Progress in the synthesis of iridoids and related natural products

A number of iridoids and secoiridoids, which possess a wide range of biological activity, have been isolated from plants and insects—for example, dihydronepetalactone, isodihydronepetalactone, iridomyrmecin, isoiridomyrmecin, neoneptalactone, nepetalactone, actinidine (iridoid alkaloid), and dihydroactinidiolid (carotenoid metabolite), the mixture being a potent attractant for cat, have been isolated from Actinidia polygama Miq. Similarly, neomatatabiol, isoneomatatabiol, dehydroiridodiol, iridodiol, and matatabiol have been isolated from the same plant and the mixture serves as a potent attractant for lacewing. From a synthetic and biosynthetic point of view, dehydroiridodial, chrysomelidial, and iridodial are considered to be the central intermediates for the biosynthesis of other iridoids from Actinidia polygama Miq. The chemical interconversion of these iridoids is presented in the chapter. The broad diversity of both structure and biological activity exhibited by iridoids and secoiridoids has generated much interest in their general synthesis starting from a common intermediate. The chapter introduces two general methodologies for the synthesis of polyfunctional iridoids and related natural products.