2'-hydroxyoleacein from Olea europaea: Isolation, synthesis and anti-inflammatory evaluation

Olive leaves are an abundant agro-industrial by-product rich in phenolic secoiridoids and a constant source of bioactive compounds. An ultrasound-assisted extraction of ambient air-dried Olea europaea leaves from the "Lianolia" variety with water at room temperature followed by ethyl acetate partitioning, afforded an oleacein-rich fraction. HPLC-DAD identified oleacein as the major constituent, while LC-HRMS (Orbitrap) analysis revealed a prominent oleacein-like metabolite bearing one additional oxygen atom among the eluting peaks. Guided fractionation by MPLC and preparative HPLC led to the isolation of this previously undescribed secoiridoid. Comprehensive 1D/2D NMR spectroscopy combined with HRMS/MS analysis established its structure as 2'-hydroxyoleacein (2'-OH OLEA), a previously unreported natural compound, occurring as an approximately equimolar mixture of (2'R) and (2'S) epimers. To corroborate the structural assignment and provide reference material, 2'-OH OLEA was synthesized from oleuropein. Moreover, two methoxy-derivatives of the previously undescribed compound, namely 3,3-dimethoxy-2'-hydroxyoleacein and 3,3,2'-trimethoxy-oleacein, were isolated in small amounts and characterized. In inflammation-relevant assays, 2'-OH OLEA potently inhibited isolated human recombinant 5-lipoxygenase (IC₅₀ = 0.22 ± 0.09 μM) but failed to suppress 5-lipoxygenase product formation in activated human neutrophils and showed no inhibition of isolated COX-1/COX-2. Overall, this work expands the phytochemical landscape of olive-leaf secoiridoids and links a previously undescribed oleacein derivative to selective cell-free 5-lipoxygenase inhibition.