抄録
In the transformation of a 1,2-diol to a deoxyaldehyde catalyzed by cobamide coenzyme, the reaction mechanism is supposed to be a direct hydrogen shift because of the absence of deuterium in the aldehyde prcduced in D_2O. It appears interesting to study whether the reaction may proceed through a transition state involving a substrate-coenzyme complex as an active intermediate. This paper deals with the syntheses and properties of several analogues of cobamide coenzyme containing hydroxyalkyl group linked to the cobalt atom. Co-β, γ-dihydroxypropyl-, Co-β-hydroxypropyl-, and Co-hydroxyethylcobalamins were prepared by reacting glycerol α-monochlorohydrin, propylene bromohydrin and ethylene chlorohydrin with hydridocobalamin, respectively. Co-β, γ-dihydroxypropylcobinamide was synthesized by the reaction of gycerol α-monochlorohydrin with a reduced product of codinamide with NaBH_4. Absorption spectra of the three hydroxyalkyl derivatives of cobalamin were similar to those of cobamide coenzymes or Co-alkylcobalamins, e. g. Co-methylcobalamin, and the spectrum of the hydroxyalkyl cobinamide was analogous to those of cobinamide coenzyme or Co-alkylcobinamide. These four compounds, alike cobamide- and cobinamide coenzymes, were very unstable in light and almost completely decomposed. When allowed to stand in the dark in 0.017 M KCN solution, they only partly converted to dicyano-forms alike the alkyl derivatives. Hydroxyalkylcobalamin, for example β, γ-dihydroxypropylcobalamin, showed almost equal activity on vitamin B_<12>-requiring microorganism. However, these compounds did not only exhibit the coenzyme activity, but also exerted an inhibitory effect, alike the alkyl derivatives, in the Abeles・Lee's dioldehydrase system. From the result it would be concluded that the hydroxyalkyl derivatives of cobamide coenzyme so far tested are not the active intermediate of the diol・deoxyaldehyde conversion system.
