Stereochemical assignments of rubiaquinones A–C,naphthoquinone derivatives from Rubia yunnanensis

Three new naphthoquinone derivatives, rubiaquinones A–C (1–3), were isolated from the roots of Rubia yunnanensis. Rubiaquinone A (1) was a racemic naphthoquinone dimer consisting of a 1,4-dihydroxynaphthalene and a 4-hydroxy-1,2-naphthoquinone moieties with a 2-oxo-propyl group. Rubiaquinones B (2) and C (3) were structurally unique trimeric naphthoquinones with a racemic nature possessing one chiral axis and one chiral carbon in common. The planar structures of 1–3 were assigned by detailed spectroscopic analyses, and enantiomers of 1–3 were obtained by optical resolutions. The absolute configurations of (+)-1 and (?)-1 were elucidated by interpretation of the ECD spectra with the aid of TDDFT ECD calculation, while those of enantiomers obtained from 2 and 3 were assigned by analyses of the composite ECD spectra generated by summing appropriate ECD spectra of enantiomers. Rubiaquinone A (1) exhibited antimicrobial activity against Bacillus subtilis.     

Nitrosopurines En Route to Potently Cytotoxic Asmarines

A nitrosopurine ene reaction easily assembles the asmarine pharmacophore and transmits remote stereochemistry to the diazepine‐purine hetereocycle. This reaction generates potent cytotoxins which exceed the potency of asmarine A (1.2 μM IC₅₀) and supersede the metabolites as useful leads for biological discovery.     

Highly Sensitive Bioluminescent Probe for Thiol Detection in Living Cells

The sensitive detection of thiols including glutathione and cysteine is desirable owing to their roles as indispensable biomolecules in maintaining intracellular biological redox homeostasis. Herein, we report the design and synthesis of SEluc‐1 (s ulfinate e ster luc iferin), a chemoselective probe exhibiting a ratiometric and turn‐on response towards thiols selectively in fluorescence and bioluminescence, respectively. The probe, which was designed based on the “caged” luciferin strategy, displays excellent selectivity, high signal/noise ratio (>240 in the case of bioluminescence), and a biologically relevant limit of detection (LOD, 80 nm for cysteine), which are all desirable traits for a sensitive bioluminescent sensor. SEluc‐1 was further applied to fluorescence imaging of thiol activity in living human cervical cancer HeLa cell cultures, and was successfully able to detect fluctuations in thiol concentrations induced by oxidative stress in a bioluminescent assay utilizing African green monkey fibroblast COS‐7 cells and human breast adenocarcinoma MCF‐7 cells.     

Estimation of partial optical path length in the brain in subject-specific head models for near-infrared spectroscopy

Three-dimensional head models with the structures constructed from the MR head images of 40 volunteers were constructed to analyze light propagation in the subject-specific head models. The mean optical path length in the head and the partial optical path length in the brain at 13 fiducial points for each volunteer were estimated to evaluate the intersubject and spatial variability in the optical path lengths. Although the intersubject variability in the optical path lengths is very high, the spatial variability in the average of the mean optical path length and partial optical path length is similar to the previously reported data. The mean optical path length in the head increases, whereas the partial optical path length in the brain decreases with an increase in the depth of the brain surface. The partial optical path length is highly correlated with the depth of the brain surface in comparison to the mean optical path length in the head.     

Conditions Implying Self-adjointness of Operators

In this paper, we show that if is a quasi-class A operator and S is an arbitrary operator for which and ST = T*S, then T is self-adjoint, and we also show that quasisimilar quasi-class A operators have equal spectra and essential spectra. This work of the second author was supported by the University of Incheon Research Grant in 2008.     

Synthesis and Degradation of Vinyl Polymers with Evenly Distributed Thioacetal Bonds in Main Chains: Cationic DT Copolymerization of Vinyl Ethers and Cyclic Thioacetals

We report a novel method to synthesize degradable poly(vinyl ether)s with cleavable thioacetal bonds periodically arranged in the main chains using controlled cationic copolymerization of vinyl ethers with a 7-membered cyclic thioacetal ( 7-CTA ) via degenerative chain transfer (DT) to the internal thioacetal bonds. The thioacetal bonds, which are introduced into the main chain by cationic ring-opening copolymerization of 7-CTA with vinyl ethers, serve as in-chain dormant species to allow homogeneous propagation of vinyl ethers for all internal segments to afford copolymers with controlled overall and segmental molecular weights. The obtained polymers can be degraded into low- and controlled-molecular-weight polymers with narrow molecular weight distributions via hydrolysis. Various vinyl ethers with hydrophobic, hydrophilic, and functional pendants are available. Finally, one-pot synthesis of multiblock copolymers and their degradation into diblock copolymers are also achieved.     

Novel pyromellitic diimide-based macrocycle with a linear pi-electronic system and bis(phenylethynyl)pyromellitic diimide: syntheses, structures, photophysical properties, and redox characteristics

We report the syntheses, structures, photophysical properties, and redox characteristics of the [2 + 2] pyromellitic diimide-based macrocycle with a linear pi-electronic system 2 as well as the 3,6-bis(phenylethynyl)pyromellitic diimide derivative 3. The interesting solid state structural properties of the clathrates of 3 with pi-donors are also reported. The macrocycle 2 was synthesized by the direct cyclocondensation followed by the Sonogashira coupling reaction. X-ray crystallographic studies showed that the phenylacetylene moieties in 2 formed the intramolecular benzene dimer structures, and the bis(phenylethynyl)pyromellitic diimide moieties in both 2 and 3 were stacked in a parallel and slanted arrangement. Theoretical calculations for 2' and 3 suggested the existence of electrostatic interactions between the bis(phenylethynyl)pyromellitic diimide moieties. The UV/vis spectral measurements and TDDFT calculations of 2, 2', and/or 3 were performed to understand their electronic transitions. The fluorescence spectral measurements showed that 2 and 3 have visible fluorescence properties and 2 displays an excimer fluorescence at ca. 590 nm. The cyclic voltammetry measurements revealed that the electrostatic repulsion between the diimide moieties in 2 is greater than that in 1 according to the extension of the pi-electronic systems. X-ray crystallography of the clathrates of 3 with various pi-donors demonstrated the formation of the segregated donor-acceptor structures, indicating the strong aggregation ability of the bis(phenylethynyl)pyromellitic diimide moiety.     

Enantiopure anthrylene-ethynylene cyclic tetramer and racemization via rotation of anthracene unit about acetylenic axes

Four anthracene and four acetylene units are used to construct a chiral pi-conjugate macrocycle, the chirality of which is due to the restricted rotation about acetylenic axes. Enantiomers were readily resolved by chiral HPLC and racemized slowly even at 70 degrees C.     

High-resolution ESR study of the H...CH3, H...CHD2, D...CH2D, and D...CD3 radical pairs in solid argon

High-resolution electron spin resonance (ESR) spectra of radical pairs of a hydrogen atom that coupled with a methyl radical (H...CH3, H...CHD2, D...CH2D, and D...CD3) were observed for X-ray irradiated solid argon containing selectively deuterium-labeled methanes, CH4, CH2D2, and CD4, at 4.2 K. The double-quartet 1H-hyperfine (hf) splittings of ca. 26 and 1.16 mT at the Deltam(s) = +/-1 and Deltam(s) = +/-2 transitions, which are one-half of the isotropic 1H-hf splittings of an isolated H-atom and a CH3 radical, were attributed to the H...CH3 pair. The 1H-hf splittings at the Deltam(s) = +/-1 transition were further split by the fine structure (fs) due to the electron dipole-dipole coupling. Because of the high-resolution spectra, three different sets of the fs splitting, d, are clearly resolved in the spectra of both the H...CH3 and the D...CD3 pairs. The separation distance (inter-spin distance), R, between the H-atom and the CH3 radical being in pairs was evaluated from the d values based on a point-dipole interaction model. For the case of the H...CH3 pair, the observed d values of 4.2, 4.9, and 5.1 mT yield the respective separations, R = 0.87, 0.83, and 0.82 nm, to probe the trapping site of the pair in an Ar crystalline lattice (fcc). For the pair with R = 0.87 nm, for example, we propose that the CH3 radical occupies a substitutional site and the counter H-atom occupies either the interstitial tetrahedral sites directed away from the CH3 radicals by a distance of 0.87 nm or the interstitial octahedral sites by a distance of 0.88 nm. When a mixture of CH4 and CD4 in a solid Ar matrix was irradiated, only two different radical pairs, H...CH3 and D...CD3, were observed. This result clearly demonstrates that the hydrogen atom and methyl radicals, which undergo a pairwise trapping, can originate from the same methane molecule.