Identification of two key genes involved in flavonoid catabolism and their different roles in apple resistance to biotic stresses

Biosynthesis of flavonoid aglycones and glycosides is well established. However, key genes involved in their catabolism are poorly understood, even though the products of hydrolysis and oxidation play important roles in plant resistance to biotic stress. Here, we report on catabolism of dihydrochalcones (DHCs), the most abundant flavonoids in domesticated apple and wild Malus. Two key genes, BGLU13.1 and PPO05, were identified by activity-directed protein purification. BGLU13.1-A hydrolyzed phlorizin, (the most abundant DHC in domesticated apple) to produce phloretin which was then oxidized by PPO05. The process differed in some wild Malus, where trilobatin (a positional isomer of phlorizin) was mainly oxidized by PPO05. The effects of DHC catabolism on apple resistance to biotic stresses was investigated using transgenic plants. Either directly or indirectly, phlorizin hydrolysis affected resistance to the phytophagous pest two-spotted spider mite, while oxidation of trilobatin was involved in resistance to the biotrophic fungus Podosphaera leucotricha. DHC catabolism did not affect apple resistance to necrotrophic pathogens Valsa mali and Erwinia amylovara. These results suggest that different DHC catabolism pathways play different roles in apple resistance to biotic stresses. The role of DHC catabolism on apple resistance appeared closely related to the mode of invasion/damage used by pathogen/pest.

New compounds from the stems of Fissistigma acuminatissimum Merr. and their in vitro anti-inflammatory activity

Three new compounds, 4,5,6,7-tetramethoxy-3-benzoylbenzofuran (1), 4-hydroxy-3,5,6-trimethoxydihydrochalcone-2-O-β-D-glucopyranoside (2) and 2-hydroxy-3,4,5,6-tetramethoxyphenylethyl benzoate (3) along with five known flavonoids were isolated from the dichloromethane fraction of the stems of Fissistigma acuminatissimum Merr.'s ethanol extracts. The compounds were obtained by chromatographic methods and the structure elucidation was completed primarily on the basis of spectroscopic analyses, all of these compounds were isolated from F. acuminatissimum for the first time. All the fractions and compounds were evaluated for their anti-inflammatory activity against lipopolysaccharide (LPS)-stimulated tumor necrosis factor α (TNF-α) production in RAW264.7 cells in vitro. The dichloromethane fraction showed the most potent inhibition(38.2%) at 60 μg/mL, compound 1 (70.2%) and 3 (65.2%) showed significant inhibition at 10 μM.

Comprehensive Analysis of Metabolome and Transcriptome in Fruits and Roots of Kiwifruit

Kiwifruit (Actinidia chinensis) roots instead of fruits are widely used as Chinese medicine, but the functional metabolites remain unclear. In this study, we conducted comparative metabolome analysis between root and fruit in kiwifruit. A total of 410 metabolites were identified in the fruit and root tissues, and of them, 135 metabolites were annotated according to the Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway. Moreover, 54 differentially expressed metabolites (DEMs) were shared in root and fruit, with 17 DEMs involved in the flavonoid pathway. Of the 17 DEMs, three flavonols (kaempferol-3-rhamnoside, L-Epicatechin and trifolin) and one dihydrochalcone (phloretin) showed the highest differences in the content level, suggesting that flavonols and dihydrochalcones may act as functional components in kiwifruit root. Transcriptome analysis revealed that genes related to flavonols and dihydrochalcones were highly expressed in root. Moreover, two AP2 transcription factors (TFs), AcRAP2-4 and AcAP2-4, were highly expressed in root, while one bHLH TF AcbHLH62 showed extremely low expression in root. The expression profiles of these TFs were similar to those of the genes related to flavonols and dihydrochalcones, suggesting they are key candidate genes controlling the flavonoid accumulation in kiwifruit. Our results provided an insight into the functional metabolites and their regulatory mechanism in kiwifruit root.

Effects of Polyphenols on Glucose-Induced Metabolic Changes in Healthy Human Subjects and on Glucose Transporters

Dietary polyphenols interact with glucose transporters in the small intestine and modulate glucose uptake after food or beverage consumption. This review assesses the transporter interaction in vitro and how this translates to an effect in healthy volunteers consuming glucose. As examples, the apple polyphenol phlorizin inhibits sodium-glucose linked transporter-1; in the intestinal lumen, it is converted to phloretin, a strong inhibitor of glucose transporter-2 (GLUT2), by the brush border digestive enzyme lactase. Consequently, an apple extract rich in phlorizin attenuates blood glucose and insulin in healthy volunteers after a glucose challenge. On the other hand, the olive phenolic, oleuropein, inhibits GLUT2, but the strength of the inhibition is not enough to modulate blood glucose after a glucose challenge in healthy volunteers. Multiple metabolic effects and oxidative stresses after glucose consumption include insulin, incretin hormones, fatty acids, amino acids, and protein markers. However, apart from acute postprandial effects on glucose, insulin, and some incretin hormones, very little is known about the acute effects of polyphenols on these glucose-induced secondary effects. In summary, attenuation of the effect of a glucose challenge in vivo is only observed when polyphenols are strong inhibitors of glucose transporters.

Anti-Obesity Evaluation of Averrhoa carambola L. Leaves and Assessment of Its Polyphenols as Potential α-Glucosidase Inhibitors

Averrhoa carambola L. is reported for its anti-obese and anti-diabetic activities. The present study aimed to investigate its aqueous methanol leaf extract (CLL) in vivo anti-obese activity along with the isolation and identification of bioactive compounds and their in vitro α-glucosidase inhibition assessment. CLL improved all obesity complications and exhibited significant activity in an obese rat model. Fourteen compounds, including four flavone glycosides (1–4) and ten dihydrochalcone glycosides (5–12), were isolated and identified using spectroscopic techniques. New compounds identified in planta included (1) apigenin 6-C-(2-deoxy-β-D-galactopyranoside)-7-O-β-D-quinovopyranoside, (8) phloretin 3′-C-(2-O-(E)-cinnamoyl-3-O-β-D-fucopyranosyl-4-O-acetyl)-β-D-fucopyranosyl-6′-O-β-D fucopyranosyl-(1/2)-α-L arabinofuranoside, (11a) phloretin3′-C-(2-O-(E)-p-coumaroyl-3-O-β-D-fucosyl-4-O-acetyl)-β-D-fucosyl-6′-O-(2-O-β-D-fucosyl)-α-L-arabinofuranoside, (11b) phloretin3′-C-(2-O-(Z)-p-coumaroyl-3-O-β-D-fucosyl-4-O-acetyl)-β-D-fucosyl-6′-O-(2-O-β-D-fucosyl)-α-L-arabinofuranoside. Carambolaside M (5), carambolaside Ia (6), carambolaside J (7), carambolaside I (9), carambolaside P (10a), carambolaside O (10b), and carambolaside Q (12), which are reported for the first time from A. carambola L. leaves, whereas luteolin 6-C-α-L-rhamnopyranosyl-(1-2)-β-D-fucopyranoside (2), apigenin 6-C-β-D-galactopyranoside (3), and apigenin 6-C-α-L-rhamnopyranosyl-(1-2)-β-L-fucopyranoside (4) are isolated for the first time from Family. Oxalidaceae. In vitro α-glucosidase inhibitory activity revealed the potential efficacy of flavone glycosides, viz., 1, 2, 3, and 4 as antidiabetic agents. In contrast, dihydrochalcone glycosides (5–11) showed weak activity, except for compound 12, which showed relatively strong activity.

Synthesis of Asebogenin and Balsacone A Precursor by a Novel Synthetic Strategy: Recent Opportunities for and Challenges of Total Synthesis of Balsacone A

One of the main areas of interest of synthetic organic chemistry is the rapid construction of small molecules with proven diverse biological activities for the development of new strategies to cure human health. In particular, the development of novel synthetic strategies is the most important option for reaching the molecular scaffolds of active molecules of natural origin. Balsacone A and asebogenin are compounds that exhibit a wide variety of important biological activities. In this respect, it has become very important to develop new strategies for the construction of biologically active natural and synthetic balsacone analogues. In particular, balsacone derivatives with hydroxy-substituted dihydrochalcone skeletons can be isolated from plant sources or obtained by hemi-syntheses using bio-sourced precursors. An efficient synthetic strategy to synthetically obtain balsacone A is the aim of the present study that considers the limited natural availability of these molecules as well as other factors, such as cost and time. Starting with phloroglucinol, a nine-step synthesis of the precursor of balsacone A was achieved at a 10% overall yield. Furthermore, asebogenin, which has a dihydrochalcone structure and plays a key role in the synthesis of balsacone A, was synthesised with a good yield.

Snailase: A Promising Tool for the Enzymatic Hydrolysis of Flavonoid Glycosides From Plant Extracts

Plants typically contain a broad spectrum of flavonoids in varying concentrations. As a rule, several flavonoid classes occur in parallel, and, even for a single flavonoid, divergent glycosylation patterns are frequently observed, many of which are not commercially available. This can be challenging in studies in which the distribution between flavonoid classes, or features that are not affected by glycosylation patterns, are adressed. In addition, hydrolysis simplifies the quantification process by reducing peak interferences and improving the peak intensity due to the accumulation of the respective aglycone. Effective removal of glycose moieties can also be relevant for technological applications of flavonoid aglycones. Herein, we present a fast and reliable method for the enzymatic hydrolysis glycosides from plant extracts using the commercial enzyme mix snailase, which provided the highest aglycone yields across all investigated flavonoids (aurones: leptosidin, maritimetin, sulfuretin; chalcones: butein, lanceoletin, okanin, phloretin; dihydroflavonols: dihydrokaempferol; flavanones: eriodictyol, hesperetin; flavones: acacetin, apigenin, diosmetin, luteolin; flavonols: isorhamnetin, kaempferol, myricetin, quercetin; isoflavones: biochanin A, formononetin, genistein) from methanolic extracts of nine plants (Bidens ferulifolia, Coreopsis grandiflora, Fagus sylvatica, Malus × domestica, Mentha × piperita, Petunia × hybrida, Quercus robur, Robinia pseudoacacia, and Trifolium pratense) in comparison to four other enzymes (cellobiase, cellulase, β-glucosidase, and pectinase), as well as to acidic hydrolysis by hydrochloric acid.

Dihydrochalcones from the leaves of Lithocarpus litseifolius

Three new phlorizin derivatives, 6"-O-vanilloylphlorizin (1), 6"-O-(4-hydroxybenzoyl)phlorizin (2), 6"-O-feruloylphlorizin (3), along with four known dihydrochalcones, phlorizin (4), 3-hydroxyphlorizin, trilobatin, and 6"-O-acetylphlorizin were isolated from the leaves of Lithocarpus litseifolius. Their structures were established by analysis of extensive spectroscopic data. The new compounds were shown to be non-cytotoxic when tested against A549, HeLa, HepG2, and MCF-7 cell lines.

Enzymatic Production of 3-OH Phlorizin, a Possible Bioactive Polyphenol from Apples, by Bacillus megaterium CYP102A1 via Regioselective Hydroxylation

Phlorizin is the most abundant glucoside of phloretin from the apple tree and its products. Phlorizin and its aglycone phloretin are currently considered health-beneficial polyphenols from apples useful in treating hyperglycemia and obesity. Recently, we showed that phloretin could be regioselectively hydroxylated to make 3-OH phloretin by Bacillus megaterium CYP102A1 and human P450 enzymes. The 3-OH phloretin has a potent inhibitory effect on differentiating 3T3-L1 preadipocytes into adipocytes and lipid accumulation. The glucoside of 3-OH phloretin would be a promising agent with increased bioavailability and water solubility compared with its aglycone. However, procedures to make 3-OH phlorizin, a glucoside of 3-OH phloretin, using chemical methods, are not currently available. Here, a biocatalytic strategy for the efficient synthesis of a possibly valuable hydroxylated product, 3-OH phlorizin, was developed via CYP102A1-catalyzed regioselective hydroxylation. The production of 3-OH phlorizin by CYP102A1 was confirmed by HPLC and LC–MS spectroscopy in addition to enzymatic removal of its glucose moiety for comparison to 3-OH phloretin. Taken together, in this study, we found a panel of mutants from B. megaterium CYP102A1 could catalyze regioselective hydroxylation of phlorizin to produce 3-OH phlorizin, a catechol product.

Hemisynthesis and Biological Evaluation of Cinnamylated, Benzylated, and Prenylated Dihydrochalcones from a Common Bio-Sourced Precursor

Several families of naturally occurring C-alkylated dihydrochalcones display a broad range of biological activities, including antimicrobial and cytotoxic properties, depending on their alkylation sidechain. The catalytic Friedel-Crafts alkylation of the readily available aglycon moiety of neohesperidin dihydrochalcone was performed using cinnamyl, benzyl, and isoprenyl alcohols. This procedure provided a straightforward access to a series of derivatives that were structurally related to natural balsacones, uvaretin, and erioschalcones, respectively. The antibacterial and cytotoxic potential of these novel analogs was evaluated in vitro and highlighted some relations between the structure and the pharmacological properties of alkylated dihydrochalcones.

A new dimethoxy dihydrochalcone isolated from the shoots of Empetrum nigrum L

A new dihydrochalcone, 2',4'-dimethoxydihydrochalcone (1), together with 7 known compounds, 2',4'-dihydroxydihydrochalcone (2), 2'-hydroxy-4'-methoxydihydrochalcone (3), 2'-hydroxy-4'-methoxychalcone (4), 1-(3,5-dihydroxy-4-methoxyphenyl)-2-(3-hydroxyphenyl) ethane (5), 2,3,4,7-tetramethoxy-9,10-dihydrophenanthrene (6), 5-hydroxy-2,3,4-trimethoxy-9,10-dihydrophenanthrene (7) and 5,7-dihydroxy-6,8-dimethyl flavanone (8) were isolated from the shoots of Empetrum nigrum L. The structures of these compounds were elucidated using 1D and 2D NMR experiments along with HR-ESI-MS. Compound 6 is reported for the genus Empetrum for the first time.

Overexpression of chalcone isomerase in apple reduces phloridzin accumulation and increases susceptibility to herbivory by two-spotted mites

Apples (Malus spp.) accumulate significant quantities of the dihydrochalcone glycoside, phloridzin, whilst pears (Pyrus spp.) do not. To explain this difference, we hypothesized that a metabolic bottleneck in the phenylpropanoid pathway might exist in apple. Expression analysis indicated that transcript levels of early phenylpropanoid pathway genes in apple and pear leaves were similar, except for chalcone isomerase (CHI), which was much lower in apple. Apples also showed very low CHI activity compared with pear. To relieve the bottleneck at CHI, transgenic apple plants overexpressing the Arabidopsis AtCHI gene were produced. Unlike other transgenic apples where phenylpropanoid flux was manipulated, AtCHI overexpression (CHIox) plants were phenotypically indistinguishable from wild-type, except for an increase in red pigmentation in expanding leaves. CHIox plants accumulated slightly increased levels of flavanols and flavan-3-ols in the leaves, but the major change was a 2.8- to 19-fold drop in phloridzin concentrations compared with wild-type. The impact of these phytochemical changes on insect preference was studied using a two-choice leaf assay with the polyphagous apple pest, the two-spotted spider mite (Tetranychus urticae Koch). Transgenic CHIox leaves were more susceptible to herbivory, an effect that could be reversed (complemented) by application of phloridzin to transgenic leaves. Taken together, these findings shed new light on phenylpropanoid biosynthesis in apple and suggest a new physiological role for phloridzin as an antifeedant in leaves.

Management of periorbital hyperpigmentation: An overview of nature-based agents and alternative approaches

Periorbital hyperpigmentation (POH) is a common dermatological condition that presents as dark periorbital area beneath the lower eyelids, and it is commonly found in females belonging to the age group of 16 to 45 years. The data presented in this review include studies conducted on patients with a clinical/histological diagnosis of POH or melasma. Many diverse topical depigmenting agents comprising an array of naturally obtained actives such as arabinoxylans, α-arbutin, asiaticoside, azelaic acid, beta-carotene, boswellic acid, caffeine, chrysin, curcumin, cyanidin-3-glucoside, d-glucoronic acid, dihydrochalcone, dipalmitoyl-hydroxyprolene, fucoxanthin, genistein, glabridin, b-glucogallin, hyaluronic acid, lactic acid, lycopene, niacinamide, pycnogenol, retinol, salidroside, and xymenynic acid demonstrated significant benefits in the management of POH. An exhaustive literature search revealed that other techniques such as blepharoplasty, carboxytherapy, calcium hydroxylapatite fillers, tear trough implant, Q-switched ruby laser, medicated tattoo, fat transfer, micro-needling, chemical peels, nitrogen plasma skin regeneration, intense pulsed light, and radiofrequency have been evaluated and reported to be beneficial in the treatment of POH. The use of topical depigmenting agents is the most widely reported method in the clinical management of POH. Of these, α-arbutin, caffeine, cyanidin-3-glucoside, and dihydrochalcone are reported to exhibit significant benefits. Combination products containing a blend of actives are reported to be better than single active containing products. This review aims to provide a comprehensive perspective on the role of several topical actives in the modulation of melanin and tyrosinase biosynthesis pathway involved in the complex pathophysiology of POH. It also presents the advantages of combination products and other alternative therapies used in the management of POH.

Dihydrochalcone Derivatives from Populus balsamifera L. Buds for the Treatment of Psoriasis

Psoriasis is a skin disorder characterized by epidermal hyperplasia, hyperkeratosis, and inflammation. The treatments currently available on the market only improve patients' quality of life and are associated with undesirable side effects. Thus, research leading to the development of new, effective, and safer therapeutic agents is still relevant. Populus balsamifera L. buds were used traditionally by Native Americans to treat various skin pathologies such as eczema and psoriasis. In this study, the antipsoriatic activities of dihydrochalcone derivatives from Populus balsamifera L. buds, known as balsacones, were investigated. The experiments were performed in vitro using a psoriatic skin substitute model. Also, anti-inflammatory and antioxidant activities were investigated. The tested balsacones showed promising antipsoriatic properties by slowing down cell growth and by regulating the expression of involucrin, loricrin, and Ki67 better than methotrexate in psoriatic substitutes. All five tested compounds could be an effective topical treatment for psoriasis, with promising anti-inflammatory and antioxidant actions that may contribute to clinical improvement in patients with psoriasis.

A unique C-linked chalcone-dihydrochalcone dimer from Dracaena cinnabari resin

A new C-linked chalcone-dihydrochalcone dimer, named dracidione, was isolated from the ethyl acetate extract of dragon's blood resin of Dracaena cinnabari Balf. f. Structure elucidation of the new compound was carried out by means of one- and two-dimensional NMR spectroscopy in addition to high resolution mass spectrometry. The unique structure incorporated a chalcone and a dihydrochalcone, which is reported for the first time from nature. Furthermore, dracidione showed moderate α-glucosidase inhibitory activity with IC₅₀= 40.27 µg/ml.

Effective Hydrogenation of 3-(2"-furyl)- and 3-(2"-thienyl)-1-(2'-hydroxyphenyl)-prop-2-en-1-one in Selected Yeast Cultures

Biotransformations were performed on eight selected yeast strains, all of which were able to selectively hydrogenate the chalcone derivatives 3-(2"-furyl)- (1) and 3-(2"-thienyl)-1-(2'-hydroxyphenyl)-prop-2-en-1-one (3) into 3-(2"-furyl)- (2) and 3-(2"-thienyl)-1-(2'-hydroxyphenyl)-propan-1-one (4) respectively. The highest efficiency of hydrogenation of the double bond in the substrate 1 was observed in the cultures of Saccharomyces cerevisiae KCh 464 and Yarrowia lipolytica KCh 71 strains. The substrate was converted into the product with > 99% conversion just in six hours after biotransformation started. The compound containing the sulfur atom in its structure was most effectively transformed by the Yarrowia lipolytica KCh 71 culture strain (conversion > 99%, obtained after three hours of substrate incubation). Also, we observed that, different strains of tested yeasts are able to carry out the bioreduction of the used substrate with different yields, depending on the presence of induced and constitutive ene reductases in their cells. The biggest advantage of this process is the efficient production of one product, practically without the formation of side products.

3'-O-β-d-glucopyranosyl-α,4,2',4',6'-pentahydroxy-dihydrochalcone, from Bark of Eysenhardtia polystachya Prevents Diabetic Nephropathy via Inhibiting Protein Glycation in STZ-Nicotinamide Induced Diabetic Mice

Previous studies have shown that accumulation of advanced glycation end products (AGEs) can be the cause of diabetic nephropathy (DN) in diabetic patients. Dihydrochalcone 3′-O-β-d-glucopyranosyl α,4,2′,4′,6′-pentahydroxy–dihydrochalcone (1) is a powerful antiglycation compound previously isolated from Eysenhardtia polystachya. The aim was to investigate whether (1) was able to protect against diabetic nephropathy in streptozotocin (STZ)-induced diabetic mice, which displayed renal dysfunction markers such as body weight, creatinine, uric acid, serum urea, total urinary protein, and urea nitrogen in the blood (BUN). In addition, pathological changes were evaluated including glycated hemoglobin (HbA1c), advanced glycation end products (AGEs) in the kidney, as well as in circulation level and pro-inflammatory markers ICAM-1 levels in diabetic mice. After 5 weeks, these elevated markers of dihydrochalcone treatment (25, 50 and 100 mg/kg) were significantly (p < 0.05) attenuated. In addition, they ameliorate the indices of renal inflammation as indicated by ICAM-1 markers. The kidney and circulatory AGEs levels in diabetic mice were significantly (p < 0.05) attenuated by (1) treatment. Histological analysis of kidney tissues showed an important recovery in its structure compared with the diabetic group. It was found that the compound (1) attenuated the renal damage in diabetic mice by inhibiting AGEs formation.

Antioxidant Structure⁻Activity Relationship Analysis of Five Dihydrochalcones

The study determined the comparative antioxidant capacities of five similar dihydrochalcones: phloretin, phloridzin, trilobatin, neohesperidin dihydrochalcone, and naringin dihydrochalcone. In the ferric-reducing antioxidant power (FRAP) assay, the antioxidant activities of pairs of dihydrochalcones had the following relationship: phloretin > phloridzin, phloretin > trilobatin, trilobatin > phloridzin, trilobatin > naringin dihydrochalcone, and neohesperidin dihydrochalcone > naringin dihydrochalcone. Similar relative antioxidant levels were also obtained from 1,1-diphenyl-2-picryl-hydrazl radical (DPPH•)-scavenging, 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) (ABTS•⁺)-scavenging, and superoxide radical (•O₂⁻)-scavenging assays. Using ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC−ESI−Q−TOF−MS/MS) analysis for the reaction products with DPPH•, phloretin, phloridzin, and trilobatin were found to yield both dihydrochalcone-DPPH adduct and dihydrochalcone-dihydrochalcone dimer, whereas naringin dihydrochalcone gave a naringin dihydrochalcone-DPPH adduct, and neohesperidin dihydrochalcone gave a dimer. In conclusion, the five dihydrochalcones may undergo redox-based reactions (especially electron transfer (ET) and hydrogen atom transfer (HAT)), as well as radical adduct formation, to exert their antioxidant action. Methoxylation at the ortho-OH enhances the ET and HAT potential possibly via p-π conjugation, whereas the glycosylation of the –OH group not only reduces the ET and HAT potential but also hinders the ability of radical adduct formation. The 2′,6′-di-OH moiety in dihydrochalcone possesses higher ET and HAT activities than the 2′,4′-di-OH moiety because of its resonance with the adjacent keto group.

A dihydrochalcone derivative and further steroidal saponins from Sansevieria trifasciata Prain

Phytochemical investigation of the aerial parts of Sansevieria trifasciata, one of the most common Dracaenaceae plants, has resulted in the isolation of a new dihydrochalcone derivative named trifasciatine C (1), four previously unreported steroidal saponins as two pairs of inseparable regioisomers: trifasciatosides K/L (2/3), M/N (4/5), together with the known 1,2-(dipalmitoyl)-3-O-β-D-galactopyranosylglycerol (6), aconitic acid (7), and 1-methyl aconitic acid (8). Their structures were elucidated mainly by extensive spectroscopic analysis (1D and 2D nuclear magnetic resonance) and high-resolution electronspray ionization-mass spectrometry, as well as chemical methods and comparison of their spectral data with those of related compounds. Compounds 2/3 and 4/5 were evaluated for their antiproliferative activity on Hela cells, and no significant effect was observed.

Stenotrophomonas maltophilia: A Gram-Negative Bacterium Useful for Transformations of Flavanone and Chalcone

A group of flavones, isoflavones, flavanones, and chalcones was subjected to small-scale biotransformation studies with the Gram-negative Stenotrophomonas maltophilia KB2 strain in order to evaluate the capability of this strain to transform flavonoid compounds and to investigate the relationship between compound structure and transformation type. The tested strain transformed flavanones and chalcones. The main type of transformation of compounds with a flavanone moiety was central heterocyclic C ring cleavage, leading to chalcone and dihydrochalcone structures, whereas chalcones underwent reduction to dihydrochalcones and cyclisation to a benzo-γ-pyrone moiety. Substrates with a C-2–C-3 double bond (flavones and isoflavones) were not transformed by Stenotrophomonas maltophilia KB2.

Dihydrochalcones and Diterpenoids from Pteris ensiformis and Their Bioactivities

Two new dihydrochalcone enantiomers (+)-1 and (-)-1, along with eight known compounds 3-10, were obtained from Pteris ensiformis. The planar structures were determined on the basis of extensive 1D and 2DNMR and HRESIMS. The resolution of (+)-1 and (-)-1 was achieved by chiral HPLC analysis. The absolute configurations of (+)-1 and (-)-1 were established by the bulkiness rule using Rh₂(O₂CCF₃)₄-induced circular dichroism (ICD) method. Compounds (+)-1, (-)-1, 8, 9 and 10 exhibited the inhibitory assay of NO production in mouse macrophages stimulated by LPS, with IC₅₀ values of 2.0, 2.5, 8.0, 9.5 and 5.6 μM, respectively. Otherwise, compound 10 showed moderate cytotoxic activity against HCT-116, HepG-2 and BGC-823 cell lines with IC₅₀ values of 3.0, 10.5 and 6.3 μM, respectively.

Silencing a phloretin-specific glycosyltransferase perturbs both general phenylpropanoid biosynthesis and plant development

The polyphenol profile of apple (Malus × domestica) is dominated by the dihydrochalcone glycoside phloridzin, but its physiological role is yet to be elucidated. Biosynthesis of phloridzin occurs as a side branch of the main phenylpropanoid pathway, with the final step mediated by the phloretin-specific glycosyltransferase UGT88F1. Unexpectedly, given that UGTs are sometimes viewed as 'decorating enzymes', UGT88F1 knockdown lines were severely dwarfed, with greatly reduced internode lengths, narrow lanceolate leaves, and changes in leaf and fruit cellular morphology. These changes suggested that auxin transport had been altered in the knockdown lines, which was confirmed in assays showing that auxin flux from the shoot apex was increased in the transgenic lines. Metabolite analysis revealed no accumulation of the phloretin aglycone, as well as decreases in many non-target phenylpropanoid compounds. This decreased accumulation of metabolites appeared to be mediated by the repression of the phenylpropanoid pathway via a reduction in key transcript levels (e.g. phenylalanine ammonia lyase, PAL) and enzyme activities (PAL and chalcone synthase). Application of exogenous phloridzin to the UGT88F1 knockdown lines in tissue culture enhanced axial leaf growth and partially restored some aspects of 'normal' apple leaf growth. Together, our results strongly implicate dihydrochalcones as critical compounds in modulating phenylpropanoid pathway flux and establishing auxin patterning early in apple development.

The Occurrence, Fate and Biological Activities of C-glycosyl Flavonoids in the Human Diet

The human diet contains a wide variety of plant-derived flavonoids, many of which are glycosylated via an O- or less commonly a C-glycosidic linkage. The distribution, quantity, and biological effects of C-glycosyl flavonoids in the human diet have received little attention in the literature in comparison to their O-linked counterparts, however, despite being present in many common foodstuffs. The structural nature, nomenclature, and distribution of C-glycosyl flavonoids in the human diet are, therefore, reviewed. Forty-three dietary flavonoids are revealed to be C-glycosylated, arising from the dihydrochalcone, flavone, and flavan-3-ol backbones, and distributed among edible fruits, cereals, leaves, and stems. C-linked sugar groups are shown to include arabinose, galactose, glucose, rutinose, and xylose, often being present more than once on a single flavonoid backbone and occasionally in tandem with O-linked glucose or rutinose groups. The pharmacokinetic fate of these compounds is discussed with particular reference to their apparent lack of interaction with hydrolytic mechanisms known to influence the fate of O-glycosylated dietary flavonoids, explaining the unusual but potentially important appearance of intact C-glycosylated flavonoid metabolites in human urine following oral administration. Finally, the potential biological significance of these compounds is reviewed, describing mechanisms of antidiabetic, antiinflammatory, anxiolytic, antispasmodic, and hepatoprotective effects.

An allelochemical from Myrica gale with strong phytotoxic activity against highly invasive Fallopia x bohemica taxa

We report the identification of the allelochemical 3-(1-oxo-3-phenylpropyl)-1,1,5-trimethylcyclo-hexane-2,4,6-trione, known as myrigalone A, from the fruits and leaves of Myrica gale. The structure of the compound was confirmed by high-resolution techniques (UV, MS and NMR analysis). The compound is phytotoxic towards classical plant species used for allelochemical assays and also against Fallopia x bohemica, a highly invasive plant. Application of either powdered dry leaves or dry fruits of M. gale also showed in vitro phytotoxic activity. We hypothesize that M. gale could be used as a green allelopathic shield to control Fallopia x bohemica invasion, in addition to its potential use as an environmentally friendly herbicide.