16 April 2020

Abstract: A metabolite screening of cyanobacteria was performed by nuclear magnetic resonance (NMR) analysis of the soluble material obtained through sequential extraction of the biomass with three different extractive ability solvents (hexane, ethyl acetate, and methanol). Twenty-five strains from the Coimbra Collection of Algae (ACOI) belonging to different orders in the botanical code that represent three subsections of the Stainer-Rippka classification were used. The 1H NMR spectra of hexane extracts showed that only two strains of Nostoc genus accumulated triacylglycerols. Monogalactosyldiacyl- glycerols and digalactosyldiacylglycerols were the major components of the ethyl acetate extracts in a mono- to digalactosyldiacylglycerols ratio of 4.5 estimated by integration of the signals at d 3.99 and 3.94 ppm (sn3 glycerol methylene). Oligosaccharides of sucrose and mycosporine-like amino acids, among other polar metabolites, were detected in the methanolic extracts. Strains of Nostocales order contained heterocyst glycolipids, whereas sulpho- quinovosyldiacylglycerols were absent in one of the studied strains (Microchaete tenera ACOI 1451). Phosphathidylglycerol was identified as the major phospholipid in the methanolic extracts together with minor amounts of phosphatidylcholine based on 1H, 31P 2D correlation experiments. Chemo- taxonomic information could be easily obtained through the analysis of the d 3.0–0.5 ppm (fatty acid distribution) and d 1.2–1.1 ppm (terminal methyl groups of the aglycons in heterocyst glycolipids) regions of the 1H NMR spectra of the ethyl acetate and methanol extracts, respectively.

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