Synthetic phenylethanoid glycoside derivatives as potent neuroprotective agents

Efficient production of hydroxysalidroside in Escherichia coli via enhanced glycosylation and semi-rational design of UGT85A1

Hydroxysalidroside is an important natural phenylethanoid glycoside with broad application prospects in the food and pharmaceutical fields. However, its low concentration in plants and complex extraction hinder its production. Despite being a promising way to synthesize hydroxysalidroside in Escherichia coli, glycosylation remains the limiting factor for its production. A de novo biosynthetic pathway for hydroxysalidroside was successfully constructed in E. coli via the screening of glycosyltransferase, overexpressing phosphoglucomutase (pgm) and UDP-glucose pyrophosphorylase (galU) to ensure a sufficient supply of UDP-glucose (UDPG). Additionally, a semi-rational design of UGT85A1 was conducted to expand the acceptor-binding pocket to eliminate steric hindrance interfering with the binding of hydroxytyrosol. The endogenous genes ushA and otsA were knocked out to further reduce the consumption of UDPG. Finally, a titer of 5837.2 mg/L was achieved in a 5 L fermenter by optimizing the feeding times of carbon sources. This laid the foundation for the subsequent biosynthesis of phenylethanoid glycosides.

Novel Feruloyl Esterase from Rehmannia glutinosa Endophyte Alternaria botrytis RYF1 and Its Application in the Production of Verbasoside and Hydroxysalidroside

Verbasoside and hydroxysalidroside are derivatives of phenylethanol glycosides (PhGs) that exhibit a range of pharmacological activities and also serve as valuable precursors for synthesizing other more complex PhGs. However, chemical synthesis and plant extraction for large-scale production are impractical to date. Here, 79 fungi from four types of PhG-containing plants and their rhizospheric soils were screened out, and endophyte Alternaria botrytis RYF1 from Rehmannia glutinosa was identified with the ability to generate verbasoside from decaffeoyl acteoside. To mine the key enzymes concerning the biotransformation, RNA-seq was carried out on RYF1 and RSF6, from which novel feruloyl esterase DN417 was captured. DN417 possesses hydrolyzing capabilities toward several PhGs. DN417's ability to produce verbasoside was tested in a 5 L fermenter, yielding 50.37 g/L of verbasoside with a conversion rate of 94.51% from crude acteoside. Finally, a dual-enzyme synergy involving feruloyl esterase and rhamnosidase was designed to produce hydroxysalidroside. After optimization of the enzyme ratios and pH, the approach successfully yielded hydroxysalidroside at a concentration of 13.60 g/L with a conversion rate of 81.30%. The study is the first report on the feruloyl esterase for the PhGs and also laid a solid foundation for the production of value-added compounds of PhGs.

Chemical profiling and anti-inflammatory effect of phenolic extract of Gentiana rigescens Franch

ETHNOPHARMACOLOGICAL RELEVANCE

Gentiana rigescens Franch. (G. rigescens), known as "Dian Long Dan" in Southern Yunnan Herbal, has a long history in traditional Chinese medicine for treating hepatitis, allergies, postherpetic neuralgia, cholecystitis and rheumatism.

AIM OF THE STUDY

This study aims to comprehensively analyze the phenolic composition of G. rigescens, evaluate its potential anti-inflammatory effects, elucidate underlying mechanisms, and identify its in vivo bioactive phenolic constituents.

MATERIALS AND METHODS

The extraction of G. rigescens phenolic compounds (GRP) was optimized using the Box-Behnken response surface method, with four phenolic compounds (mangiferin, esculetin, ferulic acid and kaempferol) used as quality index markers. GRP's phytochemical composition was subsequently profiled via UPLC-Q-TOF-MS/MS analysis. Anti-inflammatory activity and mechanisms were assessed in LPS-stimulated RAW264.7 cells and murine models, utilizing NO production assays, ELISA, qRT-PCR, Western blotting and histopathological analysis. Bioactive phenolic compounds in blood were identified post-oral administration for in vivo activity prediction.

RESULTS

The optimal extraction conditions for GRP were determined as follows: Soxhlet extraction using acetone with hydrochloric acid 0.06 mol/L, at a liquid-to-solid ratio of 132: l. for 6.6 h. Seventy-one of phenolic compounds were identified in GRP using UPLC-Q-TOF-MS/MS. GRP significantly inhibited LPS-induced NO production in RAW 264.7 macrophages and reduced pro-inflammatory cytokines IL-6, IL-1β, and TNF-α while increasing anti-inflammatory IL-10. In the carrageenan-induced inflammatory model, GRP exhibited a 69.81% inhibition rate of toe swelling at high doses (1 g/kg), along with protective effects against joint injury, as observed in histological assessments. Mechanistically, GRP downregulated mRNA levels of inflammatory cytokines and reduced the expression of inflammatory proteins iNOS, COX-2, p65, p-p65 and P-IκB as shown by Western blotting. Twenty-five of phenolic compounds, including mangiferin, swertianolin, acacetin, umbelliferone and caffeic acid, were identified in vivo in the blood, indicating potential bioactive roles.

CONCLUSIONS

This study provides the first comprehensive profile of the phenolic composition of G. rigescen, alongside a detailed investigation of its anti-inflammatory activity, mechanisms, and in vivo bioactive components. These findings highlight the therapeutic potential of Dian Long Dan's phenolic constituents and support further research on G. rigescens.

Synthesis and pharmacological evaluation of nature-inspired phenacyl glycosides

Phenylethanoid glycosides are a well-studied class of bioactive compounds found throughout the plant kingdom. In contrast, research on the synthesis and pharmacological activity of phenacyl glycosides, a specific subgroup of phenylethanoid glycosides with a ketone functionality at the alpha position of the phenol ring, has been limited. In this study, we report the synthesis, cytotoxic, antiviral, and anti-inflammatory evaluation of a series of 18 4'-hydroxyphenacyl glycosides. These compounds consist of six different sugar residues (β-d-glucose, β-d-galactose, α-l-arabinose, β-d-xylose, α-l-rhamnose, and β-d-glucuronic acid) and display three distinct methoxylation patterns at the phenacyl ring, similar to the substitution motifs of anthocyanins. We obtained the target phenacyl glycosides in high yield and stereoselectivity through the coupling of benzoyl-protected trichloroacetimidate glycosyl donors and corresponding acetophenones. Our work represents the first total synthesis of the natural products 4'-hydroxyphenacyl-β-d-glucopyranoside (1) and 4'-hydroxy-3'-methoxyphenacyl-β-d-glucopyranoside (2). None of the phenacyl glycosides showed cytotoxicity against the tested cell lines. Notably, several of the synthesized compounds exhibited antiviral activity, with natural product 2 being the most active against herpes simplex virus type 1, while phenacyl arabinoside 9 and natural product 2 were the most active against human coronavirus OC43. Natural product 2 significantly inhibited the production of interleukin-6 in lipopolysaccharide-stimulated microglia cells. Overall, our findings highlight the importance of the sugar residue and phenacyl ring substitution pattern in modulating the antiviral activity of phenacyl glycosides. Natural product 2 and phenacyl arabinoside 9 emerge as promising leads for the development of antiviral agents.

Distribution, biosynthesis, and synthetic biology of phenylethanoid glycosides in the order Lamiales

Phenylethanoid glycosides (PhGs), with a C6-C2 glucoside unit as the basic skeleton, are specialized (secondary) metabolites found in several medicinal plants. As PhGs exhibit various pharmacological activities, they are expected to be used as lead compounds in drug discovery. However, mass-production systems have not yet been established even for acteoside, a typical PhG that is widely distributed in nature (more than 150 species). This review focuses on recent studies on the accumulation and distribution of PhGs in plants, biosynthetic pathways of PhGs, and the bioproduction of PhGs.

Scalable total synthesis of natural vanillin-derived glucoside ω-esters

The first total synthesis of vanilloloside, calleryanin, and a series of naturally occurring ω-esters of vanilloloside was realized through direct glycosylation of vanillin-based aglycones or late-stage derivatization of vanilloloside. All aglycones and their fragments were synthesized from vanillin as the sole aromatic precursor. Subsequently, these intermediates were used to construct various vanillin-derived glucoside ω-esters using a mild acidic deacetylation as the key synthetic step, providing the final products in the total yields of 10-50% and general purity of >95%. Additionally, the first operationally simple and sustainable synthesis of litseafoloside B was realized on large scale, avoiding the use of toxic solvents and reagents, providing an attractive alternative to isolation of this and other similar compounds from plant sources.

Combined Ultrahigh Pressure Extraction and High-Speed Counter-Current Chromatography for Separation and Purification of Three Glycoside Compounds from Dendrobium officinale Protocorm

As an alternative to Dendrobium candidum, protocorm-like bodies (PLBs) of Dendrobium candidum are of great value due to their high yield and low cost. In this work, three glycoside compounds, β-D-glucopyranose 1-[(E)-3-(4-hydroxyphenyl)-2-propenoat] (I), β-D-glucopyranose 1-[(E)-3-(3, 4-dihydroxyphenyl)-2-propenoat] (II), and 1-O-sinapoyl glucopyranoside (III), were extracted and isolated by ultrahigh pressure extraction (UPE) coupled with high-speed counter-current chromatography (HSCCC) from PLBs of D. officinale. First, the target compounds were optimized and prepared with 50% ethanol solution at a 1:30 (g/mL) solid/liquid ratio in 2 min under 300 MPa by UPE. Then, the crude extract was chromatographed with a silica gel column, and primary separation products were obtained. In addition, the products (150 mg) were separated by HSCCC under the solvent system of MTBE-n-butyl alcohol-acetonitrile-water (5:1:2:6, v/v/v/v), yielding 31.43 mg of compound I, 10.21 mg of compound II, and 24.75 mg of compound III. Their structures were further identified by ESI-MS, ¹H NMR, and ¹³C NMR. The antioxidant results showed that the three compounds expressed moderate effects on the DPPH· scavenging effect. Compound II had the best antioxidant capacity and its IC₅₀ value was 0.0497 mg/mL.

Therapeutic potential of phenylethanoid glycosides: A systematic review

Phenylethanoid glycosides (PhGs) are generally water-soluble phenolic compounds that occur in many medicinal plants. Until June 2020, more than 572 PhGs have been isolated and identified. PhGs possess antibacterial, anticancer, antidiabetic, anti-inflammatory, antiobesity, antioxidant, antiviral, and neuroprotective properties. Despite these promising benefits, PhGs have failed to fulfill their therapeutic applications due to their poor bioavailability. The attempts to understand their metabolic pathways to improve their bioavailability are investigated. In this review article, we will first summarize the number of PhGs compounds which is not accurate in the literature. The latest information on the biological activities, structure-activity relationships, mechanisms, and especially the clinical applications of PhGs will be reviewed. The bioavailability of PhGs will be summarized and factors leading to the low bioavailability will be analyzed. Recent advances in methods such as bioenhancers and nanotechnology to improve the bioavailability of PhGs are also summarized. The existing scientific gaps of PhGs in knowledge are also discussed, highlighting research directions in the future.

Comparative study of relationship between structure of phenylethanoid glycopyranosides and their activities using cell-free assays and human cells cultured in vitro

The study focused on protective potential of phytochemicals applicable in prevention and health protection is of great importance. Various structures of these compounds and a wide range of their biological activities have inspired organic chemists to sythesize their effective analogues in order to further increase their efficacy. The aims of our study were (i) to synthesize phenylethanoid glycopyranosides: salidroside (SALI - tyrosol β-d-glucopyranoside), tyrosol β-d-galactopyranoside (TYBGAL), tyrosol α-d-galactopyranoside (TYAGAL), tyrosol α-d-mannopyranoside (TYAMAN), hydroxytyrosol α-d-mannopyranoside (HOTAMA), homosyringyl β-d-glucopyranoside (HSYGLU), hydroxytyrosol β-d-xylopyranoside (HOTXYL) and hydroxysalidroside (HOSALI); (ii) to determine their antioxidant capacities (cell-free approaches); (iii) to evaluate their cytotoxicity (MTT test), protectivity against hydrogen peroxide (H₂O₂; comet assay) and effect on the intracellular glutathione level (iGSH; flow cytometry) in experimental system utilizing human hepatoma HepG2 cells. HOSALI, HOTAMA, HOTXYL and HSYGLU manifested the highest antioxidant capacity in cell-free assays and they were most active in protection of HepG2 cells against H₂O₂. On the other hand, pre-treatment of HepG2 cells with SALI had protective effects even though SALI displayed almost no activity in cell-free assays. Differences in the efficacy of the analogues revealed that structures of their molecules in terms of aglycone combined with sugar moiety affect their activities.

Neuroprotective Effects of Four Phenylethanoid Glycosides on H₂O₂-Induced Apoptosis on PC12 Cells via the Nrf2/ARE Pathway

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a key transcription factor against oxidative stress and neurodegenerative disorders. Phenylethanoid glycosides (PhGs; salidroside, acteoside, isoacteoside, and echinacoside) exhibit antioxidant and neuroprotective bioactivities. This study was performed to investigate the neuroprotective effect and molecular mechanism of PhGs. PhGs pretreatment significantly suppressed H₂O₂-induced cytotoxicity in PC12 cells by triggering the nuclear translocation of Nrf2 and reversing the downregulated protein expression of heme oxygenase 1 (HO-1), NAD(P)H quinone oxidoreductase 1 (NQO1), glutamate cysteine ligase-catalytic subunit (GCLC), and glutamate-cysteine ligase modifier subunit (GCLM). Nrf2 siRNA or HO-1 inhibitor zinc protoporphyrin (ZnPP) reduced the neuroprotective effect. PhGs showed potential interaction with the Nrf2 binding site in Kelch-like ECH-association protein 1 (Keap1). This result may support the hypothesis that PhGs are activators of Nrf2. We demonstrated the potential binding between PhGs and the Keap1-activated Nrf2/ARE pathway, and that PhGs with more glycosides had enhanced effects.

Total phenylethanoid glycosides and magnoloside IafromMagnolia officinalisvar.bilobafruits inhibit ultraviolet B-induced phototoxicity and inflammation through MAPK/NF-κB signaling pathways

Magnolia officinalisvar.bilobais used as a traditional medicine in China and as a food additive in the United Kingdom and the European Union.

Structure-activity relations of rosmarinic acid derivatives for the amyloid β aggregation inhibition and antioxidant properties

Amyloid-β aggregation inhibitors are expected to be therapeutic or prophylactic agents for Alzheimer's disease. Rosmarinic acid, which is one of the main aggregation inhibitors derived from Lamiaceae, was employed as a lead compound and its 25 derivatives were synthesized. In this study, the structure-activity relations of rosmarinic acid derivatives for the amyloid-β aggregation inhibitory effect (MSHTS assay), antioxidant properties, and xanthine oxidase inhibition were evaluated. Among the tested compounds, compounds 16d and 19 were found to the most potent amyloid aggregation inhibitors. The SAR revealed that the necessity of the presence of the phenolic hydroxyl on one side of the molecule as well as the lipophilicity of the entire molecule. The importance of these structural properties was also supported by docking simulations.

Nine phenylethanoid glycosides from Magnolia officinalis var. biloba fruits and their protective effects against free radical-induced oxidative damage

To systematically study the chemical constituents in Magnolia officinalis var. biloba fruits, nine phenylethanoid glycosides were isolated by solvent extraction, silica gel, and preparative high-performance liquid chromatography (HPLC). Their structures were elucidated by 1D and 2D NMR analyses, including COSY, HMQC and HMBC correlations, and HPLC analysis of sugar residue. Nine phenylethanoid glycosides, namely, magnoloside I_a (1), magnoloside I_c (2), crassifolioside (3), magnoloside I_b (4), magnoloside III_a (5), magnoloside IV_a (6), magnoloside II_a (7), magnoloside II_b (8) and magnoloside V_a (9), were first isolated from the n-butanol fraction of Magnolia officinalis var. biloba fruits alcohol extract. Free radical scavenging activities of the nine phenylethanoid glycosides were assessed using the DPPH, ABTS, and superoxide anion radical scavenging assays. Simultaneously, protective effects of all compounds against free radical-induced oxidative damage were evaluated by two different kinds of mitochondrial damage model. The protective effects were assessed by mitochondrial swelling, the formations of malondialdehyde (MDA) and lipid hydroperoxide (LOOH), the activities of catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD). All phenylethanoid glycosides showed significant protective effects.