A new anthraquinone glycoside from Rhamnus nakaharai and anti-tyrosinase effect of 6-methoxysorigenin

In continual study on the heartwood of Rhamnus nakaharai, a new alaternin-8-O-glucoside, namely 1,2,6,8-tetrahydroxy-3-methylanthraquinone-8-O-β-glucopyranoside (1), together with some known compounds were further isolated and characterised by 1-D, 2-D NMR and other spectral evidences. The free radical scavenging and antityrosinase activities of the isolates, including alaternin (1a), emodin (2a), emodin-8-O-β-glucopyranoside (2), 6-methoxysorigenin-8-O-β-glucopyranoside (3) and 6-methoxysorigenin (3a) were tested. Alaternin (1a) exhibited to be mild DPPH radical scavenger with half as potent as vitamin C, while both alaternin (1a) and emodin-8-O-β-glucopyranoside (2) exhibited stronger SOD-like activity than that of BHA. 6-Methoxysorigenin (3a), a reported potential antioxidant, and its 8-O-glucoside (3) both performed significant inhibitory effect on mushroom tyrosinase with about twice as potent as kojic acid, the positive control.     

Selective transport of cesium ion in polymeric CTA membrane containing calixcrown ethers

A series of calixcrown ethers for which the cavity size of the crown ring is varied from crown-6 to crown-7 to crown-8 were examined for the transport abilities toward alkali metal ions. These ligands were incorporated into supported liquid membranes (SLMs) and into polymer inclusion membranes (PIMs) composed of cellulose triacetate (CTA) as a support and 2-nitrophenyl octyl ether (NPOE) and tris(2-butoxyethyl) phosphate (TBEP) as a plasticizer. In both membrane systems, calixcrown-6 showed the best selectivity toward a cesium ion over other alkali metal ions. The polymeric CTA membrane showed more rapid transport rate as well as higher durability than did the SLMs.     

Synthesis and characterizations of free base and Cu(II) complex of a porphyrin sheet

Free base porphyrin sheet 5 was prepared by demetalation of zinc complex 1, which was now more conveniently prepared in 30% yield by oxidation of a mixture of tetraporphyrins, 8, 9, and 11. The ¹H NMR spectrum of 5 shows no indication of an aromatic ring current for the porphyrin rings and evidences the freezing of the pyrrolic NH protons at the most inner and outer corner positions, both of which contrast sharply with strong aromatic ring currents and rapid NH tautomerism of normal porphyrins. DFT calculations supported the experimental results, suggesting that the enforced planar COT core causes these unique properties. The free base 5 was transformed into Cu(II) complex 6 that exhibits antiferromagnetic interaction among the Cu(II) ions with J=−1.16 cm⁻¹.     

Living Cationic Ring-Opening Polymerization of Hetero Diels–Alder Adducts to Give Multifactor-Controlled and Fast-Photodegradable Vinyl Polymers

Precise control of multiple structural parameters associated with vinyl polymers is important for producing materials with the desired properties and functions. While the development of living polymerization methods has provided a way to control the various structural parameters of vinyl polymers, the concomitant control of their sequence and regioregularity remains a challenging task. To overcome this challenge, herein, we report the living cationic ring-opening polymerization of hetero Diels–Alder adducts. The scalable and modular synthesis of the cyclic monomers was achieved by a one-step protocol using readily available vinyl precursors. Subsequently, living polymerization of the cyclic monomers was examined, allowing the synthesis of vinyl polymers while controlling multiple factors, including molecular weight, dispersity, alternating sequence, head-to-head regioregularity, and end-group functionality. The living characteristics of the developed method were further demonstrated by block copolymerization. The synthesized vinyl polymers exhibited unique thermal properties and underwent fast photodegradation even under sunlight.     

Synthesis, characterization, and structural determination of polynuclear lithium aggregates and factors affecting their aggregation

The reaction of [(mu3,mu3-EDBP)Li2]2[(mu3-nBu)Li(0.5Et2O)]2 (1) [EDBP-H2 = 2,2'-ethylidenebis(4,6-di-tert-butylphenol)] with 1 equiv of ROH in toluene gave [(mu3,mu3-EDBP)Li2]2[(mu3-OR)Li]2 [R = Bn (2), CH2CH2OEt (3), and nBu (4)]. In the presence of 3 equiv of tetrahydrofuran (THF), the hexanuclear compound 1 slowly decomposed to an unusual pentanuclear Li complex, [(mu2,mu3-EDBP)2Li4(THF)2][(mu3-nBu)Li] (5). Further reaction of 5 with ROH gave [(mu2,mu3-EDBP)2Li4(THF)3][(mu4-OR)Li] [R = Bn (6), nBu (7), and CH2CH2OEt (8)] without a major change in its skeleton. Treatment of 2 with an excess of hexamethylphosphoramide (HMPA) yields [(mu2,mu2-EDBP)Li2(HMPA)2][(mu3-OBn)Li(HMPA)] (9). Compounds [(mu2,mu3-EDBP)2Li4(THF)][(mu4-OCH2CH2OEt)Li]2 (10) and [(mu2,mu2-EDBP)2Li4(mu4-OCH2CH2OEt)(HMPA)]-[Li(HMPA)4]+ (11) can be obtained by the reaction of 3 with an "oxygen-donor solvent" such as THF and HMPA, respectively. Among the compounds described above, 8 has shown great reactivity toward ring-opening polymerization of L-lactide, yielding polymers with very low polydispersity indexes in a wide range of monomer-to-initiator ratios.     

Synthesis of difluorinated pyridinecarboxaldehyde via electrophilic fluorination

An efficient synthesis of novel 3,5-difluoropyridine-4-carboxaldehyde using N-fluoro-benzenesulfonimide (NSFi) is described. Difluorination was achieved through the reaction of 3,5-dihalo-1,3-dioxolane pyridine with n-butyllithium followed by N-fluorobenzenesulfonimide at −120 °C in good to high yields. Maintaining the low temperature during the transmetallation was found to be critical for the selective formation of the difluoro-susbstitution over the monofluoro one.     

Heterogeneous catalyst: Amberlyst-15 catalyzes the synthesis of 14-substituted-14H-dibenzo[a,j]xanthenes under solvent-free conditions

A one-pot condensation of β-naphthol with aldehydes in the presence of Amberlyst-15 to give 14-substituted-14H-dibenzo[a,j]xanthenes under solvent-free condition is described.     

Molecular dynamics modeling in quantum chemical calculations. Optical absorption spectra of 1,3-Dimethyl-1H-Pyrazolo[3,4-b]quinoline derivatives

Paper presents the quantum chemical modeling of the optical absorption spectra of 6-fluoro, 6-bromo, 7-trifluoromethyl, 6-cyano and 6-carboethoxy derivatives of 1,3-Dimethyl-1H-Pyrazolo[3,4-b]quinoline. The calculations are performed by means of the semiempirical quantum chemical methods (AM1 or PM3) in combination with molecular dynamics (MD) simulations at T=300 K. It is shown that a particular rotational dynamics of the methyl, trifluoromethyl or ethyl groups practically does not influence the optical absorption in the spectral range 200-500 nm whereas broadening of absorption bands may be well reproduced within MD simulations including all types of nuclei vibrations. The results of calculations are compared with the measured spectra of optical absorption. The quantum chemical method AM1 in combination with MD simulations gives for all dyes the best agreement between the calculated and measured spectral positions of the first absorption band (absorption threshold).     

Interactions of native and modified cyclodextrins with some B-vitamins

Interactions of native and modified α- and β-cyclodextrins with nicotinic acid, pyridoxine and pyridoxal were studied by isothermal titration calorimetry, solution calorimetry, and ¹H NMR spectroscopy at 298.15 K and pH 6.8. Weak 1:1 complex formation was found only between α-cyclodextrin and nicotinic acid. The stability constant and corresponding thermodynamic parameters of complex formation (Δ_c G, Δ_c H and Δ_c S) were calculated using the calorimetric data. The ¹H NMR data indicate the shallow insertion of the carboxylic group of the nicotinic acid molecule into α-CD cavity. For all other compounds the weak interactions, not accompanied by complex formation, were characterized by the enthalpic virial coefficients calculated on the basis of McMillan-Mayer approach. The obtained thermodynamic parameters were analyzed in the terms of influence of the solutes’ structure on the selectivity of intermolecular host-guest interactions.