(R)-(-)-Aloesaponol III 8-Methyl Ether from Eremurus persicus: A Novel Compound against Leishmaniosis

Abstract

Leishmaniosis is a neglected tropical disease which affects several millions of people worldwide. The current drug therapies are expensive and often lack efficacy, mainly due to the development of parasite resistance. Hence, there is an urgent need for new drugs effective against Leishmania infections. As a part of our ongoing study on the phytochemical characterization and biological investigation of plants used in the traditional medicine of western and central Asia, in the present study, we focused on Eremurus persicus root extract in order to evaluate its potential in the treatment of leishmaniosis. As a result of our study, aloesaponol III 8-methyl ether (ASME) was isolated for the first time from Eremurus persicus root extract, its chemical structure elucidated by means of IR and NMR experiments and the (R) configuration assigned by optical activity measurements: chiroptical aspects were investigated with vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectroscopies and DFT (density functional theory) quantum mechanical calculations. Concerning biological investigations, our results clearly proved that (R)-ASME inhibits Leishmania infantum promastigotes viability (IC₅₀ 73 µg/mL), inducing morphological alterations and mitochondrial potential deregulation. Moreover, it is not toxic on macrophages at the concentration tested, thus representing a promising molecule against Leishmania infections.

Keywords: (R)-aloesaponol III-8 methyl ether; Eremurus persicus; drug identification; leishmaniosis; plant extract.

Figure 1

ESI-MS (positive ion mode, full scan) of the most abundant metabolite of EE.

Figure 2

HPLC-UV chromatogram of the compound isolated through flash chromatography (λ: 270 nm).

Figure 3

Chemical structure of (R)-aloesaponol III- 8 methyl ether ((R)-ASME).

Figure 4

Left: Calculated (black trace) and experimental (red trace) VCD (top) and IR (bottom) spectra of 1; Right: DFT Calculated (PCM/ACN, polarizable continuum model for acetonitrile-black trace) and experimental (blue trace) ECD (top) and UV (bottom) spectra of 1 in acetonitrile. In the inset, we repeat the magnified portions of spectra between 280 and 450 nm; in this region, we also report experimental ECD and UV data for chloroform solution (red trace). The calculations are in the PCM/CHCl₃ approximation (see text).

Figure 5

Effects of (R)-ASME on L. infantum promastigotes viability. Cultures of log-phase promastigotes (2 × 10⁶ cells·mL⁻¹) were incubated at 26 °C for 24 h at different drug concentrations. Values are expressed as means and SEM.

Figure 6

Effects of (R)-ASME on total cell number of L. infantum promastigotes, along the time of incubation. Each value represents the mean ± SEM from three independent experiments (**** p < 0.0001, compared to control; ns, not significant).

Figure 7

Optical microscopy observation of L. infantum promastigotes exposed to (R)-ASME (A); and to DMSO (control cells) (B); for 4 h (1); and 24 h (2). Hanging drop in phase contrast (magnification 100× and 200×) and Giemsa staining (magnification 1000×).

Figure 8

Effects of (R)-ASME on macrophage viability. Different concentrations (1.0 × IC₅₀, 1.5 × IC₅₀ and 2 × IC₅₀) were tested on macrophage cells (RAW 264.7) to evaluate cytotoxicity on mammalian cells.