In the course of a national program ((co)Operation SKD) for the identification of secondary metabolites in algae, specimens of the culture collection of algae at the University of Innsbruck (ASIB 505) were investigated. A promising candidate (V224; [1]) producing a mycosporin like amino acid (MAA) - tentatively assigned by the observed absorption maximum at 320 nm in LC-DAD-MS extract screening - was investigated in detail. Beside morphological classification genetically data were generated and compared with the NCBI database. Due to the lack of large sequence analogies with database entries, we assume that the investigated alga has not been sequenced before. For a further phylogenetic classification the marker genes rbcL and 18S rDNA were analyzed. Phylogenetic trees based on rbcL sequences revealed a close relation to the genus Diplosphaera, while the ones based on the 18S sequences pointed to a closer relationship with the genus Stichococcus. Based on these results the investigated microalga was identified as member of Prasiolaceae and is situated between the genera Stichococcus and Diplosphaera.
Isolation and structure elucidation of the initially detected MAA by 1D- and 2D-NMR and (HR)-LC-MS experiments identified the novel compound as N2-(4,5-dihydroxy-5-(hydroxymethyl)-2-methoxy-3-oxocyclohex-1-en-1-yl)-N2-methylasparagine (figure 1), which is structurally related to the recently published Prasiolin isolated from Prasiola calophylla [2] and supports thereby the proposed phylogenetic classification.
Acknowledgments:
The authors thank FFG Project number 845423 for the financial support.
References:
[1] Gärtner G. ASIB - the Culture Collection of Algae at the Botanical Institute of the University at Innsbruck (Austria) Catalogue of Strains, Ber. nat.-med. Verein Innsbruck, Band 83, 1996: 45-69
[2] Hartmann A, Holzinger A, Ganzera M and Karsten U. Prasiolin, a new UV sunscreen compound in the terrestrial green macroalga Prasiola calophylla (Carmichael ex Greville) Kützing (Trebouxiophyceae, Chlorophyta), Planta 2016, 243(1)