Iridoids are cyclopentan-[c]-pyran diterpenoids

In plants they mostly occur as glycosides (and therefore they can be extracted withaqueous methanol), but some of them occur in free form or as dimers

During the drying of the leaves of plant species rich in iridoids, colour changes can occurdue to the polymerization of the unstable iridoid aglycones liberated by hydrolysis.

The darkening or blackening of dried leaves can't thus be indicative of the presence of iridoids.

The valepotriates are epoxy-iridoid esters, triesters of a monoterpene alcohol, with the structure of an iridoid cyclopenta-(c)-pyran and an attached epoxide ring.

These drugs degrade during storage and this process is accelerated by heating or alkaline pH

These iridoid esters are unstable and easily form degradation products

Isovaleric acid,the compound responsible for the typical unpleasant odour of mostly older valerianroots, is also due to this degradation process.

Foeniculi fructus

Lupuli flos

Aurantii amari epicarpium et mesocarpium

Plantaginis laceaolatae folium