Rh-catalyzed asymmetric hydrogenation of prochiral olefins with a dynamic library of chiral TROPOS phosphorus ligands

A library of 19 chiral tropos phosphorus ligands, based on a flexible (tropos) biphenol unit and a chiral P-bound alcohol (11 phosphites) or secondary amine (8 phosphoramidites), was synthesized. These ligands were screened, individually and as a combination of two, in the rhodium-catalyzed asymmetric hydrogenation of dehydro-alpha-amino acids, dehydro-beta-amino acids, enamides and dimethyl itaconate. ee values up to 98% were obtained for the dehydro-alpha-amino acids, by using the best combination of ligands, a phosphite [4-P(O)2O] and a phosphoramidite [13-P(O)2N]. Kinetic studies of the reactions with the single ligands and with the combination of phosphite [4-P(O)2O] and phosphoramidite [13-P(O)2N] have shown that the phosphite, despite being less enantioselective, promotes the hydrogenation of methyl 2-acetamidoacrylate and methyl 2-acetamidocinnamate faster than the mixture of the same phosphite with the phosphoramidite, while the phosphoramidite alone is much less active. In this way, the reaction was optimized by lowering the phosphite/phosphoramidite ratio (the best ratio is 0.25 equiv phosphite/1.75 equiv phosphoramidite) with a resulting improvement of the product enantiomeric excess. A simple mathematical model for a better understanding of the variation of the enantiomeric excess with the phosphite/phosphoramidite ratio is also presented.     

Ring-closure reactions through intramolecular displacement of the phenylselenonyl group by nitrogen nucleophiles: a new stereospecific synthesis of N-tosyl and N-benzoyl-1,3-oxazolidin-2-ones from beta-hydroxyalkyl phenyl selenides

A new and convenient method for the stereospecific synthesis of variously substituted 1,3-oxazolidin-2-ones from the easily available beta-hydroxyalkyl phenyl selenides is presented. After transformation into the N-tosyl or N-benzoyl carbamates, the selenides were oxidized to the corresponding selenones. The key step of the process is the ring-closure reaction, which occurs by stereospecific intramolecular nucleophilic substitution of the selenone group by the nitrogen atom of the carbamate. Enantiomerically pure 1,3-oxazolidin-2-one derivatives can be easily prepared by using enantiomerically pure beta-hydroxyalkyl phenyl selenides as starting materials.     

Effect of the Magnetic Field on the Supramolecular Structure of Chiral Smectic C Phases: 2H NMR Studies

We present a theoretical and experimental ²H NMR study of the effect of external magnetic fields on the supramolecular organization of chiral smectic liquid‐crystalline mesophases, such as SmC* and re‐entrant SmC*. Three experimental cases in which the supramolecular helical structure of the smectic C* phase is unwound by a magnetic field (H), parallel to the helical axes of this phase, are discussed in detail. Unwinding of the helical structure is described by using a theoretical model based on the Landau‐de Gennes theory, which allows us to explain the transition temperatures among the SmA, SmC*, and uSmC* phases. The energy‐density behavior in the vicinity of the transitions and the value of the critical magnetic field H_C for unwinding the helical structure are discussed by applying this model to three ferroelectric smectogens ( MBHB , 11EB1M7 , ZLL7/* ), which are studied by ²H NMR spectroscopy at different magnetic fields (from 2.4 to 9.4 Tesla). Furthermore, the tilt angle of the three smectogens in the SmC* phase has been directly evaluated, for the first time, by comparing the quadrupolar splittings at different magnetic fields. In one case, ²H NMR angular measurements are used to obtain the tilt angle in the re‐entrant smectic C phase.     

PHOTODYNAMIC THERAPY OF B16 PIGMENTED MELANOMA WITH LIPOSOME-DELIVERED Si(IV)-NAPHTHALOCYANINE

The possibility of extending photodynamic therapy to the treatment of highly pigmented neoplastic lesions was tested by using Si(IV)-naphthalocyanine (SiNc) as a tumor-localizing agent. Si(IV)-naphthalocyanine displays intense absorbance at 776 nm (ɛ= 5 × 10⁵ M⁻¹ cm⁻¹), where melanin absorption becomes weaker. As an experimental model we selected B16 pigmented melanoma subcutaneously transplanted to C57BL mice. Upon injection of 0.5 or 1 mg kg⁻¹ of liposome-incorporated SiNc, maximal accumulation of the photosensitizer in the tumor was observed at 24 h with recoveries of 0.35 and 0.57 μg g⁻¹, respectively. However, the tumor targeting by SiNc shows essentially no selectivity, since the photosensitizer concentrations in the skin (peritumoral tissue) were very similar to those found in the tumor at all postinjection times examined by us. Irradiation of SiNc-loaded melanoma with 776 nm light from a diode laser at 24 h postinjection induces tumor necrosis and delay of tumor growth. The effect appears to be of purely photochemical nature at dose rates up to 260 mW cm⁻²; at higher dose rates, thermal effects are likely to become important.     

Vibronic activity in the two-photon spectrum of pyrene

A CNDO/S Cl calculation of the two-photon vibronic activity of some b_1u and b_2u vibrational modes of pyrene is presented. The two-photon amplitude tensor is discussed in terms of vibronic coupling coefficients calculated by means of the orbital-following method. The results are in good agreement with the experimental data taken from a recently observed two-photon spectrum of pyrene in a Shpolskii matrix. The role of the ground-state coupling with the first excited B_1u state has been investigated and is shown to be responsible for most of the vibronically induced two-photon intensity of the spectrum. The calculations also show that the 1310 cm^?1 (b_1u; observed ground-state value) mode is associated with the largest vibronic coupling coefficients and the strongest two-photon amplitude tensor and therefore must be correlated with the most intense B_1u X b_1u false origin ≈ 1496 cm^?1 from the pure (0-0) line.     

Aflatoxin M1 determination in raw milk using a flow-injection immunoassay system

A flow-injection immunoassay (FI-IA) method with amperometric detection for aflatoxin M1 (AFM1) determination in milk has been developed. The first step consists in an incubation of the sample containing AFM1 (Ag) with fixed amounts of anti-AFM1 antibody (Ab) and of the tracer (Ag^*, AFM1 covalently coupled to HRP) until equilibrium is reached. In this mixture a competition occurs between Ag and Ag^* for the Ab. The mixture is then injected into a flow system where the separation of the free tracer (Ag^*) and the antibody-bound tracer (AbAg^*) is performed in a column with immobilized Protein G. The antigen–antibody complexes are retained in the column due to the high affinity of the Protein G for the antibody. The activity of the eluted enzyme label is then amperometrically detected.

The immunoassay was optimised relative to conditions for antibody–antigen incubation (pH, incubation time, ionic strength, temperature) and enzymatic label detection. This method showed a dynamic concentration range between 20 and 500 ppt AFM1, a low detection limit (11 ppt), good reproducibility (RSD < 8%) and a high throughput (six samples per hour in triplicate). Different milk samples were analysed and the results were in good agreement with those obtained by HPLC using the AOAC 2000.08 method.     

Synthesis of some 5H,12H-[1]benzoxepino[4,3-b]indol-6-ones. A new heterocyclic ring system

The synthesis of the title compounds 5H,12H-[1]benzoxepino[4,3-b]indol-6-ones 10 was effected by the Fischer indole cyclization of some 2,3-dihydro-4-phenylhydrazono[1]benzoxepin-5-ones 9 , obtained from the 3,4-dihydro-4-hydroxymethylene[1]benzoxepin-5(2H)-ones 7 by the Japp-Klingemann reaction. The structure of these new heterocyclic compounds was supported by ir, ¹H nmr and ms spectral data.     

Nanostructured ruthenium on γ-Al2O3 catalysts for the efficient hydrogenation of aromatic compounds

Free and trioctylamine (TOA)-stabilized ruthenium nanoparticles have been prepared by decomposition of the metal precursor Ru(η⁶-cycloocta-1,3,5-triene)(η⁴-cycloocta-1,5-diene) under mild conditions (room temperature, hydrogen atmospheric pressure). The nanoparticles have been deposited on γ-Al₂O₃ supports having different surface area. The resulting systems are active in the hydrogenation of methyl benzoate to methyl cyclohexanoate with a reaction rate decreasing in the order Ru(TOA)/γ-Al₂ O₃ (high surface area, catalyst D) > Ru(TOA)/γ-Al₂O₃ (catalyst C) > Ru/γ-Al₂O₃ (high surface area, catalyst B) > Ru/γ-Al₂O₃ (catalyst A). Catalysts A-D are long lived and can be reused without loss of activity; they are considerably more active than a commercial ruthenium on γ-Al₂O₃ sample. High Resolution Transmission Electron Microscopy analyses of such systems show that the nanoparticles are homogeneously dispersed on the support and that the size distribution decreases in the order catalyst A, 2.9 nm > catalyst B, 2.8 nm > catalyst C, 2.4 nm > catalyst D, 2.3 nm. Based on the easy hydrogenation of the aromatic ring to the cyclohexane derivative, an efficient synthesis of 4-carbomethoxyformylcyclohexane, important starting material in the preparation of pharmaceutical products, from the largely available methyl 4-formylbenzoate, has been set up in the presence of catalyst D.     

Comparison of collisional activation by the ‘boundary effect’ vs. ‘tickle’ excitation in an ion trap mass spectrometer

It has been shown previously that collisional activation in an ion trap mass spectrometer can be achieved by storing parent ions within a narrow zone extending close to the theoretical boundaries β_r = 0 or β_z = 0 of the stability diagram. This procedure can be used for obtaining collision-induced dissociation of selected parent ions without the need to apply a precisely tuned resonant ‘tickle’ potential between the end-cap electrodes. In this investigation a comparison was made between the two methods (‘tickle’ and ‘boundary’) of activation based on the efficiency of parent-to-daughter conversion and on the relative abundance of daughter ions for a model system (the m/z 91/92 ratio for n-butylbenzene). The data show that, under conditions of maximum efficiency, a comparable amount of internal energy is present in the ions after activation with the two methods. However, with the ‘tickle’ technique it is possible to increase the internal energy of the parent ions even further, although at the expense of the efficiency, whereas in the case of the “boundary” activation, the conditions for optimum efficiency almost coincide with those for maximum activation and a drastic loss of ions follows any attempt to overcome these limits. It is also found that at any given q_z value used for storing and activating parent ions the permitted mass difference between parent and fragment ions is greater with ‘boundary’ than with ‘tickle’ excitation.     

Determination of fosinopril in pharmaceutical formulations containing hydrochlorothiazide by multiwavelength UV spectrophotometry

A sensitive, simple, rapid and precise method for the simultaneous determination of fosinopril (FOS) and hydrochlorothiazide (HCT) in pharmaceutical formulations is presented. These active ingredients are extracted in aqueous solution and measured by multiwavelength UV spectrophotometry using the program QUEST. HCT acts as an internal standard to verify the accuracy of the analysis. Some aspects of the chemical, spectroscopic and thermoanalytical behaviour of FOS are also reported.