Synthesis of homoceramides, novel ceramide analogues, and their lack of effect on the growth of hippocampal neurons

The synthesis of a new series of D-erythro-homoceramide analogues is described. Several synthetic approaches were investigated. Homoceramides can be successfully synthesized from L-homoserine as chiral building block and a protected Weinreb-amide as a key intermediate. The synthesis of short-chain analogues with a heptyl side chain, as well as with a phenyl residue in the sphingoid part (instead of the naturally occurring tridecyl side chain), was effected. The homoceramides 15-17 and 24 were investigated for their potential to reverse the inhibitory effect of fumonisin B(1) on axonal growth. Unfortunately, none of the tested compounds showed any biological activity due to their lack of metabolism to glucosylhomoceramide.     

Strongly isolated ferromagnetic layers in poly-trans-mu-dichloro- and poly-trans-mu-dibromobis(1-(2-chloroethyl)-tetrazole-N4)copper(II) complexes

Two new isostructural compounds, dichlorobis(1-(2-chloroethyl)tetrazole)copper(II) (1) and dibromobis(1-(2-chloroethyl)tetrazole)copper(II) (2), have been prepared. The synthesis, characterization, and spectral and magnetic properties as well as the crystal and molecular structures of 1 and 2 have been studied. Both complexes form two-dimensional, distorted square grid planes of copper and halides, distinctly separated by layers of tetrazole ligands. The differential (ac) magnetic susceptibility, chi = (deltaM/deltaH)(T), and magnetization M(H) of both complexes have been studied as a function of temperature and field. The compounds possess a ferromagnetic interaction within the isolated copper-halide layers (J/k(B) = 8.0 K, J/k(B) = 10.2 K, respectively, for the chloride and the bromide, and T(c) = 4.75 K, T(c) = 8.01 K). The magnetic coupling J'/k(B) between the different layers is found to be very weak (|J'/J| 相似文献   

Supersilylating agents from chlorosilanes

The addition of R₃SiCl to B(OTf)₃ gives “supersilylating agents” formulated as R₃SiB(OTf)₃Cl. The catalytic properties of these species are similar to those of the previously-described (but less accessible) R₃SiB(OTf)₄.     

3‐Deoxy‐β‐d‐ribo‐hexopyranose (3‐deoxy‐β‐d‐glucopyranose)

The β‐pyranose form, (III), of 3‐deoxy‐d ‐ribo‐hexose (3‐deoxy‐d ‐glucose), C₆H₁₂O₅, crystallizes from water at 298 K in a slightly distorted ⁴C₁ chair conformation. Structural analyses of (III), β‐d ‐glucopyranose, (IV), and 2‐deoxy‐β‐d ‐arabino‐hexopyranose (2‐deoxy‐β‐d ‐glucopyranose), (V), show significantly different C—O bond torsions involving the anomeric carbon, with the H—C—O—H torsion angle approaching an eclipsed conformation in (III) (−10.9°) compared with 32.8 and 32.5° in (IV) and (V), respectively. Ring carbon deoxygenation significantly affects the endo‐ and exocyclic C—C and C—O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species (III) and (V) compared with (IV). These structural changes are attributed to differences in exocyclic C—O bond conformations and/or hydrogen‐bonding patterns superimposed on the direct (intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in (III) (gt) differs from that observed in (IV) and (V) (gg).     

Novel metal-linked face-to-face porphyrazine dimer

We report the synthesis and physical studies of a novel porphyrazine (pz) dimer [1[Ni,Cu]]2, which has Ni(II) ions incorporated into the pz cores and is linked by two Cu(II) ions coordinated to bis(picolinamide) chelates attached to the pz periphery. [1[Ni,Cu]]2 was prepared from precursor pz 2 with a selenodiazole ring fused to the pz core. This ring was deprotected to form the diamino-pz 3, which reacted with 2 mol of picolinoyl chloride hydrochloride to form pz 1[2H,2H], with peripheral bis(picolinamide) chelates; this was metalated to form [1[Ni,Cu]]2. The crystal structures of 1[2H,2H] and [1[Ni,Cu]]2 are presented. The latter is a dimer in which parallel, face-to-face pz's with an average separation of 3.30 angstroms are linked through the peripheral picolinamide ligands by a pair of peripheral Cu(II) ions. Each Cu(II) is coordinated with distorted square-planar geometry by a picolinamide from each pz. In this report, we focus on the interaction of these two peripheral Cu(II) ions. We discuss the preparation and magnetic properties of the pz dimer complex [1[Ni,Cu]]2 with two Cu(II) ions in the peripheral chelate but a diamagnetic metal ion Ni(II) in the pz core. Although [1[Ni,Cu]]2 contains two Cu(II) ions (S = 1/2), we could detect no electron paramagnetic resonance signal, which suggests very strong antiferromagnetic exchange between those two Cu(II) ions. Temperature-dependent magnetic susceptibility measurement gives an exchange splitting between the S = 0 ground state and the excited triplet state of delta = 660 cm(-1).     

Convenient Asymmetric Syntheses of anti-beta-Amino Alcohols

Condensation of allylborane reagents 9 and 12 with aldehydes gave anti-3-[(diphenylmethylene)amino]-1-alken-4-ols 10 and 13 with high relative and absolute stereocontrol. Subsequent deprotection gave the corresponding free anti-3-amino-1-alken-4-ols 11 and 14. Alternatively, reaction of imines 13a, 13f, and 13g with trifluoromethanesulfonic anhydride and acidic methanol gave, via rearrangement, double inversion, and hydrolysis, the isomeric anti-4-amino-1-alken-3-ols 22, 38a, and 38b in good yield. The stereochemistry of the rearrangement products has been established by a single crystal X-ray study of compound 37 and by chemical correlation.     

A New Generation of "Cholaphanes": Steroid-Derived Macrocyclic Hosts with Enhanced Solubility and Controlled Flexibility

The macrocyclic "cholaphanes" 3a-c were synthesized from the inexpensive steroid cholic acid. Like earlier relatives they feature substantial cavities with inward-directed hydroxyl groups, suitable for binding polar molecules such as carbohydrates in nonpolar media. New features are the externally directed alkyl chains, promoting solubility in organic solvents, and (in the case of 3b/c) reduced conformational freedom resulting from truncation of the steroidal side-chain. In particular, modeling shows that the smallest macrocycle 3c possesses very little flexibility, preferring an open conformation which is also revealed in the X-ray crystal structure of its pentahydrate. NMR studies indicated that all three cholaphanes form 1:1 complexes with octyl beta-D-glucoside in CDCl(3), with K(a) = 600-1560 M(-)(1). Cholaphanes 3b/c proved able to extract methyl beta-D-glucoside from aqueous solutions into CHCl(3). The transport of methyl beta-D-glucoside across a chloroform barrier was also demonstrated for 3c.     

Synthesis of some benzimidazole‐, benzothiazole‐ and pyridine‐derived chelating agents

Procedures are given for the preparation of new linear bidentate, tetradentate and tripodal heptadentate ligands incorporating benzimidazole, benzothiazole and pyridyl groups. The compounds were characterized by their nmr, uv and mass spectra. The crystal and molecular structure is reported for a chiral benzothiazole derived from camphoric acid.     

Pulsed titration sensors: Part 1: A breath-by-breath CO2 sensor

A novel electrochemical sensor for the determination of CO₂ in expired breath is described. The sensor works by generating from the reduction of O₂ in dimethyl sulphoxide (DMSO) in a generating pulse. There is a rapid titration reaction between the and any CO₂ present. In the recovery pulse the amount of unreacted is determined. The larger the concentration of CO₂ the less is found in the recovery pulse. The solubilities and diffusion coefficients of O₂ and CO₂ in DMSO have been determined using rotating disc voltammetry and rotation speed step experiments. The stoichiometry, the product, and the rate constant of the titration reaction have been determined using ring—disc voltammetry and laser Raman spectroscopy. The operation and the effect of adventitious water on the sensor are described. Results are presented which show that the sensor can indeed measure the breath-by-breath rhythm of expired CO₂ from a human subject.