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- W2017280141 abstract "Ausgehend von der vielfachen Ähnlichkeit im chemischen Verhalten von lichtangeregtem Flavin und Proteingebundenem Flavin haben wir die Flavinabhängige Photodehydrierung systematisch untersucht: 3-Benzyllumiflavin (1) reagiert photochemisch mit Carbonsäuren wie 3-Indolessigsäure, Phenoxyessigsäure oder (tert-Buty1thio)essigsäure unter Decarboxylierung und Bildung der 4a-alkylierten 4a,S-Dihydroflavinderivate 3a- c. In Gegenwart von Thiodiessigsäure oder Dithiodiessigsäure entsteht das 5-Carboxymethyl-1,5-dihydroflavin-derivat 4 a bzw. das 4a-(Carboxymethy1thio)derivat 3d. - Alkylsulfide werden in α-Stellung unter Ausbildung von 5-substituierten 1,5-Dihydroflavinderivaten angegriffen, die, wenn β-CH2-Gruppen vorhanden sind, einer trans-Eliminierung unterliegen; im Fall des Thiolans ist das Addukt 4d aufgrund sterischer Hinderung stabil. Mit Benzaldehyd entsteht das 5-Benzoyl-l,5-dihydroderivat 4e. - Alkene werden in Allylstellung angegriffen, wobei die 4a-alkylierten 4a,5-Dihydroderivate 3e- g gebildet werden. Mit 1,4-Cyclohexadien entsteht 1,5-Dihydroflavin 4c ebenso wie mit Cycloheptatrien, im letzteren Fall oxidiert das entstandene Tropyliumkation im Dunkeln 4 c zu 1 zurück. Alle diese Reaktionen verlaufen über den ersten angeregten Triplettzustand; sie erfordern nicht notwendigerweise Radikalpaare,sondern können viel eher als ein elektrophiler Angriff des angeregten Flavins (3FlOx*) verstanden werden. Eine Spaltung von R-H in Carbeniumion und Hydridion tritt also nicht auf. - Die Flavinsubstituenten sind bis auf verständliche Ausnahmen äußerst leicht wieder abzuspalten, obwohl hier σ-Bindungen vorliegen. Der Ort der Fixierung des Substrates am Flavin hängt von der Natur des Substituenten ab : Elektrophile Gruppen treten vorzugsweise an N5, nucleophile an C4a auf. Reductive Photoalkylation of the Flavin Nucleus; Structure and Reactivity of the Photoproducts On the basis of the manifold similarities between flavin photochemistry and flavin biocatalysis, we have made an effort toward systematic investigation of flavin-dependent photodehydrogenation: 3-benzyllumiflavin (1) reacts photochemically with carboxylic acids, e. g. 3-indoleacetic acid, phenoxyacetic acid and (tert-buty1thio)acetic acid, to give 4a-alkylated 4a,5-dihydro-flavin derivatives 3a-c and COz. In the presence of thiodiacetic acid and dithiodiacetic acid the 5-carboxymethyl-l,5-dihydroflavin derivative 4a and the 4a-carboxymethylthio derivative 3d, respectively, are formed.- Alkyl sulfides are attacked in the cr-position yielding 5-substituted 1,5-dihydroflavin derivatives, which undergo trans-elimination if P-CHz-groups are present; in the case of the thiolane the adduct 4d is found to be stable because of sterical hindrance. With benzaldehyde the 5-benzoyl-l,5-dihydro derivative 4e is formed. - Alkenes are attacked in the allylic position yielding 4a-alkylated 4a,5-dihydro derivatives, 3e - g. In the presence of 1,4-cyclohexadiene the 1,5-dihydroflavin 4c is formed, as also in the case of cycloheptatriene, where the resulting tropylium cation reoxidizes 4c back to 1. These reactions, which start from the first excited triplet state, do not necessarily proceed via radical pairs; in many cases they may be interpreted in terms of an electrophilic attack by the excited flavin (3F1,*). Cleavage of R-H into carbenium ion and hydride ion does not occur.- With some reasonable exceptions, the flavin substituents can be removed easily, although they are attached via 0-bonds. The preferred site of the flavin substitution depends on the nature of the substituent: electrophilic groups occur mainly at NS, nucleophilic ones at C4a." @default.
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- W2017280141 date "1976-12-06" @default.
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- W2017280141 title "Reduktive Photoalkylierung des Flavinkerns; Struktur und Reaktivität der Photoprodukte" @default.
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