Biosynthesis significance of iridoids in chemosystematics

iridoids represent a large group of monoterpenoid compounds that apparently seem to be formed in plants by an alternative cyclization of geranyl diphosphate. the structures of these compounds are based on a cyclopentan-[c]-pyran skeleton, carbocyclic iridoids, and oxidative cleavage at the 7,8-bond of the cyclopentane moiety affords the so called secoiridoids. on biogenetic grounds the iridoid formation may be considered to start from iridodial cation and follow diversification through 27 different routes. iridoids have been used as chemical markers for the corniflorae, gentianiflorae, loasiflorae and lamiiflorae superorders. the number and nature of the iridoids occurring in plants are a measure of the complexity of the routes involved in their biosynthesis. in chemosystematics, the value of iridoid character shows important significance in plant classification, phylogeny and evolution