Oxidation with sodium peroxide Direct introduction of a γ carbonyl group into α,β unsaturated ketosteroids

Aqueous sodium peroxide oxidises the conjugated Δ⁴-3-ketosteroids $\text{1a}$-$\text{1d}$ to the corresponding Δ⁴-3-4-diones in good yield. Saturated carbonyl and alcohol groups are not affected by the reaction.     

Synthetic approach to preparation of indole derivatives fused with a bicyclo[3.3.1]nonane framework

Starting with Δ¹⁵-17-ketosteroids, applying Normant reaction with allylmagnesium bromide and anionic Cope rearrangement of the formed allyl alcohol, 15α-derivatives of androstane series were prepared. The latter were brought into Wittig reaction with an ylide generated from ethyltriphenylphosphonium bromide, and the product was subjected to ene reaction to provide 15α-substituted pregnanes.     

Acid-catalyzed hydrolyses of bridged bi- and tricyclic compounds-XII: Kinetics of hydration of 2-norbornenone,a special β,γ-unsaturated ketone

The reaction rates, activation parameters, solvent deuterium isotope effects, and dependences of rates on acid concentration measured for the hydration of 2-norbornenone and its four Me-substituted homologs in aqueous acid agree with the slow protonation of the CC double bond (A-S_E2 mechanism). Thus the mechanism differs from that reported for the isomerization (to α,β-unsaturated ketones) of unbridged β,γ-unsaturated ketones, e.g. 3-cycloalkenones and Δ⁵-3-ketosteroids, under catalysis by acid.     

Determination of Δ4-3-ketosteroids based on oxime formation by difference circular dichroism spectroscopy

Δ⁴-3-Ketosteroids exhibit an intensive negative Cotton effect on the circular dichroism (CD) spectra in the wavelength range for the n-π* electronic transition (270–¶350 nm). With hydroxylamine hydrochloride, Δ⁴-3-ketosteroid compounds can be transformed into oxime derivatives. Following oxime formation, positive ellipticity with low intensity can be registered in this wavelength range. The quantitative determination of Δ⁴-3-ketosteroids is based on the considerable difference between the ellipticities before and after oxime formation. The difference ellipticity for the six ketosteroids examined (norethisterone, levonorgestrel, levonorgestrel acetate, methyltestosterone, testosterone phenylpropionate, nortestosterone phenylpropionate) varies linearly with the concentration in the interval 6 × 10^–6–3 × 10^–3 mol/L. The method can be well applied to determination of Δ⁴-3-ketosteroid contamination of norgestimate [(+)-13-ethyl-17-hydroxy-18,19-dinor-17α-pregn-4-en-20-yn-3-one oxime acetate]; 0.02–10% impurity can be measured.     

Nicotinamide complex of silver(III) with expanded coordination number

Abstract

In strongly alkaline media ([OH^?]?≥?0.12 M), nicotinamide (nica) forms a complex with square-planar Ag(OH)₄^? [nica]?≥?0.05 M. The complex decomposes in seconds to nicotinamide N-oxide. The correlation of maximum absorbance of the complex with concentrations of nicotinamide and hydroxide requires that the complex is either the five-coordinate Ag(OH)₄(H_-1nica)^2? or the six-coordinate Ag(OH)₅(nica)^2?. Comparison with the reactions of Ag(OH)₄^? with nicotinate ion (nic^?) and acetamide under similar conditions indicates that nicotinamide coordinates with Ag(OH)₄^? by the amido group rather than the nitrogen on the pyridine ring or the amido oxygen. Kinetics of the Ag(III)-nica redox reaction are consistent with direct reaction between nicotinamide and uncoordinated Ag(OH₄)^?. Oxidation takes place at the pyridine ring, yielding nicotinamide N-oxide. Silver(III) is reduced to monovalent silver.     

Spectrometric Determination of Ti(IV) With an Azopyrazolonic Derivative

Abstract

Spectrometric studies on the complexation of Ti(IV) with a new organic reagent obtained by coupling 3-methyl-1-phenyl-5-pyrazolone with diazotized 3-amino-4-hydroxy-benzene-sulphonic acid were carried out.

A 1:2 Ti(IV):reagent complex, which is soluble in water, is formed at pH 5–6.2. The maximum absorbance of the complex lies at λ =520nm, where the absorbance of the reagent is very low. The molar absorptivity at this wavelength is 5 × 10³ L mol^?1 cm^?1; the value of log K is 8.0 ± 0.2. at 20 ± 1°C and pH=5.6.     

Spectrophotometric Determination of 8-Hydroxyquinoline (Oxine) in Aqueous Solution by Azo Dye Formation with Diazotized p-Aminoacetophenone

Abstract

A sensitive spectrophotometric method for the determination of oxine in aqueous solution is investigated. It is based on the reaction of the analyte with diazotized p-aminoacetophenone to form, in the presence of sodium hydroxide, an intense cherry-red water-soluble and stable azo dye which shows maximum absorption at 520 nm. The linear absorbance plot with the concentration indicates that Beer's law is adhered over the range 10–100μg of oxine in a final volume of 25 ml, i.e., 0.4–4 ppm, with a molar absorptivity of 3.37 × 10⁴ 1mol^?1 cm^?1, a relative error of +0.44 to –1.12%, and a relative standard deviation of 0.54–2.9%, depending on the level of analyte concentration. The optimum conditions affecting the color reaction and interference due to foreign organic compounds have been examined.     

Spectrophotometric Determination of Nitrite in Aqueous Solution by the Diazotization-Coupling Method with Orthanilic Acid-Resorcinol

Abstract

A spectrophotometric method for the determination of nitrite is described. It relies upon the reaction of this ion with an acidified orthanilic acid solution to form a diazonium ion, which is subsequently coupled with resorcinol, in alkaline medium, to form immediately a yellow-colored stable water-soluble and intense azo dye having maximum absorption at 426 nm. The linear absorbance plot with concentration indicates that Beer's law is obeyed over the range of 1-12 μg of nitrite in a final volume of 10ml, with a molar absorptivity of 38.7 × 10³1 mol^?1cm^?1, sensitivity index of 0.0012μgcm^?3, relative error of –0.5 to +0.2% and relative standard deviation of 0.43-3.5%, depending on the concentration level. The optimum conditions affecting and related to the color reaction and interference due to foreign ions have been studied.     

Spectrophotometric Determination of 1-Naphthylamine in Aqueous Solution by Coupling with Diazotized 4-Aminobenzophenone

Abstract

The coupling reaction of 1-naphthylamine with diazotized 4-aminobenzophenone in acidic media has been studied by a spectrophotometric method in order to determine trace amounts of 1-naphthylamine. the reaction involves coupling with the diazotized reagent to form an intense pink, water-soluble azo dye which shows maximum absorption at 530 nm. A graph of absorbance versus 1-naphthylamine concentration is linear, indicating that Beer's law is obeyed over the range of 5?00 μg of 1-naphthylamine in a final volume of 25 ml, i.e. 0–4 p.p.m., with a molar absorptivity of 5.15 × 10⁴ 1 m1^?1 cm^?1, a relative error of ?2.3 to +0.63% and a relative standard deviation of 0.84–3.0%, depending on the concentration level. the method represents a sensitive, rapid and simple determination of trace amount of 1-naphthylamine in aqueous solution. Interferences due to foreign organic compounds have been investigated.     

Micellar catalyzed hydrolysis of mono-2,3-dichloroaniline phosphate

The kinetics of micellar catalyzed hydrolysis of mono-2,3-dichloroaniline phosphate in the presence of different surfactants has been studied at 303?K. The rate of reaction has been found to be first order with respect to both [substrate] and [HCl]. The cationic micelles of cetylpyridinium chloride (CPC), anionic micelles of di-octyl sodium sulphosuccinate (AOT), and non-ionic micelles of polyoxyethylene sorbitan monooleate (Tween 80) enhanced the rate of reaction to a maximum value and after that the increase in concentration of surfactant decreased the reaction rate. The applicability of different kinetic models has been tested to explain the observed micellar effects. The various thermodynamic activation parameters (E_a, ΔH^≠, ΔS^≠, ΔG^≠) have been evaluated. The added salts viz. KCl, KNO₃, K₂SO₄ enhanced the rate of reaction in the presence of CPC, AOT, and Tween 80 micelles. The kinetic parameters were determined from the rate (surfactant) profile and a suitable mechanism consistent with the experimental finding has been proposed.     

Autoxidation of NO in aqueous solution

The reaction of NO with O₂ has been investigated in aqueous solution. As demonstrated by ion chromatography, the sole product is NO₂^?. Kinetic studies of the reaction by stopped-flow methods with absorbance and conductivity detection are in agreement that the rate law is -d[O₂]/dt=k[NO]²[O₂] with k = 2.1 × 10⁶ M^?2 s^?1 at 25°C. This rate law is unaffected by pH over the range from pH 1 to 13, and it holds with either NO or O₂ in excess. By studying the reaction over the temperature range from 10 to 40°C, the following activation parameters were obtained: ΔH^≠ = 4.6 ± 2.1 kJ mol^?1 and ΔS^≠=?96 plusmn; 4 J K^?1 mol^?1. © 1993 John Wiley & Sons, Inc.     

Synthesis of Functionalized Δ3 Phosphabenzenes by Means of Diels Alder Reaction with Phosphaalkenes

Abstract

Diels Alder reaction provides an easy and general access to functionalized Δ³ phosphabenzenes after aromatization with the possibilities of introducing the functional group either with the diene or the phosphaalkene.     

Studies on the CIS Dihydroxylation of Drimanediene Skeleton

The osmylation of dienic sulfone 4, a potential key intermediate in forskolin 1 and polyhydroxylated drimanes or labdanes derivatives, occurred exclusively on the Δ^6–7 double bound and preferentially from the α-face of the molecule (40–100% de). The influence of the substituent at C-1 on the stereoselectivity of the reaction is studied.     

Spectrophotometric Determination of Quintomycin Sulphate with Phloroglucinol

Abstract

A new absorptiometric procedure for the determination of quintomycin sulphate in complex galenical mixtures is proposed, based on the reaction of the sample compound with a mineral acid-containing phloroglucinol solution. Absorbance readings at 448 nm obey Lambert-Beer's law within the concentration range from 4. 0 to 32. 0 μg ml^?1. The method is operationally simple and has a good precision and an adequate selectivity.     

Structure and Catalytic Mechanism of 3-Ketosteroid Dehydrogenases

3-Ketosteroid dehydrogenases (KSTDs) are FAD-dependent enzymes that introduce a double bond in the A ring of 3-ketosteroid substrates to initiate degradation of the steroid nucleus. Δ¹-KSTD desaturates the C1-C2 bond of the steroid, while Δ⁴-KSTD targets the C4-C5 bond. Crystal structures with bound products showed that Δ¹- and Δ⁴-KSTD use different amino acid residues to catalyze an otherwise mechanistically very similar reaction (Δ¹-KSTD: Tyr318, Tyr119, and Tyr487; Δ⁴-KSTD: Ser468, Tyr319, and Tyr466). However, the substrates are rotated by ∼40° about an axis perpendicular to their plane to bring the target bond (C1-C2 or C4-C5) in the right position.     

Immobilization and sustained release of cefalexin on MCF nano-mesoporous material

Abstract

Mesocellular foams (MCF) silica nanometer mesoporous molecular sieve was successfully synthesized by hydrothermal route. This method used poly(ethylene glycol)-block-poly(propyl glycol)-block-poly(ethylene glycol) as template, tetraethyl orthosilicate as silica source and 1, 3, 5-trimethylbenzene as pore-expanding agent to prepare nano mesoporous MCF in acidic medium. The MCF mesoporous material was characterized by powder X-ray diffraction (XRD), infrared (IR) spectroscopy, low temperature nitrogen adsorption-desorption at 77?K, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The effects of pH, temperature, adsorbent dosage, cefalexin dosage and contact time on the immobilization of cefalexin were studied. Under the optimized conditions, MCF has the best effect on the drug immobilization. The maximum immobilization amount of cefalexin in MCF nano-mesoporous material is 498.8?mg/g. The behavior of adsorption of cefalexin by MCF belongs to multilayer heterogeneous adsorption, which accords with the Freundlich adsorption isotherm. In the adsorption process, all the ΔH⁰, ΔS⁰ and Gibbs free energy change ΔG⁰ are less than zero, indicating that the adsorption process is spontaneous, exothermic entropy decreasing reaction at ordinary temperature. Kinetic investigation showed that the adsorption process of cefalexin on MCF belongs to the pseudo-second-order kinetic process. The release laws of composite material cephalexin-MCF in the simulated body fluid, gastric and intestinal fluid were investigated, respectively. The maximum cumulative release rate in simulated body fluid was 99.4% at 18?h. The maximum cumulative release rate in the simulated gastric juice was 48.7% at 6?h and in the simulated intestinal fluid the maximum cumulative release rate of 61.9% was achieved at 8?h. These release processes satisfy the zero-order ordered kinetic process.     

Spectrophotometric determination of microamounts of mercury(II) and sulfide ions in aqueous solution

Ammonium (2′,3′-dihydroxy pyridyl-4′-azo)benzene-4-arsonate (DHP-4A) provides a simple, rapid, and sensitive spectrophotometric microdetermination of mercury(II) in aqueous solution. The magenta colored 1:2 metal to ligand complex formed has a molecular extinction coefficient 6.25 × 10⁴ liters mol^?1 cm^?1 at the maximum absorption of 535 nm in highly alkaline medium. Beer's law is obeyed up to 3.8 ppm and Sandell's sensitivity (for an absorbance of 0.001) is 0.0032 μg of mercury(II)/cm². The mercury(II) complexed with DHP-4A has also been used in microdetermination of sulfide ions using ligand exchange reaction. The optimum concentration range of sulfide ions which can reproducibly be determined is 0.16-5.05 μg/10 ml and sensitivity of sulfide ions determination (for an absorbance 0.001) is 7.3 × 10^?4 μg/cm².     

Specific assay for homoserine and its lactone in Pisum sativum. Preparation of homoserine hydroxamic acid

The existence of homoserine lactone in Pisum sativum seedlings is demonstrated. L-Homoserine lactone reacts with hydroxylamine, at neutral or alkaline pH, to form homoserine hydroxamic acid. Procedures are described for preparing L-homoserine lactone and L-homoserine hydroxamic acid. The hydroxamic acid yields a color with maximum absorbance at 492 nm with Fe³⁺ in 0.25 N HCl. This reaction permitted assay for total homoserine and homoserine lactone. Six-day old Pisum sativum seedlings, with cotyledons removed, were extracted with 90% ethanol. Evaporation of the ethanol and addition of Na₂SO₄ solution and toluene and centrifugation removed protein lipids and esters. After clarification with activated charcoal, homoserine lactone content was estimated by reaction with NH₂OH and Fe³⁺ reagents. For total homoserine, protein precipitation was with 2 N HCl and toluene. Evaporation to dryness at 60 °C under vacuum converted all homoserine to the lactone. The values found for total homoserine (μmols/g, wet weight) and preformed lactone (%) with the various growth media used were as follows: nitrate 87.4 (14.7%), NH₂OH 75.2 (6.3%), water 70.5 (7.9%), urea 56.4 (18.9%). Acetic anhydride added to homoserine hydroxamic acid forms acetohydroxamic acid, which yields a color with maximum absorbance at 505 nm with Fe³⁺. This color reaction is seven times as sensitive as the reaction of Fe³⁺ with homoserine hydroxamic acid itself.     

Indirect Spectrophotometric Determination of Vanadium(IV) by Flow Injection Analysis Based on the Redox Reaction with Copper(II) in the Presence of Neocuproine

Abstract

An indirect photometric method with a continuous-flow analysis is presented for the determination of trace amounts of vanadium(IV). It is based on the redox reaction of copper(II) with vanadium(1V) in the presence of neocuproine. In the presence of neocuproine, copper(I1) is reduced easily by vanadium(I V) to a copper(1)-neocuproine complex, which shows a n absorption maximum at 454 nm. By measuring t h e absorbance of the complex at this wavelength, vanadium(1V) in t h e range 2×10^?6 - 8 × mol dm^?5 mol dm^?3 can be determined at a rate of 120 samples h^?1. The fractional determination of vanadium(1V) and iron(I1) is also studied.     

Asymmetric 1,3-dipolar cycloaddition of nitrile oxides with optically active vinylboronic ester

Pinanyldioxy styrylboronic ester (1) was employed for asymmetric 1,3-dipolar cycloaddition with nitrile oxides, optically active △2-isoxazolines (3) or 4-hydroxy-△2-isoxazolines (4) were obtained. The effect of different bases on the selectivity of the cycloaddition reaction was studied.