Parametrisierung von Konjugationsklassen in\mathfrak{s}\mathfrak{l}_n

Ohne Zusammenfassung     

Über die Gelfand-Kirillov-Dimension

Ohne Zusammenfassung Bemerkung. Die Autoren möchten G. Harder, A. Joseph, M. Krämer und C. M. Ringel für hilfreiche Hinweise und Diskussionen danken.     

1,2-Epoxy-Carotinoide. 1. Mitteilung. Synthese von 1,2-Epoxy-lycopin und 1,2,1′,2′-Diepoxy-lycopin

1,2-Epoxy-Carotenoids. Synthesis of 1,2-Epoxy-lycopene and 1,2,1′,2′-Diepoxy-lycopene The synthesis of the naturally occuring 1,2-epoxy-lycopene and of 1,2,1′,2′-diepoxy-lycopene is described.     

(Cholestanyloxycarbonyl)benzyl esters as peptide substituents: Conformational properties of fully protected oligo-L-lysines with C-terminal (cholestanyloxycarbonyl)benzyl and benzyl ester moieties

This study involves L-lysine oligo peptides, protected at the N-terminus by the Nps and at the ε-amino functions by Boc groups. Two series were prepared from dimer to octamer, one containing the p-[(cholestan-3β-yloxy)carbonyl]benzyl, the other one the benzyl ester group at the C-terminus. Conformational analyses were performed by IR absorption. The occurrence of the intermolecular β-structure in the solid state and in CH₂Cl₂ solution was demonstrated for the highest oligomers. The relative stabilities of the self-associated species were determined by adding a variety of polar solvents to the CH₂Cl₂ solutions. The cholestanyl-containing peptides have a lower propensity to self-aggregate than the benzyl-ester analogues. Self-aggregation and decreasing solubility run in parallel. It was also directly shown that soluble urea derivatives may disrupt intermolecular H-bonds in CH₂Cl₂, a point of practical interest, particularly in solid-phase peptide synthesis.     

Preparation and Conformational Properties of Benzylpenicilloyl-oligo-L-lysine Conjugates

Selected oligo-L -lysine carriers and a poly-L -lysine were penicilloylated with benzylpenicillin. The resulting conjugates 2 – 6 were studied by IR. absorption in the solid state and circular dichroism measurements in solution. The IR. data demonstrate the lack of β-structure formation even in medium-sized peptides where such structures might be expected on the basis of previous studies on differently substituted oligo-L -lysines. Considerable proportions of right-handed α -helical conformation are exhibited by the icosa-L -lysine and poly-L -lysine conjugates 5 and 6 in water and 2,2,2-trifluoroethanol. Difficulties in obtaining fully penicilloylated conjugates are not related to the extent of α-helical conformation in aqueous solution.     

Stable Quinone Methides: Regioselective para-Oxidation of a 2,4-bis[(alkylthio)methyl]phenol and addition reactions to quinonemethides

The 2,4-bis-functionalized phenol 1 is dehydrogenated regioselectivity with potassium ferricyanide, affording the corresponding p-quinonemethide 2 . Hydrolysis of 2 affords a mixture of dithioacetal 5a and benzaldehyde 6 ; 1,6-addition of thiols to 2 gives the dithioacetals 5 of benzaldehyde 6 ; reaction of 2 with 2,2′-azobis(isobutyronitrile) (= 2,2′-dimethyl-2,2′-azobis(propanenitrile)) leads to 9a, 9b , and 10 , addition products of the 1-cyano-1-methylethyl radical. The structures of all products are confirmed mainly by ¹H- and ¹³C-NMR spectroscopy, and the mode of their formation is discussed.     

Thermolyse von 1,2,3-thiadiazolen

Thermolysis of 1,2,3-thiadiazoles leads to nitrogen and primary fragments, which are able to react on several routes. The rearrangement to thioketenes is particularly useful for the synthesis of thiocarboxylic acid-O-esters, which are formed in the presence of alcohols.     

Total synthesis of the microtubule stabilizing antitumor agent laulimalide and some nonnatural analogues: the power of Sharpless' asymmetric epoxidation

Three different routes are described for the synthesis of deoxylaulimalide (3), which is the immediate precursor of the marine sponge metabolite laulimalide (1). These routes mainly differ with respect to their ring closing step. Thus, route 1 uses a Still-Gennari olefination, route 2 a Yamaguchi lactonization, and route 3 an intramolecular allylsilane-aldehyde addition for establishing the macrocyclic structure. The unprotected deoxy derivative 3 was subjected to Sharpless' asymmetric epoxidation (SAE). With (R,R)-tartrate the 16,17-epoxide laulimalide (1) is formed selectively, whereas (S,S)-tartrate generates the 21,22-epoxide 142. This demonstrates the high reagent control involved in the SAE process, which in this case is used to achieve high stereo- and regioselectivity. Laulimalide and some derivatives thereof have been tested with respect to antitumor activity and compared to standard compounds paclitaxel and epothilone B.     

Cyclometalation of arylazo compounds. Part 2Regioselectivity of the Cyclopalladation of Some Substituted 1-Arylazonaphthalenes. 2nd Communication on Compounds with a Metal-Arene σ-Bond

A variety of cyclopalladated 1-arylazonaphthalenes is described, where ortho-palladation occurs at C(2) in the naphthyl ring or at C(2′ or 6′) in the phenyl moiety. Two examples of Peri-cyclopalladation at C(8) in the naphthyl ring are presented. The electronic and steric-influences of substituents at either arene moiety on the relative basicities of the azo-N-atoms and the relative nucleophilicities of the potential palladation sites C(2), C(2′ or 6′), and C(8) are discussed qualitatively in order to rationalize the observed regioselectivity.