Astramalabaricosides A–T, Highly Oxygenated Malabaricane Triterpenoids with Migratory Inhibitory Activity from Astragalus membranaceus var. mongholicus

Abstract

Twenty new malabaricane triterpenoids, astramalabaricosides A−T (1−20), were isolated from the roots of Astragalus membranaceus var. mongholicus (Astragali Radix). Their structures were determined by spectroscopic analysis, and the use of the circular dichroism exciton chirality method, quantum chemical calculations, and chemical methods. Malabaricane triterpenoids, an unusual group with the 6-6-5-tricyclic core, are distributed in plants (e.g., Simaroubaceae, Polypodiaceae, and Fabaceae), a marine sponge, and fungi, and their number obtained to date is limited. Compounds 1−20 were characterized as glycosides with a highly oxygenated side chain, and 13−20 were the first cyclic carbonate derivatives among the malabaricane triterpenoids. The stereocluster formed from the continuous hydroxylated chiral carbons in each highly oxygenated side chain and the 6-6-5-tricyclic core system were entirely segregated, and the independent identification of their stereoconfigurations required considerable effort. The migratory inhibitory and antiproliferative activities of 1−20 were evaluated by wound-healing and cell-viability assays, respectively. Most compounds showed significant migratory inhibitory activity, and a preliminary structure−activity relationship was developed. Malabaricane triterpenoids are being reported in the genus Astragalus for the first time.

Characterization of a Malabaricane-Type Triterpene Synthase from Astragalus membranaceus and Enzymatic Synthesis of Astramalabaricosides

“…All the spectroscopic data of 1, including MS, 1D NMR and 2D NMR, NOEs, and specific rotation, were in good agreement with those of arabidiol; thus, 1 was determined as arabidiol (Table S2; Figures S2 and S12− S22). 13,28 Similarly, compound 2 was elucidated as (3S,13S)malabarica-14 (27),17,21-trien-3β-ol compared with the reported data, including specific rotation (Table S2; Figures S2 and S23−S31). 17 The ratio of compounds 1 and 2 was 96:4, which is similar to that of arabidiol synthase AtPEN1.…”

“…(3S,13S)-Malabarica-14 (27),17,21-trien-3β-ol (2). White amorphous powder; [α] D 20 − 30 (c 0.1, CHCl 3 ); literature [α] D 25 − 7.88 (c 0.36, EtOH); 17 1 H NMR and 13 C NMR data, Table S2…”

“…(3S,13R)-Malabarica-14 (27) Molecular Docking of AmAS and Its Mutant. The threedimensional structure model of AmAS and its mutant were generated by Alphafold2 (Figure S7).…”

“…24−26 In addition, a few rare malabaricane-type 6,6,5-tricyclic triterpenoids, astramalabaricosides, were obtained with significant migratory inhibitory activity from Huangqi. 27 However, OSCs involved in malabaricane-type triterpenoid biosynthesis have remained undiscovered. Herein, we report, for the first time, the characterization of arabidiol synthase AmAS from A. membranaceus, which is responsible for the formation of the malabaricane-type tricyclic triterpenoid skeleton in the biosynthesis of astramalabaricosides.…”

“…Their dried root (Astragali Radix) was named as Huangqi and has been used as Tonifying Qi in traditional Chinese medicine (TCM) formulas with other Chinese herbal medicines . The chemical composition of Huangqi consists of triterpenoid saponins, polysaccharides, flavonoids, and alkaloids, which show a variety of pharmacological activities, such as antiviral, cytotoxic, immunomodulatory, and vascular protection. − Triterpenoid saponins are the main active components of Huangqi, of which cycloastragenol-type tetracyclic triterpenoids are considered as the most typically important and bioactive compounds. , Some oleanane-type, ursane-type, and lupane-type pentacyclic triterpenoids have also been isolated from Huangqi. , OSCs for the formation of these cycloartane-type, lupane-type, and oleanane-type skeletons were not characterized until recently from A. membranaceus . − In addition, a few rare malabaricane-type 6,6,5-tricyclic triterpenoids, astramalabaricosides, were obtained with significant migratory inhibitory activity from Huangqi . However, OSCs involved in malabaricane-type triterpenoid biosynthesis have remained undiscovered.…”