A Linear C=Ge=C Heteroallene with a Di-coordinated Germanium Atom**

Allenes (>C=C=C<) are classified as cumulated dienes with a linear structure and an sp-hybridized central carbon atom. We have synthesized and isolated a stable 2-germapropadiene with bulky silyl substituents. The 2-germapropadiene allene moiety adopts a linear structure both in the solid state and in solution. An X-ray diffraction electron-density-distribution (EDD) analysis of this 2-germapropadiene confirmed the linear C=Ge=C geometry with a formally sp-hybridized germanium atom that bears two orthogonal C=Ge π-bonds. Based on detailed structural and computational studies, we concluded that the linear geometry of the isolated 2-germapropadiene most likely arises from the negative hyperconjugation of the silyl substituents at the terminal carbon atoms. The 2-germapropadiene reacts rapidly with nucleophiles, indicating that the linearly oriented germanium atom is highly electrophilic.     

Unusual electronic structure of bis-isocyanide complexes of iron(III) porphyrinoids

A series of isocyanide complexes, [Fe(Porphyrinoid)((t)BuNC)(2)](+), were synthesized and examined for their physicochemical properties. The molecular structure of the bis((t)BuNC) adduct of the iron(III) porphycene (1) and corrphycene (2) adopting the (d(xy))(2)(d(xz), d(yz))(3) ground state were determined for the first time. Furthermore, 1 and 2 showed unusual crossover phenomena between different electron configurations, (d(xy))(2)(d(xz), d(yz))(3) ground state and (d(xz), d(yz))(4)(d(xy))(1) ground state, by the addition of the external stimuli.     

Amycolamicin: A Novel Broad‐Spectrum Antibiotic Inhibiting Bacterial Topoisomerase

The abuse of antibacterial drugs imposes a selection pressure on bacteria that has driven the evolution of multidrug resistance in many pathogens. Our efforts to discover novel classes of antibiotics to combat these pathogens resulted in the discovery of amycolamicin (AMM). The absolute structure of AMM was determined by NMR spectroscopy, X‐ray analysis, chemical degradation, and modification of its functional groups. AMM consists of trans‐decalin, tetramic acid, two unusual sugars (amycolose and amykitanose), and dichloropyrrole carboxylic acid. The pyranose ring named as amykitanose undergoes anomerization in methanol. AMM is a potent and broad‐spectrum antibiotic against Gram‐positive pathogenic bacteria by inhibiting DNA gyrase and bacterial topoisomerase IV. The target of AMM has been proved to be the DNA gyrase B subunit and its binding mode to DNA gyrase is different from those of novobiocin and coumermycin, the known DNA gyrase inhibitors.     

Tetracene Dicarboxylic Imide and Its Disulfide: Synthesis of Ambipolar Organic Semiconductors for Organic Photovoltaic Cells

We have designed and synthesized a new donor/acceptor‐type tetracene derivative by the introduction of dicarboxylic imide and disulfide groups as electron‐withdrawing and ‐donating units, respectively. The prepared compounds, tetracene dicarboxylic imide (TI) and its disulfide (TIDS) have high chemical and electrochemical stability as well as long‐wavelength absorptions of up to 886 nm in the thin films. The crystal packing structure of TIDS molecules features face‐to‐face π‐stacking, derived from dipole–dipole interactions. Notably, TIDS exhibited ambipolar properties of both electron‐donating and ‐accepting natures in p–n and p–i–n heterojunction organic thin‐film photovoltaic devices. Accordingly, TI and TIDS are expected to be promising compounds for designing new organic semiconductors.     

Agrocybynes A–E from the culture broth of Agrocybe praecox

Five novel compounds (1–3, 5, and 6), and two known ones (4 and 7) were isolated from the culture broth of Agrocybe praecox. Their structures were determined by the interpretation of spectroscopic data. Compounds 1–4 inhibited hypocotyl growth of lettuce, and 1, 3, and 4 inhibited the root growth.     

Asymmetric reduction of aliphatic ketones and acyl silanes using chiral anti-pentane-2,4-diol and a catalytic amount of 2,4-dinitrobenzenesulfonic acid

Aliphatic ketones were reduced to the corresponding secondary alcohols by using anti-1,3-diol and a catalytic amount of 2,4-dinitrobenzenesulfonic acid (DNBSA) in benzene at reflux. Addition of 1-octanethiol in that media improved the efficiency of the reduction. Asymmetric reduction of aliphatic ketones was performed by using chiral anti-pentane-2,4-diol, and highly asymmetric induction (up to >99% ee) was observed in the reduction of tert-alkyl ketones. Asymmetric reduction of acyl silanes using chiral anti-pentane-2,4-diol and DNBSA proceeded efficiently in the absence of octanethiol and the corresponding α-silyl alcohols were obtained in high yields with high ees.