Potent inhibition of bacterial neuraminidase activity by pterocarpans isolated from the roots of Lespedeza bicolor

The role of sialidases in the pathogenesis of bacterial vaginosis and their use as a promising pharmacological target in bacterial vaginosis

Bacterial vaginosis (BV) is an infection of the genital tract characterized by disturbance of the normally Lactobacilli-dominated vaginal flora due to the overgrowth of Gardnerella and other anaerobic bacteria. Gardnerella vaginalis, an anaerobic pathogen and the major pathogen of BV, produces sialidases that cleave terminal sialic acid residues off of human glycans. By desialylation, sialidases not only alter the function of sialic acid-containing glycoconjugates but also play a vital role in the attachment, colonization and spread of many other vaginal pathogens. With known pathogenic effects, excellent performance of sialidase-based diagnostic tests, and promising therapeutic potentials of sialidase inhibitors, sialidases could be used as a biomarker of BV. This review explores the sources of sialidases and their role in vaginal dysbiosis, in aims to better understand their participation in the pathogenesis of BV and their value in the diagnosis and treatment of BV.

Lespedeza maximowiczii flower absolute promotes skin epithelization, barrier properties, and moisturization-related beneficial responses in human keratinocytes

Lespedeza maximowiczii (LM), a member of the legume family, has tyrosinase inhibitory and estrogenic activities. However, its effects on skin-related biological activities remain unclear. Therefore, the present study aimed to explore the effects of LM flower absolute (LMFAb) on skin-related biological events, especially skin re-epithelization, barrier and moisturizing-related keratinocyte (HaCaT cell) responses. In this study, LMFAb was isolated from LM flowers via solvent extraction and its chemical composition analysis was performed using gas chromatography/mass spectrometry. 5-bromo-2'-deoxyuridine incorporation, Boyden chamber, sprout outgrowth, enzyme-linked immunosorbent, and Western blot assay were used to analyze the biological effects of LMFAb on HaCaT cells (a human epidermal keratinocyte cell line). Twelve components were identified in LMFAb. LMFAb promoted cell proliferation, migration, and sprout outgrowth in HaCaT cells. The absolute enhanced the activations of MAPKs (ERK1/2, JNK, and p38), PI3K and AKT proteins in HaCaT cells and elevated collagen type I and IV levels in HaCaT cell conditioned medium. In addition, LMFAb induced an increase in the expression levels of epidermal barrier proteins (filaggrin and involucrin) in HaCaT cells. Furthermore, LMFAb increased hyaluronan (HA) production and expression of HA synthases (HAS-1, HAS-2, and HAS-3) but decreased HYBID (HA binding protein involved in HA depolymerization) level in HaCaT cells. These findings demonstrate that LMFAb might promote skin re-epithelization, barrier and moisturizing-related beneficial responses in keratinocytes. This study suggests that LMFAb should be considered a potential starting material for the development of cosmetic or pharmaceutical agents that restore the functions of damaged skin.

Seven new secondary metabolites isolated from roots of Lespedeza bicolor

Chemical investigation of a methanol extract obtained from the roots of Lespedeza bicolor identified one new pterocarpene (1), three new pterocarpans (2-4), and three new arylbenzofurans (5-7), and two known compounds (8 and 9). Their structures were determined by interpretations obtained from combined UV, NMR, and HRTOFMS spectroscopic data. Furthermore, the absolute configurations of compounds 2 and 3 were established by the combination of electronic circular dichroism (ECD) calculations and NMR calculations with DP4+ probability analysis. All isolated compounds (1-9) were evaluated for cytotoxicity against the human lung carcinoma cell line A549 and the human hepatoma cell line Huh-7. Compound 4 showed antiproliferative activity against A549 cell line with IC50 value of 24.9 μM. Furthermore, compound 9 exhibited cytotoxicity against Huh-7 cell line with IC50 value of 68.7 μM.

2-Geranyl-1-methoxyerythrabyssin II alleviates lipid accumulation and inflammation in hepatocytes through AMPK activation and AKT inhibition

A growing proportion of the global adult and pediatric populations are currently affected by nonalcoholic steatohepatitis (NASH), leading to rising rates of liver fibrosis and hepatocellular carcinoma without effective pharmacotherapy. Here, we investigated whether 2-geranyl-1-methoxyerythrabyssin II (GMET), isolated from Lespedeza bicolor, could alleviate lipid accumulation and inflammatory responses in a NASH model. GMET exhibited potent in vitro and in vivo effects against lipid accumulation and attenuated inflammatory responses without cytotoxicity. Mechanistically, GMET inhibits acetyl-CoA carboxylase (ACC), sterol regulatory element-binding proteins-1c (SREBP1), and mammalian target of rapamycin (mTOR), and activates PPARα by activating AMP-activated kinase (AMPK), leading to the alleviation of lipid accumulation. In addition, GMET suppresses the NF-κB pathway by activating AMPK and inhibiting the activated protein kinase B (AKT)/IκB-kinase (IKK) pathway, leading to the inhibition of the inflammatory response in hepatocytes. All these protective effects of GMET on lipid accumulation and inflammation in vivo and in vitro were largely abolished by co-treatment with dorsomorphin, an AMPK inhibitor. In conclusion, GMET alleviated lipid accumulation and inflammation to preserve normal hepatocyte function in steatohepatitis. Thus, GMET is a novel potential multi-targeting compound to improve steatohepatitis.

Inhibitory Potential of Quercetin Derivatives Isolated from the Aerial Parts of Siegesbeckia pubescens Makino against Bacterial Neuraminidase

This study aimed to isolate bacterial neuraminidase (BNA) inhibitory O-methylated quercetin derivatives from the aerial parts of S. pubescens. All the isolated compounds were identified as O-methylated quercetin (1-4), which were exhibited to be noncompetitive inhibitors against BNA, with IC₅₀ ranging from 14.0 to 84.1 μM. The responsible compounds (1-4) showed a significant correlation between BNA inhibitory effects and the number of O-methyl groups on quercetin; mono (1, IC₅₀ = 14.0 μM) > di (2 and 3, IC₅₀ = 24.3 and 25.8 μM) > tri (4, IC₅₀ = 84.1 μM). In addition, the binding affinities between BNA and inhibitors (1-4) were also examined by fluorescence quenching effect with the related constants (K_SV, K_A, and n). The most active inhibitor 1 possessed a K_SV with 0.0252 × 10⁵ L mol^-1. Furthermore, the relative distribution of BNA inhibitory O-methylated quercetins (1-4) in S. pubescens extract was evaluated using LC-Q-TOF/MS analysis.

The structure characteristics, biosynthesis and health benefits of naturally occurring rare flavonoids

Rare flavonoids, a special subclass of naturally occurring flavonoids with diverse structures including pterocarpans, aurones, neoflavonoids, homoisoflavones, diphenylpropanes, rotenoids and 2-phenylethyl-chromones. They are mainly found in legumes with numerous health benefits. Rare flavonoids are regarded as minor flavonoids due to their very limited abundance in nature. This review gives an overview of the natural occurrences of rare flavonoids from previous literatures. Recent findings on the biosynthesis of rare flavonoids have been updated by describing their structural characteristics and classifications. Recent findings on the health benefits of rare flavonoids have also been compiled and discussed. Natural rare flavonoids with various characteristics from different subclasses from plant-based food sources are stated. They show a wide range of health benefits, including antibacterial, anticancer, anti-osteoporosis and antiviral activities. Studies reviewed suggest that rare flavonoids possessing different skeletons demonstrate different characteristic bioactivities by discussing their mechanism of actions and structure-activity relationships. Besides, recent advances on the biosynthesis of rare flavonoids, such as pterocarpans, rotenoids and aurones are well-known, while the biosynthesis of other subclasses remain unknown. The perspectives and further applications of rare flavonoids using metabolic engineering strategies also be expected.

Polyphenolic Compounds from Lespedeza bicolor Protect Neuronal Cells from Oxidative Stress

Pterocarpans and related polyphenolics are known as promising neuroprotective agents. We used models of rotenone-, paraquat-, and 6-hydroxydopamine-induced neurotoxicity to study the neuroprotective activity of polyphenolic compounds from Lespedeza bicolor and their effects on mitochondrial membrane potential. We isolated 11 polyphenolic compounds: a novel coumestan lespebicoumestan A (10) and a novel stilbenoid 5’-isoprenylbicoloketon (11) as well as three previously known pterocarpans, two pterocarpens, one coumestan, one stilbenoid, and a dimeric flavonoid. Pterocarpans 3 and 6, stilbenoid 5, and dimeric flavonoid 8 significantly increased the percentage of living cells after treatment with paraquat (PQ), but only pterocarpan 6 slightly decreased the ROS level in PQ-treated cells. Pterocarpan 3 and stilbenoid 5 were shown to effectively increase mitochondrial membrane potential in PQ-treated cells. We showed that pterocarpans 2 and 3, containing a 3’-methyl-3’-isohexenylpyran ring; pterocarpens 4 and 9, with a double bond between C-6a and C-11a; and coumestan 10 significantly increased the percentage of living cells by decreasing ROS levels in 6-OHDA-treated cells, which is in accordance with their rather high activity in DPPH^• and FRAP tests. Compounds 9 and 10 effectively increased the percentage of living cells after treatment with rotenone but did not significantly decrease ROS levels.

Hair Regeneration Effects of Lespedeza bicolor Extract In Vivo and In Vitro

Alopecia is a chronic inflammatory skin disease with various causes. Lespedeza bicolor extract (LBE) has been reported to have anti-inflammatory and antioxidative effects. In this study, the activity and mechanisms of LBE as a hair growth agent were investigated. Effects of cell proliferation, cytotoxicity, and cell cycle regulation of LBE and its active component protocatechuic acid (PCA) were evaluated in human dermal papilla cells (DPCs). Hair regeneration effects of LBE in 6-week-old C57BL/6 male mice were also determined using positive control 5% minoxidil. The dose-dependent proliferation of DPCs was estimated in response to LBE treatment (0.8–20 µg/mL). Additionally, significant extension of the anagen phase during the hair cell cycle upon LBE treatment was observed histologically and morphologically. Cell cycle arrest gene expression was determined by quantitative real-time polymerase chain reaction. Lespedezabicolor could be a potent treatment against alopecia through enhancing DPC proliferation and hair regrowth via anagen phase arrest.

Biologically active polyphenolic compounds from Lespedeza bicolor

We investigated the ability of six prenylated prerocarpans, stilbenoid, and a new dimeric flavonoid, lespebicolin B, from stem bark as well as two 3-O-rutinosides and a mixture of 3-O-β-D-glucosides of quercetin and kaempferol from flowers of Lespedeza bicolor to inhibit HSV-1 replication in Vero cells. Pretreatment of HSV-1 with polyphenolic compounds (direct virucidal effect) showed that pterocarpans lespedezol A₂ (1), (6aR,11aR)-6a,11a-dihydrolespedezol A₂ (2), (6aR,11aR)-2-isoprenyldihydrolespedezol A₂ (4), and (6aR,11aR,3'R)-dihydrolespedezol A₃ (5) significantly inhibited viral replication, with a selective index (SI) ≥10. Compound 4 possessed the lowest 50% - inhibiting concentration (IC₅₀) and the highest SI values (2.6 μM and 27.9, respectively) in this test. (6aR,11aR)-2-Isoprenyldihydrolespedezol A₂ (4) also had a moderate effect under simultaneous treatment of Vero cells with the tested compound and virus (IC₅₀ and SI values were 5.86 μM and 12.4, respectively). 3-O-rutinosides of quercetin and kaempferol and a mixture of 3-O-β-D-glucosides of quercetin and kaempferol (10 and 12) also showed significant virucidal activity, with SI values of 12.5, 14.6, and 98.2, respectively, and IC₅₀ values of 8.6, 12.2, and 3.6, respectively. We also performed a quantitative structure-activity relationship (QSAR) analysis of data on the virucidal activity of polyphenolics with 4 < pIC₅₀ < 6. It was found that the virucidal activity of these compounds depended on both the structure of the aromatic part and the conformation of geranyl and isoprenyl side chains of their molecules. These findings are correlated with the largest value of the principal moment of inertia (pmi) descriptor describing the geometry of molecules.

Isoprenylated Flavonoids as Cav3.1 Low Voltage-Gated Ca2+ Channel Inhibitors from Salvia digitaloides

Saldigones A-C (1, 3, 4), three new isoprenylated flavonoids with diverse flavanone, pterocarpan, and isoflavanone architectures, were characterized from the roots of Salvia digitaloides, together with a known isoprenylated flavanone (2). Notably, it's the first report of isoprenylated flavonoids from Salvia species. The structures of these isolates were elucidated by extensive spectroscopic analysis. All of the compounds were evaluated for their activities on Cav3.1 low voltage-gated Ca2+ channel (LVGCC), of which 2 strongly and dose-dependently inhibited Cav3.1 peak current.

Transition Metal-Catalyzed Hydroalkoxylation of Alkynes: An Overview

Oxygen-bearing motifs, mainly the congener heterocycles are ubiquitous due to their presence in various natural products and bioactive scaffolds. Although in literature, several strategies have been developed for their synthesis, hydroalkoxylation of alkynes has come forward as a method of choice and has been used extensively. In particular, hydroalkoxylation of alkynes has gained enormous attention from the synthetic community due to the rapid access to a very useful and reactive synthetic intermediate like 'enol ether'. Furthermore, to manifold the utility of these methods, reports have been developed elaborating the generation of 'enol ether' using hydroalkoxylation and their usage in various reactions in cascade or tandem manner. This review focuses on recent development on the hydroalkoxylation of alkynes for the synthesis of oxygen-containing entities.

1-Methoxylespeflorin G11 Protects HT22 Cells from Glutamate-Induced Cell Death through Inhibition of ROS Production and Apoptosis

This study aimed to investigate the neuroprotective effects of 1-methoxylespeflorin G11 (MLG), a pterocarpan, against glutamate-induced neurotoxicity in neuronal HT22 hippocampal cells. The protective effects of MLG were evaluated using MTT assay and microscopic analysis. The extent of apoptosis was studied using flow cytometric analysis performed on the damaged cells probed with annexin V/propidium iodide. Moreover, mitochondrial reactive oxygen species (ROS) were assessed using flow cytometry through MitoSOXTM Red staining. To determine mitochondrial membrane potential, staining with tetramethylrhodamine and JC-1 was performed followed by flow cytometry. The results demonstrated that MLG attenuates glutamate-induced apoptosis in HT22 cells by inhibiting intracellular ROS generation and mitochondrial dysfunction. Additionally, MLG prevented glutamate-induced apoptotic pathway in HT22 cells through upregulation of Bcl-2 and downregulation of cleaved PARP-1, AIF, and phosphorylated MAPK cascades. In addition, MLG treatment induced HO-1 expression in HT22 cells. These results suggested that MLG exhibits neuroprotective effects against glutamate-induced neurotoxicity in neuronal HT22 cells by inhibiting oxidative stress and apoptosis.

Rhodium-Catalyzed Diastereoselective [3 + 2] Cycloaddition of Carbonyl Ylide: An Access to the Core Ring System of Cordigol and Lophirone H

This paper describes a new synthetic strategy for the construction of tricyclic chromeno/quinolino furan frameworks via creation of two new rings and three contiguous stereogenic centers with high diastereoselectivity through a rhodium-catalyzed intramolecular carbonyl ylide cycloaddition reaction for the first time. This protocol allows the synthesis of the core ring system of natural products such as cordigol and lophirone H.

Bakkenolides and Caffeoylquinic Acids from the Aerial Portion of Petasites japonicus and Their Bacterial Neuraminidase Inhibition Ability

Petasites japonicus have been used since a long time in folk medicine to treat diseases including plague, pestilential fever, allergy, and inflammation in East Asia and European countries. Bioactive compounds that may prevent and treat infectious diseases are identified based on their ability to inhibit bacterial neuraminidase (NA). We aimed to isolate and identify bioactive compounds from leaves and stems of P. japonicas (PJA) and elucidate their mechanisms of NA inhibition. Key bioactive compounds of PJA responsible for NA inhibition were isolated using column chromatography, their chemical structures revealed using ¹ H NMR, ¹³ C NMR, DEPT, and HMBC, and identified to be bakkenolide B (1), bakkenolide D (2), 1,5-di-O-caffeoylquinic acid (3), and 5-O-caffeoylquinic acid (4). Of these, 3 exhibited the most potent NA inhibitory activity (IC₅₀ = 2.3 ± 0.4 μM). Enzyme kinetic studies revealed that 3 and 4 were competitive inhibitors, whereas 2 exhibited non-competitive inhibition. Furthermore, a molecular docking simulation revealed the binding affinity of these compounds to NA and their mechanism of inhibition. Negative-binding energies indicated high proximity of these compounds to the active site and allosteric sites of NA. Therefore, PJA has the potential to be further developed as an antibacterial agent for use against diseases associated with NA.

Polyphenolic Compounds from Lespedeza Bicolor Root Bark Inhibit Progression of Human Prostate Cancer Cells via Induction of Apoptosis and Cell Cycle Arrest

From a root bark of Lespedeza bicolor Turch we isolated two new (7 and 8) and six previously known compounds (1–6) belonging to the group of prenylated polyphenols. Their structures were elucidated using mass spectrometry, nuclear magnetic resonance and circular dichroism spectroscopy. These natural compounds selectively inhibited human drug-resistant prostate cancer in vitro. Prenylated pterocarpans 1–3 prevented the cell cycle progression of human cancer cells in S-phase. This was accompanied by a reduced expression of mRNA corresponding to several human cyclin-dependent kinases (CDKs). In contrast, compounds 4–8 induced a G1-phase cell cycle arrest without any pronounced effect on CDKs mRNA expression. Interestingly, a non-substituted hydroxy group at C-8 of ring D of the pterocarpan skeleton of compounds 1–3 seems to be important for the CDKs inhibitory activity.

Antiproliferative Pterocarpans and Coumestans from Lespedeza bicolor

Chromatographic purification of a methanol extract of the roots of Lespedeza bicolor led to the isolation of four new pterocarpans (1-4), two new coumestans (6 and 7), two new arylbenzofurans (8 and 9), and the known pterocarpan 1-methoxyerythrabyssin II (5). Their structures were identified using NMR spectroscopy, UV spectroscopy, and mass spectrometry. Cytotoxicity assays showed that compounds 1-9 exerted antiproliferative effects on blood cancer cells. Of these compounds, 1 and 6 induced mitochondrial depolarization and induced apoptosis in Jurkat cells. These compounds promoted cell death by inducing cell-cycle arrest at the G1 stage, reducing levels of BCL2, and increasing cleavage of PARP-1. These findings indicate that 1 and 6 are possible lead compounds for the treatment of human leukemia cells via intracellular signaling.

Therapeutic Potential of Lespedeza bicolor to Prevent Methylglyoxal-Induced Glucotoxicity in Familiar Diabetic Nephropathy

Lespedeza bicolor (LB) is often used in traditional medicine to remove toxins, replenish energy stores, and regulate various symptoms of diabetes. This study aimed to explore the use of LB as a therapeutic to prevent diabetic nephropathy in methylglyoxal (MGO)-treated models in vitro and in vivo. Western blotting, immunostaining, and biochemical assays were used to obtain several experimental readouts in renal epithelial cells (LLC-PK1) and BALB/c mice. These include: production of reactive oxygen species (ROS), formation of advanced glycation end-products (AGEs), expression of receptor for advanced glycation end-products (RAGE), apoptotic cell death, glucose levels, fatty acid and triglyceride levels, expression of pro-inflammatory cytokines IL-1β and TNF-α, glyoxalase 1 (Glo1), and nuclear factor erythroid 2-related factor 2 (Nrf2). Pretreatment with LB significantly reduced MGO-induced cellular apoptosis, intracellular production of ROS, and formation of AGEs to ameliorate renal dysfunction in vitro and in vivo. Interestingly, administering LB in MGO-treated cells and mice upregulated the expression of Nrf2 and Glo1, and downregulated the expression of IL-1β and TNF-α. Moreover, LB reduced MGO-induced AGE accumulation and RAGE expression in the kidneys, which subsequently reduced AGE-RAGE interactions. Overall, LB ameliorates renal cell apoptosis and corrects renal dysfunction in MGO-treated mice. These findings extend our understanding of the pathogenic mechanism of MGO-induced nephrotoxicity and regulation of the AGE/RAGE axis by Lespedeza bicolor.

Metabolites of Medicarpin and Their Distributions in Rats

Medicarpin is a bioactive pterocarpan that has been attracting increasing attention in recent years. However, its metabolic fate in vivo is still unknown. To clarify its metabolism and the distribution of its metabolites in rats after oral administration, the HPLC-ESI-IT-TOF-MSⁿ technique was used. A total of 165 new metabolites (13 phase I and 152 phase II metabolites) were tentatively identified, and 104, 29, 38, 41, 74, 28, 24, 15, 42, 8, 10, 3, and 17 metabolites were identified in urine, feces, plasma, the colon, intestine, stomach, liver, spleen, kidney, lung, heart, brain, and thymus, respectively. Metabolic reactions included demethylation, hydrogenation, hydroxylation, glucuronidation, sulfation, methylation, glycosylation, and vitamin C conjugation. M1 (medicarpin glucuronide), M5 (vestitol-1'-O-glucuronide) were distributed to 10 organs, and M1 was the most abundant metabolite in seven organs. Moreover, we found that isomerization of medicarpin must occur in vivo. At least 93 metabolites were regarded as potential new compounds by retrieving information from the Scifinder database. This is the first detailed report on the metabolism of ptercarpans in animals, which will help to deepen the understanding of the metabolism characteristics of medicarpin in vivo and provide a solid basis for further studies on the metabolism of other pterocarpans in animals.

Cytotoxic polyphenolic compounds from Lespedeza bicolor stem bark

Four new pterocarpans (6aR,11aR)-6a,11a-dihydrolespedezol A₂ (2), (6aR,11aR)-2-isoprenyl-6a,11a-dihydrolespedezol A₂ (3), (6aR,11aR,3'R)-6a,11a-dihydrolespedezol A₃ (4), (6aR,11aR,3'S)-6a,11a-dihydrolespedezol A₃ (5) and one new stilbenoid with 1,2-diketone fragment named bicoloketone (6) along with one previously known pterocarpen lespedezol A₂ (1) have been isolated from Lespedeza bicolor stem bark using multistage column chromatography on polyamide and silica gel. The structures of the isolated polyphenolic compounds were determined by spectroscopic methods. The absolute configurations of 4 and 5 were determined by comparison of their electronic circular dichroism (ECD) spectra obtained experimentally and the spectra calculated using time-dependent density functional theory (TDDFT). The isolated compounds exhibited a moderate DPPH scavenging effect and ferric reducing power compared to the reference antioxidant quercetin. The cytotoxicity of compounds against three human cancer cell lines, HTB-19, Kyse-30, and HEPG-2, and two normal cell lines, RPE-1 and HEK-293, was tested using the MTT assay. Compound 3 showed the strongest cytotoxic activity against all cell lines (IC₅₀ 6.0-19.1 μM) compared with the positive control cisplatin. The other tested compounds possessed moderate cytotoxic activity against cancer cells.

Design, synthesis, and evaluation of curcumin analogues as potential inhibitors of bacterial sialidase

Sialidases are key virulence factors that remove sialic acid from the host cell surface glycan, unmasking receptors that facilitate bacterial adherence and colonisation. In this study, we developed potential agents for treating bacterial infections caused by Streptococcus pneumoniae Nan A that inhibit bacterial sialidase using Turmeric and curcumin analogues. Design, synthesis, and structure analysis relationship (SAR) studies have been also described. Evaluation of the synthesised derivatives demonstrated that compound 5e was the most potent inhibitor of S. pneumoniae sialidase (IC50 = 0.2 ± 0.1 µM). This compound exhibited a 3.0-fold improvement in inhibitory activity over that of curcumin and displayed competitive inhibition. These results warrant further studies confirming the antipneumococcal activity 5e and indicated that curcumin derivatives could be potentially used to treat sepsis by bacterial infections.

Pterocarpan scaffold: A natural lead molecule with diverse pharmacological properties

Phytoalexins are substances produced by plants that act as potent inhibitors of pathogens. Pterocarpans are biologically active isoflavonoids most commonly found in the family Fabaceae that have the ability to act as phytoalexins. It is made up of a tetracyclic ring system possessing benzofuran-benzopyran. A very great number of pterocarpans have been isolated from natural sources and they are proved to have significant biological activities such as anti-microbial, anti-cancerous, anti-inflammatory and anti-malarial activities. Recently, pterocarpans gained lot of attention because of the broad range of anti-cancer activities in various cancer cell lines such as breast, leukemia, cervical, lung, colon and melanoma. Interestingly, pterocarpans exhibited inhibitory potency against many enzymes such as PTP1B, Neuraminidase, and α-glycosidase. In addition, they were shown to have anti-estrogenic and anti-diabetic activities. This review is a comprehensive inventory of the structures and sources of pterocarpans and it emphasizes on the biological evaluations of pterocarpans from various plant sources and their scope as a lead molecule.

Plant Natural Products Targeting Bacterial Virulence Factors

Decreased antimicrobial efficiency has become a global public health issue. The paucity of new antibacterial drugs is evident, and the arsenal against infectious diseases needs to be improved urgently. The selection of plants as a source of prototype compounds is appropriate, since plant species naturally produce a wide range of secondary metabolites that act as a chemical line of defense against microorganisms in the environment. Although traditional approaches to combat microbial infections remain effective, targeting microbial virulence rather than survival seems to be an exciting strategy, since the modulation of virulence factors might lead to a milder evolutionary pressure for the development of resistance. Additionally, anti-infective chemotherapies may be successfully achieved by combining antivirulence and conventional antimicrobials, extending the lifespan of these drugs. This review presents an updated discussion of natural compounds isolated from plants with chemically characterized structures and activity against the major bacterial virulence factors: quorum sensing, bacterial biofilms, bacterial motility, bacterial toxins, bacterial pigments, bacterial enzymes, and bacterial surfactants. Moreover, a critical analysis of the most promising virulence factors is presented, highlighting their potential as targets to attenuate bacterial virulence. The ongoing progress in the field of antivirulence therapy may therefore help to translate this promising concept into real intervention strategies in clinical areas.

Seasonal Variations of Metabolome and Tyrosinase Inhibitory Activity of Lespedeza maximowiczii during Growth Periods

Lespedeza species are useful for pasture and energy crops as well as medical plants. We determined the metabolites discriminated from the each growth period (3, 4, 6, 8, 15, and 18 months) after germination in leaves and stems of Lespedeza maximowizii by a metabolomics technique. Specifically, levels of sugars and luteolin-dominated derivatives were significantly elevated in samples harvested in November. This may be related to the cold tolerance mechanism against the low temperatures of the winter season. The concentrations of secondary metabolites, isoflavones and flavanones, as well as tyrosinase inhibitory activity were the highest in the 6 month samples, which were harvested in September, during the fall season. The tyrosinase inhibitory activity in leaves was higher than that in stems irrespective of the growth period. This study suggests that mass spectrometry-based metabolite profiling could be used as a tool to examine quantitative or qualitative metabolite changes related to seasonal variations and to understand the correlation between activity and metabolites.

Velucarpins A-C, three new pterocarpans and their cytotoxicity from the roots of Dalbergia velutina

Three new pterocarpans, named velucarpins A-C (1-3), along with three known pterocarpans (4-6) were isolated from the roots of Dalbergia velutina. Their structures were determined by spectroscopic analysis. All isolated compounds were evaluated for their cytotoxicity against KB and HeLa cell lines. Compounds 3 and 5 showed good cytotoxicity against KB and HeLa cells with IC50 values of 8.22, 8.09 μM and 5.99, 8.69 μM, respectively.

Structural basis of sialidase in complex with geranylated flavonoids as potent natural inhibitors

Sialidase catalyzes the removal of a terminal sialic acid from glycoconjugates and plays a pivotal role in nutrition, cellular interactions and pathogenesis mediating various infectious diseases including cholera, influenza and sepsis. An array of antiviral sialidase agents have been developed and are commercially available, such as zanamivir and oseltamivir for treating influenza. However, the development of bacterial sialidase inhibitors has been much less successful. Here, natural polyphenolic geranylated flavonoids which show significant inhibitory effects against Cp-NanI, a sialidase from Clostridium perfringens, are reported. This bacterium causes various gastrointestinal diseases. The crystal structure of the Cp-NanI catalytic domain in complex with the best inhibitor, diplacone, is also presented. This structure explains how diplacone generates a stable enzyme-inhibitor complex. These results provide a structural framework for understanding the interaction between sialidase and natural flavonoids, which are promising scaffolds on which to discover new anti-sialidase agents.