Asymmetric total synthesis of pseurotin A

The asymmetric total syntheses of pseurotin A and 8-O-demethylpseurotin A have been accomplished. Key reactions are a NaH-promoted intramolecular cyclization of an alkynylamide to form a gamma-lactam, an aldol reaction of a benzylidene-substituted ketone, and the late-stage introduction of the benzoyl group by a selective oxidation of a benzylidene moiety with dimethyldioxirane (DMD). [reaction: see text]     

Hydrogen bonding structure and stability of alpha-chitin studied by 13C solid-state NMR

The structure and stability of hydrogen bonds in alpha-chitin were investigated by (13)C solid-state NMR measurements at different temperatures. Splitting of the carbonyl carbon signal for alpha-chitin was interpreted as two types of hydrogen bonding; the peaks at 173.5 and 175.8 ppm were assigned, respectively, to a carbonyl carbon hydrogen bonded exclusively to the NH group and a carbonyl carbon hydrogen-bonded to both NH and C(6)-OH groups. Approximately 60% of carbonyl groups exclusively contributed to the intermolecular hydrogen bonding and ca. 40% of them to the combination of intermolecular and intramolecular hydrogen bonding. Internal rotation around the C(5)-C(6) bond was detected at 55 degrees C.     

Lipid carrier systems for targeted drug and gene delivery

For effective chemotherapy, it is necessary to deliver therapeutic agents selectively to their target sites, since most drugs are associated with both beneficial effects and side effects. The use of lipid dispersion carrier systems, such as lipid emulsions and liposomes, as carriers of lipophilic drugs has attracted particular interest. A drug delivery system can be defined as a methodology for manipulating drug distribution in the body. Since drug distribution depends on the carrier, administration route, particle size of the carrier, lipid composition of the carrier, electric charge of the carrier and ligand density of the targeting carrier, these factors must be optimized. Recently, the lipid carrier system has also been applied to gene delivery systems for gene therapy. However, in both drug and gene medicine cases, a lack of cell-selectivity limits the wide application of this kind of drug and/or gene therapy. Therefore, lipid carrier systems for targeted drug and gene delivery must be developed for the rational therapy. In this review, we shall focus on the progress of research into lipid carrier systems for drug and gene delivery following systemic or local injection.     

Simple deprotection of acetal type protecting groups under neutral conditions

When acetals such as MOM ethers, MEM ethers, and THP ethers were heated in ethylene glycol or propylene glycol, solvolysis proceeded smoothly to produce alcohols in excellent yield. This reaction is a very promising method for chemoselective deprotection of acetal type protecting groups.     

Rational Design of a Novel Intercalation System. Layer-Gap Control of Crystalline Coordination Polymers, {[Cu(CA)(H(2)O)(m)()](G)}(n)() (m = 2, G = 2,5-Dimethylpyrazine and Phenazine; m = 1, G = 1,2,3,4,6,7,8,9-Octahydrophenazine)

New copper(II) intercalation compounds, {[Cu(CA)(H(2)O)(2)](G)}(n)() (H(2)CA = chloranilic acid; G = 2,5-dimethylpyrazine (dmpyz) (1a and 1b) and phenazine (phz) (2)) have been synthesized and characterized. 1acrystallizes in the triclinic space group P&onemacr;, with a = 8.028(2) ?, b = 10.269(1) ?, c = 4.780(2) ?, alpha = 93.85(3) degrees, beta = 101.01(2) degrees, gamma = 90.04(3) degrees, and Z = 1. 1b crystallizes in the triclinic space group P&onemacr;, with a = 8.010(1) ?, b = 10.117(1) ?, c = 5.162(1) ?, alpha = 94.40(1) degrees, beta = 97.49(1) degrees, gamma = 112.64(1) degrees, and Z = 1. 2crystallizes in the triclinic space group P&onemacr;, with a = 8.071(1) ?, b = 11.266(1) ?, c = 4.991(1) ?, alpha = 97.80(1) degrees, beta = 99.58(1) degrees, gamma = 83.02(1) degrees, and Z = 1. For all the compounds, the crystal structures consist of one dimensional [Cu(CA)(H(2)O)(2)](m)() chains and uncoordinated guest molecules (G). Each copper atom for 1a, 1b, and 2 displays a six-coordinate geometry with the two bis-chelating CA(2)(-) anions and water molecules, providing an infinite, nearly coplanar linear chains running along the a-direction. Theses chains are linked by hydrogen bonds between the coordinated water and the oxygen atoms of CA(2)(-) on the adjacent chain, forming extended layers, which spread out along the ac-plane. The guest molecules are intercalated in between the {[Cu(CA)(H(2)O)(2)](k)()}(l)() layers, just like pillars, which are supported with N.H(2)O hydrogen bonding. The guest molecules are stacked each other with an interplanar distance of ca. 3.2 ? along the c-axis perpendicular to the [Cu(CA)(H(2)O)(2)](m)() chain. The EHMO band calculations of intercalated dmpyz and phz columns show an appreciable band dispersion of phz pi (b(2g) and b(3g)) and dmpyz pi (b(g)), indicative of the importance of planar pi structure for the formation of the intercalated structure. The distances of O-H---N (guest molecules) fall within the range 2.74-2.80 ?, insensitive to the guest, whereas the interlayer distances increase in the order 9.25 ? (1b), 10.24 ? (1a), and 11.03 ? (2). The degree in lengthening the distance correlates well with the size of a molecule, indicative of the stability of the 2-D sheet structure and the flexibility of the sheet packing. The magnetic susceptibilities were measured from 2 to 300 K and analyzed by a one-dimensional Heisenberg-exchange model to yield J = -1.83 cm(-)(1), g = 2.18 (1a), J = -0.39 cm(-)(1), g = 2.14 (1b), and J = -1.84 cm(-)(1), g = 2.18 (2). The absolute value of J is smaller than that value for [Cu(CA)](n)(), which has a planar ribbon structure suggesting that the magnetic orbital d(x)()()2(-)(y)()()2 is not parallel to the chloranilate plane. For comparison with phz another type of copper(II) coordination compound, {[Cu(CA)(H(2)O)](ohphz)}(n)() (ohphz = 1,2,3,4,6,7,8,9-octahydrophenazine (7)) has also been obtained. 7 crystallizes in the orthorhombic space group Cmcm with a = 7.601(2) ?, b = 13.884(2) ?, c = 17.676(4) ?, and Z = 4. Nonplanar ohphz molecules are in between [Cu(CA)(H(2)O)(2)](m)() chains with the N.H(2)O hydrogen bonding in a fashion parallel to the chain direction. The copper atom shows a five-coordinate square-pyramidal configuration with two CA and one water molecule, thus affording no hydrogen bonding links between chains, dissimilar to 1a, 1b, and 2. The magnetic susceptibilities yield J = -10.93 cm(-)(1) and g = 2.00, comparable to that of the four-coordinate [Cu(CA)](n)(). On this basis both hydrogen bonding and stack capability of a guest molecule is responsible for building the unique intercalated structure such as is seen in 1a, 1b, and 2.     

Microwave spectrum of 3-lodopropene in its torsionally excited states

The microwave spectra of the skew-3-iodopropene in its torsionally excited state were studied in the region 15 to 23 GHz. From the analyses of the a-type R-branch and b-type Q-branch transitions, the rotational constants and the elements of the χ-tensor were obtained: A₁ = 17 783.84 ± 0.77, B₁ = 1591.26 ± 0.02, C₁ = 1540.24 ± 0.02, χ_aa = ?1333 ± 8, χ_bb = 386 ± 4, χ_cc = 947 ± 6, and |χ_ab| = 1086 ± 2, each in MHz for the first torsionally excited state, and A₂ = 17 915.85 ± 1.38, B₂ = 1594.49 ± 0.03, C₂ = 1541.85 ± 0.03, χ_aa = ?1319 ± 10, χ_bb = 383 ± 5, χ_cc = 936 ± 8, and |χ_ab| = 1073 ± 3, each in MHz for the second torsionally excited state, respectively. From the observed line intensity, the torsional frequencies of the CH₂I group between the ground and the first excited states and also between the first and second excited states were obtained to be 114 ± 34 and 80 ± 24 cm^?1, respectively.     

Preparation and properties of polyamides containing p-terphenyl units

Novel polyamides that contained p-terphenyl units were prepared with inherent viscosities in the range of 0.4–1.7 dL/g by the polycondensation of 4,4″-dichloroformyl-p-terphenyl with aromatic diamines and 4,4″-diamino-p-terphenyl with aromatic dicarbonyl chlorides. Polyamides composed of only paraoriented phenylene units were insoluble in all solvents and showed a high degree of crystallinity. A series of polyamides that contained p-terphenyl units were more thermostable than corresponding polymers with p-phenylene or biphenylene linkages.     

Bent and generalized bent Boolean functions

In this paper, we investigate the properties of generalized bent functions defined on ${\mathbb{Z}_2^n}$ with values in ${\mathbb{Z}_q}$ , where q ≥ 2 is any positive integer. We characterize the class of generalized bent functions symmetric with respect to two variables, provide analogues of Maiorana–McFarland type bent functions and Dillon’s functions in the generalized set up. A class of bent functions called generalized spreads is introduced and we show that it contains all Dillon type generalized bent functions and Maiorana–McFarland type generalized bent functions. Thus, unification of two different types of generalized bent functions is achieved. The crosscorrelation spectrum of generalized Dillon type bent functions is also characterized. We further characterize generalized bent Boolean functions defined on ${\mathbb{Z}_2^n}$ with values in ${\mathbb{Z}_4}$ and ${\mathbb{Z}_8}$ . Moreover, we propose several constructions of such generalized bent functions for both n even and n odd.     

Synthesis and functionalities of poly(N‐vinylalkylamide). XII. Synthesis and thermosensitive property of poly(vinylamine) copolymer prepared from poly(N‐vinylformamide‐co‐N‐vinylisobutyramide)

The differences in the polymerization abilities of N‐vinylformamide (NVF) and N‐vinylisobutyramide (NVIBA) and the synthesis of their copolymers were studied. The polymerization abilities were fairly good and quite similar to those of N‐vinyl‐ acetamide (NVA), a monomer in the same class as N‐vinylalkylamides. Since the monomer reactivity ratios were r₁ = 1.08 and r₂ = 0.92 (M₁ = NVF, M₂ = NVIBA), respectively, it is clear that the comonomers definitely were converted to random copolymers. The resulting copolymers poly(NVF‐co‐NVIBA) exhibited the cloud points sharply. The light transmittance profiles were the same as those for poly(NVIBA) although they increased from 39 °C for poly(NVIBA), with an increase in the corresponding hydrophilic NVF component. Our final objective was to produce a cloud point controlled polymer material with primary amino groups. To achieve this, we examined the hydrolysis of poly(NVF), poly(NVA), poly(NVIBA), and poly(NVF‐co‐NVIBA) to obtain poly(vinylamine) [poly(VAm)]. The hydrolytic cleavage of poly(NVF) and poly(NVA) was promoted by an increase in temperature. However, poly(NVIBA) was not cleaved appreciably. The hydrolysis of poly(NVF‐co‐NVIBA) was done under controlled conditions, and amino groups selectively were introduced to only one of two components of the copolymer. The cloud point of the hydrolyzed copolymer shifted to a higher temperature than that of the copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3674–3681, 2000     

Initial growth behavior of GaAs on ZnSe in MOVPE

We have used atomic force microscopy to investigate the initial stages of the growth of GaAs on ZnSe by metalorganic vapor phase epitaxy. Underlying ZnSe with an atomically flat surface is achieved by growth at 450°C and post-growth annealing at the same temperature. The growth modes of GaAs on the ZnSe surface strongly depend on growth temperatures. The growth carried out at 450°C is 2-dimensional, while that at 550°C is highly 3-dimensional (3D), where the 3D islands are elongated in the [110] direction. The growth behavior, unlike homoepitaxy, is well interpreted in terms of low sticking coefficient and anisotropic lateral growth rate in the heterovalent heteroepitaxy.