Acid rearrangement of secoiridoids related to oleuropein and secologanin

Acid treatment of an iridoid glycoside results in the cleavage of the acetal bond between the sugar unit and the monoterpenoid aglycon. Iridoids possessing non-conjugated enol ether systems, however, undergo the hydration of the iridoid enol ether functionality in acid medium, as well as the hydrolysis of the bond. We examined the acid rearrangement of secoiridoids such as oleuropein (1) and secologanin (2) and their reduction products oleuropeinol (3) and secologaninol (4), to examine whether similar behaviour also occurs in this case. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).