oleanane and cycloartane

Triterpenoids and saponins have a broad range of pharmacological activities. Unlike most legumes which contain mainly oleanane-type scaffold, Astragalus membranaceus contains not only oleanane-type but also cycloartane-type saponins, for which the biosynthetic pathways are unknown.. This work aims to study the function and catalytic mechanism of oxidosqualene cyclases (OSCs), one of the most important enzymes in triterpenoid biosynthesis, in A. membranaceus.. Two OSC genes, AmOSC2 and AmOSC3, were cloned from A. membranaceus. Their functions were studied by heterologous expression in tobacco and yeast, together with in vivo transient expression and virus-induced gene silencing. Site-directed mutagenesis and molecular docking were used to explain the catalytic mechanism for the conserved motif.. AmOSC2 is a β-amyrin synthase which showed higher expression levels in underground parts. It is associated with the production of β-amyrin and soyasaponins (oleanane-type) in vivo. AmOSC3 is a cycloartenol synthase expressed in both aerial and underground parts. It is related to the synthesis of astragalosides (cycloartane-type) in the roots, and to the synthesis of cycloartenol as a plant sterol precursor. From AmOSC2/3, conserved triad motifs VFM/VFN were discovered for β-amyrin/cycloartenol synthases, respectively. The motif is a critical determinant of yield as proved by 10 variants from different OSCs, where the variant containing the conserved motif increased the yield by up to 12.8-fold. Molecular docking and mutagenesis revealed that Val, Phe and Met residues acted together to stabilize the substrate, and the cation-π interactions from Phe played the major role.. The study provides insights into the biogenic origin of oleanane-type and cycloartane-type triterpenoids in Astragalus membranaceus. The conserved motif offers new opportunities for OSC engineering.

Topics: Astragalus propinquus; Molecular Docking Simulation; Saponins; Triterpenes

Phytochemical analysis of the tubers of

Topics: Antineoplastic Agents, Phytogenic; Cell Survival; Glycosides; HL-60 Cells; Humans; Oleanolic Acid; Plant Tubers; Ranunculaceae; Triterpenes

Four new cycloartane and one new oleanane-type glycosides were isolated from Astragalus pennatulus along with five known cycloartane-type glycosides. The structures of the new compounds were established as 3-O-β-D-xylopyranosyl-6-O-β-D-glucopyranosyl-3β,6α,16β-trihydroxy-24-oxo-20(R),25-epoxycycloartane (1), 3-O-[β-D-glucuronopyranosyl-(1 → 2)-β-D-xylopyranosyl]-3β,16β,24α-trihydroxy-20(R),25-epoxycycloartane (2), 3-O-[β-D-glucuronopyranosyl-(1 → 2)-β-D-xylopyranosyl]-3β,16β,25-trihydroxy-20(R),24(S)-epoxycycloartane (3), 3,25-di-O-β-D-glucopyranosyl-6-O-β-D-xylopyranosyl-3β,6α,16β,25-tetrahydroxy-20(R),24(S)-epoxycycloartane (4), 29-O-α-L-rhamnopyranosyl-abrisapogenol B (5) by 1D and 2D-NMR experiments along with ESIMS and HRMS analyses. The aglycone of compound 1, 3β,6α,16β-trihydroxy-24-oxo-20(R),25-epoxycycloartane, is reported for the first time. The cytotoxic activity of the isolated compounds was evaluated against three cancer cell lines including A549 (human lung adenocarcinoma), A375 (human melanoma) and DeFew (human B lymphoma) cells. None of the tested compounds caused a significant reduction of the cell number.

Topics: Astragalus Plant; Cell Line, Tumor; Glycosides; Humans; Molecular Structure; Oleanolic Acid; Triterpenes

From the roots of Astragalus kahiricus DC., three known saponins, namely, astraversianin VI, astraversianin X, astragaloside VIII, and a new saponin were isolated and identified by spectral data. The structure of the latter was elucidated by spectral means and assigned as cycloastragenol 3- O-[ beta- D-(2',3'-diacetyl, 4'- trans-2-butenoyl)-xylopyranosyl], 6- O- beta- D-xylopyranoside (kahiricoside I). From the aerial parts of A. hamosus L., the known compounds azukisaponin V and peregrinoside I were isolated. As judged by in vitro tests, the saponins isolated from Astragalus spp. endemic to Egypt were not cytotoxic against a variety of human cancer cells. However, dose-related modulation of lymphocyte proliferation was observed, and structure-activity relationships are described.

Topics: Adjuvants, Immunologic; Animals; Astragalus Plant; Dose-Response Relationship, Drug; Egypt; Humans; Lymphocytes; Magnetic Resonance Spectroscopy; Medicine, Traditional; Mice; Mice, Inbred Strains; Oleanolic Acid; Phytotherapy; Plant Extracts; Plant Roots; Saponins; Triterpenes; Tumor Cells, Cultured