Aggregation-induced enhanced fluorescence emission of chiral Zn(II) complexes coordinated by Schiff-base type binaphthyl ligands

A pair of novel chiral Zn(II) complexes coordinated by Schiff-base type ligands derived from BINOL (1,1'-bi-2-naphthol), R-/S-Zn, were synthesized. X-ray crystallography revealed the presence of two crystallographically independent complexes; one has a distorted trigonal-bipyramidal structure coordinated by two binaphthyl ligands and one disordered methanol molecule (molecule A), while the other has a distorted tetrahedral structure coordinated by two binaphthyl ligands (molecule B). Numerous CH⋯π and CH⋯O interactions were identified, contributing to the formation of a 3-dimensional rigid network structure. Both R-/S-Zn exhibited fluorescence in both CH2Cl2 solutions and powder samples, with the photoluminescence quantum yields (PLQYs) of powder samples being twice as large as those in solutions, indicating aggregation-induced enhanced emission (AIEE). The AIEE properties were attributed to the restraint of the molecular motion arising from the 3-dimensional intermolecular interactions. CD and CPL spectra were observed for R-/S-Zn in both solutions and powders. The dissymmetry factors, gabs and gCPL values, were within the order of 10-3 to 10-4 magnitudes, comparable to those reported for chiral Zn(II) complexes in previous studies.

Aggregation-induced circularly polarized phosphorescence of Pt(II) complexes with an axially chiral BINOL ligand

A pair of chiral Pt(II) complexes coordinated by simple BINOL and bipyridine ligands displaying aggregation-induced phosphorescence and circularly polarized luminescence were characterized by X-ray crystallography and absorption and emission spectroscopies. The emission of the powder sample was reddish whereas the thin film dispersed in PMMA (f_Pf = 1 wt%) exhibited a white emission.

Synthesis and Properties of V-Shaped Xanthene Dyes with Tunable and Predictable Absorption and Emission Wavelengths

V-shaped xanthene dyes capable of predicting absorption and emission wavelengths are described. These dyes were synthesized by bridging a xanthene ring and an aryl moiety of fluorescein through ether covalent bonds. These dyes showed longer absorption and emission wavelengths than those of the parent fluorescein. Furthermore, substituents introduced on the aryl moiety mainly affected the lowest unoccupied molecular orbital energy level of the molecule. Therefore, the Hammett substituent constants could be used to predict the absorption and emission wavelengths of the compound.

Synthesis of Bridged Indigos and Their Thermoisomerization and Photoisomerization Behaviors

Bridged indigos were synthesized by bridging the two nitrogen atoms in the indigo structure with a carbon chain, and their properties were carefully examined. These bridged indigos have intrinsic planar chirality, and the enantiomers were separated using chiral high-performance liquid chromatography. When the chiral bridged indigos were subjected to thermo- and photoisomerization, the corresponding (Z)-indigo was not observed at all, and racemization was observed. This phenomenon is caused by the low activation energy of inversion due to the 1.5 bond order of the double bond of the indigo skeleton and the large energy difference between the ground states of (E)-indigo and (Z)-indigo.

Total Syntheses of FR-901235, Auxarthrones A-D, and Lamellicolic Anhydride

In our previous study, an unusual rearrangement reaction was discovered whereby dinaphthyl ketones with three hydroxy groups at restricted positions were transformed into a phenalenone ring and a benzene ring. Using the rearrangement as a key reaction, the first total syntheses of FR-901235 and auxarthrones A-D from an unstable triketone common intermediate are described. Furthermore, lamellicolic anhydride was synthesized from the triketone. This conversion is part of the putative biosynthetic pathway and was achieved experimentally for the first time.

Nucleophilic Addition Reaction with Dearomatization of Naphthalene Ring

Various aromatic lactones have been synthesized and their regioselectivity (1,2-addition vs. 1,4- or 1,6-addition) investigated in reactions with organolithium species, particularly n-BuLi and sec-BuLi. The regioselectivity varied greatly depending on various factors, such as the bulkiness of both substrates and organolithium species, and types of solvent and cosolvent. In particular, 1,4-addition with dearomatization occurred preferentially using sec-BuLi as the nucleophile in tetrahydrofuran (THF) with hexamethylphosphoramide (HMPA) or N,N'-dimethylpropyleneurea (DMPU) as cosolvent. For sec-BuLi, the reaction was estimated to proceed through a single-electron transfer mechanism.

Synthetic and Biological Studies of Juglorubin and Related Naphthoquinones

Juglorubin, juglorescein, and juglocombins A/B are naturally occurring naphthoquinone dimers isolated from Streptomyces sp. These dimers are proposed to be biogenetically derived from juglomycin C, a monomeric naphthoquinone isolated from the same Streptomyces sp. In this study, the dimerization of a juglomycin C derivative, a key step in the total syntheses of these natural products, was investigated. Juglorubin was synthesized from the minor product of the dimerization via the formation of the juglocombin A/B stereoisomers. A mechanism for the dimerization reaction as well as a plausible biosynthetic pathway to obtain juglorubin from juglomycin C are proposed. Furthermore, the antibacterial and cytotoxic activities of five synthetic compounds were evaluated. Among the compounds tested in this study, 1'-O-methyljuglocombin B dimethyl ester and juglomycin C exhibited antibacterial activity against Bacillus subtilis. 1'-O-Methyljuglocombin B dimethyl ester and juglomycin C showed cytotoxicity against human colon carcinoma HCT116 cells and human leukemia HL-60 cells. 1'-O-Methyljuglocombin B dimethyl ester exhibited cytotoxicity against human normal MRC-5 cells as strong as that against human cancer cells. In contrast, juglomycin C was less toxic against normal MRC-5 cells, indicating a significant selectivity toward cancer cells.

Unified Approach toward Syntheses of Juglomycins and Their Derivatives

A unified and common intermediate strategy for syntheses of juglomycins and their derivatives is reported. The use of a 1,4-dimethoxynaphthalene derivative as a key intermediate enabled easy access to various juglomycin derivatives. In this study, juglomycins A-D, juglomycin C amide, khatmiamycin and its 4-epimer, and the structure proposed for juglomycin Z were synthesized from this intermediate. The absolute configuration of natural khatmiamycin has been established to be 3R,4R through our synthesis. Unfortunately, the spectroscopic data for synthetic juglomycin Z were not consistent with the data reported for the natural one, strongly suggesting a structural misassignment.

Synthesis and Photochemical Properties of Axially Chiral Bis(dinaphthofuran)

Both enantiomers of axially chiral bis(dinaphthofuran) were prepared in only two steps from 1'-hydroxy-4'-methoxy-2,2'-binaphthalenyl-1,4-dione, followed by optical resolution via high-performance liquid chromatography (HPLC) using a chiral stationary phase (CSP). The absolute configurations were determined by comparison of experimental and calculated vibrational circular dichroism (VCD) spectra. Synthetic bis(dinaphthofuran) exhibited a broad and unstructured emission derived from an intramolecular excimer in both solution and solid state. The methylene bridge brings both chromophores close to each other and induces significant changes in the photophysical behavior. Chiral bis(dinaphthofuran) displayed a bathochromic shift in emission, as compared to the racemic mixture in the solid state. Furthermore, the compounds showed high circularly polarized luminescence (CPL) with a dissymmetry factor ( glum) of 10-3 at 405 nm upon excitation at 265 nm in a methanol solution. This compound serves as a model for the design and synthesis of organic materials having CPL activity.

Total Synthesis of Dendrochrysanene through a Frame Rearrangement

The first total synthesis of dendrochrysanene (1) was achieved. The key reaction for the construction of dendrochrysanene was an oxidative frame rearrangement reaction from a phenanthrene dimer to a spiro-lactone skeleton, which we serendipitously identified. Owing to the steric hindrance of the substituent on the peri position of the phenanthrene dimer, high-temperature conditions were required for the rearrangement reaction; however, at such temperatures, the substrate decomposed. To address this issue, we added phenylethylamine or benzylamine to the reaction system. We assumed that the amine trapped generated hydrochloric acid and acted as a ligand for iron, helping to maintain an appropriate redox potential. The total synthesis of dendrochrysanene, involving this rearrangement reaction, is an important sequence interlinking phenanthrene derivatives, phenanthrene dimers, and spiro-lactone compounds, which are frequently isolated from plants of Orchidaceae.

Investigation of antibody to severe fever with thrombocytopenia syndrome virus (SFTSV) in blood samples donated in a SFTS-endemic area in Japan

The risk of transfusion-transmitted infection (TTI) for severe fever with thrombocytopenia syndrome virus (SFTSV) is a concern because person-to-person transmission resulting from contact with SFTSV-contaminated blood has been reported. To obtain information regarding the risk of TTI-SFTSV, antibody testing was performed for blood samples donated in an severe fever with thrombocytopenia syndrome-endemic area in Japan. No antibody-positive samples were detected among 3990 samples. This finding suggested that there were few cases of SFTSV infection among donors and that the risk of TTI-SFTSV was also estimated low in Japan.

Formation of Phenalenone Skeleton by an Unusual Rearrangement Reaction

The frame rearrangement reaction of dinaphthyl ketones, possessing hydroxy groups at appropriate positions, into phenalenone derivatives under acidic conditions was discovered serendipitously. Although this rearrangement had limited scope, its mechanism was unusual, involving the division of naphthalene rings into one phenalenone ring and one benzene ring. The reaction mechanism was elucidated by direct determination of intermediate structures using ¹H NMR measurements. The generated phenalenones are expected to be key intermediates toward natural products and functional materials.

Synthesis and Structures of Zigzag Shaped [12]Cyclo-p-phenylene Composed of Dinaphthofuran Units and Biphenyl Units

A [12]Cyclo-p-phenylene 9 composed of dinaphthofuran units and biphenyl units was synthesized through reductive elimination of the corresponding trinuclear complex by applying Yamago's method. The X-ray crystallographic analyses of 9 revealed that it adopts a zigzag conformation in the solid state. The UV-vis and fluorescence measurements of compound 9 indicated that it also preferentially took a zigzag conformation in the solution state.

Syntheses and properties of the V-shaped dimeric xanthene dyes

Two new types of V-shaped dimeric xanthene fluorescent dyes were synthesized and evaluated in terms of their optical properties.

Catch and release of concanavalin A by a mannose-immobilized photoaffinity PEGA resin coupled with a cleavable disulfide linker

A photoaffinity PEGA resin containing mannose as a ligand and disulfide as a cleavable linker was prepared. The resin was crosslinked to concanavalin A, a binding protein of mannose, by UV irradiation, and the protein was subsequently released by cleavage of the disulfide linker.

Synthesis, Photochemical Properties, and Cytotoxicities of 2H-Naphtho[1,2-b]pyran and Its Photodimers

A 2H-naphtho[1,2-b]pyran, prepared by dimerization of 2-bromo-3-methyl-1,4-naphthoquinone and O-methylation, readily undergoes solid-state [2 + 2] photodimerization to give a photodimer in excellent yield and with excellent selectivity. Retro [2 + 2] cycloaddition can be achieved by irradiation of a solution of the photodimer in chloroform. Interestingly, the 2H-naphtho[1,2-b]pyran dimerizes with a skeletal rearrangement to afford 2,5-dihydro-1-benzoxepin dimers upon irradiation in methanol or via irradiation with hexamethylditin. Furthermore, treatment of the resulting dimers with triethylamine regenerates the 2H-naphtho[1,2-b]pyran monomer. Significant differences in the color, fluorescence, and cytotoxic properties of the monomer and dimers were observed.

Synthesis and structural characterization of natural benzofuranoids

The synthesis of ustusoranes A, B, and E, pergillin, dihydropergillin, (±)-penicisochroman A, and (-)-brassicadiol, starting from optically active (R)-benzolactone, is described. The synthesis of ustusoranes A and E established the absolute configurations of these natural products. The synthesis of pergillin and (±)-penicisochroman A led to the structural revision of aspergiones E and F. This study clearly indicates that (R)-benzolactone is a potential intermediate in the synthesis of natural benzofuranoids.

Oligonaphthofurans: fan-shaped and three-dimensional π-compounds

Using a bottom-up method, we prepared a series of oligonaphthofurans composed of alternating naphthalene rings and furan rings. The largest compound (compound 25) contained 8 naphthalene units and 7 furan units. DFT calculations revealed that these compounds were fan-shaped molecules and each naphthalene ring was oriented in an alternate mountain-valley fold conformation because of steric repulsion by the hydrogens at the peri-positions. We investigated the optical properties that derived from their fan-shaped and mountain-valley sequences. As the number of aromatic rings of the oligonaphthofurans increased, the peaks of the longest wavelength absorptions in the UV-vis spectra (HOMO-LUMO energy gap) of these compounds steadily red-shifted, although the shapes of spectra were not sustained because of the decreasing molar absorption coefficients (ε's) of their λ(max). We compared our results with those reported for other types of oligoaromatic compounds such as acenes 1, ethene-bridged p-phenylenes 2, rylenes 3, oligofurans 4, and oligonaphthalenes 5. The slopes of the plots between the transition energies (HOMO-LUMO energy gap) of the oligoaromatic compounds and the reciprocal of the number of aromatic rings indicated that the efficiency of π conjugation of the oligonaphthofurans was comparable with that of linear and rigid acenes and rylenes. The higher-order compounds 22 and 25 aggregated even under high dilution conditions (~10(-6) M).

Synthesis, structure, and cytotoxicity studies of some fungal isochromanes

Ustusorane D and penicisochromans B-D are natural isochromans isolated from Aspergillus ustus 094102 and Penicillium sp. PSU-F40, respectively. Herein, we report the syntheses of (-)-ustusorane D and (+)-penicisochroman B and the structures of penicisochromans C and D. The relative configuration of natural ustusorane D and the absolute configuration of natural penicisochroman B were determined. Two plausible structures for penicisochroman C were evaluated through synthesis, but their ¹H and ¹³C NMR data were not in agreement with those of the natural product. The structural revision and the determination of the absolute configuration of natural penicisochroman D were achieved. Structure-activity relationship studies of the synthetic compounds as well as a series of related isochromans indicated that the enone of the furanone moiety was essential for the cytotoxicity of these compounds toward HCT116 human colon cancer cells. Pseudodeflectusin, the related natural isochroman, suppressed cell growth and induced apoptosis in HCT116 cells.

Enhancement of intestinal immune function in mice by β-D-glucan from aureobasidium pullulans ADK-34

β-Glucans, glucose polymers that are the main constituents of the outer cell walls of micro-organisms such as fungi and yeast, are known to play an immunostimulatory role. We prepared β-glucan (β-(1-3),(1-6)-D-glucan) from an edible cultured fungus through fermentation techniques using a strain of Aureobasidium pullulans ADK-34. The purity of this β-glucan preparation (AP-FBG) was demonstrated to be high through various instrumental analyses. We then examined the effects of AP-FBG on intestinal immune systems. We prepared Peyer's patch (PP) cells and measured interleukin (IL)-5, IL-6, and IgA production in culture media with AP-FBG. We found that both cytokines and IgA increased; furthermore, IL-6 secreted by PP dendritic cells (PPDCs) cultured in the presence of AP-FBG significantly increased. We tested IgA production after oral administration of AP-FBG for 2 weeks and found that AP-FBG tended to promote the production of IgA in the small intestine. Interestingly, we observed a significant increase in IgA production in the small intestines of mice treated with cyclophosphamide (CY; an immunosuppressant) after oral administration of AP-FBG diet compared with CY-treated and control diet mice. Production of IL-6 and IgA by PP cells and IL-6 production by PPDCs in AP-FBG-fed and CY-treated mice also increased. These results demonstrate that AP-FBG has the ability to activate PPDC and induce IL-6 production and IgA secretion in PP cells. These abilities were more clearly expressed when AP-FBG was orally administered in a CY-induced immunosuppressed condition. Therefore, AP-FBG may be a useful ingredient for preparing functional foods with immunomodulatory activities.