, 250 × 4.6 mm; Waters Corporation, Milford, MA, USA) was used.…”