Three new hydroxycinnamic acid amides from <i>Helianthus annuus</i> L. tubular flowers

This study presents the first phytochemical investigation of Helianthus annuus L. tubular flowers, leading to the isolation of three undescribed polyamine-conjugated hydroxycinnamic acid amides. These were characterised as N1,N5,N10,N14-tetra-p-coumaroylspermine analogues with distinct Z/E configurations (1–3). Their structures were elucidated through comprehensive spectroscopic analysis, including 1D/2D NMR and HR-ESIMS. All isolated compounds were evaluated for their antioxidant activity using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, which demonstrated that each compound possessed significant radical scavenging properties with IC50 values ranging from 4.34 to 9.35 mM.