C13 norisoprenoids from Brassica fruticulosa

Five C13 norisoprenoids, one of them glucosilated, have been isolated from the leaves of Brassica fruticulosa (Brassicaceae). The structure (3S,4R,7E,9S)-3,4,9-trihydroxy-5,7-megastigmadiene, has been assigned to the new compound. All the structures have been determined by spectroscopic means and chemical correlations.     

A study of aryl radical cyclization in enaminone esters

Aryl radical cyclization in N-phenyl, N-benzyl, and N-phenethyl enaminone esters 1a-f was studied. N-Benzyl and N-phenethyl enaminones afforded 5-exo and 6-exo cyclization products, respectively, but radical cyclization did not occur in N-phenyl enaminones. The rate constants for the 5-exo and 6-exo cyclization processes in secondary enaminones were estimated as being on the order of 10(7) s(-1) at 353 K; since DNMR experiments showed the rate constant for rotation around the enaminone C3-N bond to be on the order of 10(4) s(-1) at this temperature, the initial enaminone configuration is maintained throughout the cyclization process. PM3 calculations suggested that the nonoccurrence of endo and 4-exo cyclizations is due to the corresponding transition structures involving significant distortion of the conjugated enaminone system.     

Dissociative electron transfer to haloacetonitriles. An example of the dependency of in-cage ion-radical interactions upon the leaving group

The reductive cleavage of the haloacetonitriles (Cl, Br, I) in DMF provides additional examples of the formation of a fragment cluster upon dissociative electron transfer, which is able to survive in this polar solvent thanks to the electron-withdrawing character of the cyano group. The remarkable sensitivity of the activation energy to small changes of the interaction energies allows, with help of the "sticky" dissociative electron-transfer model, the precise determination of interaction energies down to a few millielectronvolts from the cyclic voltammetric data. The interaction energy rapidly decreases from Cl to Br and to I, correlated with the increase of the halide radius. These observations add to the previously gathered evidence to confirm the existence of such interactions and to highlight their electrostatic character. This is further corroborated by the quantum chemical computation of the potential energy profiles, which exhibit a long-distance energy minimum. This revisiting of the notion of sigma-ion radicals and of their status in a polar medium makes them appear as an electrostatic radical-ion pair rather than covalently bound molecules. Their stability is a function of the Lewis acid-base properties of both the radical and the leaving ion and is strongly influenced by the nature of the solvent.     

Asymmetric catalytic synthesis of enantiopure N-protected 1,2-amino alcohols

[reaction: see text] The asymmetric aminolytic kinetic resolution (AKR) of racemic terminal epoxides using carbamates as the nucleophile catalyzed by (salen)Co(III) complex provides a practical and straightforward method for the synthesis of both aliphatic and aromatic N-Boc- or N-Cbz-protected 1,2-amino alcohols in almost enantiomerically pure form (ee >/= 99%). The AKR uses an easily accessible catalyst and inexpensive starting materials, and the reactions are conveniently carried out at room temperature under an air atmosphere.     

A graphical tool for the prediction of vicinal proton-proton 3J(HH) coupling constants

The easy to use and free available graphical tool MestRe-J, developed for Win-32 platforms, calculates the vicinal proton-proton coupling constants 3J(HH) from the torsion angle phi between the coupled protons for the two kinds of generalized Karplus equations developed by Altona's group as well as for equations from other authors. Besides the classical Haasnoot-de Leeuw-Altona equations, including individual substituent effects that depend on their relative Huggins's electronegativities Deltachi, the program incorporates the more recent and precise Díez-Altona-Donders equations. The substituent effects in these equations, that include effects of interactions between substituents, depend on substituent parameters lambda optimized from the 3J(HH) couplings to methyl groups. Weighted time-averaged couplings can be calculated. The equations for 3J(HH) can be solved to provide the torsion angles phi.     

An efficient synthesis of phthalocyanines based on an unprecedented double-addition of oximes to phthalonitriles

A novel and efficient method is reported for the preparation of phthalocyanines from phthalonitrile or its derivatives which utilizes low-cost reagents of hydrolytic stability, high simplicity, and easy accessibility, i.e., oximes, and proceeds via an unprecedented double addition of oximes to the nitrile group.     

Synthesis,X-ray diffraction structures,spectroscopic properties,and in vitro antitumor activity of isomeric (1H-1,2,4-triazole)Ru(III) complexes

Three ruthenium(III) complexes containing 1H-1,2,4-triazole (Htrz), viz., (H(2)trz)[cis-RuCl(4)(Htrz)(2)], 1, (H(2)trz)[trans-RuCl(4)(Htrz)(2)], 2, and (Ph(3)PCH(2)Ph)[trans-RuCl(4)(Htrz)(2)], 3, have been synthesized by reaction between RuCl(3) and excess of the triazole in 2.38 M HCl (1 and 2), while 3 was obtained by metathesis of 2 and [Ph(3)PCH(2)Ph]Cl in water. The products were characterized by IR, UV-vis, electrospray mass spectrometry, cyclic voltammetry, and X-ray crystallography (1 and 3). X-ray diffraction study revealed cis and trans arrangements of the triazole ligands in 1 and 3, correspondingly, and unprecedented monodentate coordination of the triazole through N2 and stabilization of its 4H tautomeric form, which is the disfavored one for the free triazole. The cytotoxicity of 1 and 2 has been assayed in three human carcinoma cell lines SW480, HT29 (colon carcinoma), and SK-BR-3 (mammary carcinoma). Both compounds exhibit antiproliferative activity in vitro. Time-dependent response of all three lines to 1 and 2 and a structure-activity relationship, i.e., higher activity of the trans-isomer 2 than that of cis-species 1, have been observed.     

The P\bar 1 space group changes in journal of crystallographic and spectroscopic research and in journal of chemical crystallography

The crystal structures of seven compounds, originally described in the centrosymmetric triclinic space group (No. 2), have been revised to centered monoclinic. Six are now described in space group No. 15 (C2/c or I2/a) and one in space group No. 12 (C2/m). Three structures (TADTEX, VICHIY, YAWZUR) have been re-refined in the correct space group. For six instances the decrease in symmetry results in only minor adjustments and the structure is essentially correct as it is expected when the original and the revised space groups are both centrosymmetric. However, in one instance (VICHIY) the reformulation in the higher space group changes (unexpectedly) the molecular dimension as much as 0.12 Å, even if the space group change is between two centrosymmetric space groups (from to C2/c). This was attributed to the easy decomposition of the crystal. The percentage of revised crystal structures was found to be 1.71%, namely 8 on a total of 467 analyzed structures. A low value if compared to the 3% value found by Marsh and Spek for C2 space group.