Stereoselective acid-catalyzed homoallylic rearrangement of cyclopropylsilylmethanols: an efficient route to Z-homoallyl derivatives

Treatment of cyclopropylsilylmethanols derived from cyclopropyl silyl ketones with acid catalyst gives the corresponding silyl-substituted homoallyl derivatives in high yields with good stereoselectivity, independent of the substituents on the cyclopropyl ring. Cyclopropylsilylmethanols having a n-, s-butyl or phenyl group on the carbinyl carbon react to afford the E-homoallyl derivatives selectively. On the other hand, the reaction of cyclopropylsilylmethanols having a tert-butyl group gives Z-isomers exclusively. The following protiodesilylation of the resulting homoallyl derivatives proceeds with retention of configuration.     

GENERATION AND PARTICIPATION OF O-2 IN 2-NITROPROPANE DIOXYGENASE REACTION

Abstract— 2-Nitropropane dioxygenase (EC 1. 13. 11) of the yeast Hansenula mrakii catalyzes the oxygenative denitrification of 2-nitropropane as follows:

The enzyme is significantly inhibited by superoxide dismutase and various scavengers for superoxide such as cytochrome c , epinephrine, thiols and polyhydric phenols. The scavengers added to the reaction mixture were oxidized or reduced. The addition of superoxide dismutase and the omission of 2-nitropropane or oxygen prevented the oxidation and the reduction of the scavengers. The enzyme catalyzes the formation of nitrite from 2-nitropropane by KO₂ added anaerobically.
One mole of NADH is bound per mole of the enzyme and predominantly the pro-R hydrogen of bound NADH is transferred to superoxide formed enzymatically or provided externally. The enzyme shows incomplete stereospecificity for hydrogen transfer from NADH.     

Preparation of ZnO nanoparticles in a reverse micellar system and their photoluminescence properties

ZnO nanoparticles with spherical morphology and narrow size distribution were obtained by calcination of Zn(OH)2 nanoparticles, which were prepared in a polyethylene glycol mono-4-nonylphenyl ether (NP-5)/cyclohexane reverse micellar system and incorporated into polyurea (PUA) via an in situ polymerization of hexamethylene diisocyanate (HDI). The resulting ZnO nanoparticles demonstrated a near-UV emission and a green emission, the intensity ratio of which depended on calcination conditions. For the nanoparticles studied, the calcination atmosphere influenced remarkably the photoluminescence properties such as intensity ratio of the near-UV emission to green emission, rather than the size, morphology, and crystallinity of the ZnO nanoparticles. The green emission decreased by calcination in O2 flow but increased by calcination in N2 flow, as compared with the case calcined in air flow. This finding suggests that the green emission is enhanced with the increase of the number of oxygen vacancies of the ZnO nanoparticles and thus the photoluminescence properties of the nanoparticles were successfully controlled by the calcination condition, without changing the size and morphology.     

Evidence of conformational equilibrium of 1-ethyl-3-methylimidazolium in its ionic liquid salts: Raman spectroscopic study and quantum chemical calculations

Raman spectra of liquid 1-ethyl-3-methylimidazolium (EMI+) salts, EMI(+)BF4-, EMI(+)PF6-, EMI(+)CF3SO3-, and EMI(+)N(CF3SO2)2-, were measured over the frequency range 200-1600 cm(-1). In the range 200-500 cm(-1), we found five bands originating from the EMI+ ion at 241, 297, 387, 430, and 448 cm(-1). However, the 448 cm(-1) band could hardly be reproduced by theoretical calculations in terms of a given EMI+ conformer, implying that the band originates from another conformer. This is expected because the EMI+ involves an ethyl group bound to the N atom of the imidazolium ring, and the ethyl group can rotate along the C-N bond to yield conformers. The torsion energy for the rotation was then theoretically calculated. Two local minima with an energy difference of ca. 2 kJ mol(-1) were found, suggesting that two conformers are present in equilibrium. Full geometry optimizations followed by normal frequency analyses indicate that the two conformers are those with planar and nonplanar ethyl groups against the imidazolium ring plane, and the nonplanar conformer is favorable. It elucidates that bands at 241, 297, 387, and 430 cm(-1) mainly originate from the nonplanar conformer, whereas the 448 cm(-1) band does originate from the planar conformer. Indeed, the enthalpy for conformational change from nonplanar to planar EMI+ experimentally obtained by analyzing band intensities of the conformers at varying temperatures is practically the same as that evaluated by theoretical calculations. We thus conclude that the EMI+ ion exists as either a nonplanar or planar conformer in equilibrium in its liquid salts.     

Optical resolution of new quinolone drugs by capillary electrophoresis with ligand-exchange and host-guest interactions

A method for the optical resolution of new quinolone drugs (NQs) by capillary electrophoresis has been investigated. The NQs were adequately resolved using a γ-cyclodextrin (γ-CD)-Zn(II)- -phenylalanine ( -Phe) solution as the running solution. The resolution depended on the components of the running solution and their concentrations. When -Phe was used instead of -Phe, inversion of the migration order of the enantiomers was observed. The resolution mechanism is considered to be due to a ligand-exchange interaction of the NQs with Zn(II) and -Phe, in combination with a host-guest interaction of those with γ-CD.     

Theoretical calculation of structures and proton transfer in hydrated ammonia-hydrogen chloride clusters

Ab initio molecular orbital calculations have been performed to investigate the structures and quantum effects of the proton motion in NH(3):HCl:(H(2)O)(n) (n = 0-3) clusters using a MP2/aug-cc-pVDZ level of theory. Three new stable structures and one transition-state structure are investigated for these clusters. The detailed analyses of the intermolecular interactions suggest that three-body interactions play an important role to determine the relative stability in each size of cluster. The quantum effects of the proton motion result in frequency shifts for proton-stretching modes. Our one-dimensional and two-dimensional models fairly closely reproduce the experimental proton-stretching vibrational frequency of the NH(3):HCl cluster. The most stable isomer for n = 1 has a proton-transfer structure, which is weakened by the quantum effects of the proton motion.     

An efficient 1,3-dipolar cycloaddition between aromatic selenoaldehydes and nitrile oxides or nitrile imines: an easy access to selenium-containing five-membered heterocyclic ring system

1,3-Dipolar cycloaddition between aromatic selenoaldehydes, generated by thermal retro Diels-Alder reaction of anthracene cycloadducts, and nitrile oxides or nitrile imines proceeded efficiently to give the corresponding [3+2] cycloadducts as a single isomer in good yields, being 1,4,2-oxaselenazoles or 1,3,4-selenadiazoles, respectively.     

A Synthetic Method for Preparing 3,3-Dialkyl-1,2,3,8-tetrahydroazulen-1-one

The trimethylsilyl enol ether of l-acetylcyclohepta-1,3,5-triene was transformed to 3,3-dialkyl-1,2,3,8-tetrahydroazulen-1-one by a two-step sequence involving the Mukaiyama aldol reaction with ketones and the subsequent Nazarov cyclization.     

Total synthesis of (S)-(+)-ent-phomapyrones B and surugapyrone B

Phomapyrone B ( 1 ), the 2-pyrones isolated from the phytopathogenic fungus Leptosphaeria maculans, has been synthesized as the enantiomeric form starting from (S)-2-methylbutanol ( 4 ). Surugapyrone B ( 3 ) isolated from Streptmyces sp. USF-6280 as an antioxidant has also been synthesized as a natural form. The absolute configuration of phomapyrone B ( 1 ) was estimated to be the (R)-form and that of surugapyrone B ( 3 ) being the (S)-form. A series of 2-pyrone derivatives 17 have been synthesized through the established procedure and their DPPH radical-scavenging activities have also been evaluated.