Antioxidant micropeptins from a Microcoleus autumnalis-dominated benthic cyanobacterial mat from Western Ireland

• Published in: Phytochemistry (Oxford) Vol. 223; p. 114137
• Main Authors: O'Brien, Shauna, Alvariño, Rebeca, Kennedy, Bryan, Botana, Luis M., Thomas, Olivier P.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-07-2024
• Subjects: Anatoxin; Antioxidant; Antioxidants - chemistry; Antioxidants - isolation & purification; Antioxidants - pharmacology; Biofilms - drug effects; Cyanobacteria; Cyanobacteria - chemistry; Depsipeptides - chemistry; Depsipeptides - isolation & purification; Depsipeptides - pharmacology; Humans; Ireland; Microcoleus autumnalis; Micropeptins; Molecular Structure; Ireland; Anatoxin; Micropeptins; Antioxidant; Cyanobacteria; Microcoleus autumnalis
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2024.114137

Exploring the chemical diversity present in cyanobacterial mats increasingly frequent in fresh and marine waters is imperative for both evaluating risks associated with these diverse biofilms and their potential for biodiscovery. During a project aimed at the study of the (eco)toxicity of benthic cyanobacteria blooming in some lakes of the West of Ireland, three previously undescribed ahp-cyclodepsipeptides micropeptin LOF941 (1), micropeptin LOF925 (2) and micropeptin LOF953 (3) were isolated from the Microcoleus autumnalis-dominated benthic cyanobacterial biofilm collected from the shore of Lough O'Flynn, Co. Roscommon, Ireland. Their structures remain consistent in their amino acid sequence with the presence of an unusual methionine, and differ by their exocyclic side chains. The planar structures of the previously undescribed micropeptins were elucidated by 1D and 2D NMR and HRESIMS analyses, and their 3D configurations assessed by ROESY NMR and Marfey's analyses. The three isolated compounds showed no cytotoxic effects and all three compounds were shown to exhibit antioxidant properties, with 1 showing the highest bioactivity. Additionally, several micropeptin analogues are proposed from the methanolic fraction of the biofilm extract by UHPLC-HRESIMS/MS analysis and molecular networking. Notably, the known cyanotoxins anatoxin-a and dihydroanatoxin-a were annotated in the molecular network therefore raising issues about the toxicity of this cyanobacterial mat.
Structures of the three micropeptins isolated from a cyanobacterial mat dominated by Microcoleus autumnalis in an Irish lake. [Display omitted]
•Three new micropeptins isolated from a cyanobacterial mat in a lake of the west coast of Ireland.•A methionine residue present in all analogues as shown by molecular networking analysis.•Antioxidant activity displayed by the three isolated cyclopeptides.•Anatoxin-a and dehydroanatoxin-a identified in the extract.