Líf - og heilbrigðisvísindaráðstefna Háskóla Íslands 2021

Chiral separation and spatial distribution of usnic acid enantiomers in lichens

Main author: Maonian Xu
Institution or Company: Faculty of Pharmaceutical Sciences, University of Iceland

Co-Authors, Institution or Company:
Starri Heiðmarsson, Icelandic Institute of Natural History, Akureyri Division. Elín Soffía Ólafsdóttir, Faculty of Pharmaceutical Sciences, University of Iceland.

Introduction: Life is so selective in molecular chirality that an overwhelming majority of substances are homochiral. Enantiomers of usnic acid (UA) are potent antibiotic compounds produced by lichen-forming fungi, and each enantiomer shows distinct bioactivities. This study aimed to develop a chiral UHPLC method to separate UA isomers and to characterize UA distribution in lichen.

Methods: UA enantiomers were separated using a chiral UHPLC method. Mass spectrometry imaging and fluorescence microscopy were used to visualize the spatial distribution of UA enantiomers in lichen cross sections.

Results: The optimal mobile phase for UA enantio-separation consisted MeOH:ACN:TFA 83:17:0.1 (v/v/v) with a resolution of 3.1. Usually only one predominant UA enantiomer was detected, and two isomers can be present. Total UA contents ranged from 0.55 to 5.82% in the lichen species analyzed. Spatial distribution of UA in lichen thalli showed that it is centralized and located on the surface.

Conclusions: A chiral UHPLC method has been developed and validated for UA enantio-separation and quantification. The production of usnic acids is localized on the thallus surface.


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