Cobalamin coenzymes cobaloximes

Cobalamin and Cobaloxime Substitution Reactions.— The substitution kinetics of vitamin Biaa with 8-azaguanine and 6-mercaptopurine have been investigated in aqueous media at 25 °C and ionic strength 0.1 M. The complex pH dependences are interpreted in terms of reactions of the base on aquocobalamin with protonated and deprotonated forms of the ligands. Rate constants are listed in Table 7 and are consistent with a dissociative interchange mechanism. A similar mechanism is likely in the substitution reaction of cyanocobalamin with [Fe(CN)e] . Both base on and base off forms of the coenzyme are reactive. 

R. B. Silverman and D. Dolphin (1973), A direct method for cobalt-carbon bond formation in cobalt(III)-containing cobalamins and cobaloximes. Further support for cobalt (III) r-complexes in coenzyme B12 dependent rearrangements. J. Amer. Chem. Soc. 95, 1686-1688. 

Bis[2,3-butanedione dioximato(l-)] cobalt derivatives (cobaloximes(I)) appear in most respects to be good model systems for the cobalamins of the vitamin B12 coenzyme.1 The central cobalt atom exhibits three stable oxidation states... 

We shall report here the synthesis of cobalt-carbon bond involved in coenzyme B12 and cobalamine, cobaloxime, and Schiff base analog models, together with some aspects of their reactivity. 

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