Structures Of Glycosides Research Articles

A Radical Activation Strategy for Versatile and Stereoselective N‐Glycosylation

AbstractPrevious N‐glycosylation approaches have predominately involved acidic conditions, facing challenges of low stereoselectivity and limited scope. Herein, we introduce a radical activation strategy that enables versatile and stereoselective N‐glycosylation using readily accessible glycosyl sulfinate donors under basic conditions and exhibits exceptional tolerance towards various N‐aglycones containing alkyl, aryl, heteroaryl and nucleobase functionalities. Preliminary mechanistic studies indicate a pivotal role of iodide, which orchestrates the formation of a glycosyl radical from the glycosyl sulfinate and subsequent generation of the key intermediate, a configurationally well‐defined glycosyl iodide, which is subsequently attacked by an N‐aglycone in a stereospecific SN2 manner to give the desired N‐glycosides. An alternative route involving the coupling of a glycosyl radical and a nitrogen‐centered radical is also proposed, affording the exclusive 1,2‐trans product. This novel approach promises to broaden the synthetic landscape of N‐glycosides, offering a powerful tool for the construction of complex glycosidic structures under mild conditions.

A Radical Activation Strategy for Versatile and Stereoselective N-Glycosylation.

Previous N-glycosylation approaches have predominately involved acidic conditions, facing challenges of low stereoselectivity and limited scope. Herein, we introduce a radical activation strategy that enables versatile and stereoselective N-glycosylation using readily accessible glycosyl sulfinate donors under basic conditions and exhibits exceptional tolerance towards various N-aglycones containing alkyl, aryl, heteroaryl and nucleobase functionalities. Preliminary mechanistic studies indicate a pivotal role of iodide, which orchestrates the formation of a glycosyl radical from the glycosyl sulfinate and subsequent generation of the key intermediate, a configurationally well-defined glycosyl iodide, which is subsequently attacked by an N-aglycone in a stereospecific SN2 manner to give the desired N-glycosides. An alternative route involving the coupling of a glycosyl radical and a nitrogen-centered radical is also proposed, affording the exclusive 1,2-trans product. This novel approach promises to broaden the synthetic landscape of N-glycosides, offering a powerful tool for the construction of complex glycosidic structures under mild conditions.

Carbohydrate-Functionalized Anthracene Carboximides as Multivalent Ligands and Bio-Imaging Agents.

Anthracene carboximides (ACIs) conjugated with gluco-, galacto- and mannopyranosides are synthesized, by glycosylation of N-hydroxyethylanthracene carboximide acceptor with glycosyl donors. Glycoconjugation of anthracene carboximide increases the aq. solubility by more than 3-fold. The glycoconjugates display red-shifted absorption and emission, as compared to anthracene. Large Stokes shift (λabs/λem=445/525 nm) and high fluorescence quantum yields (Φ) of 0.86 and 0.5 occur in THF and water, respectively. The ACI-glycosides undergo facile photodimerization in aqueous solutions, leading to the formation of the head-to-tail dimer, as a mixture of syn and anti-isomers. Solution phase and solid-state characterizations by dynamic light scattering (DLS), microscopic imaging by atomic force (AFM) and transmission electron (TEM) microscopies reveal self-assembled vesicle structures of ACI glycosides. These self-assembled structures act as multivalent glycoclusters for ligand-specific lectin binding, as evidenced by the binding of Man-ACI to Con A, by fluorescence and turbidity assays. The conjugates do not show cellular cytotoxicity (IC50) till concentrations of 50 μM with HeLa and HepG2 cell lines and are cell-permeable, showing strong fluorescence inside the cells. These properties enable the glycoconjugates to be used in cell imaging. The non-selective cellular uptake of the glycoconjugates suggests a passive diffusion through the membrane.

Nematicidal glycosylated resorcylic acid lactones from the fungus Pochonia chlamydosporia PC-170 and their key biosynthetic genes.

Chemical study of the nematicidal biocontrol fungus Pochonia chlamydosporia PC-170 led to discovery of six resorcylic acid lactones (RALs), including three nematicidal glycosylated RALs, monocillin VI glycoside (1), colletogloeolactone A (2) and monocillin II glycoside (3), and three antibacterial non-glycosylated RALs, monocillin VI (4), monocillin IV (5) and monocillin II (6). The planar structure of the new compound monocillin VI glycoside (1) was elucidated using HRESIMS and NMR data, and its monosaccharide configuration was further determined through sugar hydrolysis experiment and GC-MS analysis method. Furthermore, their two biosynthetic-related PKS genes, pchE and pchI, were identified through the gene knockout experiment. The glycosylated RALs 1-3 exhibited nematicidal activity against Meloidogyne incognita, with LC50 values of 94, 152 and 64 μg/mL, respectively, and thus had great potential in the development of new nematicidal natural products to control M. incognita in the future.

Elucidating the influence and mechanism of different phenols on the properties, food quality and function of maize starch

This study discusses interaction differences between three phenols (protocatechuic acid, naringin and tannic acid) and starch helix, investigates influences of phenols at different doses on properties of maize starch, and further determines their effects on quality and function of maize-starchy foods. Simulated results indicate variations of phenolic structure (phenolic hydroxyl group amount, glycoside structure and steric hindrance) and dose induce phenols form different complexes with starch helix. Formation of different starch-phenols complexes alters gelatinization (1.65–5.63 J/g), pasting form, water binding capacity (8.83–12.69 g/g) and particle size distribution of starch. Meanwhile, differences in starch-phenols complexes are reflected in fingerprint area (R1045/1022: 0.920 to 1.047), crystallinity (8.3% to 17.0%), rheology and gel structure of starch. Additionally, phenols change texture and color of cold maize cake, giving them different antioxidant capacity and lower digestibility. Findings are beneficial for understanding interaction between starch and different phenols and their potential application.

Chaenomelin, a New Phenolic Glycoside, and Anti-Helicobacter pylori Phenolic Compounds from the Leaves of Salix chaenomeloides.

Salix chaenomeloides Kimura, commonly known as pussy willow, is a deciduous shrub and tree belonging to the Salicaceae family. The genus Salix spp. has been known as a healing herb for the treatment of fever, inflammation, and pain relief. The current study aimed to investigate the potential bioactive natural products from S. chaenomeloides leaves and evaluate their antibacterial activity against Helicobacter pylori. A phytochemical investigation of the ethanol (EtOH) extract of S. chaenomeloides leaves led to the isolation of 13 phenolic compounds (1-13) from the ethyl acetate (EtOAc) fraction, which showed antibacterial activity against H. pylori strain 51. The chemical structure of a new phenolic glycoside, chaenomelin (1), was established by a detailed analysis of 1D and 2D (1H-1H correlation spectroscopy (COSY), heteronuclear single-quantum coherence (HSQC), and heteronuclear multiple-bond correlation (HMBC)) nuclear magnetic resonance (NMR), high-resolution electrospray ionization mass spectroscopy (HR-ESIMS), and chemical reactions. The other known compounds were identified as 5-O-trans-p-coumaroyl quinic acid methyl ester (2), tremulacin (3), citrusin C (4), benzyl 3-O-β-d-glucopyranosyl-7-hydroxybenzoate (5), tremuloidin (6), 1-[O-β-d-glucopyranosyl(1→2)-β-d-glucopyranosyl]oxy-2-phenol (7), arbutin cinnamate (8), tremulacinol (9), catechol (10), 4-hydroxybenzaldehyde (11), kaempferol 3-rutinoside (12), and narcissin (13), based on the comparison of their NMR spectra with the reported data and liquid chromatography/mass spectrometry (LC/MS) analysis. The isolated compounds were evaluated for antibacterial activity against H. pylori strain 51. Among the isolates, 1-[O-β-d-glucopyranosyl(1→2)-β-d-glucopyranosyl]oxy-2-phenol (7) and arbutin cinnamate (8) exhibited antibacterial activity against H. pylori strain 51, with inhibitions of 31.4% and 33.9%, respectively, at a final concentration of 100 μM. These results were comparable to that of quercetin (38.4% inhibition), which served as a positive control. Generally, these findings highlight the potential of the active compounds 7 and 8 as antibacterial agents against H. pylori.

Antidepressant-Like Effect of the Polymethoxylated Flavone Tangeretin from Citrus Peels: The Role of Serotonergic Mechanisms

Objective: Depression is a mood disorder characterized by a set of emotional, cognitive, physical and behavioral symptoms. Low response rate to antidepressant treatment in patients with depression, late onset of action, side effects due to long-term drug use, and pharmacogenetic variations limit the effectiveness and tolerability of these drugs and lead to compliance problems in patients. Therefore, studies on the discovery and development of new antidepressant drugs continue, and molecules of natural origin are becoming the focus of attention of researchers. Tangeretin, which is commonly found in citrus peels and has a pentamethoxyflavone structure, is an important member of flavonoids. Since it lacks a glycoside structure, it is easily absorbed from the intestines and can easily pass through the blood-brain barrier due to its lipophilic structure. Previous studies indicating that tangeretin may be effective on the central nervous system suggest that it may be possible for this phytochemical to have an effect on mood. Based on this idea, this study aimed to investigate the possible antidepressant-like effects of tangeretin and to elucidate the pharmacological mechanisms mediating this effect. Methods: Male Balb/c mice of the same age, weighing 30-35 g, were used for the experiments. The antidepressant-like effect of tangeretin (10, 20 ve 40 mg/kg, p.o.) was examined by tail suspension and modified forced swimming tests, while its effect on the motor coordination of experimental animals was evaluated using the Rota-rod method. Results: The data obtained revealed that doses of 10 and 20 mg/kg tangeretin decreased the immobility time of mice in tail suspension test and immobility number of mice in modified forced swimming tests compared to control animals not receiving tangeretin. These findings indicated that tangeretin showed an antidepressant-like activity comparable to the reference drug fluoxetine (30 mg/kg) when administered at doses of 10 and 20 mg/kg. Tangeretin, at the same doses, did not alter the climbing number of mice in modified forced swimming tests, but significantly increased their swimming number. The 40 mg/kg dose of this flavonoid did not cause a statistically significant effect in either test. While α-methyl-para-tyrosine methyl ester (an inhibitor of catecholamine synthesis; 100 mg/kg i.p.) and ondansetron (a 5-HT3 receptor antagonist; 0.3 mg/kg i.p.) pretreatments did not change the antidepressant-like activity induced by 20 mg/kg dose of this flavonoid in the tail suspension tests; pretreatment of p-chlorophenylalanine methyl ester (an inhibitor of serotonin synthesis; 100 mg/kg i.p., administered for 4-consecutive days), NAN-190 (a 5-HT1A receptor antagonist; 0.5 mg/kg i.p.) and ketanserin (a 5-HT2A/2C receptor antagonist; 1 mg/kg i.p.), reversed this activity. These findings indicated that tangeretin has antidepressant-like activity mediated by the serotonergic system and that 5-HT1A and 5-HT2A/5-HT2C serotonergic receptor subtypes participate in this effect. Conclusion: The findings of this study suggest that tangeretin may be a useful drug candidate in the treatment of depression. However, it is clear that for tangeretin to be considered an antidepressant agent, the antidepressant-like activity presented in this preclinical study must be confirmed by well-designed clinical studies conducted on various groups of patients with depressive disorders.

2-D NMR studies of geneoside, a novel pregnane pentaglycoside of 2-deoxy and 2, 6 dideoxy monosaccharides from ‘Wattakaka lanceolata’

Plants of Asclepiadaceae and Apocynaceae family are a rich source of pregnane and pregnane glycosides. They are found in nature either in free state or as their glycosides. They have shown antitumor, anticancer, and hypoglycaemic, antioxidant and antimicrobial activities. In our continued studies on the isolation of pregnane glycosides we have isolated a novel pregnane pentaglycoside comprised of 2-deoxy and 2, 6-dideoxy monosaccharides from Wattakaka lanceolata (Asclepiadaceae). The structure of the new glycoside, Geneoside was established as11α, 12β-O-diacetyl-drevogenin-P-3-O-β-D-cymaropyaranosyl (1→4)-β-D-cymaropyranosyl (1→4) -β-D-Oleandropyranosyl (1→4)-β-D-digitalopyranosyl (1→4)-β-D-digitalopyranoside. The stereoscopic structure was established by chemical degradation, chemical transformation and recent physicochemical techniques viz 1H,13C, 2-D NMR (COSY, TOCSY, HSQC and HMBC) and Mass spectrometry.

Efficient Synthesis of Natural Product Inspired Naphthoquinone-Fused Glycohybrids and Their In Silico Docking Studies

AbstractNaphthoquinones, a diverse group of natural compounds with a 1,4-naphthoquinone core structure, have gained attention for their pharmacological properties. The anticancer activity of these compounds is attributed to their ability to accept electrons, leading to the generation of reactive oxygen species that cause DNA damage and cell death. In recent studies, hydroxy-1,4-naphthoquinone derivatives, including daunorubicin, have shown promising inhibitory effects against several human cancers, such as acute myeloid leukemia, chronic myelogenous leukemia, and Kaposi’s sarcoma. To further explore their potential as anticancer agents, this research article focuses on the design and synthesis of natural product inspired naphthoquinone-based glycohybrids. These glycohybrids are designed based on the structures of bioactive aryl glycosides and quinones, aiming to enhance their binding affinity and specificity towards cancer-related protein targets. The interactions between the synthesized glycohybrids and target proteins through computational docking simulations has been studied and better binding affinity was found.

Naturally Occurring Simple Oxygenated Benzophenones: Structural Diversity, Distribution, and Biological Properties

Naturally occurring benzophenones represent a relatively small group of plant metabolites with narrow distribution, mainly in members of Clusiaceae, Gentianaceae, Hypericaceae, Polygalaceae, Myrtaceae, etc.; however, there were reports of several compounds derived from microorganisms belonging to the Aspergillaceae and Valsaceae families and propolis. Benzophenones exhibit many biological activities, such as antioxidant, anti-inflammatory, cytotoxic, antimicrobial, etc. Few reviews on benzophenones that have appeared in the literature were focused on their prenylated derivatives. Summarized information on structural diversity, distribution, and biological activities of simple oxygenated naturally occurring benzophenones and their glycosides has not been found in the literature. Until 2000, only benzophenone C-glycosides were known to occur in nature. Since then, many O-glycosides have been isolated, structurally, and biologically characterized. This review covers the years from 1850 to 2023 and was compiled using databases such as Chemical Abstracts, Scopus, Google Scholar, PubMed, and ResearchGate. Based on their degree of oxidation, 210 chemical structures of benzophenone derivatives and glycosides were grouped into six categories. In addition, in one group of 40 miscellaneous benzophenones, where one or several protons are replaced by a methyl, alcohol, carboxyl, or acyl group, glycosidic forms with such an aglycone and dimeric compounds with xanthone was included. Simple oxygenated benzophenones and their glycosides were found in 77 plant genera belonging to 44 families. The allergy-associated bezophenone-1, benzophenone-2 and benzophenone-3 have limited distribution across natural sources. A wide range of biological activities (antioxidant, anti-inflammatory, cytotoxic, antitumor, cytoprotective, antimicrobial, MAO-A, antiarthritic, anticholinesterase, anti-atherosclerotic, laxative, etc.) of simple oxygenated benzophenones and their glycosides that appeared in the literature were discussed.

Anti-cancer activity of Marsdenialongise A, a new C21 steroidal glycoside isolated from Marsdenia longipes W.T. Wang (Apocynaceae)

C21 steroidal glycosides are a group of natural compounds with biological activities such as anti-cancer, anti-microbial, and anti-viral properties. In this study, we isolated and determined the structure of a new C21 steroidal glycoside, named Marsdenialongise A from Marsdenia longipes W.T. Wang, using nuclear magnetic resonance spectroscopy and mass spectra data. Marsdenialongise A is a derivative of tenacigenin B and was isolated for the first time from a plant. The inhibitory effect of Marsdenialongise A on cancer cells was evaluated through MTT and cell migration assays, cell cycle, and apoptosis analyses. The results of the MTT assay showed that Marsdenialongise A reduces the cell viability of cancer cells, with the AGS cell line being more sensitive than other cell lines, with an IC50 value of 5.69 µM (for 48 h of treatment). Marsdenialongise A also exhibited an ability to prevent the migration of cancer cells in AGS cells. Further analysis using flow cytometry has revealed that Marsdenialongise A is capable of inducing cell cycle arrest and apoptosis. The overexpression of reactive oxygen species (ROS) production induced by Marsdenialongise A can be considered a cause that leads to the influence on the cell cycle and apoptosis of cancer cells. Thus, Marsdenialongise A can be considered a potential anti-cancer agent.

Insight into property, function, and digestion of potato starch modified by phenolic compounds with varying structures.

Influences of structural characteristics of phenolic compounds on the properties of potato starch were investigated, and their effects on the quality, function, and digestion of potato starch noodles were further determined. All testing phenolic compounds (including protocatechuic acid [PA], naringin [NA], and tannic acid [TA]) exhibited the significant capability to modify the thermal properties, rheological properties, and enzymatic hydrolysis of potato starch. The high amount of hydroxyl groups, the presence of glycoside structure, appropriate molecular size, and steric hindrance were beneficial to enhance their effects on potato starch. In addition, by changing the microstructure of starch hydrocolloids, PA, NA, and TA could affect the color, texture properties, and cooking properties of potato starch noodles. Meanwhile, PA and TA could endow potato starch noodles with remarkable antioxidant activity. Furthermore, the in vitro digestion of potato starch noodles was obviously inhibited by phenolic compounds, especially for TA. All present results suggested that structural characteristics of phenolic compounds affected their interaction affinity and combination degree with potato starch molecules, so as to modify the properties of starch and affect the quality, function, and digestion of starchy foods, which showed the valuable applications in food and chemical industries. PRACTICAL APPLICATION: The property, function, and digestion characteristics of potato starch show the significant effects on the quality of potato starch products in food industry. In present study, the thermal properties, rheological properties, and enzymatic hydrolysis of potato starch were modified by different phenolic compounds (including protocatechuic acid, naringin, and tannic acid) in varying degrees, whereas the quality, antioxidant activity, and digestion characteristic of potato starch noodles were modified by phenolic compounds with different structures. All results showed the potential application and interaction regularities of phenolic compounds as natural additives for potato starch processing in food industry.

The Chemistry and the Anti-Inflammatory Activity of Polymethoxyflavonoids from Citrus Genus.

Polymethoxyflavonoids (PMFs) are a large group of compounds belonging to the more general class of flavonoids that possess a flavan carbon framework decorated with a variable number of methoxy groups. Hydroxylated polymethoxyflavonoids (HPMFs), instead, are characterized by the presence of both hydroxyl and methoxy groups in their structural unities. Some of these compounds are the aglycone part in a glycoside structure in which the glycosidic linkage can involve the -OH at various positions. These compounds are particular to Citrus genus plants, especially in fruits, and they are present mainly in the peel. A considerable number of PMFs and HPMFs have shown promising biological activities and they are considered to be important nutraceuticals, responsible for some of the known beneficial effects on health associated with a regular consumption of Citrus fruits. Among their several actions on human health, it is notable that the relevant contribution in controlling the intracellular redox imbalance is associated with the inflammation processes. In this work, we aim to describe the status concerning the chemical identification and the anti-inflammatory activity of both PMFs and HPMFs. In particular, all of the chemical entities unambiguously identified by isolation and complete NMR analysis, and for which a biochemical evaluation on the pure compound was performed, are included in this paper.

Comparative coexpression networks pinpoint acyltransferases decorating structures of major iridoid glycosides in a medicinal herb, Picrorhiza kurroa

Picrorhiza kurroa, a hepatoprotective Himalayan medicinal herb contains a variety of iridoid glycosides mainly present in stolons and roots, contributing to several medicinal properties. However, off late the herb has been declared as endangered, therefore, warranting alternate production routes for those iridoid glycosides. Catalpol, the major intermediary compound, is transformed into several iridoid glycosides through acylation by acyltransferase enzymes. In current study, we performed comparative gene co-expression-networks analysis among transcriptomes derived from different tissues/organs of P. kurroa varying for contents of iridoid glycosides to pinpoint major hubs associated with BAHD class of acyltransferases. Our analysis also captured other components co-expressed with major Acyltransferases hubs, which provided us leads as novel edges possibly contributing to other components of biosynthetic machinery. Some of the key interacting components such as Phytyl ester synthase (PES1 and PES2), callose synthase, serine carboxy peptidase like protein, polyphenol oxidase and UDP-glycosyltransferase were identified, which are possibly contributing to variations in the contents of iridoid glycosides in different tissues/organs of P. kurroa. Furthermore, the functional association of identified BAHD-ATs (SS_3469, STS_4084, STS_4241, STS_8424, SR_4494, and SR_4510) was evaluated through molecular docking to pinpoint probable BAHD-ATs transforming structural modifications of iridoid glycosides.

A pair of novel phenylethanol glycosides from Cistanche tubulosa (Schenk) Wight

A pair of differential epimers with opposite C-7 configurations, crenatosides A and B (1 and 2), and 10 known phenylethanoid glycosides (PhGs) (3‐12) were obtained from the succulent stem of Cistanche tubulosa. The structures were elucidated based on extensive spectral data (UV, IR, 1D and 2D NMR, HR-ESIMS), which are first reported natural products with unique glycoside structures. After acid hydrolysis, the configuration of the sugar was determined by comparing it with the normative sugar by HPLC. The absolute configurations of both compounds were determined by ECD spectrum analysis. All the obtained compounds were examined for their inhibitory effect on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in mouse microglial cells (BV-2 cells), and compounds 1 and 2 showed potent inhibition on NO production with IC50 values of 5.62 μM and 6.30 μM, respectively.

Polydatin, A Glycoside of Resveratrol, Is Better Than Resveratrol in Alleviating Non-alcoholic Fatty Liver Disease in Mice Fed a High-Fructose Diet.

Resveratrol (RES) is considered to be an activator of AMP-activated protein kinase (AMPK) with many reported health benefits. Polydatin (POD) is a natural precursor and glycosylated form of RES. The glycoside structure of POD alters the bioactivity. Overnutrition-stimulated reactive oxygen species (ROS) promote the AMPK suppression and metabolic dysregulation. The present work compared the effects of POD and RES in ameliorating energy homeostasis imbalance in mice fed a high-fructose diet and elucidated the underlying mechanisms of action. Our results showed that POD elevated the fecal levels of valeric acid and caproic acid via modification of gut microbiota, while RES did not significantly influence the levels of fecal short-chain fatty acids (SCFAs). Both POD and RES markedly decreased the oxidative stress and activated the AMPK signaling pathways in the liver. POD and RES exerted a similar effect in alleviating glucose dysmetabolism, but POD was more effective in ameliorating lipid dysmetabolism than RES. Furthermore, valeric acid and caproic acid alone can activate the AMPK and ameliorate hypercholesterolemia, and enhance the effects of POD on improving lipid metabolism in mice. Overall, for the first time, we demonstrated that POD administration elevated the fecal levels of valeric acid and caproic acid by modifying gut microbiota, thus promoting AMPK activation may be the underlying mechanism that POD is superior to RES in alleviating the lipid dysmetabolism. Our results suggest that POD may be an alternative for RES as an AMPK activator.

The Chirality of Aggregated Yariv Reagents Correlates with Their AGP-Binding Ability.

Yariv reagents are glycosylated triphenylazo dyes that bind to arabinogalactan proteins (AGPs), proteoglycans found in plant cell walls that are integral for plant growth and development. Yariv reagents are widely utilized as imaging, purification, and quantification tools for AGPs and represent the only small molecule probe for interrogating AGP function. The ability of Yariv reagents to bind to AGPs is dependent on the structure of the terminal glycoside on the dye. The reason for this selectivity has not been understood until the present work. Using circular dichroism spectroscopy, we show that the Yariv reagents form supramolecular aggregates with helical chirality. More significantly, the ability of the Yariv reagent to bind AGPs is correlated with this helical chirality. This finding paves the way towards developing a more detailed understanding of the nature of the Yariv-AGP complex, and the design of AGP-binding reagents with higher affinities and selectivities.

Secondary structure of muramyl dipeptide glycoside in pristine state and immobilized on nanosilica surface

Fourier transform infrared spectroscopy (FT-IR) and temperature programmed desorption mass spectrometry (TPD-MS) data of O-glycoside MDP in pristine and immobilized on silica surface states indicate that O-glycoside MDP binds to the silica surface by means of carboxylic and NH moieties of isoglutamine. Moreover, pyrolysis of O-glycoside MDP on the silica surface proceeds through formation of additional product 3-iminopyridine-2(3H)-one, which identified in mass spectra as molecular ion with m/z 108 and its fragment ions with m/z 79, 77, 51. FTIR and TPD-MS data confirm existence of a MDP first β-turn on the silica surface resulting from the formation of a hydrogen bond between the NAc carbonyl and the L-Ala NH for MDP and its analogs, as reported previously.

Comparison of quercetin and rutin inhibitory influence on Tartary buckwheat starch digestion in vitro and their differences in binding sites with the digestive enzyme

Inhibitory effects of flavonoids on starch digestibility were well known, but the structural mechanism was not clear. This study was focused on the diverse effect of quercetin and rutin on digestibility of Tartary buckwheat starch. Results showed that quercetin and rutin reduced the starch digestion by altering starch structure in bound forms and inhibiting digestive enzyme activity in free forms simultaneously, and quercetin showed a stronger effect than rutin. Molecular docking and saturation transfer difference-nuclear magnetic resonance (STD-NMR) revealed different binding site of rutin from quercetin was due to its hydroxyl and hydrogen on the glycoside structure. Rutin interacted with enzymes mainly by CH and OH on the glycoside structure which induced steric hindrance and restricted the inhibitory effect of quercetin fraction. The glycoside structure weakened inhibition of rutin on digestive enzymes in free forms rather than influence its anti-digestive effects in bound forms with starch.

Analysis of Intact Glycosidic Aroma Precursors in Grapes by High-Performance Liquid Chromatography with a Diode Array Detector.

Nowadays, the techniques for the analysis of glycosidic precursors in grapes involve changes in the glycoside structure or it is necessary the use of very expensive analytical techniques. In this study, we describe for the first time an approach to analyse intact glycosidic aroma precursors in grapes by high-performance liquid chromatography with a diode array detector (HPLC-DAD), a simple and cheap analytical technique that could be used in wineries. Briefly, the skin of Muscat of Alexandria grapes was extracted using a microwave and purified using solid-phase extraction combining Oasis MCX and LiChrolut EN cartridges. In total, 20 compounds were selected by HPLC-DAD at 195 nm and taking as a reference the spectrum of phenyl β-D-glucopyranoside, whose DAD spectrum showed a first shoulder from 190 to 230 nm and a second around 200–360 nm. After that, these glycosidic compounds were identified by High-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (HPLC-qTOF-MS). Disaccharides hexose pentose were the most abundant group observed with respect to the sugars and monoterpendiols the main aglycones found.