Ab initio through‐space/bond interaction analysis of the long C–C bonds in Bi(anthracene‐9,10‐dimethylene) photoisomers

The bi(anthracene‐9,10‐dimethylene) photoisomer has remarkably long C–C single bonds. To examine the lengthening of the C–C bond, we propose a novel procedure for quantitatively analyzing orbital interactions in a molecule at the level of the ab initio molecular orbital method. In this procedure, we can cut off the specific through‐space/bond interactions in a molecule by artificially increasing the absolute magnitude of the exponents in a Gaussian function. Then, the spatial orbital interactions were perfectly cut off, and, each term that makes up the total energy, that is, the nuclear–electron attractions, the electron–electron repulsions, and the nuclear–nuclear repulsions cancel each other. Several model molecules of the photoisomer were analyzed by this procedure. It was found that the orbital interaction between the p orbital on the benzene ring and the σ* orbital on the C–C bond in question, σ→σ* electron transfer through π orbital, weakens the C–C bond efficiently when these orbitals were located in the “periplanar” conformation. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Effects of poly(ethylene glycol) (PEG) concentration on the permeability of PEG-grafted liposomes

Poly(ethylene glycol)-grafted liposomes (PEG-liposomes) were prepared from dipalmitoylphosphatidylcholine (DPPC) with various amounts of distearoyl-N-monomethoxy poly(ethylene glycol)-succinyl-phosphatidylethanolamines (DSPE-PEG) with PEG molecular weights of 1000, 2000, 3000 and 5000. The effects of DSPE-PEG concentration on the permeability of PEG-liposomes were investigated using carboxyfluorescein (CF). In the gel state, the CF leakage from PEG-liposomes was decreased with increasing mole fractions of DSPE-PEG for all PEG molecular weights. In the liquid-crystalline state, the CF leakage from PEG-liposomes containing DSPE-PEG1000 gradually increased with increasing mole fractions of DSPE-PEG, while that of PEG-liposomes whose molecular weight in PEG units was above 2000 rapidly decreased by the addition of DSPE-PEG. Furthermore, no effect of PEG molecular weight on CF leakage was observed. The relationship between the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) (or 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH)) and the mole fraction of DSPE-PEG for PEG-liposomes was also investigated. No significant changes in fluorescence polarization of DPH for liposomal bilayer membranes was observed in the gel and liquid-crystalline states due to the addition of DSPE-PEG, while that of TMA-DPH was decreased compared with that of liposomes without DSPE-PEG in both states.     

Simultaneous discrimination of diastereotopic groups and faces: the first example in intramolecular [3+2] and [2+2+1] cycloaddition reactions

To explore a novel concept for controlling diastereoselectivity, systematic studies on the sense and degree of diastereotopic groups and face selections in intramolecular [3 + 2] (nitrile oxide and nitrone) and [2 + 2 + 1] (Pauson-Khand) cycloadditions have been conducted. Optically pure methyl (S)-3,4-O-isopropylidene-3,4-dihydroxybutanoate (5) and methyl (S)-2,3-O-isopropylidene-2,3-dihydroxypropanoate (6) were converted to substrate aldehydes (1-4) that bear geminal allyl groups and four types of controllers with the intention of imparting a stereochemical bias to the allylic groups and their faces. The controllers involve 1,2-bis(tert-butyldimethylsiloxy), 1,3-bis(tert-butyldimethylsiloxy), 1,2-acetonide, and 1,3-acetonide groups, which are referred to as 1,2-(TBDMSO)(2), 1,3-(TBDMSO)(2), 1,3-dioxolane, and 1,3-dioxane, respectively. Twelve runs of cycloaddition reactions as combinations between the three types of reactions and the four types of substrates were performed to provide bicyclo[4.3.0] or -[3.3.0] adducts of synthetic importance in which isoxazolidine, isoxazoline, or cyclopentenone segments were fused. For every case, high levels of diastereoselectivity have been achieved: >99% (in eight cases), 82%, and 76% for the discrimination of diastereotopic groups and 68-->99% for the discrimination of diastereotopic faces. On the basis of the absolute structures of the cycloadducts, plausible stereochemical models are proposed.     

Direct coupling of microcolumn liquid chromatography with in-tube solid-phase microextraction for the analysis of antidepressant drugs

The direct coupling of in-tube solid-phase microextraction (in-tube SPME) with microcolumn liquid chromatography (micro-LC) has been investigated for the analysis of antidepressants in human urine. The use of in-tube SPME has been clearly shown to be advantageous for the on-line coupling of the SPME method, as the sample pretreatment technique, with micro-LC as the separation technique. This is because much smaller amounts of the sample solutions, desorption solvents and the mobile phase are required compared with conventional SPME-LC systems. The parameters for preconcentration have been investigated for the extraction capillary with the newly developed 'wire-in-tube' configuration.     

DNA cleavage reaction of antitumour antibiotic, kapurimycin A3, with deoxytetranucleotide d(CGCG)2

Kapurimycin A3 (kap A3, 1 ), an antitumour antibiotic, alkylates N7 of guanine₂ (G₂) and G₄ of d(C₁G₂C₃G₄)₂ to produce their covalent adducts 2 (64 %) and 3 (7.0 %), respectively. Heating at 90 °C for 5 min degraded both adducts to kap A3 - G adduct (5) with the concurrent release of their respective abasic-site containing oligomers 4 and 6.     

Furanodictine A and B: amino sugar analogues produced by cellular slime mold Dictyostelium discoideum showing neuronal differentiation activity

We investigated the constituents of Dictyostelium discoideum to clarify the diversity of secondary metabolites of Dictyostelium cellular slime molds and to explore biologically active substances that could be useful in the development of novel drugs. From a methanol extract of the multicellular fruit body of D. discoideum, we isolated two novel amino sugar analogues, furanodictine A (1) and B (2). They are the first 3,6-anhydrosugars to be isolated from natural sources. Their relative structures were elucidated by spectral means, and the absolute configurations were confirmed by asymmetric syntheses of 1 and 2. These furanodictines potently induce neuronal differentiation of rat pheochromocytoma (PC-12) cells.