Showing papers on "Hydrazone published in 1999"

The Hydrogen Bond Mimic Approach: Solid-Phase Synthesis of a Peptide Stabilized as an α-Helix with a Hydrazone Link

Abstract: Proteins are characterized by extensive hydrogen bonding that defines regular and irregular substructures. However, hydrogen bonds are weak and insufficient for stabilizing peptide conformation in water. Consequently, the biological activity of peptides is reduced. This led us to test whether a covalent mimic of the hydrogen bond could be used to stabilize peptide conformation in water. A solid-phase synthesis is described for replacing a main-chain hydrogen bond (NH → OCRNH) with a hydrazone link (N−NCH−CH2CH2) in peptides. The synthesis is easy to implement, rapid, and capable of high yields. The replacement of a putative (i + 4 → i) hydrogen bond with the hydrazone at the N terminus of acetyl-GLAGAEAAKA-NH2 (1) to give [JLAZ]AEAAKA-NH2 (2) converts it to a full-length α-helix in water at ambient temperature as indicated by NMR spectroscopy. The observation of weak dαN(i, i + 3), medium dNN(i, i + 1), and strong dαβ(i, i + 3) NOEs that span 2 establish the formation of a full-length α-helix in water. Jα...

Liquid Chromatography Analysis of Carbonyl (2,4-Dinitrophenyl)hydrazones with Detection by Diode Array Ultraviolet Spectroscopy and by Atmospheric Pressure Negative Chemical Ionization Mass Spectrometry.

Abstract: The (2,4-dinitrophenyl)hydrazones of carbonyls are separated by liquid chromatography and detected by ultraviolet spectroscopy (diode array detector) and by atmospheric pressure negative chemical ionization mass spectrometry. Results are presented for 78 carbonyls including 18 1-alkanals (from formaldehyde to octadecanal), 16 other saturated aliphatic carbonyls (5 C4−C7 aldehydes and 11 C3−C9 ketones), 16 unsaturated aliphatic carbonyls (9 C3−C11 aldehydes and 7 C4−C9 ketones), 13 aromatic carbonyls (including hydroxy- and/or methoxy-substituted compounds), 10 C2−C10 aliphatic dicarbonyls, 3 aliphatic carbonyl esters, and 2 other carbonyls. Isomers were observed for α,β-unsaturated ketones and saturated carbonyls that bear other oxygen-containing substituents, e.g. methoxyacetone, 2-furaldehyde, and the 3 carbonyl esters. For all but two of the carbonyls studied, the base peak in the negative APCI mass spectrum was the M − 1 ion (NO2)2C6H3NNCR1R2 (R1 = H for aldehydes), where M is the molecular mass of th...

Lipophilic aldehydes and related carbonyl compounds in rat and human urine.

Abstract: Rat and human urine samples were analyzed for lipophilic aldehydes and other carbonyl products of lipid peroxidation. The following compounds were identified as their 2,4-dinitrophenyl hydrazones by cochromatography with pure standards using three solvent systems: butanal, butan-2-one, pentan-2-one, hex-2-enal, hexanal, hepta-2,4-dienal, hept-2-enal, octanal, non-2-enal, deca-2,4-dienal, 4-hydroxyhex-2-enal, and 4-hydroxynon-2-enal. In general, fasted rats excreted less of these compounds than fed rats, indicating they were partially of dietary origin or that the endogenous compounds were excreted in a form not susceptible to hydrazone formation. The compounds excreted in human urine were similar to those excreted in rat urine but were present in lower concentrations. Identification of the conjugated forms fo the lipophilic aldehydes and related carbonyl compounds excreted in urine may be a source of information about their reactions in vivo.

Quantitative RP-HPLC Determination of Some Aldehydes and Hydroxyaldehydes as Their 2,4-Dinitrophenylhydrazone Derivatives.

Abstract: A high-performance liquid chromatographic (HPLC) method is described for the quantitative determination of some aliphatic aldehydes and β-hydroxyaldehydes as their 2,4-dinitrophenylhydrazone derivatives. A method is described for the preparation of derivatives for those β-hydroxyaldehydes where no reference compounds of known purity are available. The detection limit of the method was 4.3-21.0 μg/L, depending on the aldehyde.

Synthesis, Characterization and Biological Activity of Rare Earth Complexes of 1-Phenyl-3-Methyl-5-Hydroxy-4-Pyrazolyl Phenyl Ketone Isonicotinoyl Hydrazone

Abstract: The ligand, 1-phenyl-3-methyl-5-hydroxy-4-pyrazolyl phenyl ketone isonicotinoyl hydrazone (H2L), was prepared by condensation of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone with isoniazid. Seven complexes of rare earths with H2L have been synthesized and characterized on the basis of elemental analyses, IR, UV, 1H NMR spectra and thermal analyses. The general formula of the complexes is RE(HL)3·3.5H2O (where RE = La3+ - Gd3+). It has been discovered that the ligand and its complexes of the light rare earth metals possess antioxidative activity and inhibitory action on lipid peroxidation.

Synthesis of some new biologically-active coumarin derivatives

Abstract: Coumarin and 6-nitrocoumarin hydrazones (2a,b), respectively, were prepared via the reaction of 2-thiocoumarin (1a,b) derivatives with hydrazine hydrate. The hydrazones were used as key intermediates for the preparation of some benzopyrano[2,3-c]pyrazoles (21-24) through the reaction of different acyl halides and subsequent cyclization in N,N-dimethylaniline. Benzopyrano[2,3-c]pyrazole-3-thione (25a,b) was prepared by the reaction of 1a with CS2 on which some alkylation, acylation and Mannich reactions were studied. Alternative procedures, other reactions and biological activity of some new compounds were given.

A Convenient and Mild Procedure for the Synthesis of Hydrazones and Semicarbazones from Aldehydes or Ketones under Solvent-free Conditions

Abstract: Hydrazone and semicarbazone derivatives are readily prepared from the corresponding aldehydes or ketones, hydrazine derivatives and semicarbazides under solvent-free conditions

Azo-containing tertiary phosphines: synthesis, reactivity and structural characterisation

Abstract: 6-Bromo-2-methoxynaphthalene 1 was converted into 6-diphenylphosphanyl-2-methoxynaphthalene 2a by preparing its Grignard and quenching with PPh2Cl. Compound 2a was demethylated on refluxing in HBr yielding 6-(diphenylphosphanyl)naphthalen-2-ol 2b in good yield. Oxidation of 2b with either H2O2 or S8 afforded the corresponding phosphine oxide 3a or sulfide 3b respectively. Treatment of 2b with a stoichiometric amount of NaH and quenching of the anion with [4-R-C6H4N2][BF4] (R = H, Me, Et, iPr, tBu, NO2 or NMe2) yielded the C–N coupled azo-containing phosphines in good yield; similar coupling reactions of 3a, 3b afforded analogous compounds, again in good yield. Evidence is presented that shows the coupling reaction does not proceed through a P–N coupled intermediate, which would subsequently need to rearrange to the observed C–N coupled products. The latter all exist as tautomeric mixtures of the azo and hydrazone forms. The tautomerisation in some cases was suppressed on conversion into their acetic acid esters by reaction with NaH followed by acetyl chloride. All of the new compounds have been characterised by elemental analysis (C, H, N), FAB mass spectrometry, 1H, 13C-{1H}, 31P-{1H} NMR and in selected cases by Uv-visible spectroscopy. The position of the C(2) resonance in the 13C-{1H} NMR spectra has been used to calculate the position of the azo/hydrazone equilibrium and hence the mole fraction of each tautomer present in solution. These data were used to interpret the Uv-visible data. In addition, three compounds have been further characterised by single crystal X-ray diffraction studies.

Generation of diphenyldiazomethane by oxidation of benzophenone hydrazone with magtrieve

Abstract: Diphenyldiazomethane, a red crystalline solid is a useful reagent for the protection of carboxylic acids by conversion to their diphenylmethyl (dpm, benzhydryl) esters. Dpm protecting group has been widely used due to its easy deprotection by mild acidic condition or hydrogenolysis, especially in the field of β-lactams and peptides. Diphenyldiazomethane has been prepared by the oxidation of benzophenone hydrazone with mercuric oxide, peracetic acid, iodosobenzene diacetate or OXONE.4d However, some methods suffer from a disadvantage such as toxic nature of reagent, strong oxidative conditions or incompatibility with certain functional groups. For example, OXONE may not be employed for the in situ protection of carboxylic acid containing sulfide group due to the possibility of the concomitant oxidation of sulfide group. Recently, Magtrieve, a magnetically retrievable oxidant (CrO2) has been shown to oxidize alcohols in high yields. We have already shown that this reagent can serve as an oxidant for the aromatization of 1,4-dihydropyridines in high yields. We now report that Magtrieve can also serve as an efficient reagent for the oxidation of benzophenone hydrazone to diphenyldiazomethane, enabling the one-pot protection of carboxylic acids including N-protected amino acids, as shown in Table 1. Treatment of benzophenone hydrazone with Magtrieve in dichloromethane gave a purple color characteristic of diphenyldiazomethane, immediately. The oxidation was completed within 15 min at room temperature, based on TLC analysis (Rf of hydrazone = 0.33, Rf of product = 0.60 in EtOAc : hexanes (1 : 5)). Then, a solution of acid was added to the purple solution and the progress of the reaction was monitored with TLC. The reaction time was in a range of 0.1 h ~ 5 h, depending on the substrate. After the reaction was finished, Magtrieve was retrieved with magnet and the solution was concentrated to give a crude product, which was purified by column chromatography. The yield was good, except for the entry 6, where the dpm ester was decomposed during the column chromatography.

Clusters in bis-tridentate tethered domains of an iron chelating drug†

Abstract: The tridentate metal binding domains of iron chelating agents have been tethered via a variable length methylene (CH2)n linker (n = 1, 2, 4, 6, 8, 10, 14). The single-crystal X-ray structures of monomeric ([Fe(HL8)]·2.5H2O n = 8; H4L8 is 1,10-decanedioyl di(salicylaldehyde hydrazone)) and dimeric ([{Fe(H2PL4)}2]Cl2·2H2O n = 4; H4PL4 is 1,6-hexanedioyl di(pyridoxal hydrazone)) iron(III) complexes have been determined. The complexes exhibit oligomerism: with chain lengths of n ≥ 6 monomers are prevalent whereas for shorter chains this is not possible and a series of clusters exist as shown by ESMS and molecular modelling.

Synthesis of new polypyrroles by oxidative polymerization of N-(benzylideneamino)pyrroles and properties of the polymers

Abstract: Synthesis of New Polypyrroles by Oxidative Polymerization of N -(Benzylideneamino)pyrroles and Properties of the Polymers

Flow-Injection Determination of Copper(II) Based on Its Catalytic Effect on the Oxidative Coupling of 3-Methyl-2-benzothiazolinone Hydrazone with N-Ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline in a Micellar Medium.

Abstract: A highly sensitive flow-injection spectrophotometric method has been developed for the determination of copper(II). It is based on the catalytic effect of copper(II) on the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline to form a red compound (λmax=525 nm) in the presence of hydrogen peroxide and pyridine as an activator. A higher sensitivity and sampling rate were achieved by adding ben-zyldimethyltetradecylammonium chloride (Zephiramine) as a surfactant to this reaction system. The calibration graph for copper(II) was linear over the range 0.005 - 0.75 ng cm-3 at a rate of 40 samples h-1. The relative standard deviations for ten determinations of 0.5 and 0.05 ng cm-3 were 0.21 and 2.0%, respectively. The proposed method was successfully applied to the determination of copper in pepperbush.