Carla Boga

Asymmetric Michael additions catalysed by Ni(II) and Co(II) complexes with homochiral ligands

Abstract Two Michael-type addition reactions of nitromethane to chalcone, reaction (1a), and of methyl 1-oxo-2-indanecarboxylate to methyl vinyl ketone (reaction (1b)) have been tested for catalytic asymmetric induction when carried out in the presence of Ni(II) or Co(II) and homochiral ligands. Proline-derived ligands in conjunction with Ni(II) are found to be moderately effective asymmetric inductors in the former addition (up to 59% e.e.). For this addition the absolute configuration of the adduct ( 2 ) has been established via correlation with ( S )-(+)-1-(dimethylamino)-2,4-diphenylbutan-4-one ( 21 ). For reaction (1b), Co(II) complexes appear to be the more effective catalysts; the highest e.e. (38%) was obtained with a tetradentate ligand, a diaminodiol ( 16 ). Although the e.e.s so far obtained are not much better than those previously obtained, the method appears to allow further improvement.

Diastereoselective allylation of chiral imines. Novel application of allylcopper reagents to the enantioselective synthesis of homoallyl amines

Abstract The addition of allylcopper reagents to imines derived from S-valine occurs with excellent diastereoselectivity (e.e. 98 %).

Determination of 4-hydroxy-2-nonenal at cellular levels by means of electrospray mass spectrometry

trans-4-Hydroxy-2-nonenal (HNE) is an end-product of lipid peroxidation in biological systems which produces a variety of powerful biological effects. A method based on electrospray mass spectrometry was developed for the determination of 4-HNE at cellular levels. Quantification was carried out by using HNE-d(11) as internal standard; the mass chromatograms were acquired in the single ion monitoring mode (SIM) on the [M + H](+) monoisotopic species for HNE and HNE-d(11). With this approach a higher precision and lower detection limit and biological sample size than those typical of the methods so far employed are achieved. Furthermore the determination of the analyte from the cell extract is directly performed without the need of any HNE derivatization. As a first application the method was used to identify and quantify HNE in human T cell leukemia extracts.

Tetrahalogenomethanes: simple reagents for the synthesis of monohalogenated and mixed dihalogenated aromatic heterocycles via metal–halogen exchange from lithium compounds

Abstract Tetrabromo- or tetrachloromethane and 2-lithio derivatives of aromatic heterocycles rapidly produce the corresponding 2-bromo or 2-chloro derivatives in high yields through a metal–halogen exchange mechanism. This kind of reaction was also used to obtain, in good yields, 5-bromo-2-chlorothiazole and 5-bromo-2-chloro-N-methylimidazole.

Synthesis and antimicrobial activity of novel structural hybrids of benzofuroxan and benzothiazole derivatives

New compounds containing both benzofuroxan and benzothiazole scaffolds were synthesized through electrophile/nucleophile combination of nitrobenzofuroxan derivatives and 2-mercapto- or 2-aminobenzothiazole derivatives and their biological effect on the natural strain Vibrio genus and different bacterial lux-biosensors was studied. Among all the compounds synthesized, that obtained from 2-mercaptobenzothiazole and 7-chloro-4,6-dinitrobenzofuroxan was toxic for bacterial cells, and also able to activated the 1st type Quorum Sensing system. The reaction between 7-chloro-4,6-dinitrobenzofuroxan and 2-aminobenzothiazole derivatives gave two products, one bearing the benzofuroxan moiety linked to the exocyclic amino nitrogen, and the second derived from the attack of two molecules of electrophile to both the nitrogen atoms of the benzothiazole reagent. Their relative ratio is modifiable by tuning the reagents ratio and the reaction time.

Cytotoxic and cytostatic effects induced by 4-hydroxynonenal in human osteosarcoma cells

Several studies point to the existence of an inverse correlation between cellular lipid peroxidation and both cell proliferation and neoplastic transformation. Furthermore, numerous results demonstrate that lipid peroxidation products affect central biochemical pathways and intracellular signalling at physiological concentrations. 4-Hydroxynonenal (HNE) is one of the most active products of lipid peroxidation. This work has focused on the evaluation of HNE nuclear content, so far never directly measured, by electrospray-ionization-mass-spectrometry (ESI/MS) and on the correlation between its concentration and the induced effects after exogenous administration. In a human osteosarcoma cell line (SaOS2), HNE exhibited an early cytotoxic effect characterized by apoptosis, cytostatic and differentiating effects characterized by slow growth, increase in alkaline phosphatase (ALP), and alpha5 integrin subunit content with decrease in tumorigenicity.

Diastereoselective addition of methylcopper- and diemthylcuprate-boron trifluoride reagents to (S)-(N-alkylidine)-1-phenylethylamines

Abstract The reactions of methylcopper- and diemthylcuprate-boron trifluoride reagents with aldimines derived from (S)-1-phenylethylamine afford with good diastereoselectivity (S,S)-amines from aromatic imines, but the (R,S)-amine from an aliphatic imine.

Diastereoselective synthesis of 2,5-dimethylpyrrolidines and 2,6-dimethylpiperidines by reductive amination of 2,5-hexanedione and 2,6-heptanedione with hydride reagents

Abstract The reductive amination of 2,5-hexanedione and 2,6-heptanedione with ammonia and primary amines in the presence of hydride regents afforded 2,5-dimethylpyrrolidines and 2,6-dimethylpiperidines with variable diastercoselectivity, as the cis/trans ratio was affected by the size of the ring formed and the steric and electronic properties of the nitrogen substituent. Increasing the bulkiness of the nitrogen substituent, the cis pyrrolidines and the trans -piperidines were obtained with enhanced selectivity.

On the antibacterial activity of roots of Capparis spinosa L.

A decoction of Capparis spinosa L. roots, widely used in the traditional folk medicine of southern Italy, was prepared and submitted to antibacterial activity tests, which showed an interesting bacteriostatic activity on the growth of Deinococcus radiophilus. Heterocyclic compounds were also recovered from the chloroformic extract of the roots.

Reactions of Hydroxypyridines with 1-Chloro-2,4,6-trinitrobenzene − Product Structure, Kinetics, and Tautomerism

Reactions between 1-chloro-2,4,6-trinitrobenzene and 2-hydroxypyridine, 3-hydroxypyridine, and 4-hydroxypyridine are reported. 4-Hydroxypyridine produces the product of attack at the nitrogen atom, while 3-hydroxypyridine reacts at the oxygen atom. 2-Hydroxypyridine reacts as an ambidentate nucleophile, providing a mixture of products arising from attack at both the oxygen and the nitrogen atom. Reactions between X-substituted-3-hydroxypyridines (X = H, 5-Cl, 6-CH3) and 1-chloro-2,4,6-trinitrobenzene provided 3-pyridinyl 2,4,6-trinitrophenyl ethers, analysed by 1H and 13C NMR spectra and by X-ray diffraction. Moderate heating of methanolic solutions of 3-pyridinyl 2,4,6-trinitrophenyl ether and of 6-methyl-3-pyridinyl 2,4,6-trinitrophenyl ether caused a methylation reaction of the pyridine nitrogen ring through trinitroanisole, providing 3-hydroxy-1-methylpyridinium picrate and 1,2-dimethyl-5-hydroxypyridinium picrate. Kinetic data are compared and discussed.