Flavine und Zimtsäurederivat im Zusammenhang mit der lichtinduzierten Blattöffnung bei Albizia julibrissin

Flavins and Chinamoyl Derivatives in Relation to the Light-induced Leaf Opening in Albizia julibrissin In search of blue-light photoreceptors for light-induced leaf opening we isolated from the aqueous extract of Albizia julibrissin Durazz. two flavins by adsorption on XAD-4 and separation with HPLC. One sample was identified as riboflavin 1a. In the hydrolysate of the second flavin fraction we found another dimethylisoalloxazine with a C₅-side chain. Furthermore we isolated the cinnamoyl derivatives 3-O-(4-hydroxy-trans-cinnamoyl) quinic acid 2 and 3-O-(3,4-dihydroxy-trans-cinnamoyl)-4-O-malonyl-quinic acid 3 which formed charge transfer complexes with the flavins in the XAD-fraction. As a model complex we examined the absorption behaviour of the complex between riboflavin and chlorogenic acid. Using the association constant, we calculated the absorption spectrum and could show that a complex between a flavin and a phenolic compound is a possible blue-light photoreceptor for the light-induced leaf opening in Albizia julibrissin.     

TcdB of Clostridioides difficile Mediates RAS-Dependent Necrosis in Epithelial Cells

A Clostridioides difficile infection (CDI) is the most common nosocomial infection worldwide. The main virulence factors of pathogenic C. difficile are TcdA and TcdB, which inhibit small Rho-GTPases. The inhibition of small Rho-GTPases leads to the so-called cytopathic effect, a reorganization of the actin cytoskeleton, an impairment of the colon epithelium barrier function and inflammation. Additionally, TcdB induces a necrotic cell death termed pyknosis in vitro independently from its glucosyltransferases, which are characterized by chromatin condensation and ROS production. To understand the underlying mechanism of this pyknotic effect, we conducted a large-scale phosphoproteomic study. We included the analysis of alterations in the phosphoproteome after treatment with TcdA, which was investigated for the first time. TcdA exhibited no glucosyltransferase-independent necrotic effect and was, thus, a good control to elucidate the underlying mechanism of the glucosyltransferase-independent effect of TcdB. We found RAS to be a central upstream regulator of the glucosyltransferase-independent effect of TcdB. The inhibition of RAS led to a 68% reduction in necrosis. Further analysis revealed apolipoprotein C-III (APOC3) as a possible crucial factor of CDI-induced inflammation in vivo.     

Pyryliumverbindungen. 38. Zur Ringtransformation von 2,4,6-Triaryl-thiopyryliumsalzen mit Essigsäureanhydrid zu Arylbenzenen und Thiobenzophenonen

Pyrylium Compounds. 38. About the Ring Transformation of 2,4,6-Triarylthiopyrylium Salts by Acetic Acid Anhydride to Arylbenzenes and Thiobenzophenones 2,4,6-Triarylthiopyrylium salts 5 react in the presence of an appropriate condensing agent (sodium acetate, carbonate, methoxide, tert-butoxide or potassium acetate) with acetic acid anhydride to yield arylbenzenes 3 and thiobenzophenones 6 . This ring transformation represents the first example of the conversion of the moiety into the thiocarbonyl group Under the same conditions 3,5-dimethyl-2,4,6-triphenylthiopyrylium perchlorate ( 13 ) forms via [1,5]-sigmatropic rearrangement the thiobenzophenone 15 . The structure of the new compounds 6 was proved by spectroscopic methods as well as by degradation reactions. Thus, hydrogen peroxide converts 6a to the known benzophenone 4 . Alkaline saponification gives the 2-hydroxy-benzophenone 8 , whereas heating with hydrochloric acid causes a selective cleavage of the acetoxy group to the 2-hydroxy-thiobenzophenone 7 .     

Pyryliumverbindungen. XVIII, 2-Alkoxy-2H-pyrane aus tetra- und pentasubstituierten Pyryliumsalzen

Pyrylium Compounds. XVIII. 2-Alkoxy-2H-pyrans from Tetra- and Pentasubstituted Pyrylium Salts Alkali alkoxides add regioselectively to 2,3,4,6-tetrasubstituted pyrylium salts 7 (R' H), affording high yields of colourless crystalline 2-alkoxy-2H-pyrans 9 . The latte are also formed simply on refluxing 7 in the corresponding alcohol with triethylamine as proton acceptor. 3,5-Dialkylsubstituted 2,4,6-triarylpyrylium salts react analogously. The 2H-pyran structure of the adducts obtained follows from their n.m.r., i.r., u.v. and mass spectra as well as from their reaction with tetracyanoethylene to cycloadducts of type 10 . Acids regenerate from 9 the original pyrylium cations, whereas reaction of 9 with nitromethane or ethyl cyanoacetate provides benzene derivatives. -- The novel starting pyrylium salts 7b--o are characterized by u.v./vis data and by transformation into the corresponding pyridine derivatives     

Pyryliumverbindungen. 37. Arylbenzene aus 2,4,6-Triaryl-pyryliumsalzen und Carbonsäureanhydriden

Pyrylium Compounds. 37. Arylbenzenes from 2,4,6-Triarylpyrylium Salts and Carboxylic Acid Anhydrides Refluxing 2,4,6-triarylpyrylium salts 1 with excess carboxylic acid anhydrides (RCH₂CO)₂O ( 2a : R = H, 2b : R = Me) in the presence of condensing agents like sodium or potassium acetate, sodium carbonate or methoxide, triethylamine or pyridine results in 1,3,5-triarylbenzenes 3 (R = H, Me). Under similar conditions, phenylacetic acid anhydride ( 2c ), generated in situ from sodium phenylacetate and excess 2a or 2b , yields 1,2,3,5-tetraarylbenzenes 3 (R = Ph). Thus, the reaction 1 + 2 → 3 represents a new and simple method for replacing the pyrylium heteroatom =O^⊕– by the =CR– moiety (R = H, Me, Ph). The structure of the arylbenzenes 3 was proved by spectroscopic methods, by comparison with literature data or by independent synthesis. As by-products 2-acyloxy-benzophenones 10 are formed. Reaction of 3,5-dimethyl-2,4,6-triphenyl-pyrylium perchlorate ( 11 ) with acetic acid anhydride/sodium acetate (or sodium phenylacetate) takes another course leading to 2-acetoxy-3,5-dimethyl-4,6-diphenyl-benzophenone ( 15 ), whereas treatment of 11 with propionic acid anhydride/sodium acetate follows the reaction scheme 1 + 2 → 3 giving 1,3,5-trimethyl-2,4,6-triphenylbenzene ( 16 ). The mechanisms of the different pyrylium ring transformations are discussed.     

Untersuchungen zur Tautomerie von o,o'-Dihydroxy-azofarbstoffen der Eriochrom-Reihe

Investigations on the Tautomerism of o,o'-Dihydroxy Azo Dyes of the Eriochrome Type Investigation of the u.v.-vis-, ¹H- and ¹³C-n.m.r. spectra of the title substances and the isomers 3 and 3p at different pH-values and in different solvent mixtures as well as of O,O'-dimethyl derivatives of 2 and 3 show that in aqueous solution as well the monoanions as the trianions exist in the azo forms only. The dianions exist in dependence on the solvents as mixtures of tautomers. The results of PPP calculations for different prototropic structures are in good accordance with the experimental results.     

Pyryliumverbindungen. 31 [1]. Reaktion 3-alkylsubstituierter 2,4,6-Triaryl-pyryliumsalze mit 1,3-Diketonaten: Ein Weg zur Darstellung 3-acylsubstituierter Benzophenone

Pyrylium Compounds. 31. Reaction of 3-Alkyl-2,4,6-triarylpyrylium Salts with 1,3-Diketonates: A Method for the Preparation of 3-Acylsubstituted Benzophenones Reaction of 3-alkyl-2,4,6-triarylpyrylium salts with 1,3-diketones in the presence of one equivalent of triethylamine or potassium tert-butoxide does not lead — as originally suspected — to the primary adducts of 2H-pyran structure 6 , but to the open-chain valence isomers 7 . Treatment of the latter with one equivalent of tert-butoxide in tert-butyl alcohol gives the same 3-alkyl-2,4,6-triarylacetophenones 9 which are obtained directly from 5 , 1,3-diketones and two equivalents of potassium tert-butoxide. However, on treating 7 with aqueous ethanolic sodium hydroxide 3-acylsubstituted benzophenones 10 are formed in good yields. The reaction sequence 5→7→10 can also be performed through a one-pot-procedure. — The i.r., u.v., n.m.r. and mass spectroscopic data of the novel products 7, 9 , and 10 are reported.     

Ringöffnungs- und SubstitutionsReaktionen von 4,4-Dihalogen-pyrazolin-5-onen durch Nucleophile

Ring Opening and Substitution Reactions of 4,4-Dihalo-pyrazolin-5-ones with Nucleophiles 1-Aryl-4,4-dihalo-3-methyl-pyrazolin-5-ones ( 1a – c ) undergo ring opening with alkoxides and form alkyl 3-arylazo-2-halo-2-butenoats ( 2a – d ). Analogous reactions take place with ammonia and amines. 4-Nitro-phenoxide reacts with substitution of both halogens to the 4,4-bis(4-nitro-phenyl)-compound ( 5 ). Phenols are selectively orthobrominated by the title compounds 1a and b .