Daming Zhu1* and Wenbin Tuo2
QS-21 is one of the active fractions of the bark of Chilean tree, Quillaja saponaria, purified using a reverse-phase chromatography (RP-HPLC) [1-3]. QS denotes its source as Q. saponaria and the number 21 as the identity of the RP-HPLC peak [2]. QS-21 is an acylated 3, 28-bisdesmodic triterpene glycosides (1,3) or “saponin” with a molecular formula of C92O46H148 and molecular weight of 1990 Da [1]. It is one of the most potent immunological adjuvants that has been widely used [4-8].
