Investigation of euphrasianins as novel chemotaxonomic lipid markers of Euphrasia species

Eyebright (Euphrasia rostkoviana Hayne) is a medicinal plant belonging to the Orobanchaceae family. Extracts such as decoctions of Euphrasia have long been used for the treatment of inflamed eyes, conjunctivitis, stye and blepharitis. GC-MS and HPLC-APCI-MSⁿ analyses revealed the presence of five homologous acetyl monoacylglycerols of 3-hydroxyfatty acids (C14-C18) in CH₂Cl₂ extracts of E. rostkoviana. These compounds were named euphrasianins A-E, being members of a novel class of lipid constituents. For structure verification, a three-step total synthesis of one homologue (euphrasianin A) was performed which was characterized by 1D- and 2D-NMR. After alkaline hydrolysis of an E. rostkoviana CH₂Cl₂ extract and methylation with BF₃/MeOH the 3-hydroxy fatty acid methylesters thus obtained, were analyzed by chiral GC. By comparison with reference compounds the absolute configuration was found to be 'R'. Thus, the novel compounds were identified as 1-O-acetyl-3-[(3R)hydroxyfatty acid]-glycerols. While euphrasianins A and C were predominant in E. rostkoviana, another species, i.e. E. tetraquetra (seacliff eyebright), only revealed the occurrence of euphrasianins C and E, thus indicating that these target compounds may be utilized as chemotaxonomic markers.

References:

[1] Lorenz P, Knittel DN, Conrad J, Lotter EM, Heilmann J, Stintzing FC, Kammerer DR. 1-O-Acetyl-3-[(3R)-hydroxyfatty acid]-glycerols from cuticular waxes of Euphrasia rostkoviana Hayne and E. tetraquetra (Brébiss.) Arrond., manuscript in preparation.