Chemical Constituents of the Aquatic Plant Schoenoplectus lacustris: Evaluation of Phytotoxic Effects on the Green Alga Selenastrum capricornutum

Forty-nine secondary metabolites were isolated from aqueous and alcoholic extracts of the aquatic plant Shoenoplectus lacustris. All compounds were characterized based on spectroscopic data. Eleven free and glycosylated low-molecular polyphenols, 17 cinnamic acid and dihydrocinnamic acid derivatives, 11 flavonoids, and 10 C₁₃ nor-isoprenoids were identified. The structure of the new compound, 1-benzoyl-glycerol-2-α-l-arabinopyranoside, was elucidated by 2D NMR experiments (COSY, HSQC, HMBC, NOESY). To evaluate potential phytotoxic effects, all compounds were tested on the green alga Selenastrum capricornutum, a unicellular organism commonly used in tests of toxicity as a bioindicator of eutrophic sites. The most active compound was (−)-catechin, showing an inhibition similar to that of the algaecide CuSO₄.