Cascade reaction including a formal [5 + 2] cycloaddition by use of alkyne-Co2(CO)6 complex

A new cascade reaction including formal [5?+?2] cycloaddition was developed. Treatment of homocinnamyl alcohol and Co₂(CO)₆-complexed arylpropynal with BF₃·OEt₂ resulted in the generation of hydrobenzocycloheptafuran having an alkyne-Co₂(CO)₆ complex. The reaction consists of 5-membered ring selective Prins cyclization and subsequent Friedel-Crafts cyclization. The cascade reaction was applied to a further multi-step cascade cyclization, which resulted in the formation of more complex polycyclic hydrofurans.     

HSulf-2, an extracellular endoglucosamine-6-sulfatase, selectively mobilizes heparin-bound growth factors and chemokines: effects on VEGF, FGF-1, and SDF-1

Background  

Heparin/heparan sulfate (HS) proteoglycans are found in the extracellular matrix (ECM) and on the cell surface. A considerable body of evidence has established that heparin and heparan sulfate proteoglycans (HSPGs) interact with numerous protein ligands including fibroblast growth factors, vascular endothelial growth factor (VEGF), cytokines, and chemokines. These interactions are highly dependent upon the pattern of sulfation modifications within the glycosaminoglycan chains. We previously cloned a cDNA encoding a novel human endosulfatase, HSulf-2, which removes 6-O-sulfate groups on glucosamine from subregions of intact heparin. Here, we have employed both recombinant HSulf-2 and the native enzyme from conditioned medium of the MCF-7-breast carcinoma cell line. To determine whether HSulf-2 modulates the interactions between heparin-binding factors and heparin, we developed an ELISA, in which soluble factors were allowed to bind to immobilized heparin.     

Axially chiral guanidine as highly active and enantioselective catalyst for electrophilic amination of unsymmetrically substituted 1,3-dicarbonyl compounds

A newly designed axially chiral guanidine is found to function as an effective platform for asymmetric induction at the alpha-carbon of unsymmetrically substituted 1,3-dicarbonyl compounds. Highly efficient and enantioselective electrophilic amination of various 1,3-dicarbonyl compounds with azodicarboxylate was successfully achieved using the present chiral guanidine catalyst, which provides efficient access to the construction of nitrogen-substituted quaternary stereocenters in an optically active form.     

A Simple Fabrication Method for Three‐Dimensional Gold Nanoparticle Electrodes and Their Application to the Study of the Direct Electrochemistry of Cytochrome c

A simple method for constructing gold nanoparticle‐modified electrodes with three‐dimensional nanostructures is demonstrated. The electrodes were prepared by casting citrate‐reduced AuNPs onto polycrystalline gold electrodes. The resultant electrodes had a large surface area‐to‐volume ratio, adequate for high protein loading and conferring high stability. The gold nanoparticle electrodes were covered with a self‐assembled monolayer of 11‐mercaptoundecanoic acid for electrostatic immobilization of cytochrome c (cyt c). At the electrode, direct, reversible electron transfer from cyt c was observed with remarkable stability. Moreover, an extremely high surface coverage of electrochemically active cyt c, 167 fully packed monolayers, was obtained through use of the electrode.     

Four New Lignan Glycosides from Osmanthus fragrans Lour. var. aurantiacus Makino

Four new tetrahydrofuranoid lignan glycosides, (7S,8R,7′R,8′S)‐4,9,4′,7′‐tetrahydroxy‐3,3′‐dimethoxy‐7,9′‐epoxylignan 9‐O‐β‐D ‐glucopyranoside ( 2 ), (7R,8S,7′S,8′R)‐4,9,4′,7′‐tetrahydroxy‐3,3′‐dimethoxy‐7,9′‐epoxylignan 9‐O‐β‐D ‐glucopyranoside ( 3 ), (7R,8S,7′R,8′S)‐4,9,4′,9′‐tetrahydroxy‐3,3′‐dimethoxy‐7,7′‐epoxylignan 9‐O‐β‐D ‐glucopyranoside ( 4 ), and rel‐(7R,8S,7′S,8′R)‐4,9,4′,9′‐tetrahydroxy‐3,3′‐dimethoxy‐7,7′‐epoxylignan 9‐O‐β‐D ‐glucopyranoside ( 5 ), and ten known lignan glycosides, 1 and 6 – 14 , were isolated from the leaves of Osmanthus fragrans Lour. var. aurantiacus Makino . Their structures were established on the basis of spectral and chemical studies.     

New heteroleptic bis-phenanthroline copper(I) complexes with dipyridophenazine or imidazole fused phenanthroline ligands: spectral, electrochemical, and quantum chemical studies

Two new sterically challenged diimine ligands L(1) (2,9-dimesityl-2-(4'-bromophenyl)imidazo[4,5-f][1,10]phenanthroline) and L(2) (3,6-di-n-butyl-11-bromodipyrido[3,2-a:2',3'-c]phenazine) have been synthesized with the aim to build original heteroleptic copper(I) complexes, following the HETPHEN concept developed by Schmittel and co-workers. The structure of L(1) is based on a phen-imidazole molecular core, derivatized by two highly bulky mesityl groups in positions 2 and 9 of the phenanthroline cavity, preventing the formation of a homoleptic species, while L(2) is a dppz derivative, bearing n-butyl chains in α positions of the chelating nitrogen atoms. The unambiguous formation of six novel heteroleptic copper(I) complexes based on L(1), L(2), and complementary matching ligands (2,9-R(2)-1,10-phenanthroline, with R = H, methyl, n-butyl or mesityl) has been evidenced, and the resulting compounds were fully characterized. The electronic absorption spectra of all complexes fits well with DFT calculations allowing the assignment of the main transitions. The characteristics of the emissive excited state were investigated in different solvents using time-resolved single photon counting and transient absorption spectroscopy. The complexes with ligand L(2), bearing a characteristic dppz moiety, exhibit a very low energy excited-state which mainly leads to fast nonradiative relaxation, whereas the emission lifetime is higher for those containing the bulky ligand L(1). For example, a luminescence quantum yield of about 3 × 10(-4) is obtained with a decay time of about 50 ns for C2 ([Cu(I)(nBu-phen)(L(1))](+)) with a weak influence of strong coordinating solvent on the luminescence properties. Overall, the spectral features are those expected for a highly constrained coordination cage. Yet, the complexes are stable in solution, partly due to the beneficial π stacking between mesityl groups and vicinal phenanthroline aromatic rings, as evidenced by the X-ray structure of complex C3 ([Cu(I)(Mes-phen)(L(2))](+)). Electrochemistry of the copper(I) complexes revealed reversible anodic behavior, corresponding to a copper(I) to copper(II) transition. The half wave potentials increase with the steric bulk at the level of the copper(I) ion, reaching a value as high as 1 V vs SCE, with the assistance of ligand induced electronic effects. L(1) and L(2) are further end-capped by a bromo functionality. A Suzuki cross-coupling reaction was directly performed on the complexes, in spite of the handicapping lability of copper(I)-phenanthroline complexes.     

Studies on the constituents of Lagochilus leiacanthus (Labiatae)

Two flavanones, 5,2',6'-trihydroxy-7,8-dimethoxyflavanone (1), 5,2',6'-trihydroxy-6,7,8-trimethoxyflavanone (2) and their 2'-O-β-D-glucosides (3, 4), and a neoclerodane-type diterpene, 15-demethoxyscupolin I (5), together with twenty-eight known compounds were isolated from the extracts of Lagochilus leiacanthus. The structures of the new compounds were determined by spectroscopic means. The two new flavanones and some known flavonoids showed the inhibitory activity on the release of β-hexosaminidase from RBL-2H3 cells.     

A facile synthesis of novel pyrazolo[5′,1′:3, 4]-[1, 2, 4]triazino[6, 5-f][1, 3, 4]thiadiazepines

The reaction of the 3-substituted 4-aminopyrazolo[5, 1-c][1, 2, 4]triazines 1a-d with thiosemicarbazide hydrochloride in acetic acid gave new pyrazolo[5′,1′:3, 4][1, 2, 4]triazino[6, 5-f][1, 3, 4]thiadiazepines 3, 4 and 6 , which were converted into the 5-oxo derivatives 5 and 7 by hydrolysis in hydrochloric acid/acetic acid.     

The structure of a biosynthetic intermediate of pyrroloquinoline quinone (PQQ) and elucidation of the final step of PQQ biosynthesis

Pyrroloquinoline quinone (PQQ) is a tricyclic o-quinone, which serves as a cofactor in several enzyme-catalyzed redox reactions in certain bacteria. PQQ is also important for human health, and its role as a vitamin in mammals has recently been suggested. Although much is known about the function of enzymes that use PQQ as cofactor, relatively little is known about the biosynthesis of this coenzyme. Six gene products in Klebsiella pneumoniae (PqqA-F) are involved in PQQ biosynthesis, and PqqC has been shown to catalyze the last step in the pathway. The chemical structure of the substrate for PqqC has remained elusive and has hampered our understanding of the nature of this reaction. In this report we describe the purification and structure of the substrate as deduced by a number of spectroscopic and chemical methods. The substrate is 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid-a fully reduced derivative of PQQ, which has not undergone ring cyclization. These results show that PqqC catalyzes a novel reaction, which involves ring closure and an amazing eight-electron oxidation of the substrate.