Euphrasianins A-E, novel acylglycerol lipids from Euphrasia rostkoviana and E. tetraquetra

Plant cuticles form a hydrophobic layer covering all aerial parts of terrestrial plants as a protective barrier against environmental impacts such as desiccation, extreme temperature changes, microbial infection and intense UV radiation [1]. We herein identified in CH₂Cl₂ extracts of E. rostkoviana by use of GC-MS and HPLC-APCI-MSⁿ methods a novel class of homologous acylglycerol lipids derived from 3-hydroxy fatty acids (C14-C18), henceforth named euphrasianins A-E [2]. Based on MS data, the structure of one representative homologue (euphrasianin A) was elucidated as 1-O-acetyl-3-(3-hydroxymyristoyl)-glycerol, which was verified by total synthesis of this compound. The absolute configuration of the 3-hydroxyfatty acid moiety of euphrasianins was found to be 'R', based on alkaline hydrolysis and methylation experiments and subsequent chiral GC analysis. Interestingly, euphrasianins C and E were exclusively detected by GC-MS in extracts of E. tetraquetra (seacliff eyebright) collected in Ireland, suggesting potential chemotaxonomic relevance of these novel cuticular wax constituents.

References:

[1] Yeats T. H., Rose J. K. C. The Formation and Function of Plant Cuticles, Plant Physiology 2013; 163: 5 – 20.

[2] Lorenz P., Knittel D. N., Conrad J., Lotter E. M., Heilmann J., Stintzing F. C., Kammerer D. R. 1-O-Acetyl-3-[(3R)-hydroxyfatty acid]-glycerols from cuticular waxes of Euphrasia rostkoviana Hayne and E. tetraquetra (Brébiss.) Arrond., manuscript in preparation.