Enantioselektive Reaktionen an porphinoiden Nickelkomplexen

Enantioselective Reactions on Porphine Type Nickel Complexes The thermodynamically controlled addition of alcohols to (+)-(1R)-[1-methyl-8H-HDP]nickelperchlorate ( 1 ; e.e. 92%) yields exclusively the corresponding cis-1,11-disubstituted porphinoids. Chemical transformation of functional groups in the alkoxy side-chain of the chiral addition product followed by acid catalyzed elimination yields the derived alcohols and 1 . By this procedure, the following enantioselective transformations were studied: methylation of meso-2,3-butandiol ( 5 ) to (+)-(2R,3S)-3-methoxy-2-butanol ( 8a ; e.e. 87%), diimide reduction of 2-ethylallyl alcohol ( 9 ) to (+)-(2R)-2-methyl-1-butanol ( 12a ; e.e. 15%), and hydride reduction of 4-hydroxy-2-butanone ( 13 ) to (+)-(3S)-1,3-butandiol ( 16a ; e.e. 20%). Addition of 2,2-dimethyl-1,3-propandiol ( 17 ) to 4 , followed by esterification of the free hydroxy group with trifluoromethanesulfonic anhydride and solvolysis of the sulfonate 19 yielded a bridged complex with unrearranged alkyl chain for which structure 20 is proposed.     

The Molecular and Crystal Structure of the Glycopeptide A-40926 Aglycone

The crystal structure of a glycopeptide antibiotic A–40926 aglycone was investigated by X-ray analysis at ?120°. A-40926 crystallises in the orthorhombic space group P2₁2₁2₁ with two monomers in the asymmetric unit, a = 21.774(4), b = 28.603(7), c = 29.757(4) Å. ‘Conventional’ direct methods approach failed to solve the structure, but a novel iterative real/reciprocal space procedure was successful. Refinement against 11248 F² data led to R1 = 13.3% for 6770 F > 4σ (F). The two monomers of A-40926 have similar conformations and are bound by antiparallel H-bonds to form a ‘chain’ structure of connecting dimers. The antibiotic molecule possesses a ‘binding pocket’ for the C-terminal carboxy group of the cell-wall protein, which is consisten with suggestions based on NMR data and the recently reported crystal structure of ureido-balhimycin. In A-40926 the monomers are polymerically linked by H-bonds, quite unlike the tight dimer formation observed in ureido-balhimycin.     

Reactivity sequences of dipolarophiles towards diazocarbonyl compounds - MO perturbation treatment

Whereas diazomethane cycloadditions are only accelerated by electron-attracting substituents in the olefinic or acetylenic dipolarophile, the cycloadditions of diazoacetic, diazomalonic and diazo(phenylsulfonyl)acetic ester show in accordance with the PMO treatment U-shaped activity functions when log k₂ is plotted versus the lowest IP of the dipolarophiles.     

Sorellin und Hobartin,zwei neue Indolalkaloide aus Aristotelia peduncularis (LABILL.) HOOK. F. 173. Mitteilung über organische Naturstoffe

Sorelline and Hobartine, Two New Indole Alkaloids from Aristotelia peduncularis (LABILL .) HOOK . F. From Aristotelia peduncularis (LABILL .) HOOK . F. two new indole alkaloids, sorelline ( 1 ) and hobartine ( 2 ), have been isolated. Their structures were elucidated on the basis of spectroscopic data (the formulae represent their relative configurations). The alkaloids 1 and 2 have closely related structures with a monosubstituted indole moiety and an unrearranged monoterpene unit in the aliphatic part.     

Asymmetric synthesis of (R)-reticuline. A new strategy for the asymmetric synthesis of isoquinolines via enantioselective epoxidation or dihydroxylation

A new strategy for the asymmetric synthesis of 1-benzyl-1,2,3,4-tetrahydroisoquinolines7 − 9 has been developed. The route involves introduction of asymmetry via enantioselective epoxidation or dihydroxylafion of corresponding stilbene precursors followed by aminolysis and Pomeranz-Fritsch cyclization. The strategy has been successfully applied to the asymmetric synthesis of (R)-reticuline (9), the key-intermediate in the synthesis of morphine alkaloids on the biomimetic route.     

Molecular information on the dissolution of polydisperse polymers: Mixtures of long and short poly(ethylene oxide)

A systematic study of the dissolution of dry, polydisperse poly(ethylene oxide) (PEO) samples, obtained from mixtures of low-molecular-weight and high-molecular-weight PEO, was made. During the dissolution process, the individual release of the low- and high-molecular-weight fractions was monitored. The high-molecular-weight/low-molecular-weight ratio controls the release rate, and the fraction of high-molecular-weight polymers dominates the effect on the overall release rate in mixed PEO tablets. Both fractions are released at the same rate during the main part of the dissolution process; however, during the initial dissolution period a fractionation occurs. The release rate is not a unique function of the average molecular weight of the polymer, but also depends on the polydispersity. By contrast, the average dimension of a polymer coil, as given by the intrinsic viscosity, gives a good prediction of the release rate irrespective of the polydispersity or details of the molecular weight distribution.     

Nucleoside 5'-triphosphates: self-association, acid-base, and metal ion-binding properties in solution

Adenosine 5'-triphosphate (ATP(4-)) and related nucleoside 5'-triphosphates (NTP(4-)) serve as substrates in the form of metal ion complexes in enzymic reactions taking part thus in central metabolic processes. With this in mind, the coordination chemistry of NTPs is critically reviewed and the conditions are defined for studies aiming to describe the properties of monomeric complexes because at higher concentrations (>1 mM) self-stacking may take place. The metal ion (M(2+)) complexes of purine-NTPs are more stable than those of pyrimidine-NTPs; this stability enhancement is attributed, in accord with NMR studies, to macrochelate formation of the phosphate-coordinated M(2+) with N7 of the purine residue and the formation degrees of the resulting isomeric complexes are listed. Furthermore, the formation of mixed-ligand complexes (including also those with buffer molecules), the effect of a reduced solvent polarity on complex stability and structure (giving rise to selectivity), the use of nucleotide analogues as antiviral agents, and the effect of metal ions on group transfer reactions are summarized.     

Vitamin-B12-katalysierte C,C-Bindungsverknüpfung: Synthese von Jasmonaten via sequentielle Radikal-Reaktion

Vitamin-B₁₂-Catalyzed C, C-Bond Formation: Synthesis of Jasmonates via Sequential Radical Reaction The Cbl-catalyzed electroreduction of 3-(2′-bromo-1′-ethoxyethoxy)cyclopenten ( 1a ) in presence of 1-cyanovinyl-acetate ( 8 ) gave, in a sequential radical reaction (5-exo-trig-cyclization of 1a followed by addition to 8 ), 1-cyano-2-(2′-ethoxy-hexahydro-2′H-cyclopenta[b] furan-4′-yl)ethyl acetate ( 10a ). This intermediate was transformed to methyl jasmonate ( 7 ; four steps) and epituberolide ( 9 ; three steps) in 20 and 31% yield, respectively, from cyclopent-2-en-l-ol.     

The Interaction of Walsh-Orbitols in Diademane and Related Hydrocarbons

To obtain further information concerning the interaction between Walsh-orbitols of ‘conjugated’ cyclopropane rings, the photoelectron spectra of the following compounds have been recorded: bicyclo[4.1.0]heptane 1 , cis- and trans-tricyclo[5.1.0^{3, 5}]octane 2, 3 , diademane 4 , trans-pentacyclo[3.3.2.0^{2, 9}.0^{4, 10}, 0^{6, 8}]decan 5 and bicyclo[4.1.0]heptene-2 6 . The first bands in the PE.-spectra of these compounds have been assigned on the basis of a ZDO HMO-approximation. For 2 and 4 the value for resonance integral between linked 2p atomic orbitals of two adjacent eclipsed cyclopropane rings is found to be ?1.73 eV.     

Zur Reaktion von Pyridin-2,6-dicarbonsäure mit Aluminium(III) in wäßriger Lösung

Contrary to the informations in the literature our results of equilibrium and kinetic measurements indicate that Al(III) and Pyridine-2,6-dicarboxylic Acid in the range ofpH=(3...5) only formed the complexes AlHL ²⁺ (log=7.44±0.2) and AlL ⁺ (log=11.37±0.06).