Saponins from Quillaja saponaria and Quillaja brasiliensis: Particular Chemical Characteristics and Biological Activities

<i>Quillaja saponaria</i> Molina represents the main source of saponins for industrial applications. <i>Q. saponaria</i> triterpenoids have been studied for more than four decades and their relevance is due to their biological activities, especially as a vaccine adjuvant and immunostimulant, which have led to important research in the field of vaccine development. These saponins, alone or incorporated into immunostimulating complexes (ISCOMs), are able to modulate immunity by increasing antigen uptake, stimulating cytotoxic T lymphocyte production (Th1) and cytokines (Th2) in response to different antigens. Furthermore, antiviral, antifungal, antibacterial, antiparasitic, and antitumor activities are also reported as important biological properties of <i>Quillaja</i> triterpenoids. Recently, other saponins from <i>Q. brasiliensis</i> (A. St.-Hill. &amp; Tul.) Mart. were successfully tested and showed similar chemical and biological properties to those of <i>Q. saponaria</i> barks. The aim of this manuscript is to summarize the current advances in phytochemical and pharmacological knowledge of saponins from <i>Quillaja</i> plants, including the particular chemical characteristics of these triterpenoids. The potential applications of <i>Quillaja</i> saponins to stimulate further drug discovery research will be provided.