Iron tethering

Huq, I., Tamilarasu, N., and Rana, T.M. (1999) Visualizing tertiary folding of RNA and RNA-protein interactions by a tethered iron chelate analysis of HIV-1 Tat-TAR complex. Nucleic Acids Res. 27, 1084-1093. 

Bodenant B, Fages F, Delville MH (1998) Metal-induced self-assembly of a pyrene-tethered hydroxamate ligand for the generation of multichromophoric supramolecular systems. The pyrene excimer as switch for iron(III)-driven intramolecular fluorescence quenching. J Am Chem Soc 120 7511-7519... 

In other reports, /i-cyclodcxtrins have been used to induce asymmetry in borohydride reduction of ketones,166 a diastereoselective reduction has been controlled167 by a real lyltricarbonyl iron lactone tether , a phosphinamide has been combined with a dioxaborolidine unit as an activated, directed catalyst for ketone reduction,168 reductive amination using benzylamine-cyanoborohydride converts 3-hydroxy ketones into syn-1,3-amino alcohols,169 l-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propan-l-one has been reduced diastereoselectively,170 and production of chiral alcohols via (i) Itsuno-Corey and Brown procedures171 and (ii) lithium aluminium hydride modified by chiral nucleophiles172 has been reviewed. 

An Fe(II) complex with a tethered axial thiolate has also been prepared (12.29) as the CO adduct. This complex exhibits UV-visible and magnetic circular dichroism spectra similar to the analogous CO complexes of the iron P-450 family. 

Cyclization of trienes.1 In combination with 2,2-bipyridyl (bpy), an iron(O) species prepared by reduction of iron(III) 2,4-pentanedionate with A1(C2H5)3 (3 equiv.) promotes cyclization of trienes (1) in which a 1,3-diene unit is tethered to an ally lie or homoallylic ether group. vic-Disubstituted cyclopentanes or cyclohexanes are formed, and the cisltrans disposition of the substituents is controlled by the geometry of the allylic double bond. Thus (Z,E-)1 is cyclized to trans-2, whereas (E,E)-1 is cyclized to cis-2. 

Two measures to reproduce the key aspects of the enzyme have had some success to use an aromatic thiol and to block attack on the iron by building organic frameworks over the metal. Other approaches, illustrated in Fig. 4.10, include substituting iron with manganese, which is less sensitive to aerial oxidation, and to tether a cyclodextrin to the porphyrin so that the organic substrate could be positioned correctly for oxidation. 

Baylis-Hillman adducts such as 55 and 56 derived from 2-nitrobenzaldehydes were shown to function as useful precursors to functionalized (1H)-quinol-2-ones and quinolines. Treatment of 55 and 56 with iron and acetic acid at 110 °C afforded 57 and 58, respectively <02T3693>. A variety of other cyclization reactions utilized in the preparation of the quinoline scaffold were also reported. An iridium-catalyzed oxidative cyclization of 3-(2-aminophenyl)propanols afforded 1,2,3,4-tetrahydroquinolines <02OL2691>. The intramolecular cyclization of aryl radicals to prepare pyrrolo[3,2-c]quinolines was studied <02T1453>. Additionally, photocyclization reactions of /rans-o-aminocinnamoyl derivatives were reported to provide 2-quinolones and quinolines <02JHC61>. Enolizable quinone and mono- and diimide intermediates were shown to provide quinolines via a thermal 6jt-electrocyclization <02OL4265>. Quinoline derivatives were also prepared from nitrogen-tethered 2-methoxyphenols. The corresponding 2-methoxyphenols were subjected to a iodine(III)-mediated acetoxylation which was followed by an intramolecular Michael addition to afford the quinoline OAc O... 

Veal is a specialty meat that is produced from young animals that are kept in very close confinement for their entire lives. The highest-quality, epicurean veal is pale-colored and very tender. To achieve this product grade, veal calves are tethered and confined closely so they cannot move very much, and they are fed a diet that is highly deficient in iron, which helps to lighten the color of their flesh. They are also removed from their mothers before they are fully weaned, because a milk diet also promotes the development of a less tender, red-colored flesh. 

Hydroxyl radical induced strand scission is used for probing of the ribose moiety. The probe is insensitive to local conformations and not useful for detailed structural predictions however, the nonselective reactivity and small size makes hydroxyl radical probing a powerful approach for footprinting proteins on RNA. Recently methods have been developed where the hydroxyl radicals are generated locally by attaching the iron ion, which catalyses the radical formation in the Fenton reaction, to specific sites on RNA binding proteins. RNA located in the neighborhood of the tethered Fe2+ will then be modified selectively.7,8... 

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