Convenient Synthesis of tert‐Butyl Esters of Indole‐5‐carboxylic Acid and Related Heterocyclic Carboxylic Acids

The tert‐butyl esters of indole‐5‐carboxylic acid and related compounds such as benzofuran‐ and benzothiophene‐5‐carboxylic acid were readily accessed by reacting the appropriate carboxylic acids with tert‐butyl trichloroacetimidate. To obtain the tert‐butyl esters of the 5‐carboxylic acids of 1H‐benzotriazole and 1H‐benzimidazole, position 1 of these heterocycles had to be protected by acetylation prior to reaction with tert‐butyl trichloroacetimidate. Cleavage of the acetyl residue of the obtained intermediates by dilute aqueous NaOH in ethanol led to the desired tert‐butyl 1H‐benzotriazole‐and 1H‐benzimidazole‐5‐carboxylates.     

Structure elucidation of β-carotene isomers by HPLC-NMR coupling using a C30 bonded phase

The separation of cis/trans isomers of β-carotene has been performed with a C₃₀ stationary phase employing ¹H NMR spectroscopy as an on-line detection technique. 1D as well as 2D NMR spectra have been recorded in the stopped-flow mode for the predominant chromatographic peaks. Structural assignment of the five identified isomers was performed via comparison of simulated 1D ¹H NMR spectra on the basis of the structures of β-carotene cis/trans isomers with the experimental data, and also by the analysis of the proton-proton connectivities in the 2D NMR spectra of three isomers with the highest concentration. The chromatographic retention behaviour of the isomers agreed well with previously reported data. The advantage of the applied hyphenated coupling technique compared to conventional off-line techniques lies in the fact that chromatographic separation and NMR detection are performed in a closed system, so that reisomerization of the separated compounds is inhibited. Received: 29 May 1996 / Revised: 1 July 1996 / Accepted: 4 July 1996     

Influence of UVB,UVA and UVA1 irradiation on histamine release from human basophils and mast cells in vitro in the presence and absence of antioxidants

UV irradiation is widely used for the treatment of atopic eczema. In recent years, UVA1 phototherapy has gained increasing attention. This study analyzed the influence of different UV wavelengths--especially UVA1--on histamine release from human basophils and mast cells. The modulation of this parameter might be responsible for some of the therapeutic effects of UV irradiation. Enriched human basophils and human mast cells (HMC1 cell line) were irradiated with increasing doses of UVB, UVA and UVA1 in vitro. After irradiation, different stimulants were added to induce histamine release. In additional experiments, basophils were preincubated with superoxide dismutase, ascorbate or trolox to study the role of antioxidants in the modulation of histamine release after UV irradiation. UVA and UVA1 significantly inhibited histamine release from basophils and mast cells. UVB only had an inhibitory effect on mast cells. Preincubation with superoxide dismutase and ascorbate did not influence the inhibitory effect of UVA1 on basophil histamine release, whereas trolox decreased significantly the histamine release from nonirradiated basophils.     

On Lyapunov Exponents and Rotation Number of Random Linear Hamiltonian Systems

We consider linear Hamiltonian differential systems in R²ⁿ depending on a stationary ergodic Markov process. The induced processes on the Lagrangian manifolds L_p and L_p?1, p (1 ≦ p ≦ n) are studied. From this we derive representations for the Lyapunov exponents, especially the lowest non-negative exponent, and a (suitably defined) rotation number of the system.     

Disproof of the Overall Enzymatic Biosynthesis of Vindoline from Tryptamine and Secologanin by Cell-Free Extracts from the Leaves of Catharanthus roseus (L.) G. DON

A cell-free extract, which was isolated from the leaves of mature Catharanthus roseus plants by a previously published procedure, does not convert a mixture of secologanin and radiolabelled tryptamine to vindoline, as was recently claimed. The radioactivity in the purified alkaloid extract determined by earlier workers is certainly due to ‘impurities’ in the presumed ‘vindoline’. This was shown by extensive purification of the alkaloid extract (which contained added unlabelled vindoline as a carrier) followed by chemical conversion of vindoline to two derivatives and subsequent purification, ultimately giving unlabelled deacetylvindoline.