Isolation of iridoid glucosides from Euphrasiae herba using droplet counter-current chromatography

Euphrasia officinalis is a hemiparasite belonging to the family of Orobanchaceae. It grows unattached or attached to various host plants in grasslands of Eurasia. Traditionally but not evidence based used for various eye sufferings it is also known as eyebright (Augentrost). Typical active constituents beside phenolics such as phenylethanoids, lignans, phenolic acids and flavonoids are iridoids like aucubin, catalpol, euphroside, melampyroside, boschnaloside and others. Interestingly, the transfer of iridoids from the host plant to Euphrasia species was described, too [1]. For isolation of iridoid glucosides from Euphrasiae herba a practicable droplet counter-current chromatography method was developed according to iridoid isolations from Premna japonica [2]. On the basis of TLC pre-experiments the solvent system CHCl₃:MeOH:H₂O:n-PrOH 9:12:8:1 was used in descending mode. The iridoid enriched sample was gained from a methanolic extract by separation against apolar solvents and by a column chromatography with Al₂O₃. The structures of isolated iridoids were established by spectroscopic evidence. Thus the results obtained provide possible marker compounds useful for future pharmacopoeial analytics as well as for pharmacological investigations on eye diseases.

Acknowledgements: Leipzig University, Tobias Liebold

References: 1. Rasmussen, L.S. et al. (2006) Biochem. Syst. Ecol. 34: 763–765.

2. Otsuka, H. et al. (1991) Phytochemistry 30: 1917–1920.