Inhibitory activity of brown algal phlorotannins against glycosidases from the viscera of the turban shell Turbo cornutus

The crude phlorotannins from the brown alga Eisenia bicyclis showed inhibitory activity against 10 of 13 kinds of glycosidases present in the viscera of the turban shell Turbo cornutus. Phloroglucinol and its oligomers – eckol (a trimer), phlorofucofuroeckol A (a pentamer), dieckol and 8,8′-bieckol (hexamers), and an unidentified tetramer – were isolated from the crude phlorotannins by column and thin-layer chromatography. Phlorofucofuroeckol A, dieckol and 8,8′-bieckol inhibited α-fucosidase, β-galactosidase and β-mannosidase partially purified from T. cornutus, while phloroglucinol, eckol and the unidentified tetramer were weakly active. Dieckol was a competitive inhibitor of α-fucosidase with an inhibition constant (K _i) of 0.12?mM. The amounts of phlorotannins released after the immersion of freshly collected E. bicyclis in seawater or deionized water were estimated by high-performance liquid chromatography. Nearly all the phlorotannins were exuded into the medium following the death of the algae, whereas no phlorotannins were detected in the medium of living algae. These findings indicate that the phlorotannins deter the feeding of marine herbivorous gastropods by inhibiting the glycosidases.     

Biosynthesis of pterocarpan and isoflavan phytoalexins in Medicago sativa: the biochemical interconversion of pterocarpans and 2′-hydroxyisoflavans

Feeding experiments have shown that 2′-7-dihydroxy-4′-methoxy-isoflavone-[Me-¹⁴C] and -isoflavanone-[Me-¹⁴C] are efficient precursors of the phytoalexins demethylhomopterocarpin, sativan and vesitol in CuCl₂-treated lucerne (Medicago sativa) seedlings. Demethylhomopterocarpin-[Me-¹⁴C] was also incorporated into sativan and vestitol, and vestitol-[Me-¹⁴C] was incorporated into demethylhomopterocarpin and sativan. Thus, the pterocarpan demethylhomopterocarpin and the 2′-hydroxy-isoflavan vestitol are interconvertible in M. sativa, but incorporation data, and the results of kinetic feeding experiments with l-phenylalanine-[U-¹⁴C] suggest that these compounds are synthesized simultaneously from a common intermediate, which could be involved in the interconversion. A carbonium ion, derived from an isoflavanol, a likely intermediate in the biosynthetic reductive sequence from 2′,7-dihydroxy-4′-methoxy-isoflavone and -isoflavanone, is proposed as this common intermediate. 7-Hydroxy-2′,4′-dimethoxyisoflavone-[4′-Me-¹⁴C] was a very poor precursor of all three phytoalexins. Sativan, then, is most probably derived by methylation of vestitol. The incorporation of vestitol-[Me-¹⁴C] into demethylhomopterocarpin, but not into maackiain, pterocarpan phytoalexins of red clover (Trifolium pratense), is also demonstrated.     

Inhibitory effects of polyphenols isolated from marine alga Ecklonia cava on histamine release

In order to clarify the modern anti-allergy activity of crude extract of Ecklonia cava, which is an edible marine brown alga used as food ingredient and folk drug against allergy disease in Korea due to the abundant content of phlorotannin derivatives, the continuous chemical investigation led to the isolation of the two main bioactive phlorotannin derivatives 6,6′-bieckol (3) and 1-(3′,5′-dihydroxyphenoxy)-7-(2′′,4′′,6-trihydroxyphenoxy)-2,4,9-trihydroxydibenzo-1,4-dioxin (4) for the first time from this genus, together with phloroglucinol (1) and dieckol (2). Their structures were confirmedly elucidated by the comprehensive analyses of MS and NMR spectroscopic data. Meanwhile, these derivatives were assessed by histamine release assay on human basophilic leukemia (KU812) and rat basophilic leukemia (RBL-2H3) cultured cell lines, respectively. Furthermore, flow cytometric analysis indicated that the potential anti-allergic mechanism is the suppression of binding activity between IgE and Fc?RI. Finally, the relationships of structure–activity were also suggested. This research indicated that these main derivatives can be used as potential candidates for foodstuff, cosmetic and pharmaceutical industries.     

Discovery of potent,selective, and orally bioavailable 3H-spiro[isobenzofuran-1,4′-piperidine] based melanocortin subtype-4 receptor agonists

Design, synthesis, and SAR of a series of 3H-spiro[isobenzofuran-1,4′-piperidine] based compounds as potent, selective and orally bioavailable melanocortin subtype-4 receptor (MC4R) agonists are disclosed.     

Biosynthesis of the 3-benzylchroman-4-one eucomin in Eucomis bicolor

Feeding experiments have demonstrated the specific incorporation of radioactivity from dl-phenylalanine-[1-¹⁴C], l-phenylalanine-[U-¹⁴C], sodium acetate-[2-¹⁴C] and l-methionine-[methyl-¹⁴C] into the 3-benzylchroman-4-one eucomin in Eucomis bicolor. The labelling patterns indicate that eucomin is biosynthesized by the addition of a carbon atom derived from methionine onto a C₁₅ chalcone-type skeleton. Radioactivity from 2′,4′,4-trihydroxy-6′-methoxychalcone-[methyl-¹⁴C] and 2′,4′-dihydroxy-4,6′-dimethoxychalcone-[6′-methyl-¹⁴C] was incorporated into eucomin, the latter compound being the better precursor, demonstrating the feasibility that 2′-methoxychalcones are biosynthetic precursors of the “homoisoflavonoids”. Possible biosynthetic relationships in this class of compounds are discussed.     

Cytotoxic Polyphenols from a Sponge‐Associated Fungus Aspergillus versicolor Hmp‐48

A new dibenzo[1,4]dioxin 1 , and two new prenylated diphenyl ethers, 2 and 3 , together with six known compounds, 4 – 9 , were isolated from a sponge‐associated fungus Aspergillus versicolor Hmp‐F48 by bioactivity‐guided fractionation. Their structures were elucidated by 1D‐ and 2D‐NMR, and MS analyses. The compounds showed potent cell growth inhibitory activities against HL‐60 cell line.     

Phytochemicals from the stem wood of Sorbus lanata (D. Don.) Schauer

Three new phenolic compounds, sorlanin (4-(3-(hydroxymethyl)-5-methoxy-7-phenyl-2,3-dihydrobenzo[b][1,4]dioxin-2-yl)-2-methoxyphenol, 1), sorbanin (2-((3,5-dimethoxy-[1,1′-biphenyl]-4-yl)oxy)-1-(4-hydroxy-3-methoxyphenyl)propane-1,3-diol, 2) and sorbalanin (4-(3-(hydroxymethyl)-5,6-dimethoxy-2,3-dihydrobenzo[b][1,4]dioxino[2,3-g]benzofuran-2-yl)-2-methoxyphenol, 3), together with eight known compounds, polystachyol (4), isolariciresinol (5), dihydrodehydrodiconiferyl alcohol (6), tuberculatin (7), ovafolinin E (8), aucuparin (9), 2′-methoxyaucuparin (10), and tetracosyl-3-(3,4-dihydroxyphenyl)acrylate (11), were isolated from Sorbus lanata. The structures of these phytoconstituents were elucidated through extensive spectroscopic techniques, including UV, IR, 1D and 2D NMR, ESI-MS and HRESI-MS experiments. All the compounds except 9 and 10 were isolated for the first time from the genus Sorbus. The isolated compounds were also tested in DPPH radical scavenging reaction where compounds 6, 7, 10 and 11 showed significant activities with IC₅₀ values of 9.2, 11.7, 23.0 and 33.7 μM, respectively.     

Nature-inspired pyrrolo[2,3-d]pyrimidines targeting the histamine H3 receptor

Inspired by marine compounds the derivatization of the natural pyrrolo[2,3-d]pyrimidine lead scaffold led to a series of novel compounds targeting the histamine H₃ receptor. The focus was set on improved binding towards the receptor and to establish an initial structure-activity relationship for this compound class based on the lead structure (compound V, K_i value of 126 nM). As highest binding affinities were found with 1,4-bipiperidines as basic part of the ligands, further optimization was focused on 4-([1,4′-bipiperidin]-1′-yl)-pyrrolo[2,3-d]pyrimidines. Related pyrrolo[2,3-d]pyrimidines that were isolated from marine sponges like 4-amino-5-bromopyrrolo[2,3-d]pyrimidine (compound III), showed variations in halogenation pattern, though in a next step the impact of halogenation at 2-position was evaluated. The chloro variations did not improve the affinity compared to the dehalogenated compounds. However, the simultaneous introduction of lipophilic cores with electron-withdrawing substitution patterns in 7-position and dehalogenation at 2-position (11b, 12b) resulted in compounds with significantly higher binding affinities (K_i values of 7 nM and 6 nM, respectively) than the initial lead structure compound V. The presented structures allow for a reasonable structure-activity relationship of pyrrolo[2,3-d]pyrimidines as histamine H₃ receptor ligands and yielded novel lead structures within the natural compound library against this target.     

Incorporation of shikimate and 4-(2′-carboxyphenyl)-4-oxobutyrate into phylloquinone

The patterns of incorporation of d-[G-¹⁴C]shikimate and variously labelled ¹⁴C-4-(2′-carboxy-phenyl)-4-oxobutyrate into the naphthoquinone nucleus of phylloquinone by maize shoots have been investigated. The results show that (a) the alicyclic ring and C-7 of shikimate give rise to Ring A and either C-1 or C-4, and (b) the phenyl ring, 2′-carboxy and C-4, and C-2 and -3 of 4-(2′-carboxyphenyl)-4-oxobutyrate give rise to Ring A, C-1 and -4 and C-2 and -3. Radioactivity from α-[1-¹⁴C]naphthol, 1,4-[1,4-¹⁴C]naphthoquinone and [Me-¹⁴C]menadione is not incorporated into phylloquinone to any significant extent.     

Biflavones from the leaves of Araucaria excelsa

Eight biflavones have been isolated from the leaf extracts of Araucaria excelsa. 7″-O-Methylamento-flavone, 7,7″-di-O-methylamentoflavone, 4′ or 4″', 7-di-O-methylcupressuflavone, 7,7″,4″'-tri-O-methyl agathisflavone and 7,4′,7″-tri-O-methylamentoflavone are new compounds and are being reported for the first time. The others are 7,7″-di-O-methylagathisflavone,7,4′,7″,4″'-tetra-O-methylamentoflavone and 7,4′,7″,4″'-tetra-O-methyl-cupressuflavone. Mass and NMR spectral studies are used for structural elucidation. In addition, the presence of several other biflavones has been indicated by TLC examination of methylated products.     

The utility of 1-[18F]fluoro-3-iodopropane for the synthesis of certain dopamine D-1 and benzodiazepine receptor radioligands

No-carrier-added (NCA) R(+)-7-chloro-8-hydroxy-3-(3′-[¹⁸F]fluoropropyl)-1-phenyl-2,3,4,5-tetrahydro-3-benzazepine (2b) (an analog of dopamine D-1 receptor ligand SCH 23390), ethyl 8-fluoro-5,6-dihydro-5-(3′-fluoropropyl)-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate (4b) and 3′-[¹⁸F]fluoropropyl 8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate (6b) (analogs of the benzodiazepine RO 15-1788) were synthesized by alkylation of the corresponding nor-compound with NCA 1-[¹⁸F]fluoro-3-iodopropane in 10–15% yield (EOB) in ~110min and with a mass of 2–3nmol. Compound 2 is less potent (~ 12–14 times) than SCH 23390 in binding to rat striatal membranes in vitro. Compounds 2b, 4b and 6b exhibit no specific anatomical distribution to mouse brain. These results suggest that the substituent at position 3 of SCH 23390, and position 5 and carboxylate group of RO 15-1788 are critical determinants both of affinity and selectivity for receptor binding, and underscores the evaluation necessary when even minor changes (C1 to C3) are made in bioactive compounds.     

Chemical components and its antioxidant properties in vitro: An edible marine brown alga,Ecklonia cava

Seven phlorotannins were isolated and characterized from an edible marine brown alga Ecklonia cava (EC), along with three common sterol derivatives (fucosterol, ergosterol, and cholesterol) according to the comprehensive spectral analysis of MS and NMR data. Compounds 5 (7-phloro eckol) and 7 (6,6′-bieckoll) of phlorotannin derivatives were obtained for the first time with the high yields. No reports of compound 3 (Fucodiphloroethol G) was published up to date. The antioxidant properties of all phlorotannins were assessed by total antioxidant activity in a linoleic acid model, free radicals scavenging assay using electron spin resonance spectrometry (ESR) technique, cellular reactive oxygen species (ROS) assay by DCFH-DA, membrane protein oxidation assay; measurement of cellular glutathione (GSH) level in RAW264.7 cell line, and myeloperoxidase (MPO) assay in HL-60 cell line. The results revealed that all phlorotannins had antioxidant properties in vitro, especially, compounds 7 (6,6′-bieckol), 6, and 3 showed the significant activities compared to the other phlorotannins. Furthermore, the structure–activity relationship (SAR) was discussed based on the structural differences of the tested phlorotannins which have polymeriged phloroglucinal units with diverse skeletons and linkages. It could be suggested that phlorotaninns from this genus would be more potential candidates for the development of unique natural antioxidants for further industrial applications as functional foods, cosmetics and pharmaceuticals. As well as our results makes it clear to understand the reason behind the use of EC as traditional folk herb for a long history.     

Novel phenanthrene and isocoumarin from the rhizomes of Dioscorea nipponica Makino subsp. rosthornii (Prain et Burkill) C. T. Ting (Dioscoreaceae)

The investigation of the constituents in the rhizomes of Dioscorea nipponica Makino subsp. rosthornii (Prain et Burkill) C. T. Ting afforded one new phenanthrene 2,2′,7,7′-tetramethoxy-[1,1′-biphenanthrene]-4,4′,6,6′-tetrol (7) and one new isocoumarin diorosthornoumarin (8), together with 16 known compounds (1–6 and 9–18). Their structures were established on the basis of extensive spectroscopic evidences (IR, HR-ESI-MS, NMR and optical rotation), as well as comparison with literature values. All the compounds 1–18 were firstly isolated from Dioscorea nipponica Makino subsp. Rosthornii (Prain et Burkill) C. T. Ting, and compound 9 was firstly obtained as a natural product from plants, while the compounds 11 and 14 were obtained from both the genus Dioscorea and the family Dioscoreaceae for the first time. Moreover, the antitumor activities of the compounds were tested against lung carcinoma NCI-H460 cell line. Compound 12, 13, 15 and 16 showed significant cytotoxic activities, whereas 7 displayed moderate cytotoxicity.     

Chemical Constituents of Daphne giraldii Nitsche

In a search for structurally interesting substances from traditional Chinese medicines, eight compounds were isolated from an ethanolic extract of the stem bark of Daphne giraldii Nitsche. On the basis of one- and two-dimensional nuclear magnetic resonance and mass spectrometry data, and chemical methods, their structures were determined to be 2H-1-benzopyran-2-one-8-hydroxy-7-O-β-D-glucopyranosyl-5-（2-oxo- 2H-1-benzopyran-7-hydroxy-8-yloxy） （compound 1）, 1-pentanone, 1-（4-hydroxyphenyl）-5-phenyl （compound 2）, octadecyl caffeate （compound 3）, （＋）syringaresinol-4,4＇-diglycoside （compound 4）, daphnetin-8-O-β-D- glucopyranoside （compound 5）, p-hydroxybenzoic acid （compound 6）, 7,7＇-dihydroxy-[6, 8＇-bi-2H-benzopyran]- 2, 2＇-dione （compound 7）, and daphnorin （compound 8）, respectively. Of the compounds isolated, compounds 1 and 2, which we named daphnolin and daphnolon, respectively, were new, and the others were obtained from this plant for the first time.     

Isolation and structure elucidation of flavonoids from Amburana cearensis resin and identification of human DNA topoisomerase II-α inhibitors

Amburana cearensis, a plant in the Fabaceae family, is extensively used in folk medicine to treat grippes, coughs, bronchitis, sinusitis and external ulcers. Ultra-performance liquid chromatography coupled with diode array and quadrupole time-of-flight mass spectrometry (UPLC-DAD-QTOF-MS/MS) and combined use of data-independent acquisition (MSE) were used for profiling and structural characterization of the phenolic compounds observed in the resin of A. cearensis (16 isoflavones, 11 flavanonols, 3 chalcones, 1 isoflavonolignan and 1 isoflavoquinone). The isoflavonolignan (1”R,2”R-trans-1”-(7”-hydroxy-6”,8”-dimethoxyphenyl)-1′-(3′-hydroxy-4′-methoxyphenyl)-2”-hydroxymethyl-5-methoxy-1”,2”-dihydro-7H-1,4-dioxino[1”,2”-h]chromen-4-one) and an isoflavone (3′-hydroxy-7,8,4′-trimethoxyisoflavone) were identified as novel compounds. In this study, we isolated 15 principal phenolics and established their structures by different spectroscopic methods, including 1D and 2D NMR experiments, as well HR-ESI–MS analysis. The isolated reference compounds were used to explore fragmentation pathways. Compound identification was based on the exact mass, general fragmentation behaviors, retention times and UV absorption. The activity of the principal compounds against human DNA topoisomerase II-α was evaluated.     

Pisum sativum stress metabolites: Two cinnamylphenols and a 2′-methoxychalcone

An HPLC study of copper(II) chloride treated Pisum sativum has shown that the cinnamylphenols obtustyrene [E-1-(4-hydroxy-2-methoxybenzyl)-2-phenylethylene] and xenognosin [E-1-(4-hydroxy-2-metboxy-benzyl)-2- (4-hydroxyphenyl)ethylene] as well as the chalcone 4,4′-dihydroxy-2′-methoxychalcone accumulate as de novo metabolites in the stressed plant. This chalcone has not previously been identified from a plant source. The biosynthetic and stress response relationships of these compounds are discussed.     

Oxidation of polycyclic aromatic hydrocarbons and dibenzo[p]-dioxins by Phanerochaete chrysosporium ligninase

The lignin peroxidase (ligninase) of Phanerochaete chrysosporium catalyzes the oxidation of a variety of lignin-related compounds. Here we report that this enzyme also catalyzes the oxidation of certain aromatic pollutants and compounds related to them, including polycyclic aromatic hydrocarbons with ionization potentials less than or equal to approximately 7.55 eV. This result demonstrates that the H2O2-oxidized states of lignin peroxidase are more oxidizing than the analogous states of classical peroxidases. Experiments with pyrene as the substrate showed that pyrene-1,6-dione and pyrene-1,8-dione are the major oxidation products (84% of total as determined by high performance liquid chromatography), and gas chromatography/mass spectrometry analysis of ligninase-catalyzed pyrene oxidations done in the presence of H2(18)O showed that the quinone oxygens come from water. We found that whole cultures of P. chrysosporium also transiently oxidize pyrene to these quinones. Experiments with dibenzo[p]dioxin and 2-chlorodibenzo[p]dioxin showed that they are also substrates for ligninase. The immediate product of dibenzo[p]dioxin oxidation is the dibenzo[p]dioxin cation radical, which was observed in enzymatic reactions by its electron spin resonance and visible absorption spectra. The cation radical mechanism of ligninase thus applies not only to lignin, but also to other environmentally significant aromatics.     

A highly atom economic,chemo-, regio- and stereoselective synthesis and evaluation of spiro-pyrrolothiazoles as antitubercular agents

The 1,3-dipolar cycloaddition of azomethine ylides derived from substituted isatins and 1,3-thiazolane-4-carboxylic acid to a series of 1-methyl-3,5-bis[(E)-arylmethylidene]-tetrahydro-4(1H)-pyridinones afforded novel spiro-pyrrolothiazoles chemo-, regio- and stereoselectively in quantitative yields. These compounds were screened for their in vitro activity against Mycobacterium tuberculosis H37Rv (MTB) and multi-drug resistant M. tuberculosis (MDR-TB) using agar dilution method. Among the synthesized compounds, spiro[5.3′′]-5′′-nitrooxindole-spiro-[6.3′]-1′-methyl-5′-(2,4-di-chlorophenylmethylidene)tetrahydro-4′(1H)-pyridinone-7-(2,4-dichlorophenyl)tetra-hydro-1H-pyrrolo[1,2-c][1,3]thiazole (9k) was found to be the most active with a minimum inhibitory concentration (MIC) of 0.6 μM against MTB and MDR-TB.     

An atom economic synthesis and antitubercular evaluation of novel spiro-cyclohexanones

The 1,3-dipolar cycloaddition of azomethine ylides derived from acenaphthenequinone and α-amino acids viz. sarcosine, phenylglycine, 1,3-thiazolane-4-carboxylic acid and proline to a series of 2,6-bis[(E)-arylmethylidene]cyclohexanones afforded novel spiro-heterocycles chemo-, regio- and stereoselectively in quantitative yields. These compounds were screened for their in vitro activity against Mycobacterium tuberculosis H37Rv (MTB) using agar dilution method. Two compounds, 4-(2,4-dichlorophenyl)-5-phenylpyrrolo(spiro[2.2″]acenaphthene-1″-one)spiro[3.2′]-6′-(2,4-dichlorophenylmethylidene)cyclohexanone (4i) and spiro[5.2″]acenaphthene-1″-onespiro[6.2′]-6′-(2,4-dichlorophenylmethylidene)cyclohexanone-7-(2,4-dichlorophenyl)tetrahydro-1H-pyrrolo[1,2-c][1,3]thiazole (5i) display maximum activity in vitro with a MIC value of 0.40 μg/mL against MTB and were 4 and 15.6 times more potent than ethambutol and pyrazinamide, respectively.     

Antioxidant activities of phlorotannins isolated from Japanese Laminariaceae

The antioxidant activities of brown algal phlorotannins were evaluated using the inhibition of phospholipid peroxidation in the liposome system, and by determining radical scavenging activities against the superoxide anion and 1,1-diphenyl-2-picrylhydrazyl (DPPH). Oligomers of phloroglucinol (1,3,5-trihydroxybenzene), eckol (a trimer), phlorofucofuroeckol A (a pentamer), dieckol and 8,8′-bieckol (hexamers), isolated from the Laminarian brown algae Eisenia bicyclis, Ecklonia cava and Ecklonia kurome, showed potent inhibition of phospholipid peroxidation at 1 μM in the liposome system. The phlorotannins had significant radical scavenging activities against the superoxide anion (50% effective concentration values: 6.5–8.4 μM) and DPPH (50% effective concentration values: 12–26 μM), and were more effective compared to ascorbic acid and α-tocopherol. For the purpose of using phlorotannins as functional food ingredients, the antioxidant activity of a complex of crude phlorotannins and soybean protein was examined. The complex had a pronounced DPPH-radical scavenging activity. These results suggest that phlorotannins are potent anti-inflammatory substances, and that the Laminariaceous brown algae, which are abundant in phlorotannins, may be useful as a new functional foodstuff or supplement with anti-inflammatory activity.