The Cannizzaro-like metabolites of secoiridoid glucosides in some olive cultivars

Oleuropein (the most abundant bitter principle) and its analogue ligstroside, both secoiridoid biophenols, were extracted from Hojiblanca black olives and analysed by preparative flash chromatography and HPLC. During olive growth, maturation and processing, these compounds undergo biological and technological degradation to various metabolites, by enzymatic degradation through esterases, phenoloxidases and β-glucosidases. An enzymatic system with regiospecific Cannizzaro-like activity could be responsible for two novel metabolites, isolated and characterised by 1H- NMR, 12C NMR and FAB-MS as hydroxycarboxylic and lactone derivatives of terpenoid origin from the precursor oleoside-11-methylester, formed from both secoiridoid biophenols. The occurrence of these two secoiridoid metabolites requires a thermodynamically controlled sequential process, via hydride rearrangements, through the complex metabolic pathway. The possible reaction sequence was interpreted by molecular calculations performed on competitive isomers. Copyright © 2004 Society of Chemical Industry