Methylrhodibalamin and 5′-Deoxyadenosylrhodibalamin, the Rhodium Analogues of Methylcobalamin and Cobalamin Coenzyme

Treatment of α-(5,6-dimethylbenzimidazolyl)hydrogenobamide with rhodium carbonyl chloride [Rh(CO)2Cl]2 in ethyl alcohol-glacial acetic acid in the presence of sodium acetate produces chlororhodibalamin as the principal rhodium corrinoid. Chlororhodibalamin, when reacted with silver nitrate, is converted into aquorhodibalamin. In the absence of oxygen, chloro- and aquorhodibalamin are readily reduced by sodium borohydride to rhodibalamin s, the corresponding rhodium(I) complex. Addition of methyl iodide or 5'-iodo-5'-deoxyadenosine to rhodibalamin s yields as the major products methylrhodibalamin and 5'-deoxyadenosylrhodibalamin, respectively. The structure of methylrhodibalamin was demonstrated by the synthesis of [14C]methylrhodibalamin, containing the expected radioactive label in stoichiometric proportion. Methylrhodibalamin exhibits a signal for 3 protons in the NMR spectrum at -1.64 ppm, proving the attachment of the methyl group to rhodium. The structure of 5'-deoxyadenosylrhodibalamin is confirmed by its conversion into dicyanorhodibalamin, adenine, and the cyanhydrin of d-erythro-2,3-dihydroxypent-4-enal in the presence of cyanide. The rhodium analogue of cobalamin coenzyme is also obtained when Propionibacterium shermanii is grown in the absence of cobalt with chloro- or aquorhodibalamin as precursors. The new compounds are characterized by their spectral and electrophoretic properties and their biological activity. All four analogues are active as weak antimetabolites to vitamin B12 in suppressing the growth of Lactobacillus leichmanii (ATCC 7830) and Escherichia coli 113–3.