Development of Methodologies toward the Unified Synthesis of Ellagitannins.

Ellagitannins, a class of polyphenols with divergent structures, have attracted considerable attention from synthetic organic chemists. The basic structures in ellagitannins contain esters of D-glucose with galloyl or hexahydroxyldiphenoyl groups, as well as diaryl ether structures. Thus, the synthesis methodologies of such components have been developed by various groups, including our group. This review describes the synthetic methods reported by our group during 2017-2023, aimed at increasing the number of ellagitannins that can be chemically synthesized. In addition, recent related reports are introduced.

Isolation of Hydrolyzable Tannins from Castanea sativa Using Centrifugal Partition Chromatography.

Castanea sativa wood is a rich source of hydrolyzable tannins, known for their diverse bioactivities. To investigate these bioactive properties further, it is crucial to isolate and characterize hydrophilic compounds effectively. To address this issue, we developed a centrifugal partition chromatography (CPC) method and applied it to an aqueous C. sativa wood extract. We determined the partition coefficients (KD) of the six major compounds using four butanol-/water-based biphasic solvent systems. Initially, we utilized the n-butanol/propanol/water (3:1:4, v/v/v) systems for the first fractionation step. Subsequently, we employed the water/methyl tert-butyl ether/butanol/acetone (8:5:3:4, v/v/v/v) system to fractionate moderately and highly hydrophilic fractions. We calculated the KD values for major compounds of the most hydrophilic fractions using the butanol/ethanol/water (4:1:5, v/v/v) and butanol/isopropanol/water (2:1:3, v/v/v) systems. In total, we isolated 23 compounds through a combination of CPC, size exclusion chromatography, and preparative HPLC. Among these compounds, six have never been previously described. We characterized them by 1D and 2D NMR experiments and high-resolution mass spectroscopy acquisitions.

[Dynamic Chemistry of Tannins].

Tannins are a group of polyphenols that possess the ability to precipitate proteins, causing an undesirable astringent taste by interacting with salivary peptides. This interaction deactivates the digestive enzymes; therefore, tannins are considered as plant defense substances. The health benefits of tannins and related polyphenols in foods and beverages have been demonstrated by biological and epidemiological studies; however, their metabolism in living plants and the chemical changes observed during processing of foods and medicinal herbs raises some questions. This review summarizes our studies concerning dynamic changes observed in tannins. Ellagitannins present in the young leaves of Camellia japonica and Quercus glauca undergo oxidative degradation as the leaves mature. Similar oxidative degradation is also observed in whiskey when it is kept for aging in oak barrels, and in decaying wood caused by fungi in natural forests. In contrast, ellagitannins have been observed to undergo reduction in the leaves of Carpinus, Castanopsis, and Triadica species as the leaves mature. This phenomenon of reductive metabolism in leaves enabled us to propose a new biosynthetic pathway for the most fundamental ellagitannin acyl groups, which was also supported by biomimetic synthetic studies. Polyphenols undergo dynamic changes during the process of food processing. Catechin in tea leaves undergo oxidation upon mechanical crushing to generate black tea polyphenols. Though detailed production mechanisms of catechin dimers have been elucidated, structures of thearubigins (TRs), which are complex mixtures of oligomers, remain ambiguous. Our recent studies suggested that catechin B-ring quinones couple with catechin A-rings during the process of oligomerization.

Tannin complexation with metal ions and its implication on human health, environment and industry: An overview.

Tannins, also known as plant polyphenols (PPs), are secondary metabolites widely existing in higher plants and are a kind of natural renewable resource with wide distribution, variety and quantity. Tannin has become an important class of fine chemicals due to the easily modified molecular structure and the properties of antibacterial and antioxidant, combining with protein and complexing with metal ion. Besides being used for tanning leather, tannins are also widely used in wood adhesive, concrete water-reducing agents, oil drilling fluid viscosity-reducing agents, pharmaceutical, mineral processing, water treatment, gas desulfurization, metal anticorrosion, wood anticorrosion, printing and dyeing, liquor clarification, oil antioxidant, daily chemical products and other products preparation. There are two groups of tannins: condensed tannins (CTs) (flavonoid-derived proanthocyanidins) and hydrolysable tannins (HTs) (gallic acid ester-derived). Tannins can form complexes with metals through the ortho-dihydroxyphenolic group(s), especially with transition metals. The structure-activity relationships, stoichiometry, and origin of the insolubility of which were emphasized. Furthermore, this paper proposed an in-depth discussion of the associations of tannins-metal complexes in human health, environment and industries.

Affinity of Tannins to Cellulose: A Chromatographic Tool for Revealing Structure-Activity Patterns.

Food, feed and beverage processing brings tannins into contact with macromolecules, such as proteins and polysaccharides, leading to different chemical and physical interactions. The interactions of tannins with proteins are well known but less is known about the affinity of tannins to polysaccharides. We used bacterial cellulose from nata de coco as a model compound to investigate how tannins and cellulose interact by adsorption measurements using UPLC-DAD. We also explored how the structure of tannins influences these interactions. The model tannins included nine individual structurally different hydrolysable tannins (HTs) and eight well-defined proanthocyanidin (PA) fractions with different monomeric units, mean degree of polymerization and both A- and B-type linkages. Tannins were found to have both strong and weak interactions with bacterial cellulose, depending on the exact structure of the tannin. For HTs, the main structural features affecting the interactions were the structural flexibility of the HT molecule and the number of free galloyl groups. For PAs, prodelphinidins were found to have a higher affinity to cellulose than procyanidins. Similarly to HTs, the presence of free galloyl groups in galloylated PAs and the flexibility of the PA molecule led to a stronger interaction. Adsorption measurements by UPLC-DAD proved to be a sensitive and rapid tool to evaluate the affinity of tannins to cellulose.

Divergent Synthesis of Stachyurin and Casuarinin Focusing on C-Glycosidic Bond Reactivity.

Stachyurin and casuarinin are ellagitannins, a class of polyphenols that exhibit various biological activities that have an impact on human health. Casuarinin is a stachyurin stereoisomer. These compounds contain the characteristic C-glycosidic bond between the open-chain d-glucose and the phenol aromatic ring. Therefore, chemical elucidation of the C-glycosidic bond reactivity is required to exploit their multiple bioactivities. This study developed a method for the divergent synthesis of stachyurin and casuarinin via the α-selective C-glycosylation as well as the ß-selective introduction of the oxygen functional group, focusing on structural specificity. The proposed method applies to the syntheses of stachyurin and casuarinin analogues, thereby facilitating the utilisation of their beneficial bioactivities.

Identification of Unstable Ellagitannin Metabolites in the Leaves of Quercus dentata by Chemical Derivatization.

The identification of unstable metabolites of ellagitannins having ortho-quinone structures or reactive carbonyl groups is important to clarify the biosynthesis and degradation of ellagitannins. Our previous studies on the degradation of vescalagin, a major ellagitannin of oak young leaves, suggested that the initial step of the degradation is regioselective oxidation to generate a putative quinone intermediate. However, this intermediate has not been identified yet. In this study, young leaves of Quercus dentata were extracted with 80% acetonitrile containing 1,2-phenylenediamine to trap unstable ortho-quinone metabolites, and subsequent chromatographic separation afforded a phenazine derivative of the elusive quinone intermediate of vescalagin. In addition, phenylenediamine adducts of liquidambin and dehydroascorbic acid were obtained, which is significant because liquidambin is a possible biogenetic precursor of C-glycosidic ellagitannins and ascorbic acid participates in the production of another C-glycosidic ellagitannin in matured oak leaves.

Metabolomic fingerprint of Hamamelis virginiana L. gallotannins by suspect screening analysis with UHPLC-qToF and their semiquantitative evaluation.

The evolution of the regulatory framework for medical devices in the EU (Reg 2017/745) has opened the study of complex systems emerging properties. This makes necessary to identify new analytical approaches able of characterizing complex natural substrates as completely as possible. Therefore, omics approaches and advanced analytical methods for the determination of metabolite classes appear to be at the forefront to meet this need. In this perspective, a new approach based on the suspect screening was developed to detect gallotannins. Gallotannins are a class of phenols with a polymeric nature; thus, there are no pure analytical standards available for all possible structures and their quali-quantitative determination in complex natural substrates can be a challenge. A new UHPLC-qToF method was developed and used to create an "in-house tannin database" with a dual purpose: (1) as a classic list of suspects and (2) to identify core fragments common to gallotannins to have another list of putative suspects based on the common fragment. The method was validated. The application of the method to a "system of molecules" extracted from the leaves of Hamamelis virginiana L. (Witch-hazel) allowed to the characterization of a total of 29 phenols by a suspect screening approach. Therefore, 15 gallotannins were putatively annotated while another 3 were confidently identified. All the gallotannins were semiquantified according to external regression curves of gallic acid and hamamelitannin based on core fragments at m/z 125.0244 and m/z 169.0142, the building blocks of the polymers. This new method provides a practical fit-to-purpose approach for the quali-quantitative screening evaluation of gallotannins, useful for creating multivariate control charts applicable in process development of complex natural systems or in quality control. The approach is innovative, and after specific checks, it can in principle be suitable for metabolomic fingerprint analysis of gallotannins among witch-hazel extract (WHE) samples.

[Hydrolyzable tannins from flowers of Punica granatum and their anti-diabetic activities].

To investigate the active components against diabetes, the present study isolated eight hydrolyzable tannins from the ethyl acetate extract of Punica granatum flowers by MCI, reversed-phase chromatography(ODS), Sephadex LH-20 chromatography, and HPLC, and the structures were elucidated as 1-O-galloyl-6-O-feruloyl-ß-D-glucose(1), 1,2,3,4,6-penta-O-gally-ß-D-glucopyranose(2), punicafolin(3), corilagin(4), telimagrandin Ⅰ(5), 1,2-di-O-galloyl-4,6-O-(S)-hexahydroxydiphenoyl-ß-D-glucose(6), heterophylliin A(7), and eugeniin(8) on the basis of spectral data and literature records. Among them, compound 1 is a new compound, and compounds 5-8 were isolated from this species for the first time. All isolated compounds were tested for inhibitory activities against α-glucosidase and DPP-Ⅳ. The results indicated that compounds 2, 3, and 5-8 showed significant inhibitory activities against α-glucosidase, while compounds 1 and 4 exhibited moderate inhibitory activities. Compounds 5, 7, and 8 showed moderate inhibitory effects on DPP-Ⅳ. In addition, the type of enzyme inhibition of compound 5 was determined.

Diverse gallotannins with α-glucosidase and α-amylase inhibitory activity from the roots of Euphorbia fischeriana steud.

A phytochemical investigation of the roots of Euphorbia fischeriana Steud. led to the isolation of eleven undescribed gallotannins, fishertannins A-K, together with four known analogues. Their structures were elucidated by the comprehensive spectroscopic data including UV, IR, HR-ESI-MS, and NMR, while the absolute configurations of the sugar moiety were determined by the acid hydrolysis and HPLC analyses. Fishertannin A possessed an unusual skeleton comprised of acetophenone, galloyl group, arabinofuranosyl and glucopyranosyl moieties. Fishertannin B, fishertannin H, fishertannin K, 1,2,3-tri-O-galloyl-ß-D-glucopyranose, 3,4,6-tri-O-galloyl-D-glucopyranose, and 1,6-di-O-galloyl-ß-D-glucopyranose displayed the potent α-glucosidase inhibitory activities with the IC50 values of 15.48-177.13 µM. Examination of the structure-activity relationships (SAR) demonstrated that the galloyl and glucopyranosyl moieties played a key role in the inhibitory activity for both α-glucosidase and α-amylase inhibitory activity. Among all isolates, 1,2,3-tri-O-galloyl-ß-D-glucopyranose showed the most potent and highly specific inhibitory activity against α-glucosidase with an IC50 value of 15.48 ± 0.60 µM. The kinetic analysis of 1,2,3-tri-O-galloyl-ß-D-glucopyranose disclosed the mixed inhibition type on α-glucosidase, and the molecular docking visualized the stable binding with the catalytic pocket of α-glucosidase (pdb 3A4A). These findings indicated the excellent antidiabetic potential of the gallotannins from E. fischeriana, while 1,2,3-tri-O-galloyl-ß-D-glucopyranose could be developed as a promising candidate for the treatment of T2DM with fewer side effects.

Influence of the Hydrolyzable Tannin Structure on the Characteristics of Insoluble Hydrolyzable Tannin-Protein Complexes.

Precipitation of bovine serum albumin (BSA) by 21 hydrolyzable tannins (HTs) and the characteristics of the insoluble complexes were studied stoichiometrically by ultra-performance liquid chromatography. With regard to HT monomers, the protein precipitation and the characteristic of the formed precipitates were unique for each studied HT and depended upon the functional groups present in the structures. The monomeric units comprising the oligomers formed the functional units important for the protein precipitation capacity, and small structural differences among the monomer units were less important than the overall oligomer size and flexibility. In addition, the greater tendency of certain HTs to form insoluble complexes when mixed with BSA was partially linked to the higher self-association and consequent stronger cooperative binding of these HTs with BSA.

Molecular Interactions of Tannic Acid with Proteins Associated with SARS-CoV-2 Infectivity.

The overall impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on our society is unprecedented. The identification of small natural ligands that could prevent the entry and/or replication of the coronavirus remains a pertinent approach to fight the coronavirus disease (COVID-19) pandemic. Previously, we showed that the phenolic compounds corilagin and 1,3,6-tri-O-galloyl-ß-D-glucose (TGG) inhibit the interaction between the SARS-CoV-2 spike protein receptor binding domain (RBD) and angiotensin-converting enzyme 2 (ACE2), the SARS-CoV-2 target receptor on the cell membrane of the host organism. Building on these promising results, we now assess the effects of these phenolic ligands on two other crucial targets involved in SARS-CoV-2 cell entry and replication, respectively: transmembrane protease serine 2 (TMPRSS2) and 3-chymotrypsin like protease (3CLpro) inhibitors. Since corilagin, TGG, and tannic acid (TA) share many physicochemical and structural properties, we investigate the binding of TA to these targets. In this work, a combination of experimental methods (biochemical inhibition assays, surface plasmon resonance, and quartz crystal microbalance with dissipation monitoring) confirms the potential role of TA in the prevention of SARS-CoV-2 infectivity through the inhibition of extracellular RBD/ACE2 interactions and TMPRSS2 and 3CLpro activity. Moreover, molecular docking prediction followed by dynamic simulation and molecular mechanics Poisson-Boltzmann surface area (MMPBSA) free energy calculation also shows that TA binds to RBD, TMPRSS2, and 3CLpro with higher affinities than TGG and corilagin. Overall, these results suggest that naturally occurring TA is a promising candidate to prevent and inhibit the infectivity of SARS-CoV-2.

Ellagic Acid: A Review on Its Natural Sources, Chemical Stability, and Therapeutic Potential.

Ellagic acid (EA) is a bioactive polyphenolic compound naturally occurring as secondary metabolite in many plant taxa. EA content is considerable in pomegranate (Punica granatum L.) and in wood and bark of some tree species. Structurally, EA is a dilactone of hexahydroxydiphenic acid (HHDP), a dimeric gallic acid derivative, produced mainly by hydrolysis of ellagitannins, a widely distributed group of secondary metabolites. EA is attracting attention due to its antioxidant, anti-inflammatory, antimutagenic, and antiproliferative properties. EA displayed pharmacological effects in various in vitro and in vivo model systems. Furthermore, EA has also been well documented for its antiallergic, antiatherosclerotic, cardioprotective, hepatoprotective, nephroprotective, and neuroprotective properties. This review reports on the health-promoting effects of EA, along with possible mechanisms of its action in maintaining the health status, by summarizing the literature related to the therapeutic potential of this polyphenolic in the treatment of several human diseases.

Identification of gallotannins and ellagitannins in aged wine spirits: A new perspective using alternative ageing technology and high-resolution mass spectrometry.

This research was focused on identifying gallotannins and ellagitannins degradation pathways to better understand their behavior in complex media such as wine spirits (WS). A WS was aged with chestnut wood staves with three levels of micro-oxygenation, nitrogen, and using wooden barrels. Gallotannins and ellagitannins were identified by LC-ESI-HRMS/MS using a Q-TOF in samples collected at 8, 21, 60, 180, 270, and 365 days of ageing, allowed comparing their relative abundances according to the ageing technology. It was established for the first time, the importance of oxygen in gallotannins and ellagitannins formation/degradation pathways in WS and shading light into the explanation for the steady increase of gallic and ellagic acid contents on WS during ageing. The results also highlighted the presence of penta-O-galloyl-ß-d-glucose, tetra-O-galloyl-ß-d-glucose, tri-O-galloyl-ß-d-glucose, di-O-galloyl-ß-d-glucose, and mono-O-galloyl-ß-d-glucose, 2,3-(S)-hexahydroxydiphenoyl-ß-d-glucose, pedunculagin, isomers vescalagin/castalagin and two products stemming from ethanol-promoted oxidation of castalagin/vescalagin and vescalin/castalin, in the composition WS aged with chestnut wood.

Do Pomegranate Hydrolyzable Tannins and Their Derived Metabolites Provide Relief in Osteoarthritis? Findings from a Scoping Review.

Osteoarthritis (OA) is the most common form of arthritis affecting both the elderly and the middle-aged population. Although various therapeutics have been developed to arrest the structural deterioration of cartilage, the current treatments are limited to delay the progress of OA clinically. Therefore, it is pivotal to study new therapeutic agents for chondroprotection and the prevention of cartilage degeneration. Hydrolyzable tannin (HT)-containing foods aroused considerable interest in recent years for their relevant anti-inflammatory effects. The focus of this scoping review is to provide an overview of the evidence of the therapeutic potential of HTs and their metabolites in preventing or alleviating the course of OA. A broad search of PubMed and Scopus databases on this topic resulted in 156 articles. After the exclusion of reviews and not relevant records, 31 articles were retrieved. Although only some papers did not consider the biotransformation of HTs, most recent studies also have investigated the effect of HT metabolites. Further larger clinical trials, with an in-deep analysis of HT metabolization, are still needed to unravel the potential benefits of these compounds in OA, paving the way towards the development of a dietary strategy for the improvement of pro-inflammatory cytokine-induced chondrocyte dysfunctions and injuries.

Chebulinic Acid Suppresses Adipogenesis in 3T3-L1 Preadipocytes by Inhibiting PPP1CB Activity.

Depletion of protein phosphatase-1 catalytic subunit beta (PPP1CB), a serine/threonine protein phosphatase and potent adipogenic activator, suppresses the differentiation of 3T3-L1 preadipocytes into mature adipocytes. Therefore, PPP1CB is considered as a potential therapeutic target for obesity. We screened 1033 natural products for PPP1CB inhibitors and identified chebulinic acid, which is abundantly present in the seeds of Euphoria longana and fruits of Terminalia chebula. Chebulinic acid strongly inhibited the hydrolysis of 6,8-difluoro-4-methylumbelliferyl phosphate by PPP1CB (IC50 = 300 nM) and demonstrated potent antiadipogenic effects in 3T3-L1 preadipocytes in a concentration-dependent manner. Additional studies have demonstrated that chebulinic acid suppresses early differentiation by downregulating key transcription factors that control adipogenesis in 3T3-L1 cells. These results suggested that chebulinic acid may be a potential therapeutic agent for treating obesity by inhibiting PPP1CB activity.

1H NMR and HPLC-DAD-MS for the characterization of ellagitannins and triterpenoids of less investigated Anogeissus leiocarpus DC (Combretaceae) stem bark.

Anogeissus leiocarpus DC is an evergreen tree, widely distributed in Asia and Africa. The stem bark is used in traditional medicine, and as chewing sticks and infusion. Nowadays, it is becoming increasingly important to define the phytochemical profile of less studied edible plants. Aim of this research was a first complete characterization of ellagitannins and triterpenoids profiles by HPLC-DAD-MS and 1H NMR and analyses. A total of 59 compounds were identified including 43 ellagitannins and 16 triterpenoids, mainly oleane derivatives and glycosylated forms. Among ellagitannins, roburin, vescalin and castalin were found for the first time. Tannins accounted for 38.9% whereas triterpenoids were 4.8%, both estimated on dry decoction. The decoction was preliminary tested against osteoarthritis in rats. The characterization of the main phytochemicals of Anogeissus leiocarpus DC stem bark decoction is a necessary step to evaluate nutraceutical properties, paving the way for possible food applications of this plant.

Anti-proliferation and anti-inflammation effects of corilagin in rheumatoid arthritis by downregulating NF-κB and MAPK signaling pathways.

ETHNOPHARMACOLOGICAL RELEVANCE: The dried aboveground part of Geranium Wilfordii Maxim. (G. Wilfordii) is a traditional Chinese herbal medicine named lao-guan-cao. It has long been used for dispelling wind-dampness, unblocking meridians, and stopping diarrhea and dysentery. Previous investigations have revealed that 50% ethanolic extract of G. Wilfordii has anti-inflammatory and anti-proliferation activities on TNF-α induced murine fibrosarcoma L929 cells. Corilagin (COR) is a main compound in G. Wilfordii with the content up to 1.69 mg/g. Pharmacology study showed that COR has anti-inflammatory, anti-tumor, anti-microorganism, anti-oxidant, and hepatoprotective effects. However, there is no any investigation on its anti-proliferation and anti-inflammation effects in rheumatoid arthritis (RA). AIM OF THE STUDY: The present study aimed to evaluate the potential pharmacological mechanisms of anti-proliferation and anti-inflammation effects of COR in RA. MATERIALS AND METHODS: In vitro, MH7A cells model induced by IL-1ß was used. The anti-proliferation activity of COR was assessed by Cell Counting Kit-8 (CCK-8) assay, and the anti-migration and anti-invasion activity of COR was determined by wound healing assay and transwell assay, respectively. Furthermore, apoptosis assay by flow cytometer was used to measure the pro-apoptotic effect of COR. The mRNA expressions of Bax, Bcl-2, IL-6, IL-8, MMP-1, MMP-2, MMP-3, MMP-9, COX-2, and iNOS were measured by qRT-PCR, and related protein were further verified by ELISA kits or Western blot. Moreover, protein levels associated with NF-κB and MAPK signaling pathways of p65, P-p65, IκBα, P-IκBα, ERK1/2, P-ERK1/2, JNK, P-JNK1/2/3, p38, and P-p38 were determined by Western blot. The nuclear translocation of NF-κB-p65 was detected by immunofluorescent staining. In vivo, adjuvant-induced arthritis (AIA) rat model was used, and the body weight, paw swelling, and arthritis score during the entire period were measured. Histopathological analysis of joints of synovial tissues was also determined. The expression of pro-inflammatory cytokines in serum including IL-6, TNF-α, IL-1ß, and IL-17 were measured. RESULTS: The in vitro results showed that COR could dose-dependently inhibit the proliferation, migration, and invasion of IL-1ß-induced MH7A cells, as well as promote its apoptosis. Moreover, it also suppressed the over-expression of Bcl-2, IL-6, IL-8, MMP-1, MMP-2, MMP-3, MMP-9, COX-2, and iNOS while up-regulated the level of Bax. Besides, the ratios of P-p65/p65, P-IκBα/IκBα, P-ERK/ERK, P-JNK/JNK, and P-p38/p38 were decreased, and the nuclear translocation of p65 induced by IL-1ß was blocked by COR. In vivo results indicated that COR significantly reduced the paw swelling and arthritis score in AIA rats, and inhibited synovial tissue hyperplasia and erosion, as well as inflammatory cells infiltration. It also decreased the serum pro-inflammatory cytokines (IL-6, TNF-α, IL-1ß, and IL-17) production. CONCLUSION: These results revealed that COR exerted anti-rheumatoid arthritis effect, and its underlying mechanisms may be related to inhibiting the proliferation, migration, and invasion of synovial fibroblasts, enhancing cell apoptosis, and suppressing inflammatory responses via downregulating NF-κB and MAPK signaling pathways.

Hydrolysable tannins change physicochemical parameters of lipid nano-vesicles and reduce DPPH radical - Experimental studies and quantum chemical analysis.

Tannins belong to plant secondary metabolites exhibiting a wide range of biological activity. One of the important aspects of the realization of the biological effects of tannins is the interaction with lipids of cell membranes. In this work we studied the interaction of two hydrolysable tannins: 1,2,3,4,6-penta-O-galloyl-ß-d-glucose (PGG) and 1,2-di-O-galloyl-4,6-valoneoyl-ß-d-glucose (T1) which had the same number of both aromatic rings (5) and hydroxyl groups (15) but differing in flexibility due to the presence of valoneoyl group in the T1 molecule with DMPC (dimyristoylphosphatidylcholine) lipid nano-vesicles (liposomes). Tannins-liposomes interactions were investigated using fluorescence spectroscopy, differential scanning calorimetry, laser Doppler velocimetry, dynamic light scattering and Fourier Transform Infra-Red spectroscopy. It was shown that more flexible PGG molecules stronger decreased the microviscosity of the liposomal membranes and increased the values of negative zeta potential in comparison with the more rigid T1. Both compounds diminished the phase transition temperature of DMPC membranes, interacted with liposomes via PO groups of head of phospholipids and their hydrophobic regions. These tannins neutralized DPPH free radicals with the stoichiometry of the reaction equal 1:1. The effects of the studied compounds on liposomes were discussed in relation to tannin quantum chemical parameters calculated by molecular modeling.

Identification of key phenolic compounds responsible for antioxidant activities of free and bound fractions of blackberry varieties' extracts by boosted regression trees.

BACKGROUND: Free fractions of different blackberry varieties' extracts are high in phenolic compounds with antioxidant activities. However, the phenolic profiles and antioxidant activities against peroxyl radicals of bound fractions of different blackberry varieties' extracts have not been previously reported. In addition, what the key antioxidant phenolic compounds are in free and bound fractions of blackberry extracts remain unknown. This study aimed to investigate the phenolic profiles and antioxidant activities of free and bound fractions of eight blackberry varieties' extracts and reveal the key antioxidant phenolic compounds by boosted regression trees. RESULTS: Fifteen phenolics (three anthocyanins, four flavonols, three phenolic acids, two proanthocyanidins, and three ellagitannins) were identified in blackberry by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry. Ferulic acid, ellagic acid, procyanidin C1, kaempferol-O-hexoside, ellagitannins hex, and gallic acid were major bound phenolics. Bound fractions of eight blackberry varieties' extracts were high in phenolics and showed great antioxidant activity. Boosted regression trees analysis showed that cyanidin-3-O-glucoside and chlorogenic acid were the most significant compounds, contributing 48.4% and 15.9% respectively to the antioxidant activity of free fraction. Ferulic acid was the most significant antioxidant compound in bound fraction, with a contribution of 61.5%. Principal component analysis showed that Kiowa was the best among the eight varieties due to its phenolic profile and antioxidant activity. CONCLUSION: It was concluded that blackberry varieties contained high amounts of bound phenolics, which confer health benefits through reducing oxidative stress. Ferulic acid was the key compound to explain the antioxidant activities of bound fractions. © 2021 Society of Chemical Industry.