Poly-glycosidic iridoids. Occurrence, chemophenetics, and biological activities

In this chapter, the occurrence, chemophenetic value, and biological activities of poly-glycosidic iridoids are reported for the first time. Literature survey has clearly shown that their base compounds are mainly aucubin, catalpol, genipin, harpagide, and mono-melittoside, whereas the main further saccharidic residues are glucose, galactose, and rhamnose, which link to different points of the iridoid base structure. Di-glycosidic iridoids represent the main compounds of this kind. Some chemophenetic markers could also be individuated: 5-O-allosyl-antirrhinoside, 5-allosyloxy-aucubin, 6-O-α-L-rhamnopyranosyl catalpol, 6-O-α-L-(4″-O-trans-cinnamoyl)-rhamnopyranosyl-catalpol, loganic acid-6′-O-β-D-glucoside, melittoside, pulverulentoside I, saccatoside, scropolioside A, scropolioside B, scrovalentinoside, sinuatol, verbaspinoside, and di-glycosidic derivatives of genipin, harpagide, teuhircoside, and theviridoside at different levels. In addition, some poly-glycosidic iridoids have been studied for their biological activities, mainly showing antioxidant, antiinflammatory, and antitumor effects, with most of these studies regarding catalpol derivatives and the major number of pharmacological effects reported for 5-allosyloxy-acubin, rehmannioside A, and sinuatol. When possible, the efficacy values of the iridoidic base compounds in comparison with those relative to their poly-glycosidic derivatives have also been presented. Yet, there is still a lot to do, and this chapter has also been meant to promote more phytochemical, chemophenetic, and biological studies on these poly-glycosidic iridoids.