13-Chloro-3-O-β-d-glucopyranosylsolstitialin from Leontodon palisae: the first genuine chlorinated sesquiterpene lactone glucoside

Apart from a number of known sesquiterpenoids, a novel chlorinated sesquiterpene lactone glucoside--13-chloro-3-O-β-d-glucopyranosylsolstitialin--has been isolated from the Southwestern European plant Leontodon palisae (Asteraceae, tribe Lactuceae). The structure has been established by high resolution mass spectrometry and 1D as well as 2D NMR spectroscopy. The compound represents the first naturally occurring chlorinated sesquiterpene lactone glucoside. The cytotoxicity of the new compound and related ones was evaluated using the MTT assay.     

A Note on Stereochemical Observations of the Deprotonation of Ethyl 2-Alkenoates

Deprotonation of ethyl (E)-2-alkenoates 1 , 3 and 4 yields after protonation the double bond migrated (3 Z)-isomers 5 , 7 and 9 as major products. In contrast, deprotonation and reprotonation of ethyl (Z)-2-pentenoate ( 2 ) gives the (3 E)-isomer 6 exclusively. These findings are explained by reaction paths starting from different ester conformations.     

Synthese von 4(5)-acyl-5(4)-alkylimidazolen aus symmetrischen 1,3-dicarbonylverbindungen

Synthesis of 4(5)-Acyl-5(4)-alkylimidazoles from Symmetrical 1,3-Diones A new synthesis of 4(5)-acyl-5(4)-alkylimidazoles 1 is described. The symmetrical 1,3-diones 5a and 5b were reacted with N₂O₄ to give the nitro compounds 7a and 7b , respectively; 5c was treated with NaNO₂ to give the nitroso compound 7c (Scheme 2). Hydrogenation of 7a , 7b and 7c over Pd/C in acetic acid/acetic formic anhydride yielded the formamides 9a , 9b and 9c , whose cyclization in formamide/formic acid afforded the 4(5)-acyl-5(4)-alkylimidazoles 1a, 1b and 1c , respectively. Oxazoles 11a and 11b were obtained from the corresponding formamides 9a and 9b with methanesulfonic acid/P₂O₅.     

Anisotropy of conductivity due to warm holes inp-type germanium andp-type silicon

The dependence of the electric conductivity on a d.c. electric field of medium intensity is measured for 3.5 ohm-cmp-type silicon and 0.9 ohm-cmp-type germanium. From these data and the symmetry properties of the cubic crystal lattice the dependence of the conductivity on crystal orientation is determined. Also, an analytical treatment is made for silicon by assuming a model of constant energy surfaces near momentum?k=0 which consists of spheroids of rotational symmetry penetrating each other. The usually accepted model of warped surfaces does not seem to be tractable. The ratio of effective masses parallel and perpendicular to the axis of rotation enters as a parameter which is determined by the experimental value of the conductivity anisotropy. This mass ratio for silicon at 275 °K is 3.25, at 193 °K 4.64 and at 77 °K 37. With germanium the observed anisotropy is stronger than the anisotropy calculated with any finite mass ratio which means that the model is not adequate.