Synthesis and Structural Characterization of Ferrocenyl-Substituted Aurones, Flavones, and Flavonols
摘要:
In the context of our studies on the modification of bioactive molecules with ferrocene, we here report the first examples of ferrocenyl flavonoids, where ferrocene replaces the B ring of the flavonoid skeleton. Ferrocenyl aurones possessing an electron-withdrawing or an electron-donating group in the 5'-position were obtained from 5'-R-2'-hydroxy-3-ferrocenyl chalcones via 1,5 oxidative exocyclization using Hg(OAc)(2) or AgOTf. Treatment of the ferrocenyl aurones with LDA resulted in a ring opening to form ferrocenyl ynones, which could then be selectively recydized to the flavone isomer by treatment with NaOEt. Ferrocenyl flavones were also obtained by isomerization of the aurones with KCN and were hydroxylated in the 3-position to form ferrocenyl flavonols with oxone in a biphasic reaction. In many cases the reactivity of the ferrocenyl compounds was significantly different from that of their organic analogues. This reactivity and regioselectivity can be rationalized by ferrocene's particular ability to destabilize alpha-anions in reaction intermediates. Representative examples of ferrocenyl aurones, ynones, and flavones were characterized by 2D NMR and X-ray crystallography, and the molecules all show a planar arrangement of the organic skeleton with the cyclopentadienyl ring of the ferrocene group. Putative MLCT bands in the visible region are responsible for the variety of highly saturated colors observed.
Synthesis and Structural Characterization of Ferrocenyl-Substituted Aurones, Flavones, and Flavonols
摘要:
In the context of our studies on the modification of bioactive molecules with ferrocene, we here report the first examples of ferrocenyl flavonoids, where ferrocene replaces the B ring of the flavonoid skeleton. Ferrocenyl aurones possessing an electron-withdrawing or an electron-donating group in the 5'-position were obtained from 5'-R-2'-hydroxy-3-ferrocenyl chalcones via 1,5 oxidative exocyclization using Hg(OAc)(2) or AgOTf. Treatment of the ferrocenyl aurones with LDA resulted in a ring opening to form ferrocenyl ynones, which could then be selectively recydized to the flavone isomer by treatment with NaOEt. Ferrocenyl flavones were also obtained by isomerization of the aurones with KCN and were hydroxylated in the 3-position to form ferrocenyl flavonols with oxone in a biphasic reaction. In many cases the reactivity of the ferrocenyl compounds was significantly different from that of their organic analogues. This reactivity and regioselectivity can be rationalized by ferrocene's particular ability to destabilize alpha-anions in reaction intermediates. Representative examples of ferrocenyl aurones, ynones, and flavones were characterized by 2D NMR and X-ray crystallography, and the molecules all show a planar arrangement of the organic skeleton with the cyclopentadienyl ring of the ferrocene group. Putative MLCT bands in the visible region are responsible for the variety of highly saturated colors observed.
Ferrocenyl-Appended Aurone and Flavone: Which Possesses Higher Inhibitory Effects on DNA Oxidation and Radicals?
作者:Jia-Feng Chen、Zai-Qun Liu
DOI:10.1021/tx500405b
日期:2015.3.16
The aim of the present work was to compare the antioxidative effect of the ferrocenyl-appended aurone with that of ferrocenyl-appended flavone; therefore, nine aurones together with the flavone-type analogues were synthesized by using chalcone as the reactant. The radical-scavenging property was evaluated by reacting with the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS'), 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH), and galvinoxyl radical, respectively. The cytotoxicity was estimated by inhibiting 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH)-induced oxidation of DNA. It was found that the introduction of the ferrocenyl group remarkably increased the radical-scavenging activities of aurone and flavone. Especially, the ferrocenyl group in flavones can quench radicals even in the absence of the phenolic hydroxyl group, while ferrocenyl-appended aurones can efficiently protect DNA against AAPH-induced oxidation. Therefore, the antioxidative effect was generated by the ferrocenyl group and enhanced by the electron-donating group attaching to the para-position of the ferrocenyl group. Introducing the ferrocenyl group into natural compounds may be a useful strategy for increasing the anticoddative effectiveness.
[EN] FERROCENYL FLAVONOIDS<br/>[FR] FLAVONOÏDES COMPRENANT UN GROUPE FERROCÉNYLE