Synthesis and Characterization of a Novel Green Cobalt Corrinoid<sup>1</sup>

Brown, Kenneth L.; Cheng, Shifa; Zubkowski, Jeffrey D.; Valente, E.

doi:10.1021/ic9513088

Cited by 8 publications

(6 citation statements)

References 26 publications

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“…The corrin fold angle (the angle between the mean planes through N21ϪC4ϪC5ϪC6ϪN22ϪC9ϪC10 and C10ϪC11ϪN23-C14ϪC15ϪC16-N24 [32] ) in SCNCbl is 4°); of the cobalt corrinoid structures reported to date only cyano-13-epi-cobalamin [33] has a larger fold angle (23.7°). The fold angle in SeCNCbl is much smaller (13.7°), close to the average corrin fold angle of about 14°.…”

Section: The Corrin Foldmentioning

confidence: 99%

Probing the Nature of the Co^IIIIon in Cobalamins − Spectroscopic and Structural Investigations of the Reactions of Aquacobalamin (Vitamin B_12a) with Ambident Nucleophiles

et al. 2003

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The rate of substitution of the H2O β‐ligand in aquacobalamin (vitamin B12a) is surprisingly fast for CoIII. This may arise as a result of transfer of electron density to CoIII by the corrin, conferring on the metal atom a softer and more labile character, and would require electronic communication between the equatorial ligand and the axial coordination sites of the metal atom. We have substituted H2O in B12a with the ambidentate nucleophiles SCN−, SeCN−, NO2− and S2O32−, examined the UV/Vis spectra of the resultant complexes, crystallised them, and determined their structures by X‐ray diffraction methods. The UV/Vis spectra of these complexes, as well as those of H2OCbl+, SO3Cbl− and MeCbl, were fitted by Gaussian functions. The principal bands move to lower energy in response to an increase in donation of electron density from the axial ligand, demonstrating direct electronic communication between the axial and the equatorial ligands. In the solid state, the thiocyanato ligand in SCNCbl is coordinated through N, although 13C NMR spectroscopy shows that the complex exists as a mixture of two linkage isomers in solution. SeCN−, NO2− and S2O32− are coordinated through the softer available donor in each case (Se, N and S, respectively). There is a regular ground‐state trans effect such that as the donor power of the β‐ligand increases, the trans Co−Nax bond length increases. A survey of the structures available in the CSD shows that this preference for the softer donor atom in ambidentate nucleophiles is not unusual in CoIII complexes. The Co−N bond length in SCNCbl is marginally long for coordination to CoIII, but the axial bond lengths of the other complexes are as expected. Hence, whereas the corrin macrocycle clearly imparts lability on CoIII, presumably by transfer of electron density onto the metal atom, this is insufficient to have a major effect on the ground‐state structures of its complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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Section: The Corrin Foldmentioning

confidence: 99%

Probing the Nature of the Co^IIIIon in Cobalamins − Spectroscopic and Structural Investigations of the Reactions of Aquacobalamin (Vitamin B_12a) with Ambident Nucleophiles

et al. 2003

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“…None of these methods were successful in producing 1 . However, since the amine, 5 , can be obtained from CNCbl- c -COO - via a modified Curtius reaction in reasonable yield, an attempt was made to hydrodeaminate 5 under modified Kollonitsch conditions …”

Section: Resultsmentioning

confidence: 99%

“…To this end, we have attempted the synthesis of a Cbl analog, 1 , in which the c side chain is truncated to a methyl group. To our surprise, the deamination of the recently reported CNCbl- c -NH 2 complex, 5 (Scheme ), gave instead a novel analog in which the C(7) corrin ring carbon is devoid of substituents due to an apparent rearrangement of the B pyrrole and its substituents. The synthesis, characterization, and kinetics of homolysis of the Np derivative of this interesting Cbl analog are the subject of this report.…”

Section: Introductionmentioning

confidence: 91%

Side Chain Entropy and the Activation of Organocobalamins for Carbon−Cobalt Bond Homolysis: Synthesis, Characterization, and Thermolysis of the Neopentyl Derivative of a Unique Cobalamin Analog Lacking a c Side Chain

et al. 1997

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Hydrodeamination of the c-amino derivative, 5, of cyanocobalamin (CNCbl) with hydroxylamine-O-sulfonic acid in aqueous base leads to an extensively rearranged product instead of the c side chain truncated derivative, 1, expected from simple deamination. The rearranged product (CNCbl-8-butanamide) crystallizes in the orthorhombic system, space group P2(1)2(1)2(1) with unit cell dimensions a = 16.041(11), b = 21.94(2), and c = 25.43(2) Å. It is devoid of substituents at corrin ring C(7) but quarternized at C(8) with an "upwardly" pseudoaxial methyl group and a d side chain expanded by one methylene group to a butanamide. The corrin ring of this rearranged derivative is significantly flatter (corrin ring fold angle 9.9 degrees ) than CNCbl itself (fold angle 18.0 degrees ). Conversion of CNCbl-8-butanamide to its neopentyl derivative (NpCbl-8-butanamide), a NpCbl analog which lacks a c acetamide side chain, permits a quantitative assessment of the influence of thermal motions of the c side chain on the entropy of activation for carbon-cobalt bond thermal homolysis in NpCbl. NpCbl-8-butanamide is shown to thermolyze homolytically to give products derived from the Np(*) radical quantitatively. The kinetics of the thermolysis of NpCbl-8-butanamide were studied in aerobic aqueous solution at temperatures between 15 and 45 degrees C. After correction of the observed first-order rate constants for the presence of the essentially unreactive base-off species using an established NMR method, an Eyring plot yields the activation parameters DeltaH()(on) = 26.7 +/- 0.1 kcal mol(-)(1) and DeltaS()(on) = 13.2 +/- 0.2 cal mol(-)(1) K(-)(1). While the enthalpy of activation is slightly reduced (6%) from that of NpCbl, the entropy of activation is reduced by 6.1 +/- 0.6 cal mol(-)(1) K(-)(1), or 32 +/- 3%. The c side chain thus contributes about one-third of the total entropic activation of NpCbl for carbon-cobalt bond homolysis, and the entropy of activation for this reaction is probably dominated by changes in the thermal motions of the "upwardly" pseudoaxial a and c acetamide side chains as the reaction progresses.

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“…Brown first showed that treatment of (CN)Cbl(c-NH 2 ) 54, synthesized from (CN)Cbl(c-NHCO 2 CH 3 ), with a basic solution under strict anaerobic conditions leads to complete elimination of the c-position forming the green corrinoid 55 in 95% yield (Scheme 14). 32 On the other hand incubation of (CN)Cbl 1 with a milder base e.g. 0.2 M NaHCO 3 for 3 weeks at 50 1C slightly cracks the B-ring giving blue corrinoid 56 in a low yield of 6% (Scheme 15).…”

Section: Modifications To the Macrocyclementioning

confidence: 99%

Vitamin B12: chemical modifications

2013

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Vitamin B12 plays a key role in many metabolic processes occurring in all mammals. Over the years its biological role has been extensively studied generating a lot of interest in the chemistry of this vital molecule. This established a variety of new methodologies for the synthesis and analysis of new cobalamin derivatives as well as creative purification techniques. This tutorial review summarizes all the advancements made in this area, providing a deeper insight into vitamin B12 chemistry.

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Synthesis and Characterization of a Novel Green Cobalt Corrinoid¹

Cited by 8 publications

References 26 publications

Probing the Nature of the Co^IIIIon in Cobalamins − Spectroscopic and Structural Investigations of the Reactions of Aquacobalamin (Vitamin B_12a) with Ambident Nucleophiles

Probing the Nature of the Co^IIIIon in Cobalamins − Spectroscopic and Structural Investigations of the Reactions of Aquacobalamin (Vitamin B_12a) with Ambident Nucleophiles

Side Chain Entropy and the Activation of Organocobalamins for Carbon−Cobalt Bond Homolysis: Synthesis, Characterization, and Thermolysis of the Neopentyl Derivative of a Unique Cobalamin Analog Lacking a c Side Chain

Vitamin B12: chemical modifications

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Synthesis and Characterization of a Novel Green Cobalt Corrinoid1

Cited by 8 publications

References 26 publications

Probing the Nature of the CoIIIIon in Cobalamins − Spectroscopic and Structural Investigations of the Reactions of Aquacobalamin (Vitamin B12a) with Ambident Nucleophiles

Probing the Nature of the CoIIIIon in Cobalamins − Spectroscopic and Structural Investigations of the Reactions of Aquacobalamin (Vitamin B12a) with Ambident Nucleophiles

Side Chain Entropy and the Activation of Organocobalamins for Carbon−Cobalt Bond Homolysis: Synthesis, Characterization, and Thermolysis of the Neopentyl Derivative of a Unique Cobalamin Analog Lacking a c Side Chain

Vitamin B12: chemical modifications

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Synthesis and Characterization of a Novel Green Cobalt Corrinoid¹

Probing the Nature of the Co^IIIIon in Cobalamins − Spectroscopic and Structural Investigations of the Reactions of Aquacobalamin (Vitamin B_12a) with Ambident Nucleophiles

Probing the Nature of the Co^IIIIon in Cobalamins − Spectroscopic and Structural Investigations of the Reactions of Aquacobalamin (Vitamin B_12a) with Ambident Nucleophiles