Iron complexes hydrolysis

Diastereoselective intermolecular nitrile oxide—olefin cycloaddition has been used in an enantioselective synthesis of the C(7)-C(24) segment 433 of the 24-membered natural lactone, macrolactin A 434 (471, 472). Two (carbonyl)iron moieties are instrumental for the stereoselective preparation of the C(8)-C(ii) E,Z-diene and the C(i5) and C(24) sp3 stereocenters. Also it is important to note that the (carbonyl)iron complexation serves to protect the C(8)-C(ii) and C(i6)-C(i9) diene groups during the reductive hydrolysis of an isoxazoline ring. 

Iron complex-catalyzed isomerization of allylic alcohols was found during the studies on the hydrolysis of 7t-allyliron tricarbonyl salts. The isomerization of allyl alcohol to propionaldehyde was observed on heating in the presence of Fe(CO)s (Equation (9)).30... 

In a related study, the diphenolic substrate 409 was oxidized with a large excess of the iron complex [Fe(DMF)3Cl2][FeCl4] to give the spirodienone 413 in 35% yield (193). The oxidative phenolic coupling of 409 to furnish 413 using vanadium oxytrichloride had been previously reported, but the yield was slightly lower (176). Alkaline hydrolysis of 413 to cleave the A -trifluoroacetamide pro-... 

In the rapid alkaline hydrolysis of thienotropylium salt 228a, two isomeric carbinols (tropols), 592a and b (Scheme 159), were detected (69ZOB2601). Likewise, tetracyclic pyrrole 335 on hydrolysis gives the tropol, whereas deprotonation (Section IV,B,4,b) occurs in the presence of anhydrous tri-ethylamine (72CB1224). Another tropol, 597 (Scheme 160), is obtained from iron complex 285 (78AJC1607). 

Azepine derivatives form a diene complex with (tricarbonyl)iron, leaving the third of the double bonds uncomplexed. If the 3-position is substituted, two different such complexes are possible and are in equilibrium, as seen in the 11 NMR spectrum. An ester group in the 1-position of the complex can be removed by hydrolysis to give an NH compound that, in contrast to the free 1 //-azcpinc, is stable (Scheme 82). The 1-position can then be derivatized in the manner usual for amines. The same (tricarbonyl)iron complex can, by virtue of the uncomplexed 2,3-double bond, serve as a dienophile with 1,2,4,5-tetrazines. The uncomplexed N-ethoxycarbonylazepine also adds the tetrazine, but to the 5,6-double bond. Thus, two isomeric adducts can be synthesized by using or not using the complex (Scheme 83). 

In common with most laboratories engaged in fundamental research on proteins, our laboratory has studied the denaturation and renaturation of proteins. Many of these studies have been with the two related homologous iron-binding proteins, human serum transferrin and chicken ovotransferrin. Earlier studies showed that on the binding of iron these proteins were greatly stabilized against denaturation by a variety of environmental stresses as well as to chemical scission of their disulfide bonds and to hydrolysis by proteolytic enzymes (8,9j. Such a seemingly simple question as to why these iron complexes, as well as some other proteins, are much more stable than others is still impossible to answer with presently available information. 

FhuD delivers the ferric-siderophore complex to the FhuBC complex in the cytoplasmic membrane. FhuB is an intrinsic cytoplasmic membrane protein through which the iron complex can pass, driven by energy supplied by ATP hydrolysis catalyzed by the ATPase FhuC. Ferrous iron may be released from the hydroxamate via reduction by the reductase FhuF, which is loosely associated with the cytoplasmic membrane and, like FhuD, appears to have a lower specificity than FhuA and is active with coprogen and ferrichrome. ... 

The reaction of (—)-151 with imines such as 2-methyl-l-pyrrolidine illustrated in Scheme 33 affords complex 222. An X-ray structure of 222 shows that the coordinated imine is oriented perpendicular to the 1,2-azaborolyl ring. This orientation which contrasts with that assumed for 219 must be due to the greater steric bulk of the imine. Reaction of 222 with allylmagnesium bromide gives 223 with excellent stereoselectivity. Hydrolysis affords the free amine 224. The reactions illustrated in Schemes 32 and 33 demonstrate that 1,2-azaborolyl iron complexes can efficiently transfer chirality to B-bound organic substrates. The development of catalytic versions of these stoichiometric reactions would be a highly desirable extension of this work. 

N, 6-N-di(2,3-dihydroxybenzoyl)-L-lysine (58) is a siderophore produced by Azotobacter vinelandii which has only two catechol groups. However, of the catecholate siderophores by far the best studied is enterobactin. A major difference between hydroxamate and catecholate siderophores occurs in their utilization as transport agents. For the former, the iron complex is taken up by the bacterial cell, the iron released, and the hydroxamate siderophore re-secreted for additional iron chelation. In contrast, enterobactin is destroyed by enzymatic hydrolysis within the cell and therefore the ligand is not recycled. This hydrolysis of the amide linkages of the iron(III) enterobactin lowers the redox potential of the chelate complex sufficiently to allow iron reduction — and thus uptake of iron into the cell metabolism (59, 60). 

Unlike the corresponding iron complexes, aroylnickel carbonylates give acyloins instead of aldehydes by hydrolysis with aqueous methanol containing hydrochloric acid. In reactions at higher temperature, or by treatment with bromine, a-diketones are formed 85L... 

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