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M. Puchberger, R. Konrat, B. Kräutler, U. Wagner, C. Kratky:
"Reduction-Labile Organo-cob(III)alamins via Cob(II)alamin: Efficient Synthesis and Solution and Crystal Structures of [(Methoxycarbonyl)methyl]cob(III)alamin";
Helvetica Chimica Acta, 86 (2003), 5; 1453 - 1466.

An efficient synthesis of Coß-[(methoxycarbonyl)methyl]cob(III)alamin (6) is reported as an example of a new method for the preparation of some easily reducible organo-cob(III)alamins via the alkylation of cob(II)alamin. The procedure represents a considerable improvement compared to earlier methods that were based on an alkylation of cob(I)alamin. Thus, aquacob(III)alamin chloride (5⁺Cl) was reduced to cob(II)alamin (4), either by controlled potential electrolytic reduction or with an excess of sodium formate as reducing agent. The solution of 4 was then treated with an excess of methyl bromoacetate while being reductively poised potentiostatically or kept reduced by the formate, to give crystalline 6 in a yield of up to 91%. The structure of 6 in aqueous solution was mainly established by the completely assigned ¹H^- and ¹³CNMR spectra (Table 1). The NOE data (Table 2) were best rationalized by the presence of a single main conformation of the (methoxycarbonyl)methyl ligand. Single crystals of 6 were obtained by crystallization from an aqueous solution, and the crystal structure was determined by X-ray analysis at cryotemperatures. The NMR and crystallographic data of 6 indicated similar structures in aqueous solution and in the crystal with the (methoxycarbonyl)methyl ligand preferring a southern' orientation in each case.

http://dx.doi.org/10.1002/hlca.200390129