Abstract
Mycosporine-like amino acids (MAAs), a group of small secondary metabolites found in algae, cyanobacteria, lichens and fungi, have become ecologically and pharmacologically relevant because of their pronounced UV-absorbing and photo-protective potential. Their analytical characterization is generally achieved by reversed phase HPLC and the compounds are often quantified based on molar extinction coefficients. As an alternative approach, in our study a fully validated hydrophilic interaction liquid chromatography (HILIC) method is presented. It enables the precise quantification of several analytes with adequate retention times in a single run, and can be coupled directly to MS. Excellent linear correlation coefficients (R2 > 0.9991) were obtained, with limit of detection (LOD) values ranging from 0.16 to 0.43 µg/mL. Furthermore, the assay was found to be accurate (recovery rates from 89.8% to 104.1%) and precise (intra-day precision: 5.6%, inter-day precision ≤6.6%). Several algae were assayed for their content of known MAAs like porphyra-334, shinorine, and palythine. Liquid chromatography-mass spectrometry (LC-MS) data indicated a novel compound in some of them, which could be isolated from the marine species Catenella repens and structurally elucidated by nuclear magnetic resonance spectroscopy (NMR) as (E)-3-hydroxy-2-((5-hydroxy-5-(hydroxymethyl)-2-methoxy-3-((2-sulfoethyl)amino)cyclohex-2-en-1-ylidene)amino) propanoic acid, a novel MAA called catenelline.
Highlights
Solar radiation reaching the Earth’s surface affects numerous biological functions in living organisms, and extensive exposure to UV-B (280–315 nm) and UV-A (315–400 nm) can cause significant stress and deleterious effects at the cellular level
Mycosporine-like amino acids are zwitterionic substances, which is relevant because hydrophilic interaction liquid chromatography (HILIC) phases are well known to exhibit ion-exchange mechanism too
Mostly due to a lack of standards, they were often quantified using “only” their specific extinction coefficients (ε); second, their isolation is tricky and extremely high ε values might lead to false “pure compounds”, purity has to be confirmed by NMR; third, their polar nature renders an analysis on conventional RP
Summary
Solar radiation reaching the Earth’s surface affects numerous biological functions in living organisms, and extensive exposure to UV-B (280–315 nm) and UV-A (315–400 nm) can cause significant stress and deleterious effects at the cellular level. Adaptation mechanisms are required for any living organism, and they have been studied extensively for higher plants already [1,2]. Mycosporine-like amino acids (MAAs), a group of small water-soluble compounds are especially relevant. Their photo protective potential can be explained by extremely high molar extinction coefficients up to 50,000, and to date more than 20 MAAs with absorption maxima between 309 and 360 nm have been identified [7,8,9]. Satisfactory separations, especially of highly polar derivatives, required either different methods for individual
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