Radical addition approach to asymmetric amine synthesis: design, implementation, and comparison of chiral N-acylhydrazones

Intermolecular radical addition to C=N bonds with acyclic stereocontrol offers excellent potential as a mild, nonbasic carbon-carbon bond construction approach to chiral amines. Here, complete details of the first radical additions to chiral N-acylhydrazones as an approach to asymmetric amine synthesis are disclosed. Novel N-acylhydrazones were designed as chiral C=N radical acceptors with Lewis acid activation, restriction of conformational mobility, and commercial availability of precursors. Amination of 4-alkyl-2-oxazolidinones with O-(mesitylenesulfonyl)hydroxylamine or O-(p-nitrobenzoyl)hydroxylamine afforded N-aminooxazolidinones which were condensed with aldehydes to afford N-acylhydrazones 3-8. Three synthetic methods were developed, implementing these N-acylhydrazones in Lewis acid-promoted intermolecular radical additions to C=N bonds. First, additions of various secondary and tertiary alkyl iodides to propionaldehyde and benzaldehyde hydrazones (3 and 7) under tin hydride radical chain conditions in the presence of ZnCl2 gave N-acylhydrazine adducts with diastereomeric ratios ranging from 93:7 to 99:1. Radical additions to a series of N-acylhydrazones with different substituents on the oxazolidinone revealed that benzyl and diphenylmethyl were more effective stereocontrol elements than those with the aromatic ring directly attached to the oxazolidinone. Second, a tin-free method, exploiting dual functions of triethylborane for both initiation and chain propagation, enabled improved yields in addition of secondary alkyl iodides. Third, under photolytic conditions with hexamethylditin, primary radical addition could be achieved with ethyl iodide in the presence of diethyl ether as cosolvent; the 1-ethoxyethyl adduct was observed as a minor product. Chloromethyl addition was achieved under both the tin-free and photolytic conditions; in this case, the adduct bears alkyl chloride functionality with potential for further elaboration.     

Formation of layered titania and zirconia catalysed by surface-bound silicatein

Silicatein immobilised on self-assembled polymer layers using a histidine-tag chelating anchor group retains its hydrolytical activity for the formation of biosilica, and catalyses the formation of layered arrangements of biotitania and biozirconia.     

Haloxylines A and B, antifungal and cholinesterase inhibiting piperidine alkaloids from Haloxylon salicornicum

Haloxylines A (1) and B (2), new piperidine alkaloids, have been isolated from the chloroform soluble fraction of Haloxylon salicornicum and their structures elucidated by spectroscopic techniques including 2D-NMR. Both the compounds displayed antifungal and cholinesterase enzymes inhibitory potentials.     

The crystal structure and thermal stability of [bis-picrate(pentaethylene glycol)] praseodymium(III)picrate complex

[Bis-picrate(pentaethylene glycol)]praseodymium(III) picrate, [Pr(pic)₂⋅(EO5]⁺[pic]⁻, was successfully obtained from the reaction of praseodymium nitrate hexahydrate, picric acid and pentaethylene glycol in acetonitrile–methanol as solvent. The crystal system is monoclinic with space group P2₁/c, a = 18.91419(11) Å, b = 9.0470(6) Å, c = 24.1209(14) Å and α = γ = 90^∘, β = 109.07(1)^∘, V = 3880.3(4) ų and Z = 4. The Pr atom is coordinated to the flexible and open EO5 ring via all the six oxygen atoms and two picrate ligands, one via phenoxo oxygen atom and the other one with both phenoxo and nitro oxygen atoms in a bidentate manner resulting a 9-coordinate tricapped trigonal prismatic geometry. The two picrate ligands coordinated to the Pr atom are at the opposite sides of the hexadentate EO5 ring with phenyl fragments almost perpendicular with dihedral angle of 89.7(3)^∘. Thermal analysis results show that the complex is stable up to 100^∘C when it began to slowly decompose and followed by an explosive decomposition at 290^∘C.     

Lipoxygenase inhibiting ethyl substituted glycoside from Symplocos racemosa

Phytochemical investigation of Symplocos racemosa resulted in the isolation of a new ethyl substituted glycoside, 1-ethyl brachiose-3'-acetate (1) along with four known compounds ketochaulmoogric acid (2), nonaeicosanol (3), triacontyl palmitate (4) and methyl triacontanoate (5). The substitution of ethyl group on 1 was natural because during the course of extraction and purification ethanol was not used. The structural elucidation of the isolated compounds was based primarily on 1D- and 2D-NMR analysis, including COSY, HMQC, and HMBC correlations. The glycoside 1 and triacontyl palmitate (4) displayed the inhibitory potential against lipoxygenase and urease enzyme, respectively.     

Parkintin: a new flavanone with epoxy-isopentyl moiety from Parkinsonia aculeata Linn. (Caesalpiniaceae)

A new flavanone with epoxy-isopentyl moiety named parkintin has been isolated from the methanol soluble part of Parkinsonia aculeata Linn. belonging to the family Caesalpiniaceae. The structure of parkintin has been established with the aid of spectroscopic techniques including COSY and HMBC experiments.     

Color versus bioactivity in the flowers of Bougainvillea spectabilis (Nyctaginaceae)

The methanolic extracts of Bougainvillea spectabilis (Nyctaginaceae) flowers (five different colors) were screened biologically by performing four bioassays: antibacterial, antifungal, brine shrimp lethality and phytotoxicity. It was observed that the methanolic extract of white flowers was the most biologically active among all tested extracts. The extracts of white, orange and shocking pink flowers inhibit, while the extracts of red and violet flowers promote, the growth of Lemna plants. The extract of white flowers also exhibits toxicity against shrimp larvae with a LD50 value of 33.5627 microg/mL. However, none of the tested samples gave positive responses against any tested fungi.     

Simulation on the response of new phosphate glass RPC for <Emphasis Type="Italic">γ</Emphasis>-rays and e<Superscript>+</Superscript>/e<Superscript>−</Superscript> particles using GEANT3

The influence of phosphate glass electrode in the configuration of resistive plate chamber has been studied using GEANT3.21 Monte Carlo code. Bakelite electrodes were replaced by phosphate glass electrodes, as these glass materials have low bulk resistivity, are portable and easy to handle. These types of RPCs in their compact form of all materials are suitable for high rate background environment. We find that these new types of RPCs give little higher response to γ-rays and e⁺/e⁻ particles, both for single-and double gap RPCs. The results of simulation are discussed.      

Resonance behaviour of viscoelastic fluid in Poiseuille flow in the presence of a transversal magnetic field

The oscillatory flow of a viscoelastic fluid in a circular pipe under the influence of a transversal magnetic field is studied. Exact solutions for the axial velocity and flow rate are presented. The velocity enhancement and the resonance behaviour are analysed both numerically and asymptotically in the case of small pipe radii. Approximations for the resonance frequencies and the achievable velocity enhancements are derived. Copyright © 2005 John Wiley & Sons, Ltd.