High stereocontrol in the allylation of chiral non-racemic α-alkoxy and α-amino nitrones

The stereocontrolled addition of allylic metals to chiral non-racemic nitrones promoted by the addition of Lewis acids is described. Whereas for α-alkoxy nitrones the stereocontrol depends on the Lewis acid used as an activator, for α-amino nitrones the diastereofacial course of the reaction depends on the protection of the α-amino group. The successful implementation of the methodology is represented by the enantiodivergent synthesis of d- and l-allylglycine.     

GC-FID/MS method for the impurity profiling of synthetic d-allethrin

A GC/FID/MS method was developed for the identification and quantification of d-allethrin (DA) and its major impurities in commercial samples. Optimisation of the experimental conditions was carried out considering such important requirements as resolution, reproducibility, detection limits of 0.1% (m/m) for the impurities, and short analysis time. Under the optimised final conditions the method was validated for specificity, precision (CV% = 0.133 at 2.10 mg/mL and CV% = 0.035 at 3.00 mg/mL), linearity (0-3.00 microg injected), limits of detection (0.09 ng injected) and quantitation (0.28 ng injected), and robustness. The DA related impurities were identified by using a GC/MS method with ion trap mass detection and also by comparison with synthesised standards. The most abundant impurities were crysolactone, allethrolone, chrysanthemic acid, and chloro-derivatives of DA.     

Iterative organometallic addition to chiral hydroxylated cyclic nitrones: highly stereoselective syntheses of alpha,alpha'- and alpha,alpha-substituted hydroxypyrrolidines

[reaction: see text]. Iteration of organometallic addition to chiral hydroxylated pyrroline N-oxides through an addition-oxidation-addition synthetic sequence allowed highly stereoselective double alkylation of pyrrolidine at C-2 or at C-2 and C-5 depending on the regioselectivity of the oxidation step. Application of this methodology has been exemplified by the synthesis of the all-substituted pyrrolidine alkaloid (-)-codonopsinine and of proline-type amino acid precursors possessing a quaternary stereogenic center, whose configuration can be controlled.     

Analysis of neutral nitromusks in incenses by capillary electrophoresis in organic solvents and gas chromatography-mass spectrometry

Nitromusks used as fragrances in a variety of personal-care products, cleansers, and domestic deodorants, including incense sticks, are neutral nitro aromatic compounds; some of these have been reported as photosensitizers. In this work, their analysis was performed by capillary electrophoresis (CE) in a methanol-based background electrolyte (BGE). In particular, a 10 mM solution of citric acid in methanol was used; under these conditions the strong suppression of the electroosmotic flow favored the use of negatively charged surfactants as additives for the anodic migration of the studied analytes. To this end, sodium taurodeoxycholate (TDC) was supplemented at high concentration (190 mM) to the organic background electrolyte (BGE), showing strong indication of the ability to give micelle-like aggregates. Since nitromusks are characterized by the presence of a nitroaromatic ring with low charge density, their association with TDC aggregates can be ascribed to donor-acceptor interactions. Separation of musk xylene, musk ketone, and the banned musk moskene and musk ambrette was obtained under full nonaqueous BGE; the addition of relatively small water percentages (15% v/v) was found to be useful in improving the separation of pairs of adjacent peaks. Under optimized conditions (190 mM sodium TDC in methanol-water, 85-15 v/v containing citric acid 10 mM) the system was applied to the analysis of nitromusks in incense sticks extracted with methanol. The results were compared with those obtained by the analysis of the same samples using gas chromatography with mass detector. The expected different selectivity of separation obtained using the two techniques can be useful in the unambiguous determination of the analytes; furthermore, a substantial accord of the preliminary quantitative results achieved with the two methods was assumed as the confirmation of the potential reliability of CE performed with high percentage of organic solvent.     

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.     

Functionalized biopolymers as soluble macromolecular chelating agents

Two different conjugates of bovine serum albumin (BSA) with lysine and a derivative of imidazole have been synthesized to obtain watersoluble macromolecules with binding properties against bivalent transition metal ions. Syntheses have been carried out using the 60 aminogroups or the 99 carboxylic groups on BSA for the coupling reactions, with such molar ratios able to produce highly substituted BSA. The skill of each conjugate to bind metal ions in aqueous medium was studied through the use of titration curves with some metal ions, characterized by a good affinity for the free ligand. Both the conjugates allow us to recover a high number of metal ions per protein molecule, close to the number of ligand molecules on the BSA surface in the case of the lysine conjugate, whereas in the case of the imidazole conjugate M3L complexes are performed.     

A new formulation of the phase change approach in the theory of conical intersections

We have reformulated the phase change approach to the theory of conical intersections suggested by Zilberg and Haas [S. Zilberg, Y. Haas, Adv. Chem. Phys. 124 (2002) 433]. We use the fact that the phase change loop variable in polar co-ordinates in the space of nuclear co-ordinates is related to the transformation of the diabatic VB states defined at the apex of the cone in a conical intersection. Thus one can use the basis transformation generated by θ to yield a sequence of orthogonal pairs of VB structures (anchors) at any value of in the loop in nuclear configuration space. In this way the branching plane concept becomes related to VB wavefunctions based on the correspondence between the two angles. The theory is developed in detail using a simple three orbital three electron example. Examples are presented for four and six orbitals. In the later case, our results differ from those of Zilberg and Haas.     

DNA separation by capillary electrophoresis with hydrophilic substituted celluloses as coating and sieving polymers. Application to the analysis of genetically modified meals

A coating procedure based on the physical adsorption of hydroxypropyl cellulose onto the wall of a capillary column has been successfully used for the separation of DNA fragments up to 500 bp. The method uses a running Tris-phosphate-EDTA buffer containing 2-hydroxyethyl cellulose as sieving polymer. The separation procedure shows good reproducibility (measured as RSD%) for consecutive runs (<0.64), for different days (< 1.15) and capillaries (<2.15), short analysis times, and a long coating lifetime. Good reproducibility and efficiency are even achieved by performing the separation in the presence of additives such as ethidium bromide and mannitol. The method is applied to the detection of GMOs in soybean and maize meals with an accurate evaluation of the length of DNA sequences, previously amplified by polymerase chain reaction.