Structural characterisation of new immunoadjuvant saponins from leaves and the first study of saponins from the bark of Quillaja brasiliensis by liquid chromatography electrospray ionisation ion trap mass spectrometry.

Abstract

Quillaja brasiliensis (St. A. -Hil. & Tul) Mart (Quillajaceae) is a species native to South America, which is rich in saponins. Saponins are used in different industries, so there is a constant demand for this type of compound. Based on the wide range of applications for the saponins found in this species, notably as immunoadjuvants, we conducted a comprehensive study of this tree and its saponins. The purpose of this work is to complete the characterisation of the immunoadjuvant saponin fraction from Q. brasiliensis leaves and further study the saponin fraction obtained from Q. brasiliensis bark. Saponin fractions were studied using mass spectrometry in combination with classical methods of monosaccharide and methylation analysis. We performed direct infusion and liquid chromatography/electrospray ionisation ion trap multiple-stage mass spectrometry (DI-ESI-IT-MSn and LC-ESI-IT-MS2 ). Seventy-five saponins, 21 from leaves and 54 from bark, were tentatively identified according to their molecular mass, fragmentation pattern and chromatographic behaviour. This work represents the first investigation of saponins from the bark of Q. brasiliensis and some of them presented new structural motifs not previously reported in the genus Quillaja. The efficiency and selectivity of the data dependent LC-MS2 method allowed the rapid profiling of saponins from Q. brasiliensis. The results of the monosaccharide and methylation analysis performed in saponins from Q. brasiliensis fractions and Q. saponaria Molina (Quillajaceae) fraction gives further support to the structures proposed according to the mass spectral data, validating the strategy used in the present work.