CHEMICAL AND BIOCHEMICAL STUDIES ON VITAMIN B12 AND ITS RELATED COMPOUNDS:XV. PROPERTIES AND PHOTOCHEMICAL DECOMPOSITIONS OF SOME HYDROXYALKYLCOBALAMINS AND HYDROXYALKYLCOBINAMIDES

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1. In the present work, several analogues of 5, 6-dimethyl benzimidazolyl cobamide coenzyme (DBCC), containing hydroxyalkyl group linked to the cobalt atom, were synthesized as the possible intermediates in the diol-dehydrase system on the assumption of active participation of the cobalt atom, and their properties, above all, behaviors in photolysis and in the enzymatic system were examined.2. Co-β, γ-dihydroxypropyl-, Co-β-hydroxypropyl-, and Co-hydroxyethylcobalamins were prepared by reacting glycerol α-monochlorohydrin, propylene bromohydrin and ethylene chlorohydrin with vitamin B12s. Co-β, γ-dihydroxypropylcobinamde was also synthesized by the reaction of glycerol α-monochlorohydrin with a reduced product of monocyanomonoaquocobinamide with NaBH4.3. Absorption spectra of the three hydroxyalkylcobalamins were similar to those of DBCC or Co-alkylcobalamins, and the spectrum of the hydroxyalkylcobinamide was analogous to those of cobinamide coenzyme or Co-alkylcobinamide. These four compounds, alike cobamide- and cobinamde coenzymes, were very unstable in light and easily decomposed to hydroxo (or aquo) forms. When they were allowed to stand in the dark in 0.017 M KCN solution, they were converted only partly to dicyano forms like the alkyl derivatives. Paper chromatographic behavior showed their higher hydrophilicity than alkyl derivatives as expected.4. Hydroxyalkylcobalamin, for example Co-β, γ-dihydroxypropyl cobalamin, showed an almost equal activity on vitamin B12-requring E. coli. However, this compound did not exhibit the coenzyme activity, and, moreover, exerted an inhibitory effect, like the alkyl derivatives, in the diol-dehydrase system. From the result it would be concluded that the hydroxyalkyl derivatives of DBCC so far tested are not the active intermediate of the diol-deoxyaldehyde conversion system.5. Co-β, γ-dihydroxypropylcobalamin was irradiated (a) under bubbling of air, (b) in the presence of dissolved oxygen, (c) in a nitrogen atmosphere, (d) in the presence of NaBH4. The photolysis products formed from the dihydroxypropyl group were as follows: (a) glyceric acid. (b) glyceraldehyde and glycerol, (c) glycerol and a small amount of an unidentified substance and, (d) glycerol. The decomposition routes of this compound are considered to be analogous to those of DBCC. The formation of glycerol is not consistent with the formation of 8, 5′-cycloadenosine from DBCC. It is similar to the formation of methanol in the photochemical decomposition of Co-methylcobalamin reported by Weissbach et al. The reaction mechanism may be interpreted on the formation of vitamin B12r and dihydroxypropyl free radical by the homolytic fission of cobalt-carbon bond.
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CHEMICAL AND BIOCHEMICAL STUDIES ON VITAMIN B12 AND ITS RELATED COMPOUNDS:XV. PROPERTIES AND PHOTOCHEMICAL DECOMPOSITIONS OF SOME HYDROXYALKYLCOBALAMINS AND HYDROXYALKYLCOBINAMIDES

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