Fine-Scale Characterization of Plant Diterpene Glycosides Using Energy-Resolved Untargeted LC-MS/MS Metabolomics Analysis.

Plant diterpene glycosides are essential for diverse physiological processes. Comprehensive structural characterization proved to be a challenge due to variations in glycosylation patterns, diverse aglycone structures, and the absence of comprehensive reference databases. In this study, a method for fine-scale characterization was proposed based on energy-resolved (ER) untargeted LC-MS/MS metabolomics analysis using steviol glycosides as a demonstration. Energy-dependent fragmentation patterns were unveiled by a series of model compounds. Distinct glycosylation sites were discerned by leveraging varying fragmentation energies for the precursor ions. The sugar moiety linkage at C19OOH (R1) exhibited facile and intact cleavage at low collision energies, while the sugar moiety at C13-OH (R2) demonstrated consecutive cleavage with increasing energy. Aglycone ions exhibited a higher relative intensity at NCE 50, with relative intensities ranging from 95% to 100%. Subsequently, aglycone candidates, R1 sugar composition, and R2 sugar sequence were deduced through ER-MS/MS analysis. The developed method was applied to Stevia rebaudiana leaves. A total of 91 diterpene glycosides were unambiguously identified, including 16 steviol glycosides with novel acetylglycosylation patterns. This method offers a rapid alternative for glycan analysis and the structural differentiation of isomers. The developed method enhances the understanding of diterpene glycosides in plants, providing a reliable tool for the in-depth characterization of complex metabolite profiles.

Ent-labdane-type diterpene glycosides obtained from Rubus chingii Hu and their inhibitory effects on PDE5A activity.

In this study, 16 new ent-labdane-type diterpene glycosides, designated as goshonosides J1-J16 (1-16), along with nine previously known diterpene glycosides (17-25) were extracted from the fruits of Rubus chingii Hu. The structures of goshonosides J1-J16 were elucidated using various analytical techniques, such as nuclear magnetic resonance, electron capture detector ECD, high-resolution electrospray ionization mass spectrometry HREIMS, single-crystal X-ray diffraction, and hydrolysis. Furthermore, the isolates' efficacy in inhibiting the activity of phosphodiesterase type 5 A was evaluated. Goshonosides J1, J2, and G effectively inhibited the activity of the aforementioned enzyme (IC50 values: 6.15 ± 1.76, 3.27 ± 0.65, and 9.61 ± 2.36 µM, respectively). Our findings highlight the remarkable structural diversity of bioactive compounds in R. chingii Hu and offer insights into the use of this shrub.

Tetra-glucopyranosyl Diterpene ent-Kaur-16-en-19-oic Acid and ent-13(S)-Hydroxyatisenoic Acid Derivatives from a Commercial Extract of Stevia rebaudiana (Bertoni) Bertoni.

Stevia rebaudiana and its diterpene glycosides are one of the main focuses of food companies interested in developing novel zero calorie sugar substitutes since the recognition of steviol glycosides as Generally Recognized as Safe (GRAS) by the United States Food and Drug Administration. Rebaudioside A, one of the major steviol glycosides of the leaves is more than 200 times sweeter than sucrose. However, its lingering aftertaste makes it less attractive as a table-top sweetener, despite its human health benefits. Herein, we report the purification of two novel tetra-glucopyranosyl diterpene glycosides 1 and 3 (rebaudioside A isomers) from a commercial Stevia rebaudiana leaf extract compounds, their saponification products compounds 2 and 4, together with three known compounds isolated in gram quantities. Compound 1 was determined to be 13-[(2-O-ß-d-glucopyranosyl-6-O-ß-d-glucopyranosyl-ß-d-glucopyranosyl) oxy]ent-kaur-16-en-19-oic acid-ß-d-glucopyranosy ester (rebaudioside Z), whereas compound 3 was found to be 13-[(2-O-ß-d-glucopyranosyl-3-O-ß-d-glucopyranosyl-ß-d-glucopyranosyl) oxy]ent-hydroxyatis-16-en-19-oic acid -ß-d-glucopyranosy ester. Two new tetracyclic derivatives with no sugar at position C-19 were prepared from rebaudiosides 1 and 3 under mild alkaline hydrolysis to afford compounds 2 13-[(2-O-ß-d-glucopyranosyl-6-O-ß-d-glucopyranosyl-ß-d-glucopyranosyl) oxy]ent-kaur-16-en-19-oic acid (rebaudioside Z1) and 4 13-[(2-O-ß-d-glucopyranosyl-3-O-ß-d-glucopyranosyl-ß-d-glucopyranosyl) oxy]ent-hydroxyatis-16-en-19-oic acid. Three known compounds were purified in gram quantities and identified as rebaudiosides A (5), H (6) and J (7). Chemical structures were unambiguously elucidated using different approaches, namely HRESIMS, HRESI-MS/MS, and 1D-and 2D-NMR spectroscopic data. Additionally, a high-quality crystal of iso-stevioside was grown in methanol and its structure confirmed by X-ray diffraction.

A Novel Diterpene Glycoside with Nine Glucose Units from Stevia rebaudiana Bertoni.

Following our interest in new diterpene glycosides with better taste profiles than that of Rebaudioside M, we have recently isolated and characterized Rebaudioside IX-a novel steviol glycoside-from a commercially-supplied extract of Stevia rebaudiana Bertoni. This molecule contains a hexasaccharide group attached at C-13 of the central diterpene core, and contains three additional glucose units when compared with Rebaudioside M. Here we report the complete structure elucidation-based on extensive Nuclear Magnetic Resonance (NMR) analysis (1H, 13C, Correlation Spectroscopy (COSY), Heteronuclear Single Quantum Coherence-Distortionless Enhancement Polarization Transfer (HSQC-DEPT), Heteronuclear Multiple Bond Correlation (HMBC), 1D Total Correlation Spectroscopy (TOCSY), Nuclear Overhauser Effect Spectroscopy (NOESY)) and mass spectral data-of this novel diterpene glycoside with nine sugar moieties and containing a relatively rare 16 α-linked glycoside. A steviol glycoside bearing nine glucose units is unprecedented in the literature, and could have an impact on the natural sweetener catalog.

New abietane-type diterpene glycosides from the roots of Tripterygium wilfordii.

Two new abietane diterpene glycosides, wilfordosides A (1) and B (2), were isolated from the roots of Tripterygium wilfordii. The structures of compounds 1 and 2 were established using spectroscopic methods including extensive 1D and 2D NMR analysis, in combination with chemical reactions.

Three new labdane-type diterpene glycosides from fruits of Rubus chingii and their cytotoxic activities against five humor cell lines.

Three new labdane-type diterpene glycosides, 15,18-di-O-ß-d-glucopyranosyl-13(E)-ent-labda-7(8),13(14)-diene-3ß,15,18-triol (1), 15,18-di-O-ß-d-glucopyranosyl-13(E)-ent-labda-8(9),13(14)-diene-3ß,15,18-triol (2), and 15-O-ß-d-apiofuranosyl-(1→2)-ß-d-glucopyranosyl-18-O-ß-d-glucopyranosyl-13(E)-ent-labda-8(9),13(14)-diene-3ß,15,18-triol (3), were isolated from the fruits of Rubus chingii. Their structures were elucidated on the basis of spectroscopic data and chemical methods. The cytotoxic activities of compounds 1-3 were evaluated against five human tumor cell lines (HCT-8, BGC-823, A549, and A2780). Compounds 3 showed cytotoxic activity against A549 with an IC50 value of 2.32µM.

Antimicrobial and cytotoxic isopimarane diterpenoid glycosides from Microlepia pilosissima Ching.

A phytochemical investigation of the EtOH extract of the dry fronds of Microlepia pilosissima Ching afforded four new isopimarane diterpene glycosides, 3α-O-α-L-rhamnopyranosyl-7ß-O-ß-D-fucopyranosyl-ent-iospimara-8(14),15-diene (1), 3α-O-[2-O-acetyl-α-L-rhamnopyranosyl]-7ß-O-ß-D-fucopyranosyl-ent-iospimara-8(14),15-diene (2), 3α-O-[ß-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl]-7ß-O-ß-D-fucopyranosyl-ent-iospimara-8(14),15-diene (3) and 3α-O-[ß-D-fucopyranosyl-(1→2)-α-L-rhamnopyranosyl]-7ß-O-ß-D-fucopyranosyl-ent-iospimara-8(14),15-diene (4) as well as their aglycone, 3α,7ß-dihydroxy-ent-iospimara-8(14),15-diene (5). Their structures were characterized by spectroscopic methods, including 1D-NMR, 2D-NMR, and HR-ESI-MS. The isolated compounds were evaluated in vitro for antimicrobial properties against three pathogen fungi and two oral pathogens and cytotoxicities against eight tumor cell lines. As a result, compounds 1-4 appeared to be promising antimicrobial potential and possessed moderate cytotoxic activities against the tested tumor cell lines.

Constituents of Vigna angularis and their in vitro anti-inflammatory activity.

Nine non-phenolic compounds, including four furanylmethyl glycosides, angularides A-D, one ent-kaurane diterpene glycoside, angularin A, and four triterpenoid saponins, angulasaponins A-D, were isolated from seeds of Vigna angularis, together with eight known compounds. Their structures were elucidated on the basis of extensive 1D and 2D NMR spectroscopic analysis as well as chemical methods. Angularin A, angulasaponins A-C, and azukisaponins III and VI showed inhibition of nitric oxide production in LPS-activated RAW264.7 macrophages, with IC50 values ranging from 13µM to 24µM.