α-Glucosidase inhibitory hydrolyzable tannins from Eugenia jambolana seeds

Glycosides from the leaves of Fraxinus Hubeiensis

Fraxinus hubeiensis is a plant endemic to China and widely used as folk medicine to treat various diseases. However, its chemical constituents have never been reported sufficiently. Thus, the primary objective of this study was to investigate the phytochemical constituents and biological activities of F. hubeiensis leaves. Hence, combined column chromatographic and spectroscopic techniques were used to identify and characterize the secondary metabolites such as a pair of 3-keto-glycoside epimers (1) and (2), along with five known compounds (3 ~ 7). The results of α-glucosidase inhibitory activity exhibited that 1 and 2 had moderate activity with IC50 values of 359.50 and 468.43 µM, respectively, compared to a positive control acarbose with the IC50 value of 164.08 µM. However, Compounds 1-6 were shown to be inactive against the tested microbes.

Chemical Constituents and α-Glucosidase Inhibitory, Antioxidant and Hepatoprotective Activities of Ampelopsis grossedentata

Ampelopsis grossedentata is a valuable medicinal and edible plant, which is often used as a traditional tea by the Tujia people in China. A. grossedentata has numerous biological activities and is now widely used in the pharmaceutical and food industries. In this study, two new flavonoids (1-2) and seventeen known compounds (3-19) were isolated and identified from the dried stems and leaves of A. grossedentata. These isolated compounds were characterized by various spectroscopic data including mass spectrometry and nuclear magnetic resonance spectroscopy. All isolates were assessed for their α-glucosidase inhibitory, antioxidant, and hepatoprotective activities, and their structure-activity relationships were further discussed. The results indicated that compound 1 exhibited effective inhibitory activity against α-glucosidase, with an IC50 value of 0.21 μM. In addition, compounds 1-2 demonstrated not only potent antioxidant activities but also superior hepatoprotective properties. The findings of this study could serve as a reference for the development of A. grossedentata-derived products or drugs aimed at realizing their antidiabetic, antioxidant, and hepatoprotective functions.

Phloroglucinol derivatives with α-glucosidase inhibitory activities from Syzygium fluviatile

Four new phloroglucinol derivatives (1 - 4) were isolated from the leaves of Syzygium fluviatile. Their structures were elucidated by means of extensive spectroscopic data. Among them, compounds 1 and 3 showed significant inhibitory activity against α-glucosidase with IC50 values of 10.60 and 5.07 µM, respectively. The structure-activity relationship was also discussed briefly.

Cordythiazole A, the first member of thiazole alkaloids from Chinese cordyceps, with α-glucosidase inhibitory activity

Chinese cordyceps, also known as Dong-Chong-Xia-Cao, is widely recognized as a famous precious tonic herb, and used as traditional Chinese medicine for centuries. It is mainly used for regulating the immune system and improving functions of the lung and kidney, with anti-tumor, anti-inflammatory, and anti-diabetic activities. Due to its rarity and preciousness, a few chemical components are isolated and identified. Moreover, most of them are common chemical components and widely distributed in other natural resources, such as nucleosides, sterols, fatty acids, sugar alcohols, and peptides. Therefore, a large number of active substances of Chinese cordyceps is still unclear. During our search for chemical constituents of Chinese cordyceps, a new thiazole alkaloid, cordythiazole A (1), was isolated and identified. Its structure was elucidated by comprehensive spectroscopic analysis and single-crystal X-ray diffraction analysis. This is the first report of the presence of thiazole alkaloid in Chinese cordyceps, which adds a new class of metabolite of Chinese cordyceps. Furthermore, a putative biosynthesis pathway of cordythiazole A was proposed based on possible biogenic precursor, genes, and literatures. In addition, it showed α-glucosidase inhibitory activity with potency close to that of acarbose. The discovery of cordythiazole A with α-glucosidase inhibitory activity adds a new class of potential anti-diabetes ingredient in Chinese cordyceps.

The α-glucosidase inhibitory activity of avicularin and 4-O-methyl gallic acid isolated from Syzygium myrtifolium leaves

Diabetes Mellitus is the main cause of death on a global scale. In 2019, there were 463 million people with diabetes, and WHO predicts that by 2030, there will be 578 million. As an antidiabetic agent, α-glucosidase inhibitors are one of the methods employed to reduce the prevalence of diabetes. Diabetes is traditionally treated with Syzygium as a primary material, medicine, fruit, ornamental plant, and source of carpentry. This investigation aimed to examine the inhibitory effect of seven species of Syzygium against α-glucosidase enzyme using an in vitro assay and isolate active substances and ascertain their concentrations in each sample. As a solvent, ethanol was used in maceration to extract the substance. Afterward, the extract underwent a series of fractionation techniques, including liquid-liquid extraction, vacuum liquid chromatography, column chromatography, and preparative Thin Layer Chromatography (TLC) for purification and isolation. The compound's structures were elucidated using TLC, UV-Visible spectrophotometry, and nuclear magnetic resonance (NMR) spectroscopy. Based on concentrations of 100 and 200 µg/mL, Syzygium myrtifolium exhibited the most significant inhibitory effect, followed by other species of Syzygium. The proportion of ethyl acetate had the strongest activity (IC₅₀ 0.40 ± 0.02 µg/mL) contrasted to positive control acarbose (IC₅₀ 55.39 ± 0.67 g/mL) and quercitrin (IC₅₀ 6.47 ± 0.40 µg/mL). Avicularin and 4-O-methyl gallic acid were discovered in the ethyl acetate fraction of Syzygium myrtifolium with IC₅₀ values of 17.05 ± 0.75 µg/mL and 25.19 ± 0.21 µg/mL, respectively. As α-glucosidase inhibitory, the results of this study indicate Syzygium myrtifolium can be used as a dietary supplement to manage hyperglycemia.

Metabolomic Characterization of Phoradendron brachystachyum Mistletoe and In-Silico and In-Vitro Investigation of Its Therapeutic Potential in Metabolic Disorders

Plants of the Phoradendron genus have been traditionally used for their lipid- and glucose-lowering effects. However, the compounds responsible for these effects and the overall chemical profile of these plants have not been thoroughly investigated. We aimed to characterize the metabolome of leaves, stems, and aerial parts of the Phoradendron brachystachyum plant. We used mass spectrometry and colorimetric screening techniques (with various solvents) to identify and characterize the metabolites present. We also evaluated the antioxidant (FRAP, ORAC, TEAC, and DPPH assays) and inhibitory effects on pancreatic lipase and α-glucosidase enzymes of hydrophilic extracts. Furthermore, we compared the molecular fingerprints between the identified metabolites and FDA-approved drugs to gain insights into the metabolites that might be responsible for the observed effects on enzymes. Our findings revealed the presence of 59 putative metabolites, primarily flavonoids. However, we also hint at the presence of peptide and carbohydrate derivatives. The leaf extracts demonstrated the most promising metrics across all assays, exhibiting strong antioxidant and enzyme inhibitory effects as well as high levels of phenolic compounds, flavonoids, and tannins. Fingerprint analysis suggested potential peptide and carbohydrate metabolites as pancreatic lipase and α-glucosidase inhibitors. Overall, our study provides evidence on specific metabolites in Phoradendron brachystachyum that could be responsible for the therapeutic effects noted in obese and type 2 diabetes subjects.

Major Bioactive Compounds from Java Plum Seeds: An Investigation of Its Extraction Procedures and Clinical Effects

Java plum is widely recognized as a plant with valuable medicinal properties, originating from Indonesia and India and distributed globally in the tropic and sub-tropic regions of the world. The plant is rich in alkaloids, flavonoids, phenyl propanoids, terpenes, tannins, and lipids. The phytoconstituents of the plant seeds possess various vital pharmacological activities and clinical effects including their antidiabetic potential. The bioactive phytoconstituents of Java plum seeds include jambosine, gallic acid, quercetin, β-sitosterol, ferulic acid, guaiacol, resorcinol, p-coumaric acid, corilagin, ellagic acid, catechin, epicatechin, tannic acid, 4,6 hexahydroxydiphenoyl glucose, 3,6-hexahydroxy diphenoylglucose, 1-galloylglucose, and 3-galloylglucose. Considering all the potential beneficial effects of the major bioactive compounds present in the Jamun seeds, in the current investigation, the specific clinical effects and the mechanism of action for the major bioactive compounds along with the extraction procedures are discussed.

Phytochemistry profile of rosella and jambolan extracts and the therapeutic effects on obesity

Hibiscus sabdariffa extract (HSE) and Syzygium cumini extract (SCE) have been used in traditional medicine due to their hypoglycemic, antidiabetic, anti-obesity and antioxidant activities. The aim of this study was...

Evaluation of cannabidiol's inhibitory effect on alpha-glucosidase and its stability in simulated gastric and intestinal fluids

OBJECTIVE

Cannabidiol (CBD) has been reported to have anti-diabetic effects in pre-clinical and clinical studies but its inhibitory effects on α-glucosidase, a carbohydrate hydrolyzing enzyme, remain unknown. Herein, we evaluated CBD's inhibitory effects on α-glucosidase using in vitro assays and computational studies.

METHODS

CBD's inhibitory effect on α-glucosidase activity was evaluated in a yeast enzymatic assay and by molecular docking. The stability of CBD in simulated gastric and intestinal fluids was evaluated by high-performance liquid chromatography analyses.

RESULTS

CBD, at 10, 19, 38, 76, 152, 304, 608, and 1216 μM, inhibited α-glucosidase activity with inhibition of 17.1, 20.4, 48.1, 56.6, 59.1, 63.7, 74.1, and 95.4%, respectively. Acarbose, the positive control, showed a comparable inhibitory activity (with 85.1% inhibition at 608 μM). CBD's inhibitory effect on α-glucosidase was supported by molecular docking showing binding energy (-6.39 kcal/mol) and interactions between CBD and the α-glucosidase protein. CBD was stable in simulated gastric and intestinal fluids for two hours (maintained ≥ 90.0%).

CONCLUSIONS

CBD showed moderate inhibitory effect against yeast α-glucosidase activity and was stable in gastric and intestinal fluids. However, further studies on CBD's anti-α-glucosidase effects using cellular and in vivo models are warranted to support its potential application for the management of type II diabetes mellitus.

Chemical constituents from Tinospora sagittata and their biological activities

Six undescribed low-polarity compounds including three rare 14-methylergostane steroids (1-3), one euphane triterpenoid (4) and two octadecanoic acid ethyl esters (5 and 6), along with ten previously reported terpenyl cometabolites (7-16), were isolated from the stems of Tinospora sagittata. Their structures were determined by detailed spectroscopic analyses and comparison with structurally related known compounds, and all of them have been reported from T. sagittata for the first time. Compounds 4-6 and 16 showed potent in vitro inhibitory activity against the diabetes target α-glucosidase, while compounds 10 and 14 displayed promising antibacterial effect toward Staphylococcus aureus ATCC 25923.

A novel fungal metabolite inhibits Plasmodium falciparum transmission and infection

Background

Malaria transmission depends on infected mosquitoes and can be controlled by transmission-blocking drugs. The recently discovered FREP1-mediated malaria transmission pathway is an excellent target to screen drugs for limiting transmission.

Methods

To identify candidate small molecules, we used an ELISA-based approach to analyze extracts from a fungal library for inhibition of the FREP1–parasite interaction. We isolated and determined one active compound by chromatography and crystallography, respectively. We measured the effects of the bioactive compound on malaria transmission to mosquitoes through standard membrane-feeding assays (SMFA) and on parasite proliferation in blood by culturing.

Results

We discovered the ethyl acetate extract of the fungus Purpureocillium lilacinum that inhibited Plasmodium falciparum transmission to mosquitoes. Pre-exposure to the extract rendered Anopheles gambiae resistant to Plasmodium infection. Furthermore, we isolated one novel active compound from the extract and identified it as 3-amino-7,9-dihydroxy-1-methyl-6H-benzo[c]chromen-6-one, or “pulixin.” Pulixin prevented FREP1 from binding to P. falciparum-infected cell lysate. Pulixin blocked the transmission of the parasite to mosquitoes with an EC₅₀ (the concentration that gave half-maximal response) of 11 µM based on SMFA. Notably, pulixin also inhibited the proliferation of asexual-stage P. falciparum with an EC₅₀ of 47 nM. The compound did not show cytotoxic effects at a concentration of 116 µM or lower.

Conclusion

By targeting the FREP1–Plasmodium interaction, we discovered that Purpureocillium lilacinum extract blocked malaria transmission. We isolated and identified the bioactive agent pulixin as a new compound capable of stopping malaria transmission to mosquitoes and inhibiting parasite proliferation in blood culture.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04677-7.

Profile of bioactive compounds in pequi (Caryocar brasilense Camb.) peel flours

The bioactive compounds of pequi peel flours were characterized. Flavonoid contents ranged from 19.67 to 87.61 mg/100 g, high in comparison to many vegetables described in the literature. Gallic acid (11.52-418.67 mg/100 g), gallate ethyl (2026.75 - 5205.90 mg/100 g), ellagic acid (509.47 - 1630.66 mg/100 g), lutein (0.17-1.36 mg/100 g), β-carotene (0.82 - 1.49 mg/100 g), and β-cryptoxanthin (0.07 - 0.11 mg/100 g) were identified by HPLC, contributing to a greater valorization of the pequi peel flours. Phytochemical tests indicated the presence of hydrolyzable tannins and saponins. The detection of these compounds makes the product commercially attractive, in addition to generating value for an agro-industrial residue. The results obtained in this study confirm the multifunctional potential of pequi peel flour as a functional ingredient.

Preparation and α-Glucosidase Inhibitory Activity of Gallic Acid-Dextran Conjugate

Phenolic acid-polysaccharide conjugates, produced in plant food and medicine processing, are thought to account for the α-glucosidase inhibitory activity of the final products. However, this speculation lacks experimental support because of the complexity of the plant system and the polysaccharide structure. In this study, with dextran (average molecular weight, 1000) as the skeleton, a gallic acid-dextran conjugate was synthesized and confirmed by ultraviolet, infrared, and nuclear magnetic resonance spectroscopic analysis for the first time. Furthermore, this gallic acid-dextran conjugate showed inhibition of α-glucosidase due to galloyl groups in a mixed competitive and noncompetitive inhibition mode, whose performance was superior to that of acarbose.

Bioactive terpenoid constituents from Eclipta prostrata

Chemical fractionation of the ethanolic extract of Eclipta prostrata yielded a series of unreported terpenoid constituents, including a rare 6/6/6/6-fused tetracyclic triterpenoid, a pentacyclic triterpenoid, two pentacyclic triterpenoid saponins, a diterpenoid and a sesquiterpenoid. Structures were assigned to these compounds on the basis of comprehensive spectroscopic analyses, with the absolute configurations of the tetracyclic triterpenoid, the diterpenoid and the sesquiterpenoid being determined via explanation of electronic circular dichroism data. Screening of these isolates in an array of bioassays revealed antibacterial, cytotoxic and α-glucosidase inhibitory activities for selective compounds. Of particular interest, the tetracyclic triterpenoid showed very strong inhibition against α-glucosidase with an IC₅₀ of 0.82 ± 0.18 μM, being 10³-fold as active as the positive control acarbose.

Phenylpropanoid glycosides from the fruit of Lycium barbarum L. and their bioactivity

Fifteen phenylpropanoid glycosides, including six undescribed compounds were isolated from the fruit of Lycium barbarum L. (Solanaceae) (goji or wolfberry). Their structures were identified by detailed spectroscopic analyses. Seven known compounds were firstly isolated from the genus Lycium, in which the 1D and 2D NMR data of one compound were reported for the first time. Notably, two undescribed compounds were a pair of rare tautomeric glycoside anomers characterized by the presence of free anomeric hydroxy. Antioxidant and hypoglycemic activities of all these compounds were assessed using DPPH radical scavenging, oxygen radical absorbance capacity (ORAC), and α-glucosidase inhibitory assays, respectively. These compounds showed different levels of oxygen radical absorbance capacity, and some isolates exhibited potent antioxidant activity with greater ORAC values than the positive control (EGCG).

Liquid state fermentation vinegar enriched with catechin as an antiglycative food product

Catechin, a natural antiglycative agent, was incorporated into fermented vinegar, and has high potential to lower the risk of diabetes. In this study, vinegar containing 5% catechin as a substrate for acetous fermentation significantly inhibited the formation of total fluorescent advanced glycation end-products (AGEs), as well as N^ε-(carboxymethyl)lysine (CML)/N^ε-(carboxyethyl)lysine (CEL), especially when added during acetic fermentation. Further study proved that catechin could not only significantly suppress the increase of blood glucose levels, but also inhibit α-amylase, α-glucosidase and β-glucosidase strongly with IC₅₀ values of 0.533 mg mL^-1, 0.307 mg mL^-1 and 0.413 mg mL^-1, respectively. Moreover, 32 volatile compounds were finally identified by headspace solid phase microextraction gas chromatography-mass spectrometry (HSPM-GC-MS) and electronic nose. The flavor of the catechin-vinegars, which possess relatively high ester and low acid contents, was superior to that of traditional vinegar. Therefore, it was helpful to use catechin as a functional food ingredient in vinegar to prevent AGE-associated diseases and alleviate postprandial hyperglycemia, through limiting the digestion of starch and inhibiting the uptake of glucose. Meanwhile, the pleasant flavor and safety of catechin-vinegar were better than traditional vinegar, which represents prominent value to attract consumers.

Butenolide Derivatives with α-Glucosidase Inhibitions from the Deep-Sea-Derived Fungus Aspergillus terreus YPGA10

Three new butenolide derivatives, namely aspernolides N–P (1–3), together with six known analogues (4–9), were isolated from the ethyl acetate (EtOAc) extract of the deep sea-derived fungus Aspergillus terreus YPGA10. The structures of compounds 1–3 were determined on the basis of comprehensive analyses of the nuclear magnetic resonance (NMR) and mass spectroscopy (MS) data, and the absolute configurations of 1 and 2 were determined by comparisons of experimental electronic circular dichroism (ECD) with calculated ECD spectra. Compound 1 represents the rare example of Aspergillus-derived butenolide derivatives featured by a monosubstituted benzene ring. Compounds 6–9 exhibited remarkable inhibitory effects against α-glucosidase with IC₅₀ values of 3.87, 1.37, 6.98, and 8.06 μM, respectively, being much more active than the positive control acarbose (190.2 μM).

Phenolics from Eugenia jambolana seeds with advanced glycation endproduct formation and alpha-glucosidase inhibitory activities

Published data suggest that dietary-derived phenolics exert beneficial effects against hyperglycemia-mediated diseases, such as diabetes, through inhibiting the formation of advanced glycation endproducts (AGEs) and carbohydrate hydrolyzing enzyme activities. In the course of our investigation on the edible berry, Eugenia jambolana (known as Jamun), 21 phenolics (1-21) were isolated and identified from its seeds. Among these, one compound (1) is new and eleven compounds (3, 6, 9-13, 17, and 19-21) are being reported from E. jambolana for the first time. The anti-AGE activities of thirteen pure isolates (2-7, 9-12, 14, 15, and 20) were either comparable or superior to the synthetic anti-glycation agent, aminoguanidine, at three test concentrations (20, 50, and 100 μM) in the BSA-fructose assay. Most of these phenolics with anti-AGE activity exhibited potent free radical scavenging activity in the DPPH assay, and attenuated intracellular levels of LPS-induced reactive oxygen species in RAW264.7 macrophage. In addition, compounds 2-6, and 14 showed superior α-glucosidase inhibitory activity (IC50 = 5.0-21.2 μM) compared to the clinical α-glucosidase inhibitor, acarbose (IC50 = 289.9 μM). This is the first report of the anti-AGE effects of compounds 2-6 and 9-12, and α-glucosidase inhibitory activities of compounds 3-6, 9, 11 and 14. The current study supports the role of phenolics in the antidiabetic properties attributed to this edible berry, and warrants further animal studies to evaluate their potential as dietary agents for the prevention and/or therapy of hyperglycemia-mediated diseases.

Hypoglycemic and hypolipidemic effects of triterpenoid-enriched Jamun (Eugenia jambolana Lam.) fruit extract in streptozotocin-induced type 1 diabetic mice

The edible berries of Eugenia jambolana Lam. (known as Jamun) are consumed in various parts of the world. Our previous studies revealed that a triterpenoid-enriched Jamun fruit extract (TJFE) showed beneficial effects on glucose homeostasis in non-diabetic mice. Herein, the anti-diabetic effects of TJFE (100 mg kg-1 by oral gavage for ten days) were evaluated in streptozotocin (STZ)-induced type 1 diabetic mice. TJFE significantly attenuated STZ-induced hyperglycemia and glucose intolerance, suppressed the abnormal elevation of hepatic gluconeogenesis, and improved dyslipidemia in the mice. Histopathology and mechanism-based studies revealed that TJFE preserved the architecture and function of pancreatic islets, attenuated insulin secretion deficiency, enhanced insulin/Akt signaling transduction, reduced lipogenic gene expression, and prevented the abnormal activation of Erk MAPK in the liver tissues of the STZ-induced diabetic mice. The current study adds to previously published data supporting the potential beneficial effects of this edible fruit on diabetes management.

Persimmon Tannin Decreased the Glycemic Response through Decreasing the Digestibility of Starch and Inhibiting α-Amylase, α-Glucosidase, and Intestinal Glucose Uptake

Regulation of postprandial blood glucose levels is an effective therapeutic proposal for type 2 diabetes treatment. In this study, the effect of persimmon tannin on starch digestion with different amylose levels was investigated both in vitro and in vivo. Oral administration of persimmon tannin-starch complexes significantly suppressed the increase of blood glucose levels and the area under the curve (AUC) in a dose-dependent manner compared with starch treatment alone in an in vivo rat model. Further study proved that persimmon tannin could not only interact with starch directly but also inhibit α-amylase and α-glucosidase strongly, with IC₅₀ values of 0.35 and 0.24 mg/mL, separately. In addition, 20 μg/mL of persimmon tannin significantly decreased glucose uptake and transport in Caco-2 cells model. Overall, our data suggested that persimmon tannin may alleviate postprandial hyperglycemia through limiting the digestion of starch as well as inhibiting the uptake and transport of glucose.

Visible-light promoted arene C–H/C–X lactonizationviacarboxylic radical aromatic substitution

Photocatalytic carboxylic radical aromatic substitution enables the synthesis of diversely substituted coumarins by inert C–X bond cleavage under mild conditions.

New Sesquiterpenoids from Eugenia jambolana Seeds and Their Anti-microbial Activities

Twenty four sesquiterpenoids, 1-24, including 11 new sesquiterpenoids, jambolanins A-K, and two new norsesquiterpenoids, jambolanes A and B, along with six known triterpenoids, were isolated from the seeds of Eugenia jambolana fruit. Their structures were elucidated on the basis of NMR and MS spectrometry data analysis. Among the isolates, compound 13 possessed a rare 6,7-seco-guaiene skeleton, and compounds 14 and 15 were norsesquiterpenoids containing a spiro[4.4]nonane skeleton. Antimicrobial assay evaluation revealed that sesquiterpenoids, 4, 5/6, 17, 19, 21, 23, and 24 inhibited the growth of the Gram-positive bacterium, Staphylococcus aureus. The current study advances scientific knowledge of E. jambolana phytochemicals and suggests that its sesquiterpenoids may contribute, in part, to the anti-infective effects attributed to the edible fruit of this plant.

Bioactive Asarone-Derived Phenylpropanoids from the Rhizome of Acorus tatarinowii Schott

Eight new (1a/1b, 2a, 3a, 4a/4b, and 5a/5b) and seven known (2b, 3b, and 6-10) asarone-derived phenylpropanoids, a known asarone-derived lignan (12), and four known lignan analogues (11 and 13-15) were isolated from the rhizome of Acorus tatarinowii Schott. The structures were elucidated via comprehensive spectroscopic analyses, modified Mosher's method, and quantum chemical calculations. Compounds 1-8 were present as enantiomers, and 1-5 were successfully resolved via chiral-phase HPLC. Compounds 1a/1b were the first cases of asarone-derived phenylpropanoids with an isopropyl C-3 side-chain tethered to a benzene core from nature. Hypoglycemic, antioxidant, and AChE inhibitory activities of 1-15 were assessed by the α-glucosidase inhibitory, ORAC, DPPH radical scavenging, and AChE inhibitory assays, respectively. All compounds except 3a showed α-glucosidase inhibitory activity. Compound 3b has the highest α-glucosidase inhibitory effect with an IC₅₀ of 80.6 μM (positive drug acarbose IC₅₀ of 442.4 μM). In the antioxidant assays, compounds 13-15 exhibited ORAC and DPPH radical scavenging activities. The results of the AChE inhibitory assay indicated that all compounds exhibited weak AChE inhibitory activities.

Oleanane-Type Saponins from the Roots of Ligulariopsis shichuana and Their α-Glucosidase Inhibitory Activities

Five new oleanane-type saponins, named ligushicosides A-E, and three known oleanane-type saponins were isolated from the roots of Ligulariopsis shichuana. Their structures were established by a combination of spectroscopic techniques, including 1D and 2D NMR and high resolution electrospray ionization mass spectroscopy (HR-ESI-MS). Furthermore, all isolates were evaluated for their yeast α-glucosidase inhibitory effects and exhibited potent inhibition against α-glucosidase, while compounds 1 and 2 showed excellent inhibitory activities. The 3-O-glycoside moiety in oleanane-type saponin is important for the α-glucosidase inhibitory effects.

Chiral resolution, absolute configuration, and bioactivity of a new racemic asarone derivative from the rhizome of Acorus tatarinowii

A new asarone-derived racemate (1) was isolated from the rhizome of Acorus tatarinowii. The structure of 1 was established by comprehensive spectroscopic analyses, and it was successfully resolved by chiral HPLC, demonstrating that it is racemic. The absolute configurations of 1a [(-)-acortatarone A] and 1b [(+)-acortatarone A] were determined using quantum chemical calculations. Compounds 1a and 1b were the first cases of asarone derivatives with the 5,7-dialkyl-6-aryl-8-oxabicyclo[3.2.1]oct-3-en-2-one core. The α-glucosidase inhibitory and acetylcholinesterase (AChE) inhibitory activities of 1 were evaluated, and it exhibited α-glucosidase inhibitory activity with potency close to that of the positive control (acarbose).

Phloroglucinol Derivatives with Protein Tyrosine Phosphatase 1B Inhibitory Activities from Eugenia jambolana Seeds

Fifteen new phloroglucinol derivatives, jamunones A-O (1-8 and 10-16, respectively), along with one known analogue spiralisone C (9), were isolated from Eugenia jambolana seeds. Their structures were elucidated by detailed nuclear magnetic resonance and mass spectrometry spectroscopic data interpretation. Compounds 1-9, 11, 12, and 14-16 inhibited protein tyrosine phosphatase 1B activity with IC₅₀ values ranging from 0.42 to 3.2 μM.

Comparison of analytical techniques for the identification of bioactive compounds from natural products

Covering: 2000 to 2016Natural product extracts are a rich source of bioactive compounds. As a result, the screening of natural products for the identification of novel biologically active metabolites has been an essential part of several drug discovery programs. It is estimated that more than 70% of all drugs approved from 1981 and 2006, were either derived from or structurally similar to nature based compounds indicating the necessity for the development of a rapid method for the identification of novel compounds from plant extracts. The screening of biological matrices for the identification of novel modulators is nevertheless still challenging. In this review we discuss current techniques in phytochemical analysis and the identification of biologically active components.

Screening for potential α-glucosidase and α-amylase inhibitory constituents from selected Vietnamese plants used to treat type 2 diabetes

ETHNOPHARMACOLOGICAL RELEVANCE

The 18 plant species investigated in this study have been used as herbal antidiabetic remedies in Vietnamese traditional medicines. This study aimed to evaluate their ability to inhibit α-glucosidase and α-amylase, two key enzymes involved in serum glucose regulation.

MATERIALS AND METHODS

Chloroform, ethanol and water extracts of 18 plants were screened for α-glucosidase and α-amylase inhibitory activity. Analytical-scale HPLC was subsequently used to investigate the most active extracts, where samples with low level of tannins were identified and fractionated into 96-well microplates, followed by α-glucosidase and α-amylase assessment of each well. High-resolution α-glucosidase and α-amylase inhibition profiles constructed from these assays allowed identification of HPLC peaks correlated with α-glucosidase and α-amylase inhibitory activity. The active constituents were subsequently isolated using preparative-scale HPLC and their structure was elucidated by HR-ESIMS and NMR.

RESULTS

Ethanol extracts of Nepenthes mirabilis, Phyllanthus urinaria, and Kandelia candel significantly inhibited α-glucosidase with IC50 values of 32.7±6.3, 39.7±9.7, and 35.4±13.9μg/mL, respectively. Water extracts of N. mirabilis, Phyllanthus amarus, P. urinaria, Lagerstroemia speciosa, Syzygium cumini, Rhizophora mucronata, and K. candel showed IC50 values of 3.3±0.8, 34.9±1.5, 14.6±4.6, 5.4±0.5, 20.9±1.8, 3.3±0.6, and 4.0±0.8μg/mL, respectively. In the α-amylase inhibition assay, ethanol extracts of K. candel and Ficus racemosa showed IC50 of 7.6±0.9 and 46.7±23.6μg/mL, respectively. Showing low tannin constituents as seen from HPLC profiles, P. amarus and P. urinaria water extracts and F. racemosa ethanol extract were subjected to microfractionation. Only high-resolution α-glucosidase inhibition profiles of P. amarus and P. urinaria water extracts showed several active compounds, which were isolated and identified as corilagin (1), repandusinic acid A (2), and mallotinin (3). IC50 of these compounds were 1.70±0.03, 6.10±0.10, and 3.76±0.15μM, respectively. Kinetics analysis revealed that 1 displayed a mixed type mode of inhibition with Ki and Ki' values of 2.37±0.90 and 2.61±0.61μM, respectively, whereas 2 and 3 competitively inhibited α-glucosidase with Ki values of 4.01±0.47 and 0.65±0.11μM, respectively.

CONCLUSION

Corilagin (1), repandusinic acid A (2), and mallotinin (3) were potent α-glucosidase inhibitors contributing significantly to the inhibitory effect observed for the water extracts of P. amarus and P. urinaria.

Magnetic Ligand Fishing as a Targeting Tool for HPLC-HRMS-SPE-NMR: α-Glucosidase Inhibitory Ligands and Alkylresorcinol Glycosides from Eugenia catharinae

A bioanalytical platform combining magnetic ligand fishing for α-glucosidase inhibition profiling and HPLC-HRMS-SPE-NMR for structural identification of α-glucosidase inhibitory ligands, both directly from crude plant extracts, is presented. Magnetic beads with N-terminus-coupled α-glucosidase were synthesized and characterized for their inherent catalytic activity. Ligand fishing with the immobilized enzyme was optimized using an artificial test mixture consisting of caffeine, ferulic acid, and luteolin before proof-of-concept with the crude extract of Eugenia catharinae. The combination of ligand fishing and HPLC-HRMS-SPE-NMR identified myricetin 3-O-α-L-rhamnopyranoside, myricetin, quercetin, and kaempferol as α-glucosidase inhibitory ligands in E. catharinae. Furthermore, HPLC-HRMS-SPE-NMR analysis led to identification of six new alkylresorcinol glycosides, i.e., 5-(2-oxopentyl)resorcinol 4-O-β-D-glucopyranoside, 5-propylresorcinol 4-O-β-D-glucopyranoside, 5-pentylresorcinol 4-O-[α-D-apiofuranosyl-(1→6)]-β-D-glucopyranoside, 5-pentylresorcinol 4-O-β-D-glucopyranoside, 4-hydroxy-3-O-methyl-5-pentylresorcinol 1-O-β-D-glucopyranoside, and 3-O-methyl-5-pentylresorcinol 1-O-[β-D-glucopyranosyl-(1→6)]-β-D-glucopyranoside.

Aldose reductase and protein tyrosine phosphatase 1B inhibitory active compounds from Syzygium cumini seeds

CONTEXT

Syzygium cumini (L.) Skeels (Myrtaceae), commonly known as jamun, is an Indian plant, traditionally well known for its medicinal properties including antidiabetic activity.

OBJECTIVE

To isolate the antidiabetic compounds from Syzygium cumini seeds and evaluate their activity using aldose reductase (AR) and protein-tyrosine phosphatase 1B (PTP1B) inhibition assays.

MATERIALS AND METHODS

The dried seeds were extracted with methanol and partitioned with ethyl acetate, butanol, and water. The extracts were screened for antidiabetic activity at a concentration of 100 µg/mL using in vitro AR and PTP 1B inhibition assays.

RESULTS AND DISCUSSION

The highly enriched fractions obtained from broad ethyl acetate fraction yielded maslinic acid (1), 5-(hydroxymethyl) furfural (2), gallic acid (3), valoneic acid dilactone (4), rubuphenol (5), and ellagic acid (6). Structures were elucidated by (1)H-NMR and (13)C-NMR. The initial ethyl acetate fraction showed AR inhibitory activity with the IC50 value of 2.50 μg/mL and PTP1B enzyme inhibition with the IC50 value of 26.36 μg/mL. Compounds 3, 4, 5, and 6 were found to inhibit AR with IC50 values of 0.77, 0.075, 0.165, and 0.12 μg/mL while the compounds 4, 5, and 6 inhibited PTP1B with IC50 values of 9.37, 28.14, and 25.96 μg/mL, respectively.

CONCLUSION

The results of this study demonstrate that the isolated constituents show promising in vitro antidiabetic activity and, therefore, can be candidates for in vivo biological screening using relevant models to ascertain their antidiabetic activity.

Dimeric Abietane Diterpenoids and Sesquiterpenoid Lactones from Teucrium viscidum

A new abietane diterpenoid, teuvisone (2), a pair of new dimeric abietane diterpenoid stereoisomers, biteuvisones A (3) and B (4), and three new sesquiterpenoid lactones, teuvislactones A-C (6, 7, and 10), were isolated from the whole plants of Teucrium viscidum, along with four known terpenoids (1, 5, 8, and 9). The structures of the new compounds were elucidated by spectroscopic analysis, and the absolute configurations of 5-10 were determined by electronic circular dichroism analysis. The isolated compounds were evaluated for their cytotoxic effects against five human cancer cell lines and for their α-glucosidase inhibitory effects.