Molecular Complexes of Ivy Triterpene Glycosides with Cholesterol

Resumo

The paper reports preparation of molecular complexes of cholesterol with dominant triterpene saponins from members of the ivy genus Hedera L. (Araliaceae Juss.), that is, monodesmosidic glycoside α-hederin (hederagenin 3-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranoside) and bisdesmosidic glycoside hederasaponin C (hederagenin 3-O-α-L-rhamnopyranosyl-(1→2)-O-α-L-arabinopyranosyl-28-О-α-L-rhamnopyranosyl-(1→4)-О-β-D-glucopyranosyl-(1→6)-О-β-D-glucopyranoside), as well as with minor monodesmosidic glycoside hederoside F (hederagenin 3-О-β-D-glucopyranosyl-(1→2)-О-β-D-glucopyranoside). The complexation has been investigated by methods of isomolar series in the spectrophotometric version and FT-IR spectroscopy with a universal optical attenuated total reflection (ATR) accessory. It has been shown that α-hederin, hederasaponin C, and hederoside F form 1 : 1 complexes with cholesterol, having a stability constants (5.6 ± 0.1) × 10⁴, (4.7 ± 0.1) × 10⁴ and (6.0 ± 0.6) × 10⁴ M^–1, respectively (in 70% aqueous ethanol at 25°С). The constants are calculated on the basis of isomolar curves. The complexes of cholesterol with ivy monodesmosidic glycosides are more stable. Intermolecular interaction in the complexes is carried out by hydrogen bonds formation of type –С=О⋅⋅⋅Н–О– (for monodesmosidic glycosides) and –(Н)О⋅⋅⋅Н–О– (for bisdesmosidic glycoside). Hydrophobic contacts of the aglycone part of glycosides (hederagenin) with a lipophilic cholesterol molecule are possible. As a result, changes in some frequencies of the absorption bands of CH bonds are observed, which was established by IR-spectroscopy.