Isolation and Structural Characterization of Echinocystic Acid Triterpenoid Saponins from the Australian Medicinal and Food Plant Acacia ligulata

Abstract

The Australian plant Acacia ligulata has a number of traditional food and medicinal uses by Australian Aboriginal people, although no bioactive compounds have previously been isolated from this species. Bioassay-guided fractionation of an ethanolic extract of the mature pods of A. ligulata led to the isolation of the two new echinocystic acid triterpenoid saponins, ligulatasides A (1) and B (2), which differ in the fine structure of their glycan substituents. Their structures were elucidated on the basis of 1D and 2D NMR, GC-MS, LC-MS/MS, and saccharide linkage analysis. These are the first isolated compounds from A. ligulata and the first fully elucidated structures of triterpenoid saponins from Acacia sensu stricto having echinocystic acid reported as the aglycone. Compounds 1 and 2 were evaluated for cytotoxic activity against a human melanoma cancer cell line (SK-MEL28) and a diploid fibroblast cell line (HFF), but showed only weak activity.

Approaches to Investigate Selective Dietary Polysaccharide Utilization by Human Gut Microbiota at a Functional Level

“…Some glycomic analyses (e.g., glycosidic linkage), however, are conducted on unfractionated food polysaccharide mixtures (Usov, 2011;Xing et al, 2013Xing et al, , 2014Xing et al, , 2015bYu et al, 2017;Wood et al, 2018;Li et al, 2019;Xiong et al, 2020). Dietary oligosaccharides are typically analyzed after crude extraction using water or ethanol solutions and purification by solid phase extraction (Jaeger et al, 2017;Xing et al, 2017;Roberts et al, 2018;Little et al, 2019). Ultraviolet-visible spectrophotometry can be used to colorimetrically quantify total carbohydrates in food samples (e.g., total starch in a plant, total glycogen in meat) (Xing et al, 2009(Xing et al, , 2013(Xing et al, , 2014.…”

“…Several methods exist to provide a more detailed understanding of carbohydrate structures. For example, GC-MS/FID is a preeminent tool for linkage analysis (methylation analysis) of food carbohydrates (Usov, 2011;Xing et al, 2013Xing et al, , 2014Jaeger et al, 2017;Yu et al, 2017;Roberts et al, 2018;Wood et al, 2018;Li et al, 2019;Little et al, 2019). While HPAEC-PAD is a conventional tool for the analysis of food oligosaccharide composition, high-resolution mass spectrometry (e.g., MALDI-TOF-MS, LC-ESI-MS/MS) using MS and tandem MS (MS/MS) acquisition modes are becoming common methods to determine the accurate mass and linkage sequence of food oligosaccharides (Xing et al, 2015a;Jaeger et al, 2017;Roberts et al, 2018;Little et al, 2019).…”

“…For example, GC-MS/FID is a preeminent tool for linkage analysis (methylation analysis) of food carbohydrates (Usov, 2011;Xing et al, 2013Xing et al, , 2014Jaeger et al, 2017;Yu et al, 2017;Roberts et al, 2018;Wood et al, 2018;Li et al, 2019;Little et al, 2019). While HPAEC-PAD is a conventional tool for the analysis of food oligosaccharide composition, high-resolution mass spectrometry (e.g., MALDI-TOF-MS, LC-ESI-MS/MS) using MS and tandem MS (MS/MS) acquisition modes are becoming common methods to determine the accurate mass and linkage sequence of food oligosaccharides (Xing et al, 2015a;Jaeger et al, 2017;Roberts et al, 2018;Little et al, 2019). Notably, recently developed ESI-MS/MS fragmentation methods (e.g., charge transfer dissociation) have proven powerful for the detailed structural characterization of natural complex oligosaccharides, such as mixed linkage glucan and sulfated anions (Ropartz et al, 2016(Ropartz et al, , 2017Buck-Wiese et al, 2020).…”

“…High-performance size-exclusion chromatography (HPSEC) systems coupled to multiple detectors including refractive index (RI) detector, viscometer, and multiple-angle laser light scattering detectors are used to determine molecular weight, size, intrinsic viscosity, and conformational parameters of dietary polysaccharides (Xing et al, 2013(Xing et al, , 2014(Xing et al, , 2015bYu et al, 2017). The detailed structural features of food carbohydrates can be further elucidated using solution-state 1 H and 13 C NMR spectroscopy (Xing et al, 2014(Xing et al, , 2015a(Xing et al, ,b, 2017Jaeger et al, 2017). Fourier-transform infrared spectroscopy (FTIR) is used for non-destructive characterization of food carbohydrates, and the determination of the degree of substitution of polysaccharides (Duarte et al, 2002;Xing et al, 2014Xing et al, , 2015b.…”

Plant‐derived medicinal entomochemicals: an integrated approach to biodiscovery in Australia

“…Arguably, the most cited example is the Monarch butterfly (Danaus plexippus), whose larvae store cardenolides from milkweed (Asclepias) host plants, rendering the adults particularly unpalatable to avian predators (Brower and Moffitt 1974). Although the pharmacological properties of the Cossidae have not yet been investigated, a number of species contain bioactive chemicals that serve as pheromones or defence chemicals in larvae and adult moths ( (ACNT 1993;Bindon 1996;Peile and Bindon 1997;Latz 2018) Antioxidant, antidiabetic (L, P); antibacterial (B, L); anticancer (P) (Gulati et al 2012;Jaeger et al 2018) Phenolics, flavonoids, triterpenoid saponins (L, P); linoleic & oleic fatty acids (S) (Brown et al 1987;ACNT 1993;Gulati et al 2012;Jaeger et al 2017;Jaeger et al 2018 (Brown et al 1987;Haridas et al 2001;Jayatilake et al 2003) (Continues) Whether these compounds are plant-derived or synthesised de novo has not been determined; however, it is not unreasonable to expect that this insect family can acquire phytochemicals from their host plants. For example, Herrera et al (2016) suggest that one of the main components of a sex pheromone produced by the South American cossid moth, Chilecomadia valdiviana, is derived from a linoleic acid precursor.…”