Tris- and tetrakis-iridoids: a review on their occurrence in plants, chemophenetic value and pharmacological activities

In this review paper, the occurrence in plants, structural variability, possible chemophenetic value and pharmacological activities of tris- and tetrakis-iridoids were reported altogether for the first time. In particular, the exact number of these compounds discovered so far was presented, listing their names and detailing the plant species of their recovery with their organs and belonging family as well as the methodologies adopted for their extraction, separation and identification. The structural characteristics of tris- and tetrakis-iridoids were displayed with a particular focus on their specific peculiarities. A chemophenetic evaluation to individuate possible chemophenetic markers among tris- and tetrakis-iridoids was performed on the base of their occurrence at the species, genus and family levels along with a parallel discussion on the regularity of their distribution in the different plant organs. The pharmacological studies on tris- and tetrakis-iridoids were shown after a complete survey of literature data. All these data were widely compared with respect to simple iridoids and bis-iridoids when possible, too. This review paper clearly demonstrates that the research on tris- and tetrakis-iridoids is far from being exhaustive under several aspects and may indeed represent a starting point for future works.