Characteristics of vellosimine reductase,a specific enzyme involved in the biosynthesis of the rauwolfia alkaloid sarpagine

A plant enzyme - vellosimine reductase - has been isolated from $\text{Rauwolfia}$ cell suspension cultures. This new enzyme has been-purified (110-fold) and characterized. The reductase is a specific enzyme of the sarpagine pathway catalyzing the NADPH dependent conversion of vellosimine into 10-deoxysarpagine. The latter alkaloid is the immediate biogenetic precursor of sarpagine as shown by its high $\text{in}$$\text{vivo}$ incorporation rate (86%) into sarpagine.     

Electronic ground states of the V2O4+/0/- species from multireference correlation and density functional studies

The molecular and electronic structures of the V2O4+/0/- species are examined by multireference averaged coupled-pair functional (MR-ACPF) and density functional B3LYP calculations. For all three species, new conformers have been found. Shallow potential energy curves imply high mobility of the oxygen atoms in the neutral and anionic species for which antiferromagnetic coupling of the weakly interacting 3dV electrons is found. Good agreement between the MR-ACPF and B3LYP results for the molecular structures and the relative energies of states with different spin multiplicity, as well as for the ionization energy and electron affinity, is observed. For the computation of the height of the transition barriers between different conformers elaborated MR-ACPF calculations are required.     

Stereoselektive totalsynthese von (±)-torreyol

Enones of formulae Ia-d undergo cyclization to give stereoselectively the enol esters IIa-d, respectively, IIa-d are suitable synthones for some sesquiterpene syntheses .— In this paper the synthesis of torreyol (1) is described by an all step stereocontrolled reaction sequence: cyclization educt 10 (Ic) was prepared by alkylation of 8 with 5 and enol ether cleavage of 9. The reaction sequence 11a (IIc)→14a 15 → 18 (ester hydrolysis, formation of the tert. alcohol, degradation of the isopropenyl group) followed by oxidation resulted in the formation of ketone 19 whose relative configuration was determined by the 2D J-resolved 400 MHz ¹H NMR spectrum. After methylation at C-8 (22→23) the tosylhydrazone 25 underwent Bamford-Stevens reaction to yield (±)-1.     

Synthetische Juvenilhormone 2. Mitteilung. p-Substituierte 2-Methyl-3-phenyl-propen(1)-carbonsäurederivate

In the second communication the synthesis of para-substituted 2-methyl-3-phenylpropen(1)-carboxylic acid derivatives is described: Phenylacetone compounds are formed by decarboxylation of a glycidicester; these react according to the Wadsworth-Emmons (Wittig-Horner)-reaction with the corresponding phosphonates to the title compounds. NMR. data show the formation of the steric isomers of 3-Phenyl-2-methyl-propen-1- and 3-Phenyl-2-methylpropen-2-carboxylic acid derivatives.     

Theory of self diffusion in electrolytes

Starting from the concept of marked ions, the problem of self diffusion in electrolyte solutions is discussed from the point of view of irreversible thermodynamics and statistical mechanics. On the basis of the diffusion approach to the theory of transport processes in electrolytes, we derive the statistical theory of self diffusion and an expression for the self diffusion coefficient in terms of the radial distribution function. Results for the concentration dependence of the self-diffusion coefficient are presented.     

Application of the isoselective relationship to diels-alder reactions

Diels-Alder reactions with “normal” and “reverse” electron demand” obey common isoselective relationships (Figure I).     

Selective Hydrogenation of Acrolein Over Pd Model Catalysts: Temperature and Particle‐Size Effects

The selectivity in the hydrogenation of acrolein over Fe₃O₄‐supported Pd nanoparticles has been investigated as a function of nanoparticle size in the 220–270 K temperature range. While Pd(111) shows nearly 100 % selectivity towards the desired hydrogenation of the C=O bond to produce propenol, Pd nanoparticles were found to be much less selective towards this product. In situ detection of surface species by using IR‐reflection absorption spectroscopy shows that the selectivity towards propenol critically depends on the formation of an oxopropyl spectator species. While an overlayer of oxopropyl species is effectively formed on Pd(111) turning the surface highly selective for propenol formation, this process is strongly hindered on Pd nanoparticles by acrolein decomposition resulting in CO formation. We show that the extent of acrolein decomposition can be tuned by varying the particle size and the reaction temperature. As a result, significant production of propenol is observed over 12 nm Pd nanoparticles at 250 K, while smaller (4 and 7 nm) nanoparticles did not produce propenol at any of the temperatures investigated. The possible origin of particle‐size dependence of propenol formation is discussed. This work demonstrates that the selectivity in the hydrogenation of acrolein is controlled by the relative rates of acrolein partial hydrogenation to oxopropyl surface species and of acrolein decomposition, which has significant implications for rational catalyst design.