Rare .alpha.-alkyl isomers of cobalamins: synthesis, characterization, and properties of two diastereomers of the .alpha.-alkylcobalamin, .alpha.-(2-oxo-1,3-dioxolan-4-yl)cobalamin

Alelyunas, Yun W.; Fleming, Paul; Finke, Richard G.; Pagano, Thomas G.; Marzillï, Luigi G.

doi:10.1021/ja00010a022

Cited by 29 publications

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“…The corrin ring (macrocyclic tetrapyrrole ring) does not possess a plane of symmetry, and consequently, there is a possibility of axial ligand diastereomerism when the two axial ligands are different. [7][8][9][10][11][12][13] The "upper", or β-face, of the corrinoid, with its upward projecting a, c and g acetamide side chain, is less sterically hindered than the "lower", or α-face, which is bracketed by the downward projecting b, d and e propionamides and the secondary amide f side chain. The electronic structure of the corrin ring has a significant effect on the properties of the Co() ion.…”

Section: Introductionmentioning

confidence: 99%

Kinetic and thermodynamic studies on the cyanation reactions and base-on/base-off equilibria of alkyl-13-epicobalamins

et al. 2003

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Ligand substitution equilibria of two different 13-epicobalamins (X-13-epiCbl, X = NCCH 2 and CN Ϫ ) with cyanide have been studied. It was found that CN Ϫ substitutes the 5,6-dimethylbenzimidazole (DMBz) moiety in the α-position to form X(CN)Cbl-13epi, which for X = NCCH 2 in the presence of CN Ϫ subsequently gives (CN) 2 Cbl-13epi. The kinetics of the displacement of DMBz by CN Ϫ showed saturation behaviour at high cyanide concentration and the limiting rate constants are characterized by the activation parameters:and ∆V ≠ = ϩ14.8 ± 0.5 cm 3 mol Ϫ1 . These parameters are interpreted in terms of a limiting D mechanism. The rate constants for the displacement of DMBz in the case of the 13-epicobalamins were found to be slower than those obtained in the case of the analogous alkylcobalamins, and consequently, the thermodynamic equilibrium constants for the 13-epicobalamins were found to be smaller than those obtained in the case of the alkylcobalmins. This clearly shows the effect of the epimerization of the e-side chain attached to the C-13 of the corrin ring on the rate and equilibrium constants for these ligand displacement reactions.

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Section: Introductionmentioning

confidence: 99%

Kinetic and thermodynamic studies on the cyanation reactions and base-on/base-off equilibria of alkyl-13-epicobalamins

et al. 2003

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“…In both compounds, the alkyl groups are attached to the Co-atom at the P(upper)-side of the corrin, as proven by X-ray analysis of (R)-and (S)-(2,3-dihydroxypropy1)cobalamin [6]. This is not obvious a priori, since alkylation of cob(1)alamin -even with sterically bulky secundary alkylation agents, containing electron-withdrawing substituents -may also take place at the t ( -side [7].…”

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confidence: 99%

Asymmetric Catalysis by Vitamin B₁₂. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

Bonhôte

Scheffold

1991

Helvetica Chimica Acta

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The isomerization of 1,2-epoxycyclopentane (1) to enantiomerically enriched (R)-cyclopent-2-enol (2) in protic solvents is catalyzed by coh(1)abdmin. The enantiomeric excess (e.e.) of (R)-2 is usually ca. 60%; it is only slightly dependent on the temperature, hut increases with decreasing dielectric constant E of the solvent. Standard kinetic methods show the reaction to be first order in vitamin B,, and zero order in 1. The rate constant increases exponentially with increasing E of the solvent. An Arrhenius plot at E = 40 gives activation parameters A H f = 78 + 4 kJ.mol-I and A S f = -49 ! C 1 J.mo1-I.K-l. The isomerization 1 + 2 proceeds in two steps (Schemes 2 and 7): i) The epoxide ring is first opened by the proton-assisted fast and irreversible nucleophilic attack of the chiral Co' catalyst to form diastereoisomeric (1 R,2R)-and (lS,2S)-(2-hydroxycyclopentyl)cob(III)alamins 6 in a ratio of ca. 4:l which are the dominant species in the steady state; ii) The intermediates 6 then decompose in the rate-limiting step to form 2 and recycled catalyst. Experiments with specifically 'H-labeled 1 showed the hydro-cobalt elimination 6 -+ 2 to be non-stereoselective. It proceeds via reversible Co-C bond homolysis to a free 2-hydroxycyclopentyl radical from which stereoelectronically controlled H-abstraction by Co" takes place.

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“…As noted above, 1 H NMR proved crucial to determining the purity of the C 6 F 5 SCbl product, particularly since extensive HPLC investigations failed to find conditions where C 6 F 5 SCbl is both stable and separable from other possible cobalamin contaminants . The aromatic 1 H NMR chemical shifts of C 6 F 5 SCbl in anaerobic CD 3 OD (δ = 7.17, 6.78, 6.42, 6.19(d), and 6.04 ppm at room temperature) are clearly different from those of the expected cobalamin contaminants, hydroxocobalamin, HOCbl (δ = 7.14, 6.84, 6.58, 6.16(d), and 6.11 ppm), or aquacobalamin, H 2 OCbl + (δ = 7.17, 6.81, 6.64, 6.18(d), and 6.11 ppm).…”

Section: Resultsmentioning

confidence: 99%

“…FABMS (in m -nitrobenzyl alcohol matrix) calcd molecular mass for [C 6 F 5 SCbl + H + ], C 68 H 89 O 14 N 13 F 5 PSCo, 1528.5; found, m / e 1528.6 ([M + H] + ) and 1329.6 ([(M + H) − C 6 F 5 S] + ) (Figures C and D of the Supporting Information). No HPLC conditions could be found where C 6 F 5 SCbl was stable …”

Section: Methodsmentioning

confidence: 99%

The Second Isolable B₁₂-Thiolate Complex, (Pentafluorophenylthiolato)cobalamin: Synthesis and Characterization

1998

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The synthesis, isolation, and characterization of (pentafluorophenylthiolato)cobalamin, C6F5SCbl, are reported, only the second isolable RSCbl known. The synthesis of C6F5SCbl in 81% yield is accomplished by the dropwise addition of 0.93 equiv of C6F5SH in MeOH under argon to 1 equiv of HOCbl·HOAc (50.7 mg) in MeOH, all at −15 °C and under darkened, red-light-only conditions. The desired C6F5SCbl product was precipitated by the addition of cold, degassed acetone, isolated, and then characterized by FABMS and UV−visible, 1H NMR, and 19F NMR spectroscopies. Also reported is a 1H NMR method for the detection of impurities in cobalamins. With the requisite, isolable RSCbl precursor to RS• and •Cbl radicals now in hand, the needed chemical precedent studies of the proposed H• abstraction step from the substrate in ribonucleoside triphosphate reductase by a RS• analogue of the protein−S• site are now possible.

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Rare .alpha.-alkyl isomers of cobalamins: synthesis, characterization, and properties of two diastereomers of the .alpha.-alkylcobalamin, .alpha.-(2-oxo-1,3-dioxolan-4-yl)cobalamin

Cited by 29 publications

References 0 publications

Kinetic and thermodynamic studies on the cyanation reactions and base-on/base-off equilibria of alkyl-13-epicobalamins

Kinetic and thermodynamic studies on the cyanation reactions and base-on/base-off equilibria of alkyl-13-epicobalamins

Asymmetric Catalysis by Vitamin B₁₂. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

The Second Isolable B₁₂-Thiolate Complex, (Pentafluorophenylthiolato)cobalamin: Synthesis and Characterization

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Rare .alpha.-alkyl isomers of cobalamins: synthesis, characterization, and properties of two diastereomers of the .alpha.-alkylcobalamin, .alpha.-(2-oxo-1,3-dioxolan-4-yl)cobalamin

Cited by 29 publications

References 0 publications

Kinetic and thermodynamic studies on the cyanation reactions and base-on/base-off equilibria of alkyl-13-epicobalamins

Kinetic and thermodynamic studies on the cyanation reactions and base-on/base-off equilibria of alkyl-13-epicobalamins

Asymmetric Catalysis by Vitamin B12. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

The Second Isolable B12-Thiolate Complex, (Pentafluorophenylthiolato)cobalamin: Synthesis and Characterization

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Asymmetric Catalysis by Vitamin B₁₂. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

The Second Isolable B₁₂-Thiolate Complex, (Pentafluorophenylthiolato)cobalamin: Synthesis and Characterization