Figure 2.

Chemical structures of major secoiridoids identified in olive leaves, pomace and in olive oil mill wastewater using MS techniques. Note that hemiacetalic forms of elenolic acid and of oleuropein and ligstroside aglycones are reported; dialdehydic open-structure isoforms are indicated for oleac(e)in, oleocanthal and decarboxymethyl-elenolic acid. The carbon atoms numbering typically adopted for secoiridoids has been reported for oleuropein and oleuroside to emphasize the positional isomerism occurring for these compounds, related to the position of the exocyclic C=C bond.