Eine einfache Methode zur Überführung von Flavanonen in Flavone¹)

Abstract

Flavanone lassen sich mit Iod in alkalischer Losung in Flavone uberfiihren. Die Hydroxylgruppen brauchen dabei nicht geschutzt zu werden. Diese Vereinfachung schlieSt im Fall der Glykoside auch die OH-Gruppen der Zucker ein.Flavanones can be converted into flavones by iodine in alkaline solution. The hydroxy groups don't have to be protected during this process. In the case of glycosides this simplification includes the OH groups of sugars.Flavanone und Flavone sind zwei Verbindungsklassen unter den Flavonoiden, die im Verhaltnis zweier Oxidationsstufen, oder priziser gesagt, in einem Dehydrierungs-kIydrierungsverhaltnis zueinander stehen. a: b: c: d: e: R 1 , R * , R 3 = O H , R 4 =OCH3 f: R', R2, R3, R4 = H R * = ORu, Rz, R3 = OH, R4 = OCH3 R 1 = ONe, R2, R3 =OH, R4 = OCH3 R1 = ONe, Rz, R4 =OH, R3 = H R1, R2, R4 = OH, R3 = H Abb. 1: Formeliibersicht Ru = Rutinosyl Ne = Neohesperidosyl Die Dehydrierung an C-2 und C-3 beseitigt die Asymmetrie an C-2 (s. Abb. 1) und bringt den y-Dihydropyranring aus der getwisteten in die flache Halbsesselform. Die Uberfiihrung von Flavanonen in Flavone ist naturlich nicht neu. Sie ist bereits mehrfach durchgefuhrt worden. So benutzte z. B. Kostanecki Brom in Schwefelkohlenstoff, um die Stammsubstanz Flavonzr3) (2a) sowie einige Hydro~y-flavone~.~) aus Flavanon la bzw . den entsprechenden Derivaten zu gewinnen.

Synthesis of 5‐Hydroxy‐3′,4′,7‐trimethoxyflavone and Related Compounds and Elucidation of Their Reversal Effects on BCRP/ABCG2‐Mediated Anticancer Drug Resistance

“…Complete hydrolysis of 9 to the aglycone hesperetin ( 10 ) required an increase in the reaction time from 2 h to 4 h and stronger dilution of 9 (from 7 %, w / v , to 3.5 %, w / v ) with 2 % sulfuric acid. Hesperetin ( 10 ) was dehydrogenated to diosmetin ( 11 ) according to a literature procedure . Methylation under conventional conditions furnished the desired 4 in a site‐selective manner.…”

“…Site‐selective deprotonation of 12 and subsequent condensation with acid chloride 13 furnished chalcone 14 a in 49 % yield, and this was followed by derivatization to 2‐hydroxychalcone 14 b by site‐selective cleavage of the methyl ether with boron tribromide to afford 14 b in 96 % yield. A combination of I 2 and pyridine for the oxidative cyclization of the 2‐hydroxychalcone furnished flavone 5 in quantitative yield.…”

“…Hesperetin (10)w as dehydrogenated to diosmetin (11)a ccording to a literaturep rocedure. [32] Methylation under conventional conditions furnished the desired 4 in asite-selective manner.…”

“…The synthesis of monoglycosylated 6 and diglycosylated 7 starting from 9 is summarized in Scheme . Dehydrogenation of 9 and subsequent acetylation provided peracetylated 15 a in 79 % yield from 9 . Compound 15 a was transformed into 15 b in 69 % yield by chemoselective removal of the phenolic acetates with sodium perborate without affecting the aliphatic or alicyclic acetyl protective groups .…”