Regioselective cycloaddition reaction of alkene molecules with the asymmetric dimer on Si(100)c(4 x 2)

We investigated the adsorption states of 2-methylpropene and propene on Si(100)c(4 x 2) using low-temperature scanning tunneling microscopy. We have found that regioselective cycloaddition reactions (di-sigma bond formation) occur between the asymmetric alkene molecules and the asymmetric dimers on Si(100)c(4 x 2). First-principles calculations have elucidated that the regioselectivity is closely related to the structures of precursor species and these precursor species have carbocation-like features. Thus, we conclude that Markovnikov's rule is applicable for the cycloaddition of asymmetric alkene with the asymmetric dimer on Si(100)c(4 x 2).     

Semi-synthesis of polymyxin B (2-10) and colistin (2-10) analogs employing the Trichloroethoxycarbonyl (Troc) group for side chain protection of alpha,gamma-diaminobutyric acid residues

Improved strategies for the chemical conversion of natural polymyxin B and colistin to their N-terminal analogs are reported. First, the protection of the side chains of five L-alpha,gamma-diaminobutyric acid (Dab) residues in natural polymyxin B and colistin was achieved with trichloroethoxycarbonyl (Troc), then the resulting pentakis(N gamma-Troc)-polymyxin B and pentakis(N gamma)Troc)-colistin were treated with trifluoroacetic acid (TFA) : methanesulfonic acid (MSA) : dimethylformamide (DMF) : H2O (10 : 30 : 55 : 5) at 40 degrees C in order to remove N alpha-alkanoyl-Dab(Troc)-OH selectively. The new key compounds, tetrakis(N gamma-Troc)-polymyxin B (2-10) and tetrakis(N gamma-Troc)-colistin (2-10), were obtained in 19% and 15% yields, respectively, which is higher than previous reports using trifluoroacetyl (Tfa) for tetrakis(N gamma-Tfa)-polymyxin B (2-10) and tetrakis(N gamma-Tfa)-colistin (2-10), respectively. Acylation of tetrakis(N gamma-Troc)-polymyxin B (2-10) and tetrakis(N gamma-Troc)-colistin (2-10) with various hydrophobic acids bearing aliphatic or aromatic ring structures, followed by the deprotection of Troc by Zn in AcOH, produced polymyxin B (2-10) and colistin (2-10) analogs which were used for structure-activity relationship studies. It was found that cyclohexylbutanoyl-, 4-biphenylacetyl-, and 1-adamantaneacetyl-polymyxin B (2-10) showed potent antimicrobial activity equal to that of polymyxin B against three Gram-negative bacterial strains. The lipopolysacharide (LPS) binding activity of cyclohexylbutanoyl-, 4-biphenylacetyl-, and cyclododecanecarbonyl-polymyxin B (2-10) increased greatly in comparison with that of polymyxin B (2-10). The various N alpha-acylated polymyxin B (2-10) analogs showed slightly higher antimicrobial and LPS binding activities than the corresponding N alpha-acylated colistin (2-10) analogs.     

A novel preparation method for microspheres of water soluble polymers using polypropyleneglycol as the dispersion medium

Polypropyleneglycol (PPG) was used as a dispersion medium for the preparation of microspheres (MS) consisting of starch, gelatin, whey protein or dextran. Aqueous solutions of the polymers were dispersed in PPG at various initial temperatures and then the systems were cooled to 0.5 degrees C to allow water in the dispersed phase to dissolve in PPG. The particle size of the starch-MS was dependent on the initial temperature of PPG in the preparation process. There were two different processes for particle generation in the procedure. One of them was via the formation of a temporary emulsion during the early phase of dispersion of the aqueous polymer solution into PPG. The other was via the stable emulsion in which the aqueous polymer solution was dispersed in water-saturated PPG. The particle size generated in the former process was dependent on the initial temperature: a high temperature gave large particles but a low temperature gave small particles, while that in the latter process was temperature-independent. This preparation method for MS will be useful for the formulation of heat-sensitive material, such as protein-containing drugs.     

Infrared spectra of organic monolayer films in a standing wave measured by photon-trap spectroscopy

Photon-trap spectroscopy, a generalized scheme of cavity ringdown spectroscopy, is applied to measure an infrared spectrum of the C-H stretching vibration of alkylsiloxane monolayer films grafted on a silicon substrate. A continuous-wave laser beam is introduced into a high-finesse Fabry-Pérot cavity containing the substrate placed exactly normal to the light beam to minimize optical losses. The lifetime of the light trapped in the cavity is measured to detect optical absorption sensitively. The results show clear dependence of the absorbance on the location of the monolayers with respect to a standing wave formed in the cavity; the absorbance is practically zero when the monolayers on both the surfaces are adjusted at nodes, whereas it is maximized at antinodes. The present experiment is materialized on the basis of the principles established by our previous study [Terasaki et al., J. Opt. Soc. Am. B 22, 675 (2005)].     

Reactions of guaiazulene with thiophene-2,5-dicarbaldehyde and furan-2,5-dicarbaldehyde in methanol in the presence of hexafluorophosphoric acid: a facile preparation and properties of delocalized dicarbenium-ion compounds stabilized by two 3-guaiazulenyl groups and a thiophene (or furan) ring

Reaction of guaiazulene (1) with thiophene-2,5-dicarbaldehyde (2) in methanol in the presence of hexafluorophosphoric acid at 25 °C for 3 h gives as high as 90% isolated yield of the delocalized dicarbenium-ion compound, 2,5-thienylenebis(3-guaiazulenylmethylium) bis(hexafluorophosphate) (3). Similarly, reaction of 1 with furan-2,5-dicarbaldehyde (4) under the same conditions as the above reaction affords the corresponding dicarbenium-ion compound, 2,5-furylenebis(3-guaiazulenylmethylium) bis(hexafluorophosphate) (5), in 84% isolated yield. Along with a facile preparation and the spectroscopic and electrochemical properties of 3 and 5, comparative studies on the ¹H and ¹³C NMR spectral and chemical properties of 3 and 5 with those of the delocalized mono- and dicarbenium-ion compounds [i.e., (3-guaiazulenyl)(2-thienyl)methylium hexafluorophosphate (7), (2-furyl)(3-guaiazulenyl)methylium hexafluorophosphate (9), α,α′-bis(3-guaiazulenylmethylium) bis(tetrafluoroborate) (10), 1,2-phenylenebis(3-guaiazulenylmethylium) bis(hexafluorophosphate) (11), and 1,4-phenylenebis(3-guaiazulenylmethylium) bis(tetrafluoroborate) (12)] are reported. Moreover, referring to the results of the X-ray crystallographic analyses of 7, 9, 11, and 12, the optimized 2,5-thienylenebis(3-guaiazulenylmethylium)- and 2,5-furylenebis(3-guaiazulenylmethylium)-ion structures for 3 and 5, calculated by a WinMOPAC (version 3.0) program using PM3 as a semiempirical Hamiltonian, are described.     

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

This review covers the literature on simple indole alkaloids and those with a nonrearranged monoterpenoid unit. Newly isolated alkaloids, structure determinations, total syntheses and biological activities are included.     

Palladium Enolate Umpolung: Cyclative Diacetoxylation of Alkynyl Cyclohexadienones Promoted by a Pd/SPRIX Catalyst

A novel palladium‐catalyzed reaction involving an unusual nucleophilic attack on a palladium enolate was developed using a spiro‐bis(isoxazoline) (SPRIX) ligand. Treatment of alkynyl cyclohexadienone substrates with a Pd/SPRIX catalyst in acetic acid under an oxygen atmosphere furnished diacetoxylated benzofuranone derivatives in good yields. This cyclative diacetoxylation proceeded enantioselectively in the presence of an optically pure SPRIX ligand.     

Expression,Purification, and Characterization of Endo-β-N-Acetylglucosaminidase H Using Baculovirus-Mediated Silkworm Protein Expression System

Endo-β-N-acetylglucosaminidase (Endo H) from Streptomyces plicatus hydrolyzes the core di-GlcNAc units of asparagine-linked oligosaccharides and is regarded as an important tool for glycobiology research. In the present study, we established a large-scale system to produce secreted Endo H using a silkworm-baculovirus expression system (silkworm-BES). The recombinant Endo H purified from silkworm hemolymph had activity comparable to that from recombinant Escherichia coli. As well as its well-characterized substrate RNase B, the Endo H from silkworm-BES was able to deglycosylate the high-mannose glycoproteins from silkworm hemolymph. Interestingly, the secretion amount of recombinant Endo H was significantly varied among the different silkworm strains, which could provide valuable information for larger-scale protein productions from silkworm-BES.     

Synthesis of 2‐Substituted 3‐Alkylidene‐2,3‐dihydro‐1H‐isoindol‐1‐imines through Cyclization of [1‐(2‐Cyanophenyl)alkylidene]aminide Intermediates Generated from the Reaction of 2‐(1‐Azidoalkyl)benzonitriles with NaH

A convenient sequence for the preparation of 3‐alkylidene‐2,3‐dihydro‐1H‐isoindol‐1‐imine derivatives 6 has been developed. Thus, 2‐(1‐azidoalkyl)benzonitriles 2 , readily accessible from 2‐alkylbenzonitriles, are allowed to react with NaH in DMF at 0° to room temperature to generate [1‐(2‐cyanophenyl)alkylidene]aminide intermediates 3 , of which cyclization and the subsequent rearrangement, followed by alkylation with alkyl halides, affords 2‐substituted 1‐alkylidene‐2,3‐dihydro‐1H‐isoindol‐2‐imines 6 in generally moderate yields.