Glycosyl compositions and structural characteristics of the potential immuno‐adjuvant active saponins in the Quillaja saponaria Molina extract Quil A

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Abstract
Fifty saponin components of Quil A, a commercially available extract from the bark of the South American tree Quillaja saponaria Molina, were partially structurally characterised. The molecular weights were determined by fast‐atom bombardment mass spectrometry. The glycosyl and elemental composition of all the saponins was determined by applying our recently developed method, monomer mapping, consisting of a computer program and accurate mass measurements. Support for the presumed identity of the aglycone, i.e. quillaic acid, was found in the accurate mass determination, 1H NMR measurement and chemical reactions. The saponin composition of Quil A was shown to consist of pairs. Within the 3‐O bound glycosyl moiety of a pair there was a structural difference: a pentose and rhamnose were interchanged. Structural differences between different pairs were located in the 28‐O bound glycosyl moiety. A structural element, unknown to date and of which the elemental composition was deduced to be C8H12O5, was found in the 28‐O bound glycosyl moiety of several saponins.