The presence of
aldehyde groups at C-23 and C-24 of the triterpen aglycon moiety was disclosed in 1H NMR spectra of both the Riedel de Haen
saponin (R) (delta 9.336) and Quillaja saponaria QuilA
saponin (delta 9.348). The sign of the C-28 acylated linked moiety (delta 176) was present in both
saponins, while the delta 171 at C-28 (carboxy group) corresponding to the deacylated
saponin, was only detected in the QuilA preparation, indicating 50% of hydrolysis of the
ester moiety, probably due to the storage in aqueous
solution. The normoterpen moiety was present in both
saponins (signals at delta 14-18). The chemical removal of
saponin glicidic moieties gave rise to their sapogenin fractions. Their 1H NMR spectra showed the presence of two signals (delta 9.226 and 9.236) for sapogenin R and two signals (delta 9.338 and 9.352) for the QuilA sapogenin. The intensity of the signals suggested two conformational isomers of sapogenin R in the ratio 53% of equatorial
aldehyde group to 47% of axial
aldehyde group, and two conformational isomers of QuilA sapogenin in the ratio 76% of equatorial
aldehyde group to 24% of axial
aldehyde group. The chemical treatment abolished the
saponin slight in vivo toxicity, reduced their hemolytic potential, did not affect their
aldehyde contents, but gave rise to an enriched axial
aldehyde-containing sapogenin R with enhanced potential on antibody humoral response (
anti-IgM,
IgG,
IgG1,
IgG2a,
IgG2b and
IgG3) and to an enriched equatorial
aldehyde-containing QuilA-sapogenin that induced a mainly cellular specific immune response (increased intradermal response to leishmanial
antigen and IFNgamma sera levels) and effective protection against murine
infection by L. donovani (77% reduction in liver parasitic load). Our results suggest that the Riedel de Haen
saponin is probably a Quillaja saponaria
saponin.