Metabolic and functional diversity of saponins, biosynthetic intermediates and semi-synthetic derivatives

Saponins are widely distributed plant natural products with vast structural and functionaldiversity. They are typically composed of a hydrophobic aglycone, which is extensivelydecorated with functional groups prior to the addition of hydrophilic sugar moieties, to resultin surface-active amphipathic compounds. The saponins are broadly classified astriterpenoids, steroids, or steroidal glycoalkaloids, based on the aglycone structure fromwhich they are derived. The saponins and their biosynthetic intermediates display a variety ofbiological activities of interest to the pharmaceutical, cosmetic and food sectors. Althoughtheir relevance in industrial applications has long been recognised, their role in plants isunderexplored. Recent research on modulating native pathway flux in saponin biosynthesishas demonstrated the roles of saponins and their biosynthetic intermediates in plant growthand development. Here we review literature on the effects of these molecules on plantphysiology, which collectively implicate them in plant primary processes. The industrial usesand potential of saponins are discussed with respect to structure and activity, highlighting theundoubted value of these molecules as therapeutics.