The aim of the bioassay-guided fractionation was the selection of the most potent group of compounds responsible for the protection of sunflower bee pollen grains. Synthesis of prospective antifungal polyamides of hydroxycinnamic acids was based on previous structural elucidation of ethanol soluble fraction by 1H,1H-PFG-COSY, 1H,13C-HSQC, FT-IR, FT-Raman, and LC-MS experiments. The main compounds found were tri- p-coumaroylspermidines accompanied by other HCAA of spermidine and putrescine. Several model HCAA derivatives were prepared to test their antifungal activity against widespread spoilage fungi ( A. niger 42 CCM 8189, F. culmorum DMF 0103, and P. verrucosum DMF 0023). A. niger CCM 8189 and F. culmorum DMF 0103 exhibited higher resistance to the antifungal effects of hydroxycinnamic acid amides, whereas P. verrucosum DMF 0023 was the most sensitive strain. It has been discovered the effect of HCAA polarity on the role of secondary metabolites in the microbial protection of pollen grains. The combination of bioassay-guided fractionation, structural elucidation, selection of prospective compounds, and their synthesis to determine their antifungal properties could be considered as an original approach.
Keywords: Helianthus annuus L.; antifungal activity; hydroxycinnamic acid amides; structural elucidation; sunflower bee pollen.