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.

INTRODUCTION: 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. OBJECTIVE: 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. METHODOLOGY: 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 ). RESULTS: 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. CONCLUSION: 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.

Aggregation Behavior of 6-Isocassine and N-Methyl-6-Isocassine: Insights into the Biological Mode of Action of Lipid Alkaloids.

The aggregation behavior of 6-isocassine and N-methyl-6-isocassine, two piperidin-3-ol alkaloids isolated respectively from the barks of Prosopis nigra and P. affinis, was investigated using a combination of NOE experiments and diffusion measurements in solvents of varying polarity and hydrogen bonding capacity. While the NOE enhancements for N-methyl-6-isocassine are positive, regardless of the solvent, those for 6-isocassine shift from negative to positive when going from chloroform-d to methanol-d(4) solution. In addition, despite the self-diffusion coefficients of both compounds being virtually identical in methanol-d4, N-methyl-6-isocassine diffuses nearly twice as fast as the non-methylated alkaloid in chloroform-d. The changes in rotational and translational dynamics observed between solvents for 6-isocassine suggest that the molecule forms dimeric head-to-head aggregates in non-polar aprotic environments, a behavior that could help explain the biological mode of action that has been proposed for this type of alkaloids.