Three new hydroxycinnamic acid amides from Helianthus annuus 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.